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Project Director Y. Administrative Network Representative Y GTRI Accounting/Grants and Contracts Y Procurement/Supply Services V Research Property Managment V Research Security Services N Reports Coordinator (OCA) Y GTRC V Project File Y Other N N STUDY OF COAL CONDITIONING EFFECTS ON DEWATERING OF PULP AND PAPER SLUDGES
by
Steven C. Young
Georgia Institute of Technology A Unit of the Universisty System of Georgia Atlanta, Georgia
School of Civil Engineering
Master of Science in Environmental Engineering
Special Research Problem
Spring 1992 STUDY OF COAL CONDITIONING EFFECTS ON DEWATERING
OF PULP AND PAPER SLUDGES
By
Steven C. Young
Approved:
K2' Dr. F. M. Saunders Advisor
Dr. A. Amirtharajah Reading Committee Member
Dr. W. Cross Reading Committee Member ACKNOWLEDGMENTS
The author wants to thank his advisor, Dr. F. M. Saunders, for selecting him to work on this special research problem and for all the guidance Dr. Saunders provided. The author also appreciates the time and assistance provided by the reading committee members,
Dr. A. Amirtharajah and Dr. W. Cross. Special thanks are due to my parents John and Janet, my brothers Patrick and Robert, and especially my wife, Megan, for their continuous support and encouragement throughout my entire graduate school experience. ABSTRACT
Many industries have recently realized that the use of polymers is not the most effective or efficient means of conditioning all sludge suspensions. Therefore, research on other means of conditioning sludges, such as physical conditioning agents, has resurfaced. This study examines the effects of the addition of pulverized coal to pulp and paper primary sludge under constant-pressure, cake filtration. The range of coal dosages selected was aimed at maintaining combustion of the filter cake in a boiler or incinerator.
A compression-permeability cell (C-P cell) was used to perform a complete expression process (filtration and consolidation) on each suspension examined. Filtration and consolidation parameters such as average specific resistance, compressibility index, ultimate cake solids concentration, moisture content, yield and cake concentration profiles were used to assess the effectiveness of coal addition. Overall, average specific resistance to filtration (&) decreased with increased coal addition up to a dosage of 1.0 gram coal per gram dry sludge solids (1.0 g/g DSS). Increased coal addition above 1.0 g/g DSS does not significantly reduce average specific resistance. Filtration yield, which accounts for rate changes, increased by a factor of approximately two with increased
ii coal addition compared to unconditioned sludge. This is a significant advantage if time limitations or reduced capital cost are considered. However, on an energy basis increased coal addition was a disadvantage. Cake solids content of a filter cake on a DSS basis decreased (or moisture content increased) with increasing coal addition. Therefore, more energy is required to combust the additional water in the filter cake.
iii TABLE OF CONTENTS Page Acknowledgment Abstract ii List of Tables vi List of Figures vii
CHAPTER 1 INTRODUCTION
1.1 Sludge Dewatering Process 1 1.2 Cake Filtration and Consolidation 2 1.3 Physical Conditioning of Sludge Suspensions 3 1.4 Purpose of Study 4
CHAPTER 2 BACKGROUND AND LITERATURE REVIEW 2.1 Filtration and Consolidation Theory 6 2.1.1 Flow Through Porous Media 6 2.1.2 Average Specific Resistance 8 2.1.3 Cake Filtration and Consolidation 9 2.1.4 Compressibility of a Sludge Suspension 12 2.2 Sludge Conditioning 13 2.2.1 Ash Conditioning 15 2.2.2 Coal Conditioning 20 2.3 Cake Solids Concentration Profiles 26
CHAPTER 3 EXPERIMENTAL APPROACHES 3.1 Origin of Sludge and Coal Samples 34 3.2 Experimental Apparatus 35 3.2.1 Capillary Suction Time (CST) Apparatus 35 3.2.2 Compression-Permeability Cell (C-P Cell) 35
3.3 Analytical Methods 37 3.3.1 Sample Characterization 37 3.3.1.1 Suspended and Volatile Suspended Solids 37 3.3.1.2 Total and Soluble Chemical Oxygen Demand 40 3.3.1.3 pH 40 3.3.2 Dewatering Properties 40 3.3.2.1 CST 40
iv 3.3.2.2 Filtration and Consolidation Phase Determination 41 3.3.2.3 Average Specific Resistance 42 3.3.2.4 Compressibility Index 42 3.3.2.5 Cake and Ultimate Cake Solids 42
3.3.3 Determination of Coal Conditioning Effects on Dewatering 43 3.3.3.1 Cake Concentration Profiles 43 3.3.3.2 Yield Values 43 3.3.3.3 Moisture Content 44
CHAPTER 4 DATA ANALYSIS AND DISCUSSION
4.1 Characterization of Sludge Samples 45
4.2 Characterization of Pulverized Coal 46
4.3 Sludge Dewaterability and Compressibility of Unconditioned Sludge Suspensions 48 4.3.1 CST 48 4.3.2 Filtration and Consolidation Results 49 4.3.3 Mass Balance on C-P Cell Runs 56 4.3.4 Comparison of Results with Previous Plant-P Samples 57
4.4 Sludge Dewaterability and Compressibility of Coal Conditioned Sludge Suspensions 59 4.4.1 Filtration and Consolidation Results 59 4.2.2 Mass Balance on C-P Cell Runs 79
4.5 Assessing the Effectiveness of Coal Conditioning 81 4.5.1 Cake Consolidation Profiles 81 4.5.2 Yield Values 95 4.5.3 Moisture Content 98
CHAPTER 5 SUMMARY AND CONCLUSIONS 105
REFERENCES 108
APPENDIX 110
v LIST OF TABLES Table Page
4.1 Sludge Characteristic Data for Plant-P Samples 45
4.2 CST Data of Plant-P Samples 49 4.3 C-P Cell Mass Balance on a Total Sludge Mass Basis at Zero Coal Addition 57
4.4 C-P Cell Mass Balance on a Dry Solids Mass Basis at Zero Coal Addition 57 4.5 Comparison of Sludge Suspension Characteristics for Plant-P Samples 58
4.6 Comparison of Dewaterability and Compressibility Characteristics for Plant-P Samples 59 4.7 Filtration Phase Slopes for -dL/dt ° ' 5 vs t Plots at 1100 and 3300 kPa and Varying Coal Dose 67 4.8 Slopes of log V vs log t Plots at 1100 and 3300 kPa and Varying Coal Dosages 68 4.9 Actual Cake Solids, Ultimate Cake Solids Contents and Degree of Completion Data for 1100 and 3300 kPa at Varying Coal Additions 77
4.10 C-P Cell Mass Balance on Total Sludge Mass Basis 80
4.11 C-P Cell Mass Balance on a Dry Solids Basis 80 4.12 Actual Filter Cake Heat Balances from C-P Cell Runs at 1100 kPa 103
4.13 Actual Filter Cake Heat Balances from C-P Cell Runs at 3300 kPa 104
v i 4.54 Cake Solids Profiles at Zero Coal Dosage and Varying Pressure 95
4.55 Filter Yield vs Coal Dose at 1100 kPa 97
4.56 Filter Yield vs Coal Dose at 3300 kPa 97
4.57 Volume Yield vs Coal Dose at 1100 and 3300 kPa 99
4.58 Cake Solids Content vs Coal Dose at 1100 kPa 99
4.59 Cake Solids Content vs Coal Dose at 3300 kPa MO
4.60 Moisture Content vs Coal Dose at 1100 and 3300 kPa 100
xi CHAPTER 1
INTRODUCTION
1.1 sludge Dewatering Process
The most common process used by the vast majority of industries to handle waste sludges is dewatering. Sludge dewatering involves the separation of suspended solids from water to produce a handleable cake. Thickened sludges generated by many industries and municipal wastewater plants usually have high water contents (e.g., greater than 95%) and require drastic volume reduction to facilitate the ultimate disposal of residual solids.
The selection of a specific dewatering process is a crucial step in the overall sludge management operation. Choices include filtration, centrifugation, sedimentation and thermal drying. As is the case for most operational decisions, cost tends to be a major factor involved. Mechanical dewatering by filtration incurs the lowest capital cost and possibly the lowest operating cost as well. Sludge characteristics, desired final cake solids concentration, and ultimate residue disposal requirements also play a key role in the selection of a dewatering process. In many cases, bench- or pilot-scale testing of dewatering processes on a particular sludge suspension can further aid the selection process. This paper focuses on sludges produced by the pulp and paper industry. The pulp and paper industry frequently dewaters its wastewater sludges by belt presses and screw presses. Therefore, this research employed constant-pressure, mechanical dewatering to evaluate dewaterability of the sludge samples received.
1.2 Cake Filtration and Consolidation The overall mechanical dewatering process consists of two distinct phases: cake filtration and consolidation. Cake filtration involves the separation of suspended matter from water via a porous medium, resulting in the formation of a filter cake beginning at the medium surface. This phase is considered herein to occur until all suspended particulates are incorporated into the filter cake, and no original sludge suspension remains above the cake surface. Two important factors during filtration which affect dewaterability of a sludge are the initial layer of particles deposited on the medium and the resistance to filtration of the filter cake. The phase following cake filtration is consolidation. In consolidation, residual liquid is removed from the filter cake by mechanical displacement of water with solids. Hence, the cake is compressed, or consolidated, resulting in a smaller cake volume than at the transition point between filtration and consolidation phases. Cake filtration is the most widely used filtration technique used in the processing industries; therefore, much research has been performed both in the past and present in this area.
Terminology in the cake filtration arena has been somewhat confusing and misleading at times. Many researchers, such as Yeh
(1985) and Shirato et al. (1987), have used the term "expression" in describing the consolidation phase. For the purposes of this study, expression is referred to as the complete dewatering process, including both filtration and consolidation phases.
Therefore, the total expression process is divided into the two stages with regard to the mechanism of flow through porous media: the first-stage flow mechanism is actually cake filtration and the second-stage flow mechanism is consolidation (Sun, 1990).
A compression-permeability cell (C-P cell) was used to perform the complete expression process in this study. Basically, the C-P cell consists of a cylinder fitted on a septum which holds a sludge suspension and a hydraulically driven piston which is inserted into the cylinder. When the initial load is applied to the suspension, cake filtration begins and a crucial initial layer of particles is retained on the medium surface. The cake grows and filtrate passes through the septum until the suspension no longer exists and the piston contacts the cake's upper surface. At this point (the transition point), cake filtration ends and consolidation begins. Compression of each layer of the cake, beginning with the layer closest to the filter medium, occurs until a uniform cake porosity is reached. For simplicity, only constant-pressure expression processes were examined in this study.
1.3 Physical Conditioning of Sludge Suspensions
Research on physical conditioning of various sludge
3 suspensions was conducted primarily in the 1970's. With the evolution of polymers used as sludge conditioners in the entire decade of the 1980's, use of physical conditioning agents was reduced during that time period. Recently, however, many industries have realized that the use of polymers was not the most effective or efficient means of conditioning all sludge suspensions. Therefore, research on physical conditioning agents such as powdered coal or ash has resurfaced. Physical conditioners basically involve three mechanisms which aid dewatering: prevent organic particles from blinding the filter media, give structure to the cake, and keep pores open in the cake to aid fluid flow. 1.4 Purpose of Study This study revolves around one basic decision involving the location of coal addition in the primary sludge treatment process at a pulp and paper mill. Figure 1.1 illustrates two alternatives for coal addition. The first alternative shows coal being introduced with dewatered filter cake at the inlet of the boiler. This is a procedure that is frequently being utilized today. Data received from C-P cell expression runs at zero coal addition represent this alternative. The second alternative indicates coal is added to the sludge suspension prior to the dewatering step. C-P cell runs at varying coal additions represent this second choice. The decision process is based on whether coal conditioning of a slurry significantly affects filtration and consolidation performance, namely average specific
4 resistance, ultimate cake solids content, yield, moisture content, and cake concentration profiles.
Stack L Dewatering Filter Cake Boiler Primary _r_„, Unit Unit Sludge I Filtrate Ash
Alternative Alternative '2, al
Figure 1.1: Primary Sludge Treatment Process Diagram
5 CHAPTER 2
BACKGROUND AND LITERATURE REVIEW
2.1 Filtration and Consolidation Theory
2.1.1 Flow Through Porous Media
A simplified diagram of a sludge suspension undergoing cake filtration involves liquid flowing through a porous membrane and
solids accumulating at the membrane surface, thus forming a cake. This system is under an applied pressure and is represented in Figure 2.1 (Sun, 1990).
F
Sludce uspensi:n ow Cake
A
Figure 2.1: Diagram of a Sludge Suspension Under Cake Filtration (Sun, 1990)
In 1856, Darcy discovered that the volumetric flow rate of a liquid passing through a porous bed was proportional to the pressure gradient across the bed and to the bed area. Under a
6 laminar flow regime, the following equation is termed Darcy's law and is represented as:
dV = PAK dt Ax (1) where dV/dt = volumetric flow rate, m3 /sec
P = pressure drop across bed, Pa A = filtration area normal to direction of flow, m2 A = viscosity of liquid, Pa•sec
K = permeability, M2
X = cake thickness measured from medium surface, m Cake resistance can be expressed on a unit cake solids volume basis by R = 1/K p . Substituting into Equ. (1) gives
dV = PA dt p.Rx (2)
Darcy's law does not apply for systems involving high flow rates where transitional or turbulent flow conditions would occur. Forchheimer (1901) developed an equation to address flow under transitional or turbulent conditions (Sun,1990): P = au + bu2 x ( 2*) where u = flow rate, m 3 /sec and a,b = constants unique for specific flow and media However, since most filtration processes are operated at flow rates appropriate for Darcy's equation, this study will be limited to laminar flow filtration. As a cake forms and builds up, resistance to flow is contributed by both the developing cake and filter medium.
7
Therefore, a term for medium resistance must be introduced into Equ. (2) (Vesilind, 1979).
dV = PA dt p(Rx + M r ) ( 3 ) where Mr = resistance to filtration by medium, /11 -1 Assuming all suspended solids are retained to form a cake, the cake volume can be expressed as xA = vV where v = volume of cake deposited per unit volume of filtrate, m3 /m3
V = volume of filtrate, m3 However, it is more convenient to replace V by an experimentally determined term w, mass of dry cake solids per unit filtrate volume. Consequently, the resistance term R (resistance per volume of filtrate) is replaced by a (resistance per unit mass of
solids). Substituting into Equ. (3) gives
dV = PAZ dt p(waV + MBA) (4)
where a = average specific resistance to filtration per unit mass of cake solids, m/kg
2.1.2 Average Specific Resistance
Average specific resistance is the most widely used
parameter to characterize dewaterability of sludge suspensions.
Rearranging and integrating Equ. (4), which is Darcy's equation adapted for filtration, assuming constant pressure over time dt = f(pwaV , MA) dV J PA2 PA (5)
8 leads to
t = AwaV2 + 11,4V PA2 PA (6) The experimental method to determine average specific resistance can be done by recording filtrate volume, V, at various filtration times, t, and plotting the data to generate a second-order curve. The average specific resistance value, 6, can be determined by performing a second-order, non-linear regression on the t versus V plot. The second order regression coefficient b is equal to
b = J2W& 2 PA2 ( 7 ) and the average specific resistance value is then obtained by
E = 2PA2b 4w ( 8 ) 2.1.3 Cake Filtration and Consolidation Constant pressure filtration is a common means for gathering test data to aid a process design, due to the ease with which filtrate volume can be measured as a function of time. A variation of Equ. (4) was developed by Ruth and is referred to herein as Ruth's filtration equation, having the form
dV r PA2 (SC - S) dt ilp saSc (V + V.) ( 9 ) where Vm = a fictitious filtrate volume required to form a filter cake of resistance equal to the medium resistance M n , m3 S = average mass fraction of solids in slurry, %
Sc = average mass fraction of solids in cake, % p s = true density of solids, kg/m3
9 Integrating Equ. (9) results in
(V + Vm ) 2 = K(t + tm) (10) where tm = fictitious filtration time corresponding to the medium resistance M r , sec K = Ruth's constant pressure filtration coefficient defined as
K = 2PA(Sc - S) 2 APsCeSc Equ. (10) reveals a parabolic relationship between cumulative filtrate volume and filtration time. After a small
initial time period, a layer of sludge solids builds up on the medium and cake resistance then becomes the controlling factor of filtration rate. Therefore, the medium resistance can be neglected and results in
V2 = Kt (11)
As stated earlier, the complete expression process includes both filtration and consolidation phases. The transition point between these two phases is often desired in experimentation and
in practice. The filtration phase will terminate, and the consolidation phase begin, at the instant when all suspended solids are deposited to form a filter cake. Recalling Equ. (11) where V = AL and taking the square root yields
AL = (Kt)" (12) Differentiating and rearranging Equ. (12) gives
- dL = (K)" d(t) 0 ' S A (13) For constant-pressure cake filtration on a constant-area septum, the term -dL/dt" is constant. The transition point is 10 determined as the point where -dL/dt ch5 begins to deviate from a constant. The transition point can also be determined graphically from a plot of -dL/dt m versus time. The consolidation phase of the expression process is referred to herein as the act of further reducing the liquid content of a filtered cake by mechanically compressing it into a more compact form. Consolidation of the bottom layer of the cake, where the solids compressive pressure is equal to the applied pressure, is however achieved during the filtration phase. The remainder of the cake under filtration has a non- uniform and increasing value of cake porosity. Therefore, consolidation must follow to result in a well dewatered cake (Sun, 1990). In consolidation, liquid flow is generated solely by solids particles displacing the liquid from the voids, or pores, within the cake. Ultimately, the cake will be compressed into one having uniform solids concentration throughout, as demonstrated by Bierck (1988) using a unique suspension under low pressures and an electron beam analysis of solids concentration. Higher pressure will lead to increased consolidation and higher solids content of the cake (Leu, 1981), where increased pressure may or may not enhance dewatering significantly during the filtration stage since specific resistance is directly proportional to the applied pressure. Hoyland et al. (1981, 1986) found that the rate of filtration during the consolidation phase was directly
11 proportional to the filtrate volume discharged. An empirical equation was then developed to project the ultimate filtrate volume,
dV = M(Vwt - V) dt (14) where V = cumulative filtrate volume, m3 Vutt = theoretical filtrate volume achieved by expression proceeding for an infinite time, m 3 M = constant of proportionality, sec-1 A plot of the measured flow rate, dV/dt, versus cumulative filtrate volume, V, in the consolidation phase portion of the expression process results in a linear relationship whose slope equals -M. The value of M represents the rate at which consolidation proceeds; the greater the M value, the faster the process reaches equilibrium. The theoretical ultimate filtrate volume can be obtained by extrapolating the gradient until the value of dV/dt equals zero. Consequently, V/Vutt , referred to as the degree of completion, may be determined at any time during the consolidation phase (Sun, 1990).
2.1.4 Compressibility of a Sludge Suspension
Compressibility of a sludge suspension is very significant in the manner the suspension behaves during an expression process. For purposes of this study, compressibility was defined as the change of average specific resistance per unit increase in effective pressure (Sun, 1990) and was typically determined by the following empirical equation: Si = a. Ps (15)
12 where a, = empirical constant equal to the specific resistance value for pressure of unity (1 bar) P = applied pressure, kPa S = compressibility index
A log-log plot of average specific resistance versus applied pressure yields the constants a, and S, the intercept and slope respectively. The validity of the empirical equation is verified if a linear relationship exists (Sun, 1990). Compressibility indexes, S, for certain sludges have been determined by several sources using the empirical approach: domestic sludges had S values ranging from 0.4 to 0.85 (WPCF, 1969), water treatment sludge between 0.8 and 1.3 (Adrian et al., 1968), and lime sludges about 1.05 (Martel and DiGiano, 1978). Incompressible materials, such as sand, have compressibility indexes of zero
(Vesilind, 1979). High applied pressures in the expression process may not enhance dewaterability of sludge suspensions that are highly compressible. Yeh (1985) concluded in his research two major points regarding pressure influencing dewaterability. For highly compressible cakes, S > 1, high pressure is beneficial in the consolidation phase only. For moderately compressible cakes,
S < 1, moderately high pressure may positively affect both filtration and consolidation.
2.2 Sludge Conditioning
Traditionally, ferric chloride and lime have been the primary conditioners used in sludge dewatering by pressure 13 filtration (Nelson and Brattlof, 1979). In the last decade, many treatment plants have adopted polymers as the chief conditioning agent in dewatering applications. Polymers have improved filter yield and reduced overall operating costs. However, polymers are expensive and are not effective on all sludges, as are inorganic chemicals (Smith et al., 1972). Hence, physical conditioning agents, such as flyash, sludge ash and powdered coal, warrant extensive research on their conditioning effects of sludge dewatering. Mechanisms by which physical conditioning agents aid sludge dewatering are described by several researchers. Tenney (1970) introduced conditioning as a process of developing a structure within a sludge by physical or chemical means resulting in ample rigidity to permit water to be withdrawn by filtration or other dewatering process. Eden (1983) indicated the effect of ash for sludge conditioning is presumably mechanical whereby ash particles hold open the cake structure to permit egress of water. Also, Albertson and Kopper (1983) stated that physical conditioners increase the structural strength of a cake, provide a drainage matrix, and prevent organic solid particles from blinding the medium during filtration. The pulp and paper industry has become increasingly interested in conditioning wastewater sludges. Many pulp and paper mills burn the dewatered sludge cakes in boilers to recover heat value and to eliminate or reduce landfill requirements. According to Albertson and Kopper (1983), when (municipal)
14 sludges are dewatered for disposal by combustion, the final cake solids concentration is of utmost importance and is the primary factor affecting the amount of fuel required for combustion of the sludge cake. This statement should be consistent with sludges from any source since it is based on the fact that most of the energy required to combust wastewater solids is utilized to evaporate water associated with the cake and raise the vapor to combustion temperature (Albertson and Kopper, 1983). It should be noted that all research presented in the following sections was conducted on municipal primary and waste activated sludges, except for Moehle (1967) which was a Uniroyal Inc. industrial waste. No literature was found to date on physical conditioning of pulp and paper sludges. However, the research cited serves as valuable background and as a starting point in studying the aid of physical conditioning agents on the dewatering of pulp and paper sludges.
2.2.1 Ash Conditioning Gerlich and Rockwell (1973), in conjunction with the EPA, conducted a study on pressure filtration with ash filter aid for the city of Cedar Rapids, Iowa. The Cedar Rapids project involved gathering pilot plant pressure and vacuum filtration data which served as the basis for the design of a full-scale pressure filter facility.
In all filtration runs, primary and secondary digested sludge was tested with a flyash conditioner obtained from a local steam generating plant. The pressure filtration pilot unit
15 consisted of a CO 2 pressure cylinder, a precoat tank, a feed tank containing the ash/sludge mixture, and a 15-cm diameter, split- plate pressure filter. Digested sludge solids concentrations ranged from approximately 3 to 7 percent, with the majority of
runs in the range of 4.5 to 5.5 percent. Flyash ratios are
expressed on the basis of dry sludge solids. Ash/sludge ratios were varied to determine the ratio corresponding to the optimum filter yield, which is expressed as pounds of dry sludge solids
per hour per square foot of filter area (Gerlich and Rockwell,
1973). Figure 2.2 relates flyash/sludge ratios to filter yield during the length of a filter run.
FILTRATION RATE VS CYCLE TIME AT vARY , NQ FLYASR / SLUDGE RATIOS I55 'A SLUDGE SOLIDS I
7- I 5
10,
- 0 9
o 08 - 0 7 6 Nss 6 % i; 0 6 • 0 G 5 1.2 .`"••-• A".1114t. o C ',44111S, 0 2. ∎
, 3 C 3 SA • i.8 1.1442'. • 21
02 L. -.1 CS 1 5 20 25 30 TIME (“OURS)
Fig. 2.2: Filter Yield vs Filtration Time for Various Flyash/Sludge Ratios (Gerlich and Rockwell, 1973)
The plot indicates that the filter yield increases as the
16
ash/sludge ratio increases until an optimum ratio is reached. At this point, the filter yield begins to decrease with increasing ash/sludge ratios. Gerlich and Rockwell also assessed the effect of ash on
dewaterability by plotting percent cake moisture versus
filtration time at various ash/sludge ratios. Cake moisture clearly decreased with an increase in flyash/sludge ratio, as
shown in Figure 2.3. As stated earlier, this reduction in cake moisture is desirable and critical for sludges burned for heat
recovery.
9 C _
60
/7 1 2 I I
..... ...... :75 5 14•-•
4 0
3C 5 0 5 2.0 2 . 5 3
—, ME HOURS
Figure 2.3: % Cake Moisture vs Filtration Time at Various Flyash/Sludge Ratios (Gerlich and Rockwell, 1973)
The vacuum filtration pilot studies by Gerlich and Rockwell
showed similar results as the pressure filtration study. Again,
the filter yield increased linearly with the ash/sludge ratio and
17 decreased with increasing ash/sludge ratio after an optimum ratio was reached. The optimum ash/sludge ratio was 1.1:1 for the vacuum filtration study; slightly lower than the optimum ratio of
1.4:1 for the pressure filtration unit. Also, the moisture content of the cake decreased with increasing ash/sludge ratio for both the vacuum and pressure filtration studies. Smith et al. (1972) performed a pilot-scale dewatering study which focused on conditioning of biological sludges with incinerated sludge ash. The influence of the ash to sludge ratio on filtration improvement (yield), cake moisture content, and filtrate quality were investigated. A multileaf vacuum filter apparatus was constructed to simulate conventional vacuum filter design. The unit consisted of six filter leaves and was operated at 37 cm Hg and 33 percent submergence.
Smith et al. (1972) varied ash/sludge ratios and presented effects on filter yield and moisture content on the same plot,
Figure 2.4. Filter yield and cake moisture content values were determined on an ash-free basis. The corrected filter yield was obtained by subtracting the amount of ash added to the sludge from the total filter yield (Smith et al., 1972). The moisture content was presented in pounds water per pound dry sludge solids, thus factoring out the ash addition. Fig. 2.4 indicates that both yield and moisture content increase linearly until an approximate ash/sludge ratio of 2.0 lbs ash/lb dry sludge solids (or 200%) is reached. Deviation from linearity at higher ash/sludge ratios is attributed to the
18 O
•
li 7.50 • • .x 6.7 • .5 • x 3 ..... ;;; . 6... 4.0 7) 0 WI 5.25 • .5 •n P sr -• * 4.5 0 7. at is 1E 3.75 is • • ": .. 3.00 a 20% II z.-t) e30% o. i: 2.2 LS 1 . Open Synnisols-fils., yi •14 es• 1.50 Solid Symbol.-hioistut• 1.0 to = Q. 0.7 asz.
100 200 300 400
0.04ntity el incift•ater Ask Added (':Sludg• Solids)
Figure 2.4: Filter Yield and Moisture Content vs Quantity of Incinerator Ash (Smith et al., 1972)
high initial solids concentration of about 13% (obtained by
thickening the sludge) which eventually led to the sludge-ash
mixture forming a paste. Furthermore, the filter yield increases
significantly with increasing ash addition, however there is some
disadvantage due to the slight increase in moisture content on an
ash-free basis.
A parameter was developed by Smith et al. (1972) correlating ash dosage on sludge yield and is referred to as the "filtration
improvement factor" or FIF.
19 FIF = Yx / Yo
where Yx = ash-free yield at dosage "x" Yo = yield with no ash addition Smith et al. (1972) determined a linear relationship existed
between the FIF and the ash/sludge ratio for each sludge
examined. Plotting FIF vs ash/sludge ratio for digested, primary, and waste activated sludges results in slope values of 0.32, 0,27, and 0.75 respectively. This indicates that ash addition has a more significant effect on dewatering of waste activated sludge over digested and primary sludge.
Moehle (1967) investigated flyash addition on dewatering of contaminated industrial waste. The study was conducted on the
full-scale vacuum filter unit in operation at this particular facility. Moehle (1967) evaluated flyash addition effects in terms of the time required to collect half of an original sample volume of sludge under vacuum filtration. Moehle (1967) found that the rate at which half the sample volume was collected decreased with increasing ash dosages until an ultimate ash/sludge ratio was achieved. At this point, a decrease in filtration rate began and a significant portion of water was adsorbed by the flyash.
2.2.2 Coal Conditioning
Hathaway and Olexsey (1977) performed a pilot-scale vacuum filtration study which evaluated the effect of pulverized coal on filtration and incineration of sewage sludge. The experiment involved a belt vacuum filter and a coal sample with a sieve
20 100
rn (7,
10- = 3 E E 0
1 1 1111111 I 1 1 111111 II 1 7 11111 0.1 0 1 10 Sieve Opening (mm)
Figure 2.5: Pulverized Coal Sieve Analysis (Data from Hathaway and Olexsey, 1977)
analysis given in Figure 2.5. Hathaway and Olexsey (1977) assessed dewaterability in terms of cake moisture content and filter yield. The researchers
determined that excellent dewatering resulted at coal to sludge
ratios from 0.1 to 0.4 pounds of coal per pound of dry sludge
solids. In this range, cake moisture content decreased with
increasing coal/sludge ratios as shown in Figure 2.6. Filter yield was also positively affected, although only slightly, and
indicated that coal addition before filtration aided the dewatering mechanism in the filter operation (Hathaway and
Olexsey, 1977). This increase in filter yield, total and corrected for coal addition, is shown in Figure 2.7. Corrected filter yield is calculated by subtracting the mass of coal from the total yield value at each coal dose. The corrected yield
21 ▪
3.80
3.60
3. 4(
3.20
0 in 3.00 a
CO 2.80
2 ' 60 27.5% 28%
'4 2.40 30. 5% 2.20
2.00 Z DENOTES SOLIDS CONTENT OF CAKE
),I 0.2 0.3 0.4 0.5 0.6
CoAL DOSE (kg (:,31/kg Dry Sludge Solids)
Figure 2.6: Cake Moisture Content vs Coal Dose (Hathaway and Olexsey, 1977)
110 1-
Total lEL Filter Yield
C,rrecrec Filter Yielri
10 0.1 0.1 0.3 COAL D,-"SE ikt real/kg dry sludge solids)
Figure 2.7: Filter Yield of Sludge vs Varying Coal Additions (Hathaway and Olexsey, 1977)
22 term represents filter yield on a dry sludge solids basis. Hathaway and Olexsey (1977) concluded coal addition was beneficial for ultimate incineration in two ways. First, a filter cake with a lower moisture content was produced and
therefore more fuel value on a dry solids basis is added per unit
of moisture. Second, the coal added to the sludge increases the thermal value of the resulting cake.
Pitzer (1977) conducted two studies, a laboratory study and
a full scale test, to evaluate coal as a conditioning agent. The lab study utilized the Buchner funnel test for dewatering purposes. Coal used in the lab study had a particle size distribution given in Figure 2.8.
0.2 0.4 0.6 08 Sieve Opening (mm)
Figure 2.8: Pulverized Coal Sieve Analysis (Pitzer, 1977)
23 Pitzer (1977) achieved a 25 percent total solids filter cake
with a heating value of 8600 Btu/lb dry cake solids at a coal to dry sludge solids ratio of 0.89/1.00. However, Pitzer (1977) determined that fuel costs would be excessive at this coal
dosage. Mixtures of coal and sludge ash were tested to remedy
this problem. Pitzer (1977) found an optimum combination, in terms of total cake solids concentration, of 0.27 part coal to
0.81 part sludge ash to 1.00 part dry sludge solids. However, when factoring out the coal and ash solids in the filter cake, an
increase in coal/ash dose resulted in a decrease in the percent sludge solids (or an increase in cake moisture per unit dry sludge solids).
A full-scale test conducted by Pitzer (1977) was performed at the Belmont Wastewater Treatment Facilities in Indianapolis, IN. The dewatering system included an Eimco continuous-belt vacuum filter. Coal and ash were added to the sludge, a mixture of primary and secondary, just prior to the vacuum filter. A clear relationship was not achieved between the cake total solids concentration and the ash to coal to dry sludge solids ratio, as was the case for the laboratory study. In the lab study, sludge feed concentration and coal, ash and polymer dosages were easily controlled. In the full-scale test, these conditions were difficult to control and led to problems in determining effects of the coal and ash additions on dewatering. Coal to ash to dry sludge solids ratios of 0.22/0.54/1.00 up to 0.50/0.54/1.00 resulted in total cake solids contents of 26 to 36 percent at
24 polymer doses of 40 to 60 pounds per ton of dry sludge solids.
Also, the filter yield, corrected for conditioner addition, decreased as the coal to ash to dry sludge solids ratio increased (Pitzer, 1977).
Albertson and Kopper (1983) performed research showing the beneficial use of coal addition on centrifugal dewatering of waste activated sludges. Although solid/liquid separation mechanisms are different in centrifugation and pressure filtration, results from this research are presented and could give insight in determining the overall effectiveness of physical conditioning agents on sludge dewatering. Albertson and Kopper (1983) found that fine coal addition significantly increased moisture removal from the cake on a dry sludge solids basis. Data collected at a coal addition of 0.2 kg coal/kg dry sludge solids was compared to moisture removal at zero coal addition. These data revealed approximately 0.6 to 0.7 kg moisture per kg dry sludge solids is removed, or about 3 kg moisture is removed per kg of coal added to the sludge. Corresponding increases in total cake solids concentration existed as well (6 - 7 percent increase). Albertson and Kopper (1983) concluded that several factors combined to improve the dewatering process. They suggested the higher density of the sludge resulting from coal addition created a higher compactive force; the coal provided a better drainage matrix; and the coal improved the structural strength of the forming cake.
25 2.3 Cake Solids Concentration Profiles
According to Bierck et al. (1988), compressible cake filtration models developed to date are not based on comprehensive understanding of the mechanisms of filter cake development. Beirck (1988) describes that these models, which are used to aid sludge filtration facility design and operation, are based on assumptions regarding solids distribution within a filter cake and other internal mechanisms. Bierck (1988) attempted to better understand these mechanisms involved during cake filtration. Bierck (1988) suggested that examination of temporal and spatial suspended solids distribution of a filter cake would provide an excellent means of understanding internal mechanisms during filtration. Bierck (1988) utilized high energy X-rays produced by the Cornell High Energy Synchrotron Source (CHESS) to look at the solids distribution within a filter cake. First, a basic understanding of suspended solids and pressure distribution within a cake is essential in examining the internal mechanisms involved during cake filtration. Figure 2.8 shows the suspended solids (SS) concentration and pressure distributions during filtration. Figure 2.9 (a) illustrates a filter cake forming, from the medium surface up, under vacuum filtration. It should be noted that the SS and pressure distribution concepts apply to all filtration applications (pressure filtration, vacuum filtration, centrifugation, etc.). Fig. 2.9 (b) depicts the constant initial
26 (A) (8) (C)
Slurry[
Coke Medium
Suspended Solids Pressure Concentration
L To Vacuum
Figure 2.9: Suspended Solids and Pressure Distribution in a Compressible Filter Cake During Filtration (Bierck and Dick, 1990)
slurry concentration above the forming filter cake. The SS concentration increases through the cake as the medium is reached. In Fig. 2.9 (c), the fluid and solids pressures are represented by P and Ps respectively, and the total pressure differential applied equals Pmm - Po where Palm is atmospheric pressure and P0 is the vacuum pressure applied beneath the filter medium. The fluid pressure, P, decreases due to frictional drag as the fluid flows through the pores of the cake (to PO and through the medium (to P o ). Following the Terzaghi (Terzaghi and
Peck, 1967) equation,
P (17) P T = P S where PT = total pressure (or stress) P atm the decrease in fluid pressure is accompanied by an equal and opposite solids pressure (or effective stress). The effective stress through the height of the filter cake is due to fluid drag on sludge particles further away from the medium. Because of the
27 compressible nature of the filter cake, the cake compacts under the imposed effective stress resulting in the SS concentration profile shown in Fig. 2.9 (b) (Bierck and Dick, 1990). Bierck (1988) concentrated his efforts on examining the SS distribution using high energy X-rays. A conventional filtration cell with an adjusting stage enabled the cell to be moved down in 0.5 mm increments where X-ray absorbance measurements were taken of the developing cake during filtration. A kaolin and distilled water slurry was used having an initial SS concentration of 308 g/L, and a 245 mm Hg (35.6 kPa) pressure differential was imposed (Bierck et al., 1988). It should be noted that Bierck's filter operating conditions were very different than those encountered in actual filtration applications in industry. Bierck (1988) examined a slurry of very high SS concentration and at very low applied pressure. In industry, slurries usually are of low SS concentration (< 5%) and operated under high pressures (1000-3000 Kpa). Results of SS concentrations versus filtration time at constant levels above the filter medium are presented in Fig. 2.10. These data were obtained from a computer generated plot. The numbered lines indicate the height (in mm) of the center of the X-ray beam above the filter medium. Suspended solids concentration profiles were generated by plotting SS versus height above the medium at various selected filtration times. The profiles are shown in Fig. 2.11.
28 •
1250
no.. 0' . 1000 0 0
750 0
N
O
V O V a) 250 rn
500 1000 1500 2000 Time, s
Figure 2.10: Temporal SS Concentration Changes (Bierck, 1988)
15-, o 17s % • 0 o 34 s '• O a 153s •• • • 0 • • • 0 o' • • • • • 0 0 0 : 3 g:: • • •0 .4' E 10- • • •• • 00 •■ • • : I • 57310s2 s o • • • • 0 • c 0 • • • 0 • v 0.• 8103472s s o • ■ ■ • •• 1 a* v o • 0 . v O` 6 0 . • • • o 6 0 . • • V • 1259 s o a • ... v I 430 s 5- a 0 on • 6, vv a go a • ..„ _V 0 0 A • 0 0 6 0 0 A' 0 o ••■ I 1 T I ' I 200 400 600 800 1000 1200 Suspended Solids Concentration, g /L
Figure 2.11: SS Concentration Profiles at Selected Filtration Times (Bierck, 1988)
29 The concept of increased fluid drag forces causing an increase in solids pressure (or effective stress) results in the progressive increase in SS concentration with decreasing cake height approaching the medium, shown in Fig. 2.11. After approximately 1000 seconds, the cake underwent consolidation of its upper regions after the slurry was totally incorporated as filter cake. Here, the SS profiles became vertical. Bierck (1988) refers to this as shrinkage. He described shrinkage as being caused by capillary menisci forming at the air/liquid interfaces of the cake surface which result in compressive forces ..■ under a vacuum (Bierck et al., 1988). Shrinkage occurred for the particular suspension examined by Bierck (1988), extremely low pressure and high SS concentration, under vacuum filtration. However, under complete expression by mechanical dewatering, consolidation acts as the process to expel residual cake moisture after the filtration phase rather than shrinkage.
Several filtration parameters used to characterize sludge dewaterability assume the SS concentration of a filter cake is constant with depth. One such parameter is average specific resistance. Here, a single specific resistance value is used to characterize a sludge under filtration which is composed of layers of solids with varying SS concentrations (Bierck, 1988).
Referring to Fig. 2.11, cakes formed at various filtration times had varying cake heights (cake height increased with increasing filtration times). If each profile was normalized with respect to cake height, each profile could be compared
30
1.0 V 8. c. 0 • V o 17s 11 : • 9 411 0 • V o 34s 0 iii ■•• A 0 • • I53s • : Vie: o 306$ 4, 4 • V • ♦ V • 408s 0 • • V • 510s 0 • • •■■ • v • 732s o 0.5 • 834s o 1072s • I259s V • 1430s •• ••
••
0 200 400 600 800 1000 1200 Suspended Solids Concentration, g/L
Figure 2.12: Normalized SS Concentration Profiles (Bierck, 1988)
directly. Normalized distance (z/H) is determined by dividing the distance the top of the filter cake is above the medium surface, z, by the maximum height of the cake, H, which is at the transition point between the filtration phase and consolidation or shrinkage. Normalized distance values therefore range from zero to 1. If SS concentration varies only with the normalized distance, z/H, the average SS concentration is constant (Bierck, 1988). Fig. 2.12 represents normalized SS profiles from Fig. 2.11. Fig. 2.12 indicates very little variation in normalized SS profiles during the major portion of the filtration phase, from about 34 to 1000 seconds. Variations do exist in the very early and late stages of the filtration process. The 17 second average
31 SS concentration was far less than the SS content during the major filtration period. This resulted from a significant pressure drop across the filter medium during the initial portion
of the run. The profiles reached a relative constant when the
pressure drop across the initial cake layers was significantly
higher than that across the medium, and a constant pressure drop per unit length of cake was established. In the latter stages of filtration (> 1000 sec) the curves approached vertical. This indicated that a homogeneous cake was formed and , according to Bierck, was caused by shrinkage (Bierck et al., 1988). Bierck (1988) established valuable insight on internal mechanisms which occur during the filtration phase of his experiment. However, Bierck (1988) did not focus on consolidation mechanisms since his unique suspension allowed only "shrinkage" instead of true consolidation to occur. More simplified techniques can be used to examine consolidation mechanisms (e.g., using manual cake-cutting method to determine cake solids concentrations rather than utilizing an X-ray beam). The proceeding literature review provided valuable direction for additional research on physical conditioning of sludges. Effects of conditioners, such as ash and coal, on sludges were evaluated mainly by filter yield and moisture content. The research in this study will focus on coal conditioning effects on filter yield and moisture content of a pulp and paper mill sludge, plus an extensive evaluation of coal effects on filtration parameters. Also, the effects of coal on cake
32 concentration profiles will be examined.
33 CHAPTER 3
EXPERIMENTAL APPROACHES
3.1 Origin of Sludge and Coal Samples
Three sludge samples were obtained from a pulp-and-paper mill,Plant-P. These three suspensions were eventually combined to form one sample for which all subsequent filtration and consolidation data were obtained. Constituents of the samples originate from several of the processes performed at a typical pulp and paper mill: pulping, bleaching and papermaking. The majority of the suspensions consist of wash waters, spent liquors and waste cellulose fiber. At Plant-P, unsegregated wastewater streams from the various processes enter two settling basin. Upon settling, the supernatant flows to an aeration basin and then through two polishing ponds before being discharged to a river. The underflow sludge in the settling basins is pumped to a holding lagoon where samples for this study were taken (Sun,
1990).
Sludge samples were sent via overnight airmail from the mill to the laboratory. The samples were kept refrigerated at 5-10 °C to prevent biological activity. Samples were identified by the date on which they were received. As an example, sample P-1242 was a Plant-P sample received on the 242 n° day of 1991, or August
34
0 0 4 1
Side viev,
I. Cylinder 2 Inner electrode 3 Outer electrodes 4 Chronometer 5 CST paper
Plan
Figure 3.1: CST Schematic Diagram (Sun, 1990)
36 of stainless steel. A detailed diagram of the C-P cell is shown in Fig. 3.2. The overall C-P cell system included a hydraulic fluid reservoir, a hydraulic ram with piston connection (Dayton model 42449A), a top loading balance (Fisher Scientific XT- 12000D-I) connected to a personal computer, and a filtrate collection flask. A diagram of the overall C-P cell system is shown in Fig. 3.3. The load applied to the hydraulic ram and piston is provided by a nitrogen gas cylinder; a second nitrogen cylinder reverses the load and raises the ram. Gas flow was controlled by three-way valves. The piston was equipped with an air release valve and two 0-rings to ensure a quality seal between the piston and the cylinder wall. Assuming wall friction is negligible, the ratio of the pressure applied to the sludge suspension by the piston versus the gauge pressure is 1.835. The filter paper used for each C-P cell expression run was Whatman No. 1.
3.3 Analytical Methods
3.3.1 Sample Characterization Sludge suspensions were characterized for physical and chemical properties. All tests were in accordance with Standard
Methods (APHA, 1986). Properties examined include Ph, suspended solids and volatile suspended solids concentrations, and total and soluble chemical oxygen demand (COD).
3.3.1.1 Suspended and Volatile Suspended Solids
Suspended solids (SS) and volatile suspended solids (VSS)
37 1 Piston 2 Air relief line 3 C-P cell cap 4 0-ring 5 C-P cell 6 Filter paper 7 Septum 8 Filtrate line
Figure 3.2: Detailed Schematic of C-P Cell (Sun, 1990)
38 concentrations were determined by the Gooch crucible method, Sections 209 C and D of Standard Methods (APHA, 1986). Fisherbrand G4 glass fiber filters were the filter papers added to the crucibles. Duplicates were performed on both SS and VSS, and the average values were recorded. 3.3.1.2 Total and Soluble Chemical Oxygen Demand Total COD values were determined by the reflux method outlined in Section 508 B in Standard Methods (APHA, 1986). All samples were diluted by a factor of 100 for total COD. Soluble
COD values were obtained by the colorimetric method outlined in Section 508 C of Standard Methods (APHA, 1986). A dilution factor of 25 was used for soluble COD determinations. A Milton Roy Company Spectronic 20D spectrophotometer was used for absorbances of soluble COD solutions. Duplicates were run for all tests and the averages were recorded. 3.3.1.3 Ph The pH of each sample was determined following Section 423 of Standard Methods (APHA, 1986). A Fisher Accumet Model 144 pH meter was used for all readings.
3.3.2 Dewatering Properties
3.3.2.1 CST A sludge volume of approximately 10 mL was added to the 10- mm diameter cylinder. The time for liquid to pass from the first electrode to the pair of outer electrodes via Whatman chromatography paper was recorded. Triplicates were run for each sample and the average value was recorded.
40 3.3.2.2 Filtration and Consolidation Phase Determination The complete sample volume was mixed thoroughly with a high speed mixer for at least 5 minutes to ensure a uniform suspension throughout. A sample volume of approximately 800 mL was added to the C-P cell cylinder for each expression run. Initial sample temperatures were very consistent and ranged between 8-10 °C. The sample introduced into the C-P cell cylinder was allowed to equilibrate for several minutes before the load was applied. This allowed the pressure on the piston to equilibrate. C-P cell runs were performed primarily at pressures of 1100 kPa and 3300 kPa. A personal computer was connected to the top loading balance and recorded filtrate mass (or volume) versus time at intervals of 1 minute for the first hour and 3 minutes for the remainder of the expression. Termination of the run occurred when the filtration rate decreased below 0.3 mL/min. For purposes of this study, this was chosen as the completion of cake consolidation. Filtrate volume versus time data were easily transformed into desired values by a spreadsheet package (Symphony). Determination of the transition point between filtration and consolidation phases was obtained by interpreting the filtrate volume versus time data with the Ruth equation (Equ. 13). A plot of -dL/dtm vs t visually indicates the time at which the transition point occurred. When the -dL/dtm term deviated from a constant, the filtration phase ends and consolidation begins. An example of a -dL/dt c/.5 vs t plot is given in Section 4.3.2,
41 Figure 4.2.
3.3.2.3 Average Specific Resistance The average specific resistance value is the most important parameter defining the filtration phase of an expression process.
The average specific resistance term was determined from a plot of time, t, versus filtrate volume, V. The data were plotted as a second-order, non-linear equation and the corresponding second- order regression coefficient was used to determined average specific resistance in Equ. (8). The additional terms in Equ.
(8) required to determine average specific resistance were applied pressure, filter area, fluid viscosity (all known values) and w which was easily calculated by dividing the mass of dry sludge solids by the total filtrate volume.
3.3.2.4 Compressibility Index CS)
Compressibility index for a sludge suspension can be determined by a log-log plot of average specific resistance versus corresponding applied pressure. The slope of the regression line for the plot is equal to the compressibility index, S. The resulting intercept, c o , is a constant equal to average specific resistance at unity (1 bar).
3.3.2.5 Cake and Ultimate Cake Solids At the end of each C-P cell run (defined by the 0.3 mL/min stopping point), the resulting filter cake was removed from the cell, weighed, and placed in a 103 °C oven for 24 hours. The cake was then removed from the oven and desiccated for approximately 4 hours. The cake was weighed again and actual
42 cake solids content was calculated and recorded. Ultimate cake solids content was determined graphically from the dV/dt vs V plot. A linear regression of the consolidation phase portion of the rate plot, dV/dt vs V, results in the ultimate filtrate volume which can be theoretically achieved for a C-P cell run. The ultimate cake solids content was easily calculated by subtracting the difference between the final and ultimate filtrate volumes from the wet cake mass value in the ultimate cake solids expression.
3.3.3 Determination of Coal Conditioning Effects on Dewatering 3.3.3.1 Cake Concentration Profiles For each filter cake produced by a C-P cell run, the cake was sectioned before drying in order for a cake concentration profile to be obtained. First, the cake was cut vertically into two halves. One half was then sectioned horizontally. Two horizontal cuts with a serrated-edged knife were made producing three filter cake layers. All four portions were placed in a
103 °C oven, and determined for cake solids contents. When these values were obtained, cake solids content versus cake height (or length) were plotted for the cake half which was sectioned in thirds. Cake concentration profiles were performed on suspensions with and without coal addition. 3.3.3.2 Yield Values Yield values were determined for each C-P cell expression on a total solids, a dry sludge solids, and a volume basis. Yield is defined as solids (or volume) deposited per unit filter area
43 per unit time for a filter run. These values were determined at
90% completion of the run for comparison reasons. Yield versus coal dosage (g coal/g DSS) data were plotted for the applied pressures of 1100 and 3300 kPa.
3.3.3.3 Moisture Content Moisture content of filter cakes produced from C-P cell expressions were determined. These values were calculated on both a total solids and a dry sludge solids (g H 20/g DSS) basis.
Moisture content versus coal dosage at both applied pressures were plotted to determine the effectiveness of coal addition on sludge dewatering.
44 CHAPTER 4
DATA ANALYSIS AND DISCUSSION
4.1 Characterization of Sludge Samples This study involved the examination of four sludge samples from Plant-P. Three of the samples, P-1242, P-1249 and P-1252, were originally obtained at Plant-P, and the fourth, P-1275, was a combined sample of the three original suspensions. Because of
the common origin of the sludge samples, variations in pH, suspended and volatile suspended solids, COD and in dewatering properties should be minimal. Sludge characteristics are presented in Table 4.1.
Table 4.1: Sludge Characteristic Data for Plant-P Samples
pH SS VSS Total COD Soluble COD Sample (q/L) (q/L) (q/L) (q/L) P-1242 6.8 24.74 17.06 28.1 2.6 P-1249 6.9 25.82 16.74 23.0 3.0 P-1252 6.6 23.83 16.31 23.4 2.8 P-1275 6.8 24.80 16.70 25.5 3.0
Values of pH ranged from 6.6 to 6.9, where the pH of the combined sample, P-1275, was 6.8. Similarly, suspended and
45 volatile suspended solids concentration varied slightly for the original samples, and resulted in values of 24.80 g/L and 16.70 g/L, respectively, for sample P-1275. Volatility of the suspended solids (VSS/SS) for all four samples were consistent, ranging from approximately 65 to 70%. Chemical oxygen demand indicates the organic strength of a sludge suspension. Detention time in a settling basin will effect the organic nature of a suspension. However, the three original samples were all taken within a 10-day period. Assuming no organic degradation occurred after the samples were taken at the mill (due to constant refrigeration), minimal variation was expected in COD values among samples. Total COD values for the three original samples were 28.1 g/L, 23.0 g/L and 23.4 g/L respectively, and sample P-1275 had a total COD of 25.5 g/L and a soluble COD of 3.0 g/L. It should be noted that unequal volumes of samples P-1242, P-1249 and P-1252 comprised the combined sample, P-1275.
Therefore, all sludge characteristic tests were performed on P-
1275 rather than averaging the values of the three original suspensions.
4.2 Characterization of Pulverized Coal
The objective in locating and selecting a pulverized coal for this study was to match its physical properties as close to the coal samples used in previous dewatering studies cited in
Chapter 2. This means of selecting of coal sample was chosen
46
since time constraints would not allow extensive testing with several coal samples. Availability of a mill for supply of the selected coal was a consideration as well. Figure 4.1 shows a
particle distribution on the coal sample used in this study (Plant-P), along with the sieve analysis of Pitzer (1977) for
comparison.
—41.— Pitzer —+— Plant-P
0 0.2 0.4 0.6 08 Sieve Opening (mm)
Figure 4.1: Particle Size Distribution of Plant-P and Pitzer (1977) Coal Samples
After selection of the coal sample, a determination of the proper coal dose to be added to the slurry before dewatering had to be made. This decision was aided by performing a heat balance on a typical dewatered filter cake produced in the pulp and paper industry. The heat balance was calculated to determine the amount of coal required for self-sustained combustion of the filter cakes in a boiler or incinerator. The balance is
47 presented in the appendix. The net energy of combustion values calculated at each coal dose indicated that self-sustaining combustion was reached at a coal addition just above 1.2 g coal/g dry sludge solids (DSS). However, this balance was performed on a typical pulp-and-paper, primary sludge filter cake (30% solids,
65% volatility, etc.) and specific heat values vary significantly in different texts for the sludge constituents. Therefore, the range of coal dosages selected in examining coal conditioning effects was 0.4 g/g DSS to 1.6 g/g DSS. In support of this selected range, several C-P cell runs were conducted on each Plant-P sample with varying coal additions to determine the coal dose at which dewatering characteristics were significantly affected. These preliminary filtration runs indicated that the same coal addition range determined from the heat balance was required to significantly improve filtration properties.
4.3 Sludge Dewaterability and Compressibility of Unconditioned Sludge Suspensions
4.3.1 CST Sludge dewatering characteristics can be affected by several factors which cannot be identified through physical and chemical sludge characteristic tests. Such factors include relative mass of fines in the suspension and the shape or structure of the organic particles. Usually, sludge suspensions with a high percentage of fines are difficult to dewater since fines result in blinding of the filter medium. The fibrous structure of the cellulose particles, which constitutes the majority of a pulp and 48 paper sludge suspension, forms a lattice under cake filtration which usually results in favorable dewatering. Conversely, waste
activated sludge has a gelatinous nature that tends to blind the filter medium in cake filtration. Therefore, it is difficult to
predict dewatering properties of a sludge by its physical and
chemical characteristics alone. The CST test serves as an acceptable preliminary method of determining sludge dewatering properties. CST data are included in Table 4.2 for all four
Plant-P samples along with their respective suspended solids concentrations. All CST tests were run at a constant temperature of 9 °C; three runs were performed for each sample and the average CST value recorded. The data in Table 4.2 indicated a significant difference in CST between the three original samples,
P-1242, P-1249 and P-1252, although their suspended solids concentrations were relatively equal.
Table 4.2: CST Data of Plant-P Samples
Sample CST(sec) SS(g/L) P-1242 369 24.7
P-1249 129 25.8
P-1252 100 23.8
P-1275 348 24.8
4.3.2 Filtration and Consolidation Results
To accommodate the large volume of a uniform sludge sample 49 needed to examine filtration at seven coal dosages and two pressures, the three original samples were combined to create a new combined sample, P-1275, of approximately 30 liters. In the initial stages of filtration, the resistance of fluid flow through the filter medium is significant and cannot be ignored. However, the constant-pressure filtration model described earlier assumes that the medium resistance is negligible. After a short time period the cake builds and the medium resistance does become negligible. At this point, the constant-pressure filtration model becomes valid. For sample P-
1275, the total length of a C-P cell run was 1.0 to 1.5 x 10 4 sec (167 to 250 min) and the filtrate in the first 1000 seconds was approximately 10% of the final filtrate volume. Therefore, data acquired in the initial 1000 seconds of a C-P run was omitted to insure that data manipulation was performed on data gathered after the system reached an operating equilibrium. Upon collection of filtrate volume versus time for an entire expression by a personal computer, spreadsheet and plotting software allowed easy conversion of data. Converting filtrate volume, V, into cake thickness, L, led to the calculation of the term -dL/de .5 . Plotting -dL/dtm versus time, t, is referred to as the Ruth plot (stemming from Ruth's filtration equation). Visual inspection of the Ruth plot indicates the transition point between filtration and consolidation phases. Ruth plots on sample P-1275 at pressure differentials of 1100 kPa and 3300 kPa are shown in Figures 4.2 and 4.3 respectively. From Equ. (13),
50 the point at which the value of -dL/dt °3 begins to deviate from a constant marks the time at which the transition point occurs. The slopes of the filtration phase for Figs. 4.2 and 4.3 are 0.05
and 0.06 respectively. The slopes are slightly greater than the
theoretical slope of zero expected during the filtration phase.
This slight variation could be caused by blinding of the pores of a filter cake by fines, or by a non-uniform cake structure forming during filtration. The transition point at the lower pressure run, Fig. 4.2, was located at 10440 sec, and at 9720 sec
for the higher pressure run. It is evident that the time to reach the transition point should decrease with increasing pressure (and increasing coal dosage described later). However, this observation cannot be used as a direct comparison between
filter runs to indicate the rate at which filtration proceeds since the initial sludge volumes are not identical for each C-P cell run. A term, referred to as yield, will be introduced later to address this issue.
The plot of log V vs log t data during the filtration phase should result in a line with a slope of 2 based on Darcy's law. A linear regression on the log V vs log t plots for P-1275 at
1100 kPa and 3300 kPa reveals slopes of 1.67 and 1.84 respectively. Both plots had excellent regression coefficients (about 1.0) and were considered to be reasonably close to the theoretical value of 2, considering that the experimental model of constant-pressure filtration incorporates many assumptions in its formulation.
51 The cake solids contents of P-1275 at 1100 kPa and 3300 kPa were 39.18% and 47.42% respectively. Further, the ultimate cake solids content for a C-P cell run can be determined from a plot of dV/dt vs V, Figs. 4.4 and 4.5 for at 1100 kPa and 3300 kPa. A linear regression of the data corresponding to the consolidation phase projects the ultimate filtrate volume. The consolidation phase data in the rate plot is the same data indicated by the Ruth plot. The linear regression coefficients of the consolidation phase data of the dV/dt vs V plots are both equal to 0.98, indicating a good linear relationship. Degree of completion for each run can be obtained by the ratio of the final filtrate volume collected and the ultimate filtrate volume projected for a C-P cell run. For the expression runs at 1100 kPa and 3300 kPa, degrees of completion were 98% and 99%, respectively. The ultimate filtrate volume was determined by extrapolating the regression of the consolidation phase data in the dV/dt vs V plot to a dV/dt value of zero. The absolute value of the slope of this regression indicates the rate at which the cake is consolidating. The runs at 1100 and 3300 kPa had similar rates of consolidation (slopes of 4.22 and 4.84 x 10 -4 respectively). Subtracting the difference between the final and ultimate filtrate volumes from the wet mass of the filter cake enables the ultimate cake solids content to be calculated. The ultimate cake solids contents at 1100 kPa and 3300 kPa were 55.9% and 61.4%, respectively, about 10 to 15 % higher than the actual cake solids contents achieved at the end of each run.
52
1.000 - • • P-1275-1100 kPa Coal Addition: 0
Consolidation: 10440 s 0.1 00 nitration phase 0 Slope = 0.05
0.010 1000 E4 1E5
4. 1_ _A
Figure 4.2: Plot of -dL/dtm vs t at a Pressure of 1100 kPa
P-1275-3300 kPa
Coal Addition: 0
Consolidation: 9720 s
• rir
= 0.06
0.010 1000 1 E 4 1 E5
t (sec)
Figure 4.3: Plot of -dL/c1.0 -5 vs t at a Pressure of 3300 kPa
53 Figure 4.5:PlotofdV/dtvsVat aPressureof3300kPa Figure 4.4:PlotofdV/dtvsVataPressure1100kPa
dV/ dt (r nL/sec ) dVdt (m L/sec) 0.000 i 0.100 1- 0.200 0.300 0.400 0.000 0.100 0.200 0.300 0.400 0 L I- 0
0 0 0 0 C 0 200 200
54 V (mL) V 400 Slope =—4.54x10 400 Degree ofcompletion:99% Coal Addition:0 P-1275-3300 kPa ( Slope =—4.22x10 Degree ofcompletion:98% Coal Addition:0 P-1275-1100 kPa m L) 600 600 -4 -4
800 800 The most common term used in research today to characterize sludge dewatering is the average specific resistance parameter (a). Plotting t vs V filtration phase data and performing a
second-order, non-linear regression can lead to the determination
of the average specific resistance. From Equ. (8), Et can be
calculated with the second order regression coefficient, pressure, filter area, fluid viscosity, and dry sludge solids deposited per volume of filtrate term, w, all being known values. Average specific resistance values at 1100 kPa and 3300 kPa were 31.46 Tm/kg and 87.83 Tm/kg, respectively. Since average specific resistance is directly proportional to applied pressure, a increases as the pressure differential increases. Hence, the run at 1100 kPa has a significantly less resistance to filtration than at 3300 kPa. Compressibility of a sludge suspension under constant- pressure filtration involves the compaction, or collapsing, of the cake structure during the consolidation phase. The compressibility index, S, which indicates degree of compressibility is equal to the slope of the applied pressure versus average specific resistance plot. Figure 4.6 shows this plot for zero coal addition. Two additional C-P cell runs were conducted at pressures of 1468 kPa and 2385 kPa and zero coal dose to verify the linearity of the P vs Er data. The compressibility index value at zero coal dose was 0.93 which indicated moderate compressibility.
55 1000
) P-1275 kg / Tm ( e 100 tanc is Res ic
if 10 ec Sp Avg.
1 100 1 000 1E4
Pressure (kPa)
Figure 4.6: Plot of Average Specific Resistance (a) vs Pressure at Zero Coal Dose
4.3.3 Mass Balance on C - P Cell Runs
An overall mass balance on the C-P cell expression process is presented in Table 4.3 on a total sludge mass basis, and on a dry solids mass basis in Table 4.4. In the tables, the
"residual" column refers to the mass ejected out of the air release valve of the piston during the application of the load.
Percent recovery was determined by the ratio of the sum of the filtrate volume, cake mass and residual mass and the input suspension. All values in Table 4.4 were obtained by multiplying the appropriate value in Table 4.3 by the initial suspended solids concentration of P-1275 (which assumes the specific
56
gravity, Sg, of the sludge suspension is approximately equal to 1). Tables 4.3 and 4.4 indicate excellent percent recoveries, between 96 and 98 %.
Table 4.3: C-P Cell Mass Balance on a Total Sludge Mass Basis at Zero Coal Addition
Mass, g Input Wet Output Percent Pressure Susp. Cake Filtrate Residual Sum Recovery 1100 kPa 819.0 49.0 717.9 28.1 795.0 97.1 3300 kPa 813.4 44.3 743.6 3.1 791.0 97.2
Table 4.4: C-P Cell Mass Balance on a Dry Solids Mass Basis at Zero Coal Addition
Mass, q Input Cake Percent Pressure DS DS Residual Sum Recovery 1100 kPa 20.3 19.2 0.7 19.9 98.0 3300 kPa 20.2 19.3 0.1 19.4 96.0
4.3.4 Comparison of Results with Previous Plant-P Samples Sun (1990) conducted extensive C-P cell expression research on six Plant-P samples. These samples were taken from similar settling basins about two years apart. Therefore, any deviation in physical or chemical sludge characteristics or in dewatering properties is due to the detention time in the basins if the
57 plant operations are assumed to be the same. Table 4.5 lists the physical and chemical sludge
characteristics of P-1275 and the previous Plant-P samples (referred to herein as P-42). The values presented for P-42 are averages of the six P-42 samples. The P-42 samples had about 2.5
Table 4.5: Comparison of Sludge Suspension Characteristics for Plant-P Samples
(g/L) pH SS VSS VSS/SS Total Sol. Susp.COD/ Sample (q/L) (q/L) (%) COD COD VSS(a/q) P-1275 6.8 24.80 16.70 67.3 25.52 2.97 1.35 P-42 * 6.6 61.58 39.42 64.0 46.81 2.63 1.12 * average of six data points times the suspended solids concentration as P-1275. This is due to the fact that P-42 samples were gravity thickened upon arrival in the lab. Volatilities and pH values were very similar. Total COD values for P-42 were approximately double the values of P- 1275, where P-1275 has a slightly higher soluble COD. A comparison of dewaterability and compressibility characteristics of Plant-P samples is presented in Table 4.6. The -dL/de -5 slopes for P-1275 were slightly greater than the zero slopes of P-42. Slope values for log V vs log t were very similar between Plant-P samples. Ultimate cake solids contents for P-1275 were about 5 to 10 % higher compared to P-42. Average specific resistance for P-1275 was significantly greater than
58 P-42, and compressibility indexes were approximately equal.
Table 4.6: Comparison of Dewaterability and Compressibility Characteristics for Plant-P Samples
Slope, (1100/3300 kPa) (1100/3300 kPa)
Sample -dL/dt m logy vs logt Ult. C k** a S P-1275 0.05/0.06 1.67/1.84 55.9/61.4 31.5/87.8 1.03
P-42 * 0/0 1.79/1.74 45.5/56.6 7.3/26.1 1.09
* average of six data points ** ultimate cake solids, percent *** average specific resistance, Tm/kg
4.4 sludge Dewaterability and Compressibility of Coal Conditioned Sludge Suspensions 4.4.1 Filtration and Consolidation Results Dewatering characteristics of sample P-1275 at various coal dosages were examined to determine the effect of pulverized coal as a physical conditioning agent. C-P cell expressions were run at the same pressure differentials of 1100 kPa and 3300 kPa and at coal dosages of 0.4, 0.8, 1.0, 1.2, 1.4, and 1.6 g/g DSS.
Figures 4.7 through 4.12 represent Ruth plots,i.e., -dL/dt m vs t, for coal additions ranging from 0.4 g/g DSS to 1.6 g/g DSS at a pressure of 1100 kPa. Following are Figs. 4.13 to 4.18 representing -dL/dt m vs t plots at 3300 kPa for the varying coal doses. All Ruth plots clearly indicated the transition point between the filtration and consolidation phases. Filtration phase slopes are slightly greater at 1100 kPa, ranging from 0.07
59
P-1275-1100 kPe, Coal Addition: 0.4 g/g DSS
C) Consolidation: 8250 s E 0.100 Filtration W-zne to o S Slope = 0.08 a C 0
0.010 1000 ;E4 1 E:.
t sec)
Figure 4.7: Plot of -dLidt°-5 vs t at a Pressure of 1100 kPa and Coal Dosage of 0.4 g/g DSS
1.000 F-1275-1100 kPa Coal Addition: 0.8 g/g DSS
yJ = Consolidation: 6660 s ® Filtration phase 0.100 0 Slope = 0.07
0 0
0.07C 1000 1 E4 1 E5
t (sec)
Figure 4.8: Plot of -dL/dt m vs t at a Pressure of 1100 kPa and Coal Dosage of 0.8 g/g DSS
60
1.000 P-1275-1100 kPa Coal Addition: 1.0 g/g DSS C C) Consolidation: 5400 s 0 Filtration phase slope = 0.10 0. 1 00 O O O
1 O
0.010 1000 1 E4 1E5
t (sec)
Figure 4.9: Plot of -dL/dt" vs t at a Pressure of 1100 kPa and Coal Dosage of 1.0 g/g DSS
P-1275-1130 kPa Cool Addition: 1.2 g/g DSS
:gamm=224 4 0 o Consolidation: 4680 s Fiftrotion phone siooe = 0.37_
C.CIC 1E4 1E5
t (sec) Figure 4.10: Plot of -dL/dt m vs t at a Pressure of 1100 kPa and Coal Dosage of 1.2 g/g DSS
61 1 .000 P-1275-1100 kPa Cool Addition: 1.4 g/g DSS ro U keEtvzomsamoP11"ml% Consolidation: 4500 s E 0 0.100 Filtration phase slope = 0.08 0 Ls-) ci 0
0
0 0 0.010 . • • • 1000 1E4 1 E5
t (sec)
Figure 4.11: Plot of -dL/dt m vs t at a Pressure of 1100 kPa and Coal Dosage of 1.4 g/g DSS
1.000 P-1275-1100 kPa to Coal Addition: 1.6 g/g DSS
U Consolidation: 3600 s E Filtration phase slope = 0.08 0.100
0 0
D
0.010 1000 1E4 1E5
t (sea)
Figure 4.12: Plot of -dL/dt m vs t at a Pressure of 1100 kPa and Coal Dosage of 1.6 g/g DSS
62 1.000 - P-1275-3300 kPa r. rn Coal Addition: 0.4 g/g DSS
E Consolidation: 7560 s 0 O Ln Filtration phase c5 0 0 Slope = 0.04 0
. 0 0 0
0.010 1000 1E4 1E5
t (sec)
Figure 4.13: Plot of -dL/dt°-5 vs t at a Pressure of 3300 kPa and Coal Dosage of 0.4 g/g DSS
1.000 P-1275-3300 kPa Coal Addition: 0.8 g/g DSS
FEENermsfifeSts I Consolidation: 4860 s
Filtratior phase slope = 0.0 O
O
O
O
O
0.010 1300 1E4 1E5
t (sec) Figure 4.14: Plot of -dL/dt m vs t at a Pressure of 3300 kPa and Coal Dosage of 0.8 g/g DSS
63
1.000 P-1275-3300 kPa Coal Addition: 1.0 g/g DSS
C) ..... • • 44 E Consolidation: 3960 s 0 0.100 Filtration phase slope = 0.08 O V O -J 0 O O O 0.010 1000 1E4 1 E5
t (sec)
Figure 4.15: Plot of -dL/dt 13-5 vs t at a Pressure of 3300 kPa and Coal Dosage of 1.0 g/g DSS
1.000 P-1275-3300 kPa Coal Addition: 1.2 g/g DSS
0 Consolidation: 4' 42 s o Eqretion — r,
0.010 1000 1E4 1E5
t (sec)
Figure 4.16: Plot of -dL/dt °5 vs t at a Pressure of 3300 kPa and Coal Dosage of 1.2 g/g DSS
64 1.000 P-1275-3300 kPa Coal Addition: 1.4 g/g DSS 1 • Consolidation: 3600 s 0
0.100 Filtration phase slope = 0.05 / tr) r 0 3 -J --a o
0
0.010 10i0 1E4 1E5
t (sec)
Figure 4.17: Plot of -dL/dt" vs t at a Pressure of 3300 kPa and Coal Dosage of 1.4 g/g DSS
1.0 0.. P-1275-3300 kPa
Coal Addition: 1.6 g/g DSS
W Hm.147 Consolidation: 3180 s Filtration phase slope = 0.07_, 3 0.100 0
-a 0 0
0
0.010 1 000 1E4 1E5
t (sec)
Figure 4.18: Plot of -dL/dt" vs t at a Pressure of 3300 kPa and Coal Dosage of 1.6 g/g DSS
65 to 0.10; slopes range from 0.04 to 0.08 at 3300 kPa. Filtration
phase slope values, including those at zero coal dose, are listed in Table 4.7. These slopes have slightly positive value, but are
relatively close to the theoretical slope of zero given by the Ruth equation for constant-pressure filtration. The time required to reach the transition point for each expression process decreased as coal dosage increased, except at 1.0 g/g DSS and 3300 kPa. This trend indicates that increased coal addition has a positive effect on the rate of filtration.
This topic will be assessed in a later section by the filter
yield term. Figure 4.19 shows the elapsed filtration time to
reach the transition point at varying coal dosages for runs at 1100 and 3300 kPa. One final observation about the -dL/dt m vs t plots is the
jump in the filtration phase portion of the plot at about three- fourths of the time to reach the transition point. This jump corresponds to a sudden increase in the rate of filtration.
Since the runs at zero coal addition (Figs. 4.2 and 4.3) show the
same jump in the filtration phase, an air pocket may be passing through the cake which would be followed by a surge of filtrate.
66 Table 4.7: Filtration Phase Slopes for -dL/dt" vs t Plots at 1100 kPa and 3300 kPa and Varying Coal Dose
Slope of Plot (cm/sec)• Coal Dose (g/q) 0 0.4 0.8 1.0 1.2 1.4 1.6
1100 kPa 0.05 0.08 0.07 0.10 0.07 0.08 0.08
3300 kPa 0.06 0.04 0.05 0.08 0.05 0.05 0.07
12.00
1100 kPa —+—
3300 kPa 1 0E3 sec) (x
6.00 Time
Filt. d se 3.00 Elap
0.00 0.00 0.50 1.00 1.50 2.00 Coal Dosage (g/g DSS)
Figure 4.19: Elapsed Filtration Time to Reach Transition Point at 1100 and 3300 kPa and Varying Coal Dose
67 Values of the slopes resulting from plots of log V versus log t for the filtration phase of the C-P cell expression process are given in Table 4.8. Average log V vs log t slopes at 1100 and 3300 kPa were 1.63 and 1.70, respectively. The slopes deviated from Darcy's theoretical value of 2. A contributing factor could be the fibrous nature of the sludge. Filtration of a colloidal-type sludge suspension, aluminum finishing sludge, resulted in a theoretical value of 2 (Johns, 1985).
Table 4.8: Slopes of log V vs log t Plots at 1100 and 3300 kPa and Varying Coal Dosages
Slope of Plot Coal Dose (g/q) 0 0.4 0.8 1.0 1.2 1.4 1.6 1100 kPa 1.67 1.61 1.64 1.48 1.68 1.65 1.65 3300 kPa 1.84 1.72 1.69 1.71 1.66 1.67 1.63
Figures 4.20 to 4.31 are dV/dt vs V plots for 1100 kPa and 3300 kPa, respectively, at varying coal additions. The plots indicate the transition point between filtration and consolidation phases when the curve deviates towards the x-axis (at approximately 90% completion of the run). Linear regression of the portion of the plot following the transition point results in the determination of the ultimate cake solids concentration. Slopes of the consolidation phase data of the dV/dt vs V plots indicate that rate of consolidation increased with increased coal dosage. Furthermore, consolidation progressed at a higher rate 68 at 3300 kPa compared to 1100 kPa at each coal dose. These results are presented in Figure 4.32. Degrees of completion for all runs at both pressures were extremely high, indicating consolidation was carried out close to completion. Degree of completion values were rounded to the nearest percent, resulting in seven runs with values of 100% (although the ultimate filtrate volume was never quite reached). Cake solids contents achieved from C-P cell expression increased with increasing coal addition. The actual cake solids values range from 39% to 56% at 1100 kPa, and 43% to 64% at 3300 kPa for the coal dosage range. Ultimate cake solids values range from 55% to 59% at 1100 kPa and 60% to 66% at 3300 kPa (except for the uncharacteristic run at 1.0 g/g DSS). Table 4.9 shows the actual and ultimate cake solids contents, as well as degrees of completion, for all C-P cell runs at 1100 kPa and 3300 kPa.
69
0.400
• n -7r 4 4 ^r, I L kai
ticn: C.4 cfc DSS
0.300 - J ) Decree of completion: 9R:*
L/sec aape = —5.74 x 10-4 C 0.200 - 0c (rn dt dV/ 0.100
0.0DC.1 0 200 400 600 800
V (rriL)
Figure 4.20: Plot of dV/dt vs V at a Pressure of 1100 kPa and Coal Dosage of 0.4 g/g DSS
0.400 P-1275-1 100 kPa Coal Addition: 0.8 g/g DSS 0.300 0 U Decree of completion: 99% Slope = —9.57 x 1C -4
0.1DC
1 £..000I 0 20. 400 600 800
V (mL)
Figure 4.21: Plot of dV/dt vs V at a Pressure of 1100 kPa and Coal Dosage of 0.8 g/g DSS
70 0.400 T P-1275-1100 kPa o Coal Addition: 1.0 g/g DSS 0.300 0 c) Degree of completion: 100% e
s 0
/ Slope = —1.65 x 10 -3 t. 0
m 0.200 t ( d / IV L 0.100
200 4-00 600 603
)
Figure 4.22: Plot of dV/dt vs V at a Pressure of 1100 kPa and Coal Dosage of 1.0 g/g
C.4.00 1
Coal Addition: 1 2 c/g DSS
) 0300;-
0 o Decree of completion: 99% L/sec
:.2 n0 ( = —1.62 x 10 - (rn 11.
uJT dV/(
0.000 0 200 400 600 800
(mL)
Figure 4.23: Plot of dV/dt vs V at a Pressure of 1100 kPa and Coal Dosage of 1.2 g/g DSS
71 0.400 T 0 P-1275-1100 kPa 0 Coal Addition: 1.4 g/g DSS 0.300 Degree of completion: 100% 0 Slope = —1.62 x 10 -3
V ( 7" )
Figure 4.24: Plot of dV/dt vs V at a Pressure of 1100 kPa and Coal Dosage of 1.4 g/g DSS
9.430 0 P-1275-11 CO kPo
1.6 g/g 055 290 ) c Decree of completion: 100% o
/sec Sioot = —1.97 x 13 — d 0.200 H it (
d1//c 0.100
0.000 0 200 400 600 600
v (mL)
Figure 4.25: Plot of dV/dt vs V at a Pressure of 1100 kPa and Coal Dosage of 1.6 g/g DSS
72
0.400 . P-1275-3300 kPa Cool Addition: 0.4 g/g DSS
0.300 ) c Decree of completion: 99% 0 L/se Slope = —9.00 x 10-4 0.200 (m dt dV/ 0.1 00 t-
0.000 200 400 600 800
•0: (r L)
Figure 4.26: Plot of dV/dt vs V at a Pressure of 3300 kPa and Coal Dosage of 0.4 g/g DSS
0.400 0 P - 1275 - 3300 kPo
o Cool Addition: 0.8 g/g DSS 0.300 !-
) Decree of completion: 99%
L/sec. Slope = —1.43 x 10 -3 0.200 (m it dV/c 0.100 r °000ocio----0
0..00 0 200 400 600 600
V (mL)
Figure 4.27: Plot of dV/dt vs V at a Pressure of 3300 kPa and Coal Dosage of 0.8 g/g DSS
73 0.400 P-1275-3300 kPa Coal Addition: 1.0 g/g DSS
) 0..300
Degree of completion: 100% L/sic.
0.200 Slope = —1.94 x 10 -3 (rri dt dV/ 0.100
0.000 a 200 400 600 800
V (mL)
Figure 4.28: Plot of dV/dt vs V at a Pressure of 3300 kPa and Coal Dosage of 1.0 g/g DSS
0.400 P-1275-3300 kPa
c Cool Addition: 1.2 g/g DSS 0.200
) c o D e ree rsf 1 L/sec 0.200 it (m
dV/c 0.100
0 200 4-00 600 BOO
V (mL)
Figure 4.29: Plot of dV/dt vs V at a Pressure of 3300 kPa and Coal Dosage of 1.2 g/g DSS
74
0.400 P-1275-3300 kPa
Coal Addition: 1.4 g/g DSS
) 0.300 1- 0 ,: I a Degree of completion: 100%
L/se 00 go 0.230 07- Slope= —2.02 x 1 0 -3 dl (m dV/ 0. 1 00
0.000 L 0 L'43 600 600
V (—L)
Figure 4.30: Plot of dV/dt vs V at a Pressure of 3300 kPa and Coal Dosage of 1.4 g/g DSS
0.430 P — 1 275 — 3300 kPa Cool Addition: 1.5 g/g 055 0.200 Decree of completion: 100% 00c • o db% S!ope = —2.93 x 10 -3
0.100
0.000 0 200 4-00 600 600
V (7-1L)
Figure 4.31: Plot of dV/dt vs V at a Pressure of 3300 kPa and Coal Dosage of 1.6 g/g DSS
75
•
1100 kPa —4--
) 3300 kPa 3 1/s 10E- (x e Slop
e Phas Cons.
0.00 0:50 1:00 1:50 2.00 Coal Dosage (g/g DSS)
Figure 4.32: Slopes of Consolidation Phase Portion of dV/dt vs V. Plots at 1100 kPa and 3300 kPa
90 .0
1100 kPa 80.0
cr) 3300 kPa 70.0 , E▪ • 60.0 - U ca T.6 50.0- U 40.0 - 4
at oC)_ 30.0- -
> 20.0-
10.0
0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Coal Dosage (g/g DSS)
Figure 4.33: Average Specific Resistance vs Coal Dosage at 1100 kPa and 3300 kPa
76 Table 4.9: Actual Cake Solids , Ultimate Cake Solids Contents, and Degree of Completion Data for 1100 and 3300 kPa at Varying Coal Additions
Cake Solids Contents (%) Coal Dose 1100 kPa 3300 kPa % Completion (gig) Actual Ultimate Actual Ultimate (1100,3300) 0 39.18 55.85 47.42 61.44 98,99
0.4 45.62 58.63 53.04 60.14 98,99 0.8 52.42 59.07 59.68 64.85 99,99
1.0 54.21 56.86 56.26 57.87 100,100
1.2 52.96 55.78 62.41 64.88 99,100
1.4 55.09 57.07 63.24 66.00 100,100
1.6 56.38 58.47 63.95 65.29 100,100
P-1275
Coo; Dose (c/c): '00 i-t 0---0 0 • -• 0.4 4, -4, 0.5 •- A 0 10 t- ❑ --- ❑ L2 ■ [. -1 1.4 v-v 1.6
1 1 .1 100 1000 1E4
Pressure (kPa)
Figure 4.34: Plot of Average Specific Resistance (E) vs Pressure at Varying Coal Additions
77 Plots of t vs V of the filtration phase data for each C-P cell run enables the average specific resistance (5) value to be calculated. The average specific resistance values for varying coal dosages at pressure differentials of 1100 kPa and 3300 kPa are included in Figure 4.33. From Figure 4.33, it is evident that resistance to filtration decreases with increasing coal additions. At both pressures, average specific resistance is reduced by about one order of magnitude. The reasons for the reduction in resistance of filtration is assumed to be that the coal particles give strength to the cake, thus providing a better drainage matrix and porosity for fluid to move through the filter cake. Figure 4.33 indicates that the majority of reduction in average specific resistance occurs from zero to 1.0 g/g DSS coal addition at both pressures, with minimal reduction at coal dosages beyond 1.0 g/g DSS. At 1100 kPa, average specific resistance values decreased from 31.5 Tm/kg to 5.8 Tm/kg at coal dosages of zero to 1.0 g/g DSS respectively, accounting for approximately 90 percent of the 5 reduction. Minimal reduction occurred at dosages 1.0 to 1.6 g/g DSS. Values decreased from 5.8 Tm/kg to 3.0 Tm/kg (about 10%). Similarly, at
3300 kPa, average specific resistance decreased from 87.8 Tm/kg to 14.4 Tm/kg at coal additions of zero to 1.0 g/g DSS respectively (approximately 93% reduction). Again, minimal & reduction was encountered between coal dosages of 1.0 to 1.6 g/g
DSS. Values decreased from 14.4 Tm/kg to 9.1 Tm/kg (about 7%).
Compressibility indexes at the various coal additions were
78 generated by plotting & versus pressure. Fig. 4.34 includes the plots for P-1275 at all coal dosages. Due to sludge volume limitations, the linear relationship verified at zero coal addition is assumed to be the case for all coal dosages and, therefore, no additional pressures were examined. From Fig. 4.34, the slopes of the regression lines for all seven coal dosages (including zero coal dose) are very consistent. Compressibility indexes, S, are approximately equal to 1, ranging from 0.82 to 1.02. The consistent S values indicate that increasing coal addition did not considerably increase the degree of compactibility of the filter cake during filtration.
4.2.2 Mass Balance on C - P Cell Runs
Mass balances on C-P cell runs at the varying coal additions are presented on a total sludge mass basis in Table 4.10, and on a dry solids mass basis in Table 4.11. The dry solids mass included both dry sludge solids and coal. Tables 4.10 and 4.11 indicate very high percent recoveries, all above approximately
95%. N residual sludge (sludge ejected out of the air release valve in the piston) was recovered in any of the runs, therefore, the tables do not include it. All values except for percent recoveries have units of grams, and the input suspension values include the respective coal additions.
79 Table 4.10: C-P Cell Mass Balance on a Total Sludge Mass Basis
(Pressure) Input Wet Output Coal Dose (q/q) Susp. Cake Filtr. Sum %Rec
(1100 kPa) 0.4 836.4 61.6 761.7 823.3 98.4 0.8 846.4 69.6 758.0 827.6 97.8 1.0 839.6 72.3 724.4 796.7 94.9 1.2 838.1 81.7 745.5 827.2 98.7 1.4 868.2 87.7 775.7 863.4 99.4 1.6 858.9 92.9 759.9 852.8 99.3
(3300 kPa) 0.4 829.1 53.9 759.9 813.8 98.2 0.8 829.3 59.8 755.0 814.8 98.2 1.0 833.6 71.0 747.2 818.2 98.2 1.2 835.1 69.3 751.4 820.7 98.3 1.4 848.5 76.2 750.4 826.6 97.4 1.6 837.9 80.4 740.8 821.2 98.0
Table 4.11: C-P Cell Mass Balance on a Dry Solids Basis
(Pressure) Coal Dose (qjg) Input DS Cake DS Sum
(1100 kPa) 0.4 28.8 28.1 97.6 0.8 37.1 36.5 98.4 1.0 40.7 39.2 96.3 1.2 44.4 43.3 97.5 1.4 50.0 48.3 96.6 1.6 53.3 52.4 98.3
(3300 kPa) 0.4 28.6 28.6 100 0.8 36.5 35.7 97.8 1.0 40.5 39.9 98.5 1.2 44.5 43.2 97.1 1.4 49.0 48.2 98.4 1.6 52.2 51.4 98.5
80 4.5 Assessing the Effectiveness of Coal Conditioning 4.5.1 Cake Concentration Profiles Theoretically, if the suspended solids concentration profile during the filtration phase is constant, a valid average specific resistance value can be determined. Bierck does show that the suspended solids content of a filter cake is constant at any point during the filtration phase by plotting normalized height, z/H, vs cake solids concentrations (Fig. 2.10). In this study, an X-ray apparatus was not accessible to confirm what happens during the filtration phase. Therefore, this study focused on the mechanisms involved during the consolidation of a filter cake under the expression process. However, the transition point profile should be equal to the constant profile achieved during the entire filtration phase. In this study, effects of coal addition on the cake concentration profiles between the time of transition and the end of the expression run were examined. The C-P cell runs were stopped at four times to produce four profiles for coal dosages of zero, 0.4 g/g DSS and 1.4 g/g DSS. In addition to the transition point and the end of the run, expression runs were stopped at two intermediate points referred to as DT1 and DT2.
Figs. 4.35 to 4.37 are the cake profile plots for P-1275 at 1100 kPa and zero, 0.4 g/g DSS and 1.4 g/g DSS coal additions respectively. The normalized distance, W/Wo, is the ratio of the cake height at any time and the height of the cake at the transition point (Wo). As described earlier, the filter cakes
81
1.000 P-1275-1100 kPa
Coal Addition: 0 0.750 o—o TRN • —• DT1
0.500 4—A DT2 • —• END • 0.250 • • 0.0 00 10 20 30 40
Note: TRN = Transition point Coke Solids b%) DTI, DT2 = Intermediate points END = End of. GP cell run
Figure 4.35: Normalized Cake Height vs Cake Solids Content at Zero Coal Dose and 1100 kPa 1.330 ! P-- ", 275-1100 kPa
Coal Addition: 0.4 a/c DSS 3-0 ;RN 3.750 !- DT1
0 -11 DT:
• A A END \
0.250
0.000 10 20 30 40 50
Note: TRN = Transition point DTI, DT2 - Intermediate points Cake Solids (%) END - End of GP cell run
Figure 4.36: Normalized Cake Height vs Cake Solids Content at 0.4 g/g DSS and 1100 kPa
82
1.000 P —1275— 1100 kPa Coal Addition: 1.4 g/g DSS 0.750 t- 0-0 TRN •—• DT1
A A DT2 0.500 END
0.250
0.000 20 30 40 50 60
Note: TRN = Transition point Cake Solids (%) DTI, DT2 = Intermediate points END = End of C-P cell run
Figure 4.37: Normalized Cake Height vs Cake Solids Content at 1.4 g/g DSS and 1100 kPa
were cut horizontally in thirds resulting in three cake solids data points at each run: TRN, DT1, DT2 and END. Also, each data point represents the average cake solids concentration for its respective third of the cake; therefore, it represents and is plotted as the mean of its third of the corresponding normalized height of the cake as well.
From Figs. 4.35 to 4.37 it is evident that the slope of each profile line increases from TRN to END at a given coal dose. The
END profile lines are near vertical, indicating a constant cake solids concentration is nearly met. Slopes of each of the four profile lines increase as coal addition increases as well. Fig.
4.37 reveals that complete consolidation is reached significantly
83 faster at a high coal dosage. It should also be noted that all profile lines in Bierck's work converged to a common point equal to the cake solids concentration at the bottom-most layer of the cake (nearest the filter medium). The reason Figs. 4.35 to 4.37 do not indicate this convergence is that the bottom point on each profile line represents the average cake solids content of the entire bottom third of the cake. Therefore, although the bottom- most layer of each run was assumed to have a common (and highest) value, the "cake cutting" method does not allow these points to be determined. Figure 4.38 to 4.46 are the -dL/dt m vs t plots for the TRN, DT1 and DT2 runs of Figs. 4.35 to 4.37. The Ruth plots indicate the various lengths of each run. The corresponding END run Ruth plots were presented in Sections 4.3.2 and 4.4.1.' These plots essentially indicate the degrees of completion at which each expression run was terminated.
The same cake solids data were plotted versus the actual cake length above the filter medium in Figs. 4.47 to 4.49. No significant change in slope of profile lines was encountered at zero, 0.4 g/g DSS or 1.4 g/g DSS coal additions. The cake solids content data for 0.4 and 1.4 g/g DSS were manipulated, or
"corrected", for coal addition by factoring out the coal added in each cake solids content calculation (subtracting mass of coal in the numerator and denominator):
% Cake Solids = Total Dry Solids = DSS + Dry Coal Wet Cake DSS + Dry Coal + Water
"Corrected" Cake Solids = DSS DSS + Water 84 Thus, cake concentration profiles can be viewed on a dry sludge solids basis. Figs. 4.50 and 4.51 represent cake profiles corrected for coal addition versus cake length at 0.4 g/g DSS and 1.4 g/g DSS. Comparing Figs. 4.48 and 4.49 to Figs. 4.50 and 4.51 respectively, it is concluded again that the slopes of the profile lines remain consistent although the lines shifted along the x-axis due to factoring out the coal. Cake solids concentration profiles have served as a useful tool in analyzing filtration and consolidation data. Cake profiles were obtained for the fourteen end runs (seven coal doses at two pressures) in which all the filtration and consolidation results were derived. Figs. 4.52 and 4.53 show the profiles at varying coal doses at 1100 kPa and 3300 kPa respectively; all runs were taken to the common end point previously established. In Fig. 4.52, all profile lines are relatively vertical, indicating that the filtration and consolidation data (cake solids, ultimate cake solids, S, etc.) can all be directly compared. In Fig. 4.53, however, profile lines at 0.4 g/g DSS and 1.0 g/g DSS coal dosages are not vertical, indicating consolidation of the upper portion of the filter cake was not completed. This indicates that consolidation data at these coal additions are not comparable with the remaining coal additions at 3300 kPa. Also, in several profile lines, the middle-third data point (cake solids concentration) was higher than the lower-third, resulting in a concave shaped curve. Possible contributing factors could be displacement of
85 some moisture between cake layers while handling and cutting the filter cake, excessive moisture was contained in the filter paper which is compressed to the bottom (therefore the bottom-third) of the cake after a C-P cell run, or other inherent experimental errors. Furthermore, Fig. 4.54 is a plot of cake concentration profiles at the same coal condition at varying pressure. The resulting profiles are very similar; their slopes are very consistent and the profile lines are separated by 3% to 4% in cake solids content along the x-axis.
86 1.000 P-1275-1100 kPa (TRN) Coal Addition: 0
U 0
E 0.100 in O
-J "r)
0.010 I. 1000 1E4 1E5
t (sec)
Figure 4.38: Plot of -dL/dt m vs t for the TRN Run at Zero Coal Dose and 1100 kPa
1 .000 P-1275-1100 kPa (DT1) Coal Addition: 0
0 xtrazu=surnmerscP2""mk.
0.1 CC ii
0.010 1 1 000 1E4 1E5
t (sec)
Figure 4.39: Plot of -dL/dt M vs t for the DT1 Run at Zero Coal Dose and 1100 kPa
87
P-1275-1100 kPc In ar-if-4 ;+6711- C
fa) -oe'rft77-r E U .1CC c) 0 F
0.010 100 C. 1E4 1E5
t (sec)
Figure 4.40: Plot of -dL/dt°* 5 vs t for the DT2 Run at Zero Coal Dose and 1100 kPa
P-1275-1100 kPa (TRN)
Coal Addition: 0.4 g/g DSS
a=m1=ettiallor="ke
Z. CZ -
1 000 1E4 1E5
t (sec)
Figure 4.41: Plot of -dL/dt m vs t for the TRN Run at 0.4 g/g DSS and 1100 kPa
88
1.000 P-1275-1100 'AP0 (DTI )
Cool Addition: C.4 g/g DSS
deq§z=gavect==' o\c o
0.010 1000 1E4 1 E5
t (sec)
Figure 4.42: Plot of -dL/dt ° '5 vs t for the DT1 Run at 0.4 g/g DSS and 1100 kPa
1 .0 00 P-1275-1100 kPc.: (0T2)
Cool Addition: 0.4 g/g DSS
6====, masgmmri?‘
0 0
C.: 1 G 1 000 1E4
(sec;
Figure 4.43: Plot of -dL/dt m vs t for the DT2 Run at 0.4 g/g DSS and 1100 kPa
89
1.000 P-1275-1100 kPa (TRN)
Coal Addition: 1.4 g/g DSS 6 U U
U 0.100 =
0.010 1000 1E4 1E5
t (sec)
Figure 4.44: Plot of -dL/dt" vs t for the TRN Run at 1.4 g/g DSS and 1100 kPa
1.000 P-1275-1100 kPa (DT1)
Cool Addition: 1.4 g/g DSS
g, I .. , q1
0
C. 1 00 0
1
0.010 1000 1E4 1E5
t (sec)
Figure 4.45: Plot of -dL/dt" vs t for the DT1 Run at 1.4 g/g DSS and 1100 kPa
90
P-1275-1100 kPa (DT2) Coal Addition: 1.4 g/g DSS C .33=zogg:54faleb '6 • o
U 0.100
0 0
0 0
0.0 1000 1 E4 1 E5
t (sec)
Figure 4.46: Plot of -dL/de' s vs t for the DT2 Run at 1.4 g/g DSS and 1100 kPa
P-1275-1100 kPa
Coal Addition: 0
2 0-0 TR'N
• —• DT 1
o —a Dig
• • ,7 NUJ
' 10 20 J u 4-0 53 60 Note: TRN = Transition point DTI. DT2 = Intermediate points Cake Solids (%) END = End of GP cell run Figure 4.47: Cake Length vs Cake Solids Content at Zero Coal Dose and 1100 kPa
91 3 P-1275-1100 kPa
Coat Addition: 0.4 g/g DSS
) 2 t- o—o TRN • —• DT1 th (cm 0 DT2
Leng 1 \\s, • —• END ke Co .tc\ 1
0 [ .
1 C.) L.) 30 40 50 60
Note: TRN = Transition point Coke Solids (%) DTI, DT2 = Intermediate points END = End of C.-I' cell run
Figure 4.48: Cake Length vs Cake Solids Content at 0.4 g/g DSS Coal Dose and 1100 kPa
0-'75 " n^ - IVV IN. N... - 1.4. g/g r
j TRN
7:1
C AO 0T2
• - • ENE
fi 1
10 23 30 40 50 60
Note: TRN = Transition point DTI, DT2 = Intermediate points Cake Soiids (%) END = End of C-P cell run
Figure 4.49: Cake Length vs Cake Solids Content at 1.4 g/g DSS Coal Dose and 1100 kPa
92
P-1275-1100 kPo
Coal Addition: 0.4 g/g DSS
)
m 2 0-0 TRN
th (c • —• DT1
0 4—A DT2 Leng • 4 ke 1 1 •---• END Ca
t 13 23 30 50 60
Note: TRN = Transition point DTI, DT2 = Intermediate points Corrected Cake Solid (%) END = End of C-P cell run
Figure 4.50: Cake Length vs Corrected Cake Solids Content at 0.4 g/g DSS and 1100 kPa
P-1275-11 00 kPa
Coal Addition: 1.4 g/g DSS
) o—o TRN
th (cm • —• DTI
• Ali A DT2 Leng
ke A---• ENC Co
0 10 20 30 40 50 60
Note: TRN = Transition point Corrected Cake Sol;ds (%) DTI, DT2 = Intermediate points END = End of C-P ccll run
Figure 4.51: Cake Length vs Corrected Cake Solids Content at 1.4 g/g DSS and 1100 kPa
93
3 i C001 Dose (g/e): P-1275-1100 kPa (END) 1
r
) 0---c zero
m • —c, 0. ..1 f dn. —a 0.8 (c •—• i th 0-0 L21.0
ng r L IIE — r 1 "...' is I
Le v---v 1.6 1
ke • i 1 ,- 6\ .\ 7
Ca F \ \ \ 7 a / 6 1; 1 I/ # , i \ \ le .0 a 0 ' 33 40 53 60 70
akeSojcs(%)
Figure 4.52: Cake Concentration Profiles for all END Runs at 1100 kPa and Varying Coal Dosage
3
Coal Dose (g/g): P-1275-3300 kPa (END)
0—c zero • —• 0.4 2 0.8 A---A 1 1 .2 1.4 v — v 1 .6 1 C
a\a 0 • 61 o \ \• c • ° 3 33 40 50 60 70
Cake Solias (%)
Figure 4.53: Cake Concentration Profiles for all END Runs at 3300 kPa and Varying Coal Dosage
94 P —1275
Coal Addition: 0
) 2 - Pressure (kPa):
th (cm 0---0 1100 • ---0 1465 & --- A 2385
Leng A---A 3300
ke 1
Ca 0 • \\ • a • \ • 0 • • 0 10 20 30 40 50 60
Cake Solids (%)
Figure 4.54: Cake Solids Profiles at Zero Coal Dose and Varying Pressure
4.5.2 Yield Values
Yield in a filtration process is defined as the mass of solids deposited per unit area of filter per unit time. In this study, the C-P cell filtration area remained constant and the mass of sludge solids remained relatively constant (all sample volumes were approximately 80 mL). Therefore, the only variable in the yield term was the filtration time. Coal addition varied as well but was a known quantity and can be accounted for in each yield calculation. To ensure that each yield term was on a comparative basis, the times used in the yield calculations were at 90% completion of the run. This t90.4 was determined from the ultimate filtrate volume. The time corresponding to 90% of the ultimate filtrate volume in the original data set was the tc,cm
95 for that C-P cell run. At 1100 and 3300 kPa, yield values were calculated on a total solids (including mass of coal) and dry sludge solids (DSS) basis to determine the effectiveness of coal addition on yield. The respective plots are Fig. 4.55 at 1100 kPa and Fig.4.56 at 3300 kPa.
At 1100 kPa, significant increase in DSS yield existed. Dry sludge solids yield, ;SS increased by a factor of 2 from zero to 1.0 g/g DSS and by a factor of 3 at 1.6 g/g DSS coal addition.
The total solids yield, Yrs , increased at each coal dosage over the YDss generally by the amount of coal initially added to the suspension. For example, at 1.0 g/g DSS coal dose the value is 3.02 kg/m2 /hr. Since the coal in this case is the same mass as the dry sludge solids, the total solids yield term should double. Hence, the YTS at 1.0 g/g DSS was 6.29 kg/m2 /hr. In Fig.
4.56 (3300 kPa), similar increases in both yields occurred with increased coal dosage. Yield terms at 0.4 g/g DSS and 1.0 g/g DSS are omitted, as well as the moisture content values at these coal doses in the following section, since Fig. 4.53 showed incomplete consolidation at these coal additions at 3300 kPa.
Therefore, incorrect t 90% values resulted, which did not allow these two runs to be compared. Fig. 4.56 omitted these values on both a dry sludge solids and total solids basis. YDss increased by a factor of 3.5 from zero to 1.6 g/g DSS coal addition.
96
15 P-1275--1100 kPa
0
) 10 0 o YIELD(TS) /hr 2
/m • • YIELD(DSS) kg
5 ELD ( YI
..... ... •• • ' ...... 40
0.000 0.500 1.000 1.500 2.000
Cool Dosage (g/g DSS)
Figure 4.55: Filter Yield vs Coal Dose at 1100 kPa
15 P-1275-3300 kPa
)
hr 10 o o YIELD(TS ) 2/ • • YIELD(Dss) /m kg ( YIELD
0.000 0.500 1.000 1.500 2.000
Coat Dosage (g/g D55)
Figure 4.56: Filter Yield vs Coal Dose at 3300 kPa
97 Increases in filtration yield are very crucial in an operation in which time limitations or capital costs are most important. At a coal dosage of 1.0 g/g DSS at either pressure, the conditioned sludge would take approximately 50% less time to filter as the same volume of unconditioned sludge. At that same coal dose, twice the mass of sludge solids is deposited per unit time which could reduce the filter size required by a factor of 2 if reduction in capital cost was desired over reduction in filtration time. Figure 4.57 is a plot of yield on a volume basis versus coal addition at both applied pressures. Volume yield, was YVOL i defined as the volume of filter cake produced at t m per unit filter area per unit time. Fig. 4.57 shows that volume yield increased with increasing coal dose and minimal differences existed between the two pressures. Therefore, if volume of filter cake produced was a critical factor (usually when cakes are landfilled), coal addition would not be beneficial. In the scope of this study, increased volume yield was of less importance since the cakes were being combusted.
4.5.3 Moisture Content On an energy basis, moisture content of a filter cake was of utmost importance. Since considerable energy was required to vaporize the water of a filter cake during combustion, removal of the maximum amount of water in the expression process was crucial. Actual cake solids data from Table 4.10 was manipulated to determine the moisture removal advantages or disadvantages of
98
50 P-1275
) 40 /hr • 2 ..'o 1100 kPa /m
3 30 .• . • • 3300 kPa • -o D (m 20
UME YIEL 10 Ir . VOL
0 0.000 0.500 1.000 1.500 2.000
Coai Dosaae (a/a DSS)
Figure 4.57: Volume Yield vs Coal Dose at 1100 and 3300 kPa
70
0 o Actuat P-1275-1100 kPa
60 - • • Corrected
(x)
0 ids l 50 So 0 ke Ca • • • 30 0.000 0.500 1 . 000 1.500 2.000
Coal Dosage (g/e DSS)
Figure 4.58: Cake Solids Content vs Coal Dose at 1100 kPa
99 70 0 0 Actua l P-1275- 3300. kPa -o 0 • • Corrected 0 60
%) ( ids l 50 So
ke
Co • -• 40
' 0.000 0.500 1.000 1.500 2.000
r-N cc Coal 7 '"
Figure 4.59: Cake Solids Content vs Coal Dose at 3300 kPa
P - 1275
DSS) 0 0 1100 kPc 0/g
2 • • 3300 kPa H (g t 2 ten Con ture is
Mo • 0.000 0.500 1.000 1.500 2.000
Coal Dosage (a/g DSS)
Figure 4.60: Moisture Content vs Coal Dose at 1100 and 3300 kPa
100 coal conditioning. Figs. 4.58 and 4.59 are plots of both actual and corrected cake solids contents vs coal dosage at 1100 and
3300 kPa, respectively. Actual cake solids contents were obtained directly from the C-P cell expression runs and are listed in Table 4.10. Corrected cake solids contents were determined by factoring out the coal in both the numerator and denominator of the actual cake solids calculations. At 1100 kPa (Fig. 4.58), actual cake solids increased as coal addition increased. However, the corrected cake solids data indicated that moisture removal decreased, resulting in a reduction in cake solids concentration rather than a desired increase. Fig. 4.59, at 3300 kPa, showed a similar result. The corrected cake solids contents decreased with increasing coal addition. Actual cake solids data were manipulated into moisture content values on a gram H2O per gram DSS basis as well. Fig. 4.60 is a plot of moisture content (g water/g DSS) vs coal addition at 1100 and 3300 kPa. Moisture content increased with increasing coal dosage at both pressures. At 1.2 g/g DSS and
1100 kPa, moisture content was approximately 0.5 g H 20/g DSS higher compared to that determined at zero coal addition. This indicates approximately 250 kg additional water to be combusted per metric ton (1000 kg) of filter cake produced at 50% cake solids. Similar numbers are encountered at 3300 kPa. Therefore, on an energy basis, coal addition to P-1275 prior to dewatering would not be beneficial due to the results of moisture content and corrected cake solids data.
101 In Section 4.2, a theoretical heat balance was discussed
(and presented in the Appendix) on a typical pulp and paper, primary sludge filter cake to determine a coal addition range. Similar heat balances were calculated on the actual filter cakes from the C-P cell runs at 1100 and 3300 kPa at the various coal dosages examined. These heat balances were calculated to aid in evaluating the effects of coal on sludge dewatering on an energy basis and are presented in Tables 4.12 and 4.13 at 1100 and 3300 kPa respectively.
E and represent the heat or energy water f Eash f EDSS I Ecoat required to combust the respective components of each filter cake. Erotat represents the net energy resulting from the combustion reaction of each filter cake. The heat balance calculations were determined by a similar method described in the
Appendix for a theoretical filter cake. Although the initial sludge suspension volumes are not all equal, the Ewater columns at 1100 and 3300 kPa indicated in general that more water was contained in the filter cake as coal addition increased. This was the same result shown in Figure 4.60, moisture content versus coal dosage. As stated in Section 2.2, the primary factor affecting the amount fuel required for combustion of filter cakes is the moisture content of the cake. Coal was added at a constant ratio of dry sludge solids; therefore, the key issue on an energy basis was how much excess water remains in the cake after the expression process. As an example (and referring to Figure 1.1), coal was added to the
102 boiler with unconditioned, dewatered filter cake at 1100 kPa in alternative one at 1.0 g/g DSS. In alternative two, coal was added at the same ratio to the sludge suspension before dewatering at 1100 kPa. Alternative one required 83.4 kJ to vaporize the water associated with the unconditioned cake. The same coal dosage added to the slurry in the second alternative required approximately 10 kJ more to vaporize the water associated with the coal conditioned cake. Therefore, more energy is required to combust, or incinerate, the filter cake in alternative two.
Table 4.12: Actual Filter Cake Heat Balances from C-P Cell Runs at 1100 kPa
Heat (Energy), kJ Coal Dose (g/g) Ewater Eal E ;Ft DSS Ecoal Total
0 -83.4 -2.6 +9.1 0 -76.9
0.4 -93.7 -2.7 +9.4 +42.5 -44.5
0.8 -92.6 -2.7 +9.5 +85.1 -0.07
1.0 -92.6 -2.6 +8.9 +105.2 +19.0
1.2 -97.7 -2.6 +9.0 +125.2 +33.9
1.4 -110.2 -2.6 +9.1 +150.5 +46.8
1.6 -113.4 -2.7 +9.3 +169.4 +62.6
103 Table 4.13: Actual Filter Cake Heat Balances from C-P Cell Runs at 3300 kPa
Heat (Energy),(Energy) kJ Coal Dose !! (g/g) ;dater Eash Ecoa l ETotat
0 -69.9 -2.6 +9.2 0 -63.3
0.4 -70.8 -2.8 +9.6 +42.5 -21.5
0.8 -67.4 -2.6 +9.2 +84.1 -23.3
1.0 -86.7 -2.7 +9.3 +104.7 +24.6
1.2 -72.7 -2.6 +8.9 +125.9 +59.5
1.4 -78.3 -2.7 +9.2 +148.1 +76.3
1.6 -81.1 -2.6 +9.1 +166.1 +91.5
104 CHAPTER 5
SUMMARY AND CONCLUSIONS
This study provided valuable information on the effects of physical conditioning agents on a sludge suspension generated by a pulp and paper mill. It should be kept in mind that the results analyzed in this study are site specific. Conclusions drawn from these particular sludge samples should be taken as general trends in filtration and consolidation of pulp and paper sludges. It is recommended that further research be conducted on sludges from other mills. A list of final conclusions is given below:
1.) Filtration phase behavior was consistent for C-P cell expressions with and wit:out coal addition. Filtration phase slopes for all -dL/dt m vs t plots were relatively close to the theoretical value of zero. Slope values ranged from 0.05 to 0.10 at 1100 kPa and 0.04 to 0.08 at 3300 kPa.
2.) Average slopes of log V vs log t plots were 1.63 and 1.70 at 1100 kPa and 3300 kPa, respectively. Slight deviation from Darcy's theoretical value of 2 could be due to the fibrous nature of the sludge.
3.) Average specific resistance values decreased with increasing coal addition at both 1100 and 3300 kPa. The majority
105 (approximately 90%) of the & reduction occurred between coal dosages of zero and 1.0 g/g DSS. Minimal reduction of average specific resistance was reached at the higher coal additions of 1.2 g/g DSS to 1.6 g/g DSS.
4.) Actual cake solids concentrations obtained at the end of each expression run increased with increasing pressure and coal dosage, ranging from 39.18 to 56.38% at 1100 kPa and 47.42 to 63.95% at 3300 kPa. Similarly, ultimate cake solids contents increased with increasing coal addition, but not as drastically as actual cake solids concentrations. Ultimate cake solids values increased from 55.85 to 58.47% at 1100 kPa and 61.44 to 65.29% at 3300 kPa.
5.) Cake consolidation profiles were used to aid understanding of consolidation mechanisms. Slopes for cake solids vs W/Wo (and Cake Length) profile lines increased with increased coal dosage. Slopes of the profile lines also increased as the length of the filter runs increased, from the transition point run (TRN) to the end of the run (END), where the
END run was near vertical. Profiles plotted as corrected cake solids vs cake length revealed the same shape and slope as the previous plot of cake solids vs W/Wo, except the profile lines were shifted along the x-axis.
6.) Cake concentration profiles at varying coal dosage and constant pressure (Figs. 4.52 and 4.53) were useful tools in determining whether expression runs were all terminated at the same point of consolidation even though a common filtrate rate
106 was used as an endpoint for C-P cell runs. This profile validated a comparison of filtration and consolidation data such
as average specific resistance, ultimate cake solids, compressibility index, etc.
7.) Filtration yield was the term used to account for all time, or rate, related changes due to coal addition. Total and dry sludge solids (DSS) yield values increased significantly with
increased coal addition. The advantage of improved yield is a reduction in the total expression time of a sludge. At 1.0 g/g
DSS coal addition at either pressure, total expression time of
the sludge sample was reduced approximately 50%. This reduction is important if time limitations or decreased capital cost of the filtration equipment was considered. No advantage was achieved on a volume yield basis.
8.) Although total cake solids content increased with increasing coal addition, cake solids content on a DSS basis decreased (or moisture content increased) with increasing coal addition. This is a disadvantage from an energy stand point since additional energy would be required to combust the excess water.
107 REFERENCES
Albertson, 0.E., and Kopper, M. (1983)."Fine-Coal-Aided Centrifugal Dewatering of Waste Activated Sludge," Journal WPCF, 55(2), 145-156. Bierck, B.R. (1988)."An Investigation of Fundamental Mechanisms of Compressible Cake Filtration," Ph.D. Dissertation, Cornell University, Ithaca, New York. Bierck, B.R., Wells, S., and Dick, R.I. (1988)."Compressible Cake Filtration: Monitoring Cake Formation and Shrinkage Using X-Rays from a Synchrotron Source," Journal WPCF, 60, 645-650.
Bierck, B.R., and Dick, R.I. (1990)."In Situ Examination of Effects of Pressure Differential on Compressible Cake Filtration," Water Science and Technology, 22(12), 125-134.
Eden, G.E. (1983)."Modern Trends in Sludge Management: Sludge Conditioning," Water Science and Technology, 15, 37-48.
Gerlich, J.W., and Rockwell, M.D. (1973)."Pressure Filtration of Wastewater Sludge with Ash Filter Aid," EPA-R2-73-231, Washington, D.C. Hathaway, S.W., and Olexsey, R.A.(1977)."Improving the Fuel Value of Sewage Sludge," Unpublished work from Pitzer (1977).
Johns, Peter (1985)."Filtration of Aluminum Finishing Sludge," M.S. Special Research Problem, Georgia Institute of Technology, Atlanta, Georgia. Leu, W.F. (1981)."Cake Filtration," Ph.D. Dissertation, University of Houston, Houston, Texas.
Moehle, F.W. (1967)."Fly Ash Aids in Sludge Disposal," Environmental Science and Technology, 1, 374-379.
Nelson, R.F, and Brattlof, B.D. (1979)."Pressure Filtration with Fly Ash Addition," Journal WPCF, 51, 1024-1031. Pitzer, Ronald L. (1977)."The Vacuum Filtration and Incineration of Sewage Sludge Using Crushed Coal as a Conditioning Agent," M.S. Thesis, Purdue University, West Lafayette, Indiana.
Smith, J.E., Jr. et al. (1972)."Sludge Conditioning with
108 Incinerator Ash," Proceedings of the 27th Industrial Waste Conference, Purdue University, West Lafayette, Indiana.
Sun, Mei (1990)."Study of Sludge Dewatering Mechanisms by Cake Filtration and Consolidation," M.S. Special Research Problem, Georgia Institute of Technology, Atlanta, Georgia.
Vesilind, P.A. (1979)."Treatment and Disposal of Wastewater Sludges," Ann Arbor Science. Yeh, S.H. (1985)."Cake Deliquoring and Radial Filtration," Ph.D. Dissertation, University of Houston, Houston, Texas.
109 APPENDIX
Heat Balance on a Typical Pulp and Paper Filter Cake:
- 50 g cake @ 30% solids (65% volatile; 35% inert) 70% moisture - Initial SS concentration: 25 g/L - Initial Temp.: 10°C - Initial suspension volume: 0.8 L - Assuming 400 °C change in temperature in boiler/incinerator Therefore, mass of each constituent:
H2O: (0.7)(50 g) = 35 g Cellulose: (0.3)(50 g)(0.65) = 9.75 g Ash: (0.3)(50 g)(0.35) = 5.25 g Coal @ 0.4 g/g: (50 g) (0.3) (0.4 g/g) = 6.0 g @ 0.8 g/g: " " (0.8 g/g) = 12.0 g @ 1.0 g/g: II " (1.0 g/g) = 15.0 g @ 1.2 g/g: II " (1.2 g/g) = 18.0 g @ 1.4 g/g: II " (1.4 g/g) = 21.0 g @ 1.6 g/g: 'I (1.6 g/g) = 24.0 g Various Heat Values/Specific Heats of Constituents: Water (latent heat of vaporization) = 2420 kJ/kg Water (specific heat) = 4.184 kJ/kg K Cellulose (specific heat) = 1.76 kJ/kg K Ash (specific heat) = 1.047 kJ/kg K Coal (heat value) = 5159 kJ/kg
Balance on filter cake without coal,
H20 : (0.035 kg)(4.184 kJ/kg K)(90 K) = -13.2 kJ (0.035 kg)(2420 kJ/kg) = -84.7 kJ Ash: (0.00535 kg)(1.047 kJ/kg K)(400 K) = -2.2 kJ Cellulose:(0.00975 kg)(1.76 kJ/kg K)(400 K) = +6.9 kJ Ecake = - 93.2 kJ Balance on filter cake with various coal additions,
ENET = Ecoat + Ecake Coal @ 0.4 g/g: (0.006 kg)(5159 kJ/kg) = +31.0 kJ ENET = 31.0 - 93.2 = -62.2 kJ @ 0.8 g/g: (0.012 kg)(5159 kJ/kg) = +61.9 kJ
110 ENET = 61.9 - 93.2 = -31.3 kJ @ 1.0 g/g: (0.015 kg)(5159 kJ/kg) = +77.4 kJ ENET = 77.4 - 93.2 = -15.8 kJ @ 1.2 g/g: (0.180 kg)(5159 kJ/kg) = +92.9 kJ ENET = 92.9 - 93.2 = -0.3 kJ @ 1.4 g/g: (0.021 kg)(5159 kJ/kg) = +108.3 kJ ENET = 108.3 - 93.2 = +15.1 kJ @ 1.6 g/g: (0.024 kg)(5159 kJ/kg) = +123.8 kJ ENET = 123.8 - 93.2 = +30.6 kJ
111
DEWATERING PROPERTIES OF PULP AND PAPER RESIDUES
A STUDY CONDUCTED FOR WEYERHAEUSER COMPANY
BY
F. M. SAUNDERS M. SUN S. YOUNG T. RAINEY
SCHOOL OF CIVIL & ENVIRONMENTAL ENGINEERING GEORGIA INSTITUTE OF TECHNOLOGY ATLANTA, GA
AUGUST 1994 ABSTRACT
As frequently employed in the solid-liquid separation processes, cake filtration separates free liquid from suspensions by flowing through a membrane or porous medium which retains suspension particles. Sludge dewatering, as referred herein, is a process in which liquid is removed by cake filtration and consolidation. The filtration phase continues until all suspension particles are transformed into a cake. In the following consolidation phase, no solids deposition occurs and liquid flow results from displacement of solids by mechanical pressure.
Constant-pressure expression was adopted in this study for its simplicity. Current development of filtration theory was reviewed and mechanisms regarding cake filtration and consolidation phases were discussed. It was demonstrated that the transition point between filtration and consolidation could be determined using Ruth's filtration equation, and a linear relationship between rate of filtrate generation and filtrate volume was examined, according to Terzaghi's conventional consolidation theory.
Twenty-one sludge samples from eight pulp and paper plants were analyzed for the study of fundamental mechanisms of constant- pressure sludge dewatering. The experimental approach included a compression-permeability cell testing at four pressure levels (1100 to 3300 kPa) were used. The effectiveness of increased pressure on sludge dewatering was analyzed with respect to cake compressibilities. Based on the sludge samples examined, it seemed that for less or moderately compressible materials, increase of pressure in a modest range could not increase cake solids content substantially.
The study documents differences in dewatering properties between mills and serves to establish a baseline for comparison of the performance of dewatering systems. The findings, equipment and test methods discussed can be employed by Weyerhaeuser facilities to determine maximum possible sludge-cake dryness for sludges, examine beneficial use of high pressure dewatering systems, and assess performance of existing equipment. Table of Contents
Page
Abstract i
CHAPTER 1 INTRODUCTION 1
1.1 Sludge Dewatering Process 1 1.2 Cake Filtration and Consolidation 2 1.3 Factors Affecting Sludge Dewatering . . . 5 1.4 Purpose of Study 7
CHAPTER 2 FILTRATION THEORY 8
2.1 Cake Filtration 8
2.1.1 Flow Through Porous Media 8 2.1.2 Average Specific Resistance 12 2.1.3 Frictional Drag on Particles 15 2.1.4 More Comprehensive Analysis of Average Specific Resistance 17 2.1.5 Material Balance 20 2.1.6 Constant Pressure Filtration 21
2.2 Cake Consolidation 22
2.2.1 Mechanisms of Consolidation 22
2.3 Determination of the Transition Point 30
2.4 Compressibility of Sludge Suspension 31
CHAPTER 3 EXPERIMENTAL APPROACHES 33
3.1 Origin of Sludge Samples 33
3.2 Sampling Procedures 35
3.3 Experimental Apparatus 35
3.3.1 Capillary Suction Time (CST) Apparatus • • 35 3.3.2 Pressure Cell Apparatus 37 3.3.3 Compression-Permeability Cell (C-P Cell) 37
3.4 Analytical Methods 40
3.4.1 Sample Characterization 40 3.4.1.1 Suspended and Volatile Suspended Solids 42
i i 3.4.1.2 Total and Soluble Chemical Oxygen Demand 42 3.4.1.3 pH 42
3.4.2 Dewatering Properties of Sludge Suspensions 43 3.4.2.1 CST Determination 43 3.4.2.2 Specific Resistance and Compressibility Index 43 3.4.2.3 C-P Cell Test 45
CHAPTER 4 DATA ANALYSIS AND DISCUSSION 48
4.1 Characterization of Sludge Samples 48
4.2 Dewaterability and Compressibility 52
4.3 Discussion of C-P cell Data 62
CHAPTER 5 SUMMARY AND CONCLUSIONS 195
REFERENCES 199
APPENDIX 201 List of Tables 202 List of Figures 206
iii CHAPTER 1
INTRODUCTION
1.1 Sludge Dewatering Process
The objective of sludge dewatering is to remove water from a sludge suspension and produce a handleable cake for reclamation or disposal. Due to high water content (usually above 98%), sludge suspensions are relatively difficult to dispose of, except where direct land application is applicable. The cost of sludge dewatering often is a major component in the overall cost of sludge waste management. Reduction of water content in a sludge suspension produces a handleable cake of much less volume and therefore reduces the cost of subsequent treatment and disposal.
The selection of a specific dewatering process depends on the type of sludge suspension, capital and operating costs and the cost of ultimate disposal. Examples of dewatering methods are filtration, centrifugation, sedimentation, hydrocloning, and thermal drying.
Since mechanical dewatering is usually far cheaper than any thermal method, it has become increasingly important in the broad fields of solid-liquid separation operations. When evaluating a sludge dewatering process, there are two major factors to be considered: feed solids capture and cake solids content. All methods of mechanical sludge dewatering are capable of good solids capture (greater than 90%) with proper conditioning and equipment selection and thus the major differential is the cake
solids content. For the purpose of this study, constant-pressure mechanical dewatering was employed to investigate the relationships among applied pressure, average dewatering flow resistance and ultimate cake solids content. Constant-pressure
filtration is typically achieved in mechanical dewatering systems used in the pulp and paper industry, such as belt presses, screw presses and recessed-chamber filter presses.
1.2 Cake Filtration and Consolidation
Generally, a complete mechanical pressure dewatering process consists of two phases, cake filtration and consolidation. In cake filtration, the solid particles from a suspension are stopped at the surface of a supporting porous medium which is permeable only to the liquid. As the process continues, additional particles are collected on the surface of the initial layer of solids, thereby building up a cake. The most important factor in cake filtration is the permeability or resistance of the filter cake. Cake filtration is the most widely used filtration method in the process industries and is especially suitable for dewatering of concentrated suspensions.
Consecutive to cake filtration in the overall dewatering process, cake consolidation further reduces cake moisture content substantially by displacing solids into the voids of cake.
Many researchers have studied different aspects of cake consolidation mechanisms. Frequently, the term expression is used interchangeably with the term consolidation. Schwartzberg
2 (1983) studied expression operations in the food processing industry. He defined expression as the act of expelling liquid from a solid-liquid mixture by squeezing or compaction which is usually produced by movement of solid or perforated barriers pressing against surfaces of the mixture. Based on his experimental approach, Shirato et al. (1987) described expression as the separation of liquid from a two-phase, solid-liquid system by mechanical compression resulting in reduction of cake volume such as by the use of a retaining wall. This would be analagous to the compression achieved near the discharge end on the internal taper in a screw press as a sludge cake is squeezed through the narrow discharge port or the compression achieved between two belts in the high-pressure zone of a belt press.
Yeh (1985) considered expression as an operation involving the use of pistons or impermeable membranes for reduction of the liquid content of cakes arising from cake filtration. In his definition, expression referred to the compression of a cake structure into a more compact form with forces applied at the cake boundary, which defines the consolidation process in this study.
For the purpose of this study, expression is referred to as the overall dewatering process which consists of cake filtration followed by consolidation. Therefore, in dealing with the mechanisms of expression, total cycle should be divided into two stages in view of the mechanism of flow through porous media. In the first stage, the flow mechanism is actually cake filtration;
3 in the second stage, the mechanism is consolidation. A C-P cell
(compression-permeability cell) was adopted to perform the overall cake filtration-consolidation cycle in this study. After the C-P cell is filled with a sludge suspension, a mechanical load is applied through a piston on the surface of the suspension. During the initial period of filtration, an initial layer of the cake must be retained on the surface of the medium, or blinding (migration of fine particles) must occur until the sizes of the pores within the medium are reduced to such a point that cake filtration proceeds. Consequently, the cake starts to form from the porous media towards the moving piston and the load is transmitted undiminished through the suspension to the cake surface. Assuming that gravity sedimentation is negligible, the suspension concentration above the developing cake remains constant throughout the filtration stage, thereby permitting the use of the traditional theoretical approach in estimating flow rate and distributions of porosity and pressure throughout the cake. The cake builds upward until the suspension disappears at the point that the piston contacts the cake surface. After the piston touches the cake surface, the liquid pressure diminishes and the particulate cake begins to carry an increasing portion of the load, filtration ends and consolidation then starts. During consolidation phase, compression of the still loose cake is achieved layer by layer through the cake and the thickness of cake continues to decrease. Finally, after the last layer (which is the surface layer) of cake is consolidated, the equilibrium
a condition is reached, and the porosity is uniform throughout the cake (neglecting wall effects). For simplicity, only constant- pressure expression operations were conducted in this study.
Furthermore, variable-pressure expression is not typically employed in sludge dewatering practice and would have required that an arbitrary available-pressure profile be developed. Since the objective was to develop a benchmark study for sludge suspensions at a variety of mills for use in comparison of differences in sludge properties dewatering performance, a projected constant-pressure filtration cycle was selected for the study.
1.3 Factors Affecting Sludge Dewatering
Many factors influence the dewaterability of a sludge suspension, including sludge source, storage time, and prior conditioning applied. Sludge characteristics (i.e. pH, particle size, particle surface charge and hydration, temperature, compressibility and volatility) related to the difficulty of consolidating sludge solids and the ease of water movement through the voids between the sludge solids (EPA, 1982).
In cake filtration, formation of cake depends upon the manner in which particulate are first laid down, subsequent rearrangement due to frictional drag of the flow, and migration and deposition of fine particles in the interstices of the medium and/or cake. According to Leu (1981), the general order in which various phenomena affect cake structure includes:
• particle and media morphology, shape and size;
5 • interaction of particles and surrounding fluid;
• particle aggregation;
• interaction of particulate and supporting medium;
• mechanical factors affecting flow patterns and particulate
motion, such as vibration, turbulence, concentration;
• effect of flowing liquid on compression of bed structure;
• and migration of fine particles and their deposition in
pores of both filter cake and supporting medium.
These phenomena are interrelated and collectively determine the behavior of filter cakes. For example, morphology, concentration, and flow patterns of particles as they approach the pores of the filter medium determine to a large extent medium blinding as well as the initial structure of the cake. These factors, in turn, influence the porosity and permeability of the cake and the associated variations with increasing pressure.
Ultimately, the flow rate and relative pressure drops across the medium and cake depend upon how the cake is formed.
Suspension concentration generally affects dewatering parameters. Cake resistance and porosity are affected as well as the medium blinding mechanisms. For example, if a very dilute suspension is filtered, each particle moves separately from the others and tends to follow streamlines of flow directed toward the filter pores. Particles may enter or cover a pore opening depending on relative sizes. If the concentration of particles is increased, more particles will arrive at a pore at the same time, thereby hindering one another as they attempt to enter the
6 pore. A bridge of particles forms over the pore.
Bridging tends to decrease the number of particles entering the pore and to augment cake porosity. Further increases in concentration cause a decrease in packing density of the cake and also its specific flow resistance.
Paper mill sludge is composed of primary- and secondary- derived sludges. Primary sludge is typically characterized by a high fiber content and may contain considerable lime solids.
Secondary sludges are typically highly gelatinous, being composed of microbial solids, and are generally difficult to dewater, especially when compared to dewatering rates of primary sludges.
1.4 Purpose of Study
The purpose of this study was to analyze the expression process under constant pressure based on fundamental filtration and consolidation theories. The experimental approach to assess dewatering properties of a sludge suspension includes sludge sample characterization and expression operations using a compression-permeability cell at different pressure levels. It is anticipated that the results will provide better understanding of expression mechanisms and insight into rational selection, design and economic evaluation of sludge dewatering systems.
7 CHAPTER 2 FILTRATION THEORY
2.1 Cake Filtration
The examination of sludge dewatering systems is facilitated by an initial examination of the fundamental principles that ultimately govern the performance of any suspension in, for example, a filter press, screw press, belt press or a centrifuge.
The fundamental principles are established by examination of (i) the flow of water through a porous media (i.e., a sludge cake) and (ii) the consolidation of a porous media, i.e., a sludge cake. The fundamentals of dewatering processes are therefore presented below as they were ultimately used in the examination of the dewatering properties of pulp and paper sludges.
2.1.1 Flow Through Porous Media
A simplified description of porous media used to describe dewatered sludge would include four types of irregularly interconnected pores encountered to varying degrees. They are straight-through, branched, dead-end and non-penetrating pores.
Pores of the first type are the most amenable to analysis but these occur infrequently. The second type is that most frequently encountered and will be of most concern. The last two types provide a difficult analysis problem, but the extent of their presence although uncertain appears to be small.
A schematic diagram of sludge suspension undergoing cake filtration is included in Figure 2.1. Darcy (1856) found that
8 L S s...sze^s [17 Ca.e
A
Fig. 2.1 Schematic diagram of sludge suspension under cake filtration the volumetric flow rate of a liquid through a porous bed was proportional to the pressure gradient across the bed and the bed area. Under the condition that the flow regime is within the laminar region, the following phenomelogical equation is usually called Darcy's law and can be represented as:
dV PAK _ dt Ax (1)
dV/dt = volumetric flow rate, m3/sec P = pressure drop across the bed, Pa A = filtration area normal to flow direction, m 2 A = viscosity of liquid, Pa•sec Ka = permeability, m2
x = cake thickness measured from the medium surface, m If cake resistance, R, is defined on the basis of unit volume of cake solids using R = 1/K p , then
dV PA dt ARx (2)
9 Darcy's law is applicable only to viscous, incompressible laminar flow. It is not applicable to turbulent (i.e., non- laminar) flow which is, fortunately, rarely encountered in sludge dewatering practice using screw presses, belt presses and filter presses. The proportionality between flow rate and pressure drop as stated in Darcy's law does not apply at high flow rates. For transition or turbulent flow conditions, as proposed by
Forchheimer (1901), the following equation should be used instead of Darcy's equation:
2 x- = au + bu (3) where u is flow rate, a and b are constants which are unique to each specific flow and media properties.
Ergun (1952) examined the dependency of Eq.(3) upon flow rate, properties of the fluid and the fractional void volume, orientation, size and shape of the porous medium. He concluded that the total energy loss (pressure drop P/x) was the sum of viscous energy loss and kinetic energy loss. The following empirical relationships for constants a and b in Forchheimer's equation were proposed:
2 150 (1 - e) y a = (4) D2 e 3
p (1 - e) (1.75) b - 3 (5) D e
10 where E = porosity of the porous media, dimensionless
D = mean equivalent diameter of the particles
comprising the porous media, m
/2/, = density of the fluid, kg/m 3
The Forchheimer equation becomes significant when super-
conditioned sludge suspensions are encountered in cake
filtration. However, when the flow rate, u, is small, the
kinetic energy loss becomes very insignificant and Eq.(3) reduces
to Darcy's equation. Since flow rates in the majority of
filtration processes give behavior consistent with Darcy's
equation, emphasis of the discussion in this study will be
limited to laminar flow filtration, typical of conventional
dewatering with, for example, screw presses, belt presses and
centrifuges.
During the period when cake is built up in a dewatering
unit, both the developing cake and the septum account for the
resistance to flow. A septum resistance term, M r , therefore needs to be included in the above equation.
dV PA dt A(Rx + Mr ) (6) where M = resistance to filtration by septum, r ml
If all solids in a suspension are retained to form a cake,
the cake volume can be calculated as the product xA or vV, i.e., xA = vV = cake volume, where v = volume of cake deposited per unit volume of filtrate, and V = volume of filtrate, m 3 . Due to
11 the difficulty in obtaining data for the term, v, practically, v is replaced by an experimentally determinable term w, mass of dry cake solids per unit volume of filtrate. Consequently, flow resistance per unit volume of filtrate, R, is replaced by a corresponding resistance term based on unit mass of solids.
Rearranging Eq.(6) leads to
2 dV PA dt = (7) g(w&V + M A) r where LC = average specific resistance to filtration per unit
mass-of cake solids, m/kg
2.1.2 Average Specific Resistance
The average specific resistance term, a, is the most frequently used means for characterizing dewaterability of a, suspension. Eq.(7) combines the resistance concept and Darcy's equation, and accounts for the increase in depth of bed solids as cake particles are deposited. Integrating Eq.(7) and assuming constant pressure over time,
ywiiv dt = ( + --)r dV (8) 2 0I 0 PA PA leads to the following:
- 2 M gV gwaV t - (9) 2 2PA PA
1 2
Rearranging Eq.(9) results in the conventional equation of batch filtration data at constant pressure.
t pwaV- M_u V (1 0) 2PA2 PA
The experimental approach to calculate the average specific resistance, a, can be done by recording volume of filtrate, V, at various times, t, then plotting the data as t/V versus V to generate a straight line. The slope of this line, b, is equal to
b - Liwac 2PA2 then the average specific resistance parameter is obtained
2 2PA b a - (12) thw
The mass of solids deposited per volume of filtrate, w, can be approximated by the feed solids concentration. It can also be accurately calculated through a material balance (Vesilind, 1979). Liquid balance:
Qo= Qf + Qk (13)
Solids balance: Q C = Q C + Q C o o f f k k (14)
13 where Q designates flow rate; C is solids concentration; and the subscripts o, f and k denote feed, filtrate and cake, respectively. The mass of dry solids deposited as cake per volume of filtrate, defined as w, is
Q C k k W = (15) Qf
Substituting from the liquid balance Eq.(13)
Ck w - QoCk - Q f (16) Q f
Rearranging the solids balance Eq.(14)
(Co - Ck ) Qf - Q_u Cf-Ck (17)
Substituting Eq.(17) into Eq.(16) and rearranging
Cip (Cf - Co ) w = ''' (18) Co - Ck
If suspended solids in the filtrate are assumed to be negligible (Cf = 0), and the solids concentrations are expressed in percent solids (mass basis), then
Ck Co (19) w = 100 (Ck - Co )
14 2.1.3 Frictional Drag on Particles
In cake filtration, sludge solids are retained on the filter medium to form a cake. Because of existing hydraulic momentum due to applied pressure gradient, each particle is subjected to skin and form drag which is communicated to the next particle.
The drag force on the particles is accumulated from the cake surface and reaches a maximum at the septum, while the hydraulic momentum is gradually transferred to the solid particles and the liquid pressure reaches a minimum at the septum. Compression of cake solids is caused by the solid cumulative-drag pressure which is defined herein as solid compressive pressure. As the solid compressive pressure increases from top to bottom of the cake, the cake is loose and porous at the cake surface and becomes more compact towards the septum. At any point inside a developing cake, the applied pressure is always balanced by hydraulic pressure in the liquid phase and cumulative drag pressure in the solids phase, and liquid flows through the interstices of the cake in the direction of decreasing hydraulic pressure.
If inertial forces are assumed to be negligible, the balance of forces acting on the solids and the liquid over the slice dw can be represented by the following equations, respectively.
aF dw + A [(1 - E) P ] dw + A F dw = 0 (20) aw Oa w L v
a A— (E P ) - A F dw = 0 (21) aw
15 where Fs = cumulative drag on the particles , N = volume of cake solids per unit filtration area ((1-6)o is equivalent to cake thickness x), m 3/m2 6 = local porosity, dimensionless P = local hydraulic pressure, Pa
Fv = viscous drag per unit volume of solids, N/m3
Combining Eq.(20) and Eq.(21) and defining the compressive drag pressure by Ps = FS/A yields
apapL s aw aw — o (22) upon integration
P + P = P (23)
As a result of the initial forces exerted by the liquid as it flows through the bed at various bulk velocities, P s combines skin and form drag produced by friction at the surface of the particles. The drag is transmitted through the points of particle contact. Inasmuch as the cross-sectional area does not equal the surface area of the particles or the contact area, P s is a fictitious or pseudopressure which is introduced for convenience. Eq.(22) and Eq.(23) simply imply that the drop in hydraulic pressure in a developing cake is exactly equal to the rise in solid compressive pressure. Typical pressure profiles in a developing cake is shown in Figure 2.2.
16
0 P P -P
V Fig. 2.2 Schematic pressure profiles in a filter cake
2.1.4 More Comprehensive Analysis of Average Specific Resistance If the internal structure of a filter cake is examined, Darcy's law, which states that the apparent liquid velocity is proportional to the hydraulic gradient and inversely proportional to the liquid viscosity and flow resistance, can be expressed on a unit area basis in the following form:
dP L dx - MRu1 (24)
do = (1 - 6) dx (25) therefore
dP gRu l L do (1 - - gp saul (26) where u1 = the apparent liquid velocity relative to solids, m/sec p s = true density of solids, kg/m3 a = local specific flow resistance, m/kg
17 The unit-solids-volume-based flow resistance term, R, is related to local specific resistance, a, by
R = p sa (1 - E) (27)
Since a is inversely proportional to local porosity, e, and E is related to solids compressive pressure, P., it is preferable to replace PL by P. in Eq.(26). Substituting Eq. (22) into Eq. (26) yields
dP dP L s PP saul dw dw A (28) rearranging
gu p dw dP 1 s s (29) A - a
Fig. 2-1 shows that the solid compressive pressure varies from zero at the cake surface to the maximum pressure, P-P m , at the septum, i.e., at w = 0, P. = P - Pm , and at w = w o , P. = 0, where wo is the total solid volume in cake per unit sectional area, and P. is the hydraulic pressure loss through septum, which relates to the resistance M r by definition
puM r P - (30) m A where u is the observed filtration rate. Assuming that the apparent liquid velocity u l is constant (i.e., ul equals the
18
filtration rate u) through the bed, integrating Eq.(29) and
substituting limits leads to
yup w dP s o yuwV s 2 (31) A A JO0 a
While a varies through the cake and increases as the septum is
approached, the normalized cake solids concentration profile
remains constant (Bierck, 1988). An average specific resistance a is then defined as
P-P dP 1 1 m s a (32) a P Pm JO
Substituting for the integral in Eq.(31) and eliminating Pm by
use of Eq.(30) produces
yuwV PA - yuMr 2 (33) A & A
therefore
2 dV PA u dt (34) p(wJev + MrA)
Comparing Ea.(34) with Eq.(7), it can be seen that
filtration rate is a function of the average specific resistance
which is a function of solid compressive pressure, P., and can be
calculated by Eq.(32). In fact, the total cake resistance
changes as the mass of cake grows as the filtration proceeds.
While it is assumed that the medium resistance R m is constant, it
19 may change under certain circumstances such as the case of septum blinding which migration of fine particles into the septum with deposition causes clogging and subsequent increase of M r .
2.1.5 Material Balance
A material balance over the total filter cake can be written in the form:
mass of slurry = mass of cake + mass of filtrate
wV_ s-- + pV (35)
where S = average mass fraction of solids in the slurry, %
Sc = average mass fraction of solids in the cake, %
p = density of the filtrate, kg/m3
V = volume of filtrate, m3
Rearranging Eq.(35) gives
pSS c (36) w S S
The thickness of the cake L can be related to the mass of the cake W (W = WV) by
W = p s (1 - i) LV (37) where E = the average porosity of the cake.
Combining Eq. (36) and (37) yields
wV pSS V c L = (38) P s ( 1 - E) P s (S c - S) (1 - i)
20 The average mass fraction of solids in a filter cake S r is related to the average porosity i as
p (1 - S - (39) c p (1 - + p s
2.1.6 Constant Pressure Filtration
Constant pressure filtration is the most commonly applied
experimental approach to study the mechanisms of cake filtration
and consolidation because of its simplicity. Consider the septum
resistance Mr as equivalent to the resistance of a fictitious
layer of filter cake of equal resistance. Combining Eq.(34)
with Eq.(36) and rearranging gives
2 dV PA (S - S) (40) dt gp s& Sc (V + Vm )
where V = fictitious filtrate volume required to form a m
filter cake of resistance equal to the septum
resistance, m3
Eq.(40) is usually referred to as Ruth's Equation. Integration
of Eq.(40) generates
2 (V + V ) = K (t + tm) (41) m where t = fictitious filtration time corresponding to the m septum resistance, sec
K = Ruth's constant-pressure filtration coefficient,
defined by
21 2 - S) 2PA (S c K - yp a S s c
Eq.(41) indicates a parabolic relationship between cumulative filtrate volume and filtration time. After a small initial period, a layer of solids is retained on the septum, the cake resistance begins to control filtration rate and the septum resistance is therefore frequently neglected, leading to
2 V = Kt (42)
Eq.(42) is used in this study to access the experimental data. According to the equation, a plot of V versus t will exhibit a parabolic curve. An increase in the filter cake resistivity is indicated by a decrease in the slope.
2.2 Cake Consolidation
2.2.1 Mechanisms of Consolidation
As discussed earlier, because the solids compressive pressure, P., varies through a filter cake, the porosity profile inside a compressible filter cake is not uniform. Consolidation of the cake bottom layer, where the solid compressive pressure P. is the greatest, is completed while in the filtration phase.
Increasing filtration pressure may increase the dryness of the cake. However, this primarily affects the cake layers near the medium and leaves the remainder essentially unchanged.
Therefore, cake filtration alone cannot attain substantial dewatering of filter cake.
22 Consolidation is referred herein to the act of reducing
liquid content of a filter cake by mechanically compressing it into a more compact form. Dewatering by consolidation is different from dewatering by filtration by the fact that the hydraulic pressure, P L , in a consolidating cake decreases continuously as liquid in the interstices of the cake is displaced by solid particles gradually. In filtration, the liquid flowing through the cake originates principally from the abrupt change in concentration when the solid particles are deposited at the cake surface. In addition, a small flow
(generally less than 10% of the total) is derived from the continued squeezing of the cake during filtration (Yeh, 1988).
In consolidation, no particle deposition occurs, and liquid flow comes entirely from the cake compression which results from the movement of solid particles into the voids.
Because the liquid flow through a consolidating cake is under a very low hydraulic pressure gradient, the compressive effect resulting from the flow is negligible in comparison to that resulting from high mechanical loads. Stresses resulting from frictional drag plus the direct load of the piston on the particulates are borne by the solid particles, which generates the pore liquid pressure. As the pore liquid in the cake is no longer more in continuity, the concept of specific resistance is no longer valid. The decrease in local porosity of consolidating cake results in a transfer of applied expression pressure from a pore liquid to a compressible solid structure.
23 A major difference between the mathematical treatment of filtration and consolidation involves the solid velocity u„ which was neglected in comparison with the liquid velocity during filtration. As the liquid movement during consolidation is primarily due to displacement by the solids into the pores, u , should be considered in the flow rate equations. As a modified form of Darcy's law, the following equation was proposed by
Shirato et al. (1969) to account for the effects of u s in filtration:
dP L dP s - gp sae (1 - e) (u - us ) (43) dR- dx
Since the consolidation phase will finally result in forming a uniform cake (Bierck, 1988), the compressing rates in the later stage of consolidation are dependent on the final equilibrium states. Higher pressure leads to further compressing and higher solids content of cake (Leu, 1981).
Hoyland et al. (1981,1986) used data from filter press systems to evaluate cake filtration behavior. They found that the rate of filtration during the compression phase was linearly proportional to the volume of filtrate discharged. Based on this, they suggested an empirical equation for the cake consolidation phase which may be used to project an ultimate filtrate volume.
dV (44) at = M (Vco - V)
24 V = cumulative volume of filtrate, m3 17,= theoretical volume of filtrate produced by allowing expression to proceed for an infinite time, m3 M = a constant which is directly proportional to the solids concentration of feed sludge and inversely proportional to the specific resistance to filtration, 112 see Plotting measured flow rate dV/dt vs. V gives a linear relationship whose gradient is equal to - M. The value of M determines the rate which consolidation proceeds, the greater the M, the faster the consolidation process reaches equilibrium. Extrapolating the gradient until dV/dt = 0 gives an approximate value for the ultimate volume V, of filtrate. Consequently, VA,, referred to as the degree of completion, may be calculated at any time during the consolidation phase; and the time required to reach a particular degree of completion or a specified cake solids content may also be estimated by integrating Eq.(34). Theoretical background for supporting the above empirical equation (44) could be found in the conventional Terzaghi theory of consolidation (Terzaghi et al., 1948). Consolidation of a porous material has been found to be dependent on not only local solid compressive pressure but also time, that is , the so-called creep effect. In the case of this study, however, the time dependent creep effect is reasonably insignificant due to the relative short time period required for each consolidation run
25
and it is therefore assumed to be negligible. Recalling the basic flow equation (26), the apparent velocity of liquid u 1 can be represented by 1 apL 1 aps ul Aap ae (45) s AaP s a '
By conducting a mass balance of liquid in an infinitesimal thickness of layer do in a consolidating sludge cake, the continuity equation can be obtained in the form:
ae au (46) at aw
where e is the local value of void ratio and t c is consolidation time. The above equation simply indicates that the net volume of liquid entering and leaving a control volume per unit time is equal to the rate of change in the volume of liquid. The coefficient of volume change, m y , of the
infinitesimal layer do under compression is defined by the following equation in soil mechanics.
1 de my = - (47) 1 + e dPs
Differentiating Eq.(45) with respect to co yields
au 1 1 a ,1 aP s, - (48) Ap aw a 8w ae s
26 Combining Eqs.(46) and (48) yields
ap ap 8e _ de s _ 1 a 1, s, (49) atc dPs atc gp s 80 `a aw 1
Substituting Eq.(45) into Eq.(49) leads to
ap a2 P s s1 da f aPs 1 2 1 (50) atc = Ce ( (302 a dPs ‘aw , J where Ce is a local value of the modified coefficient of consolidation represented by
1 C e - (51) e gap my (1 + e) s
If Ce can be assumed to be constant, Eq.(50) leads to the well-known form of the diffusion equation
2 ap 8 P s - C s (52) atc e a(,) 2
Since Ce may change with cacand t , Eq.(2) may be used as an approximation with a proper mean value of C e considered constant. Knowing the solid compressive pressure profile in a developing filter cake can be approximated by a sinusoidal curve (Shirato et al., 1974), the mathematical solution for Eq.(52) in case of the constant-pressure cake consolidation is given by
27
L - L 112 1 U - - 1 - exp (- 4 Tc ) (53) c L 1- L co where Uc= average consolidation ratio, dimensionless
L1 , L, L cT,- thicknesses of materials at t sf 0, t c and 00, respectively, m
Tc = dimensionless consolidation time factor, defined by
1.2 C t T = e c (54) c 2 o where i = number of drainage surfaces. Substituting Eq.(44) into Eq.(43) and rearranging
L - Lco - exp (-K't ) (55) L1 - Lco c where K' is called consolidation parameter, defined by
2 2 i H C e IV- 4°2o By taking logarithm and differentiating with respect of t c , Eq.(55) leads to
dL - - K'(L - Lco) (56) dtc During the course of consolidation, the following mass balances can be established for a controlled cake volume 28 Liquid phase: pe oAL = pecoALco + pVo (57)
or
E AL = e AL + V (58) o co co
where e o , e = porosities of cake at t sf 0, t , c dimensionless
Vc= filtrate volume collected during consolidation phase, m3
so V = A(e L-eL) (59) c o CO CO
Solids phase: p (1 -e )AL = p (1 - e )AL (60) co co
or
(1 - e )L = (1 - E )L (61) co co co
where p s= density of solids, kg/m3
L. c = 1 - (--)(1 - E (62) o u,)
Substituting Eq.(62) into Eq.(59)
Vc = A[L - Lim (1 - ew) - ecoLco ] = A(L - 1,03) (63)
Differentiating Eq.(63) with respect of t o
dV c dL - A (64) dtc dtc
Substituting both Eq.(63) and Eq.(64) into Eq.(56), leads to
29 dV c - - K'V (65) dtc c
Eq.(65) confirms the linear relationship between rate of filtrate generation and volume of filtrate generated during consolidation phase of expression. Equivalent to M in the empirical equation (44), K' serves as an important indicator of consolidation rate. 2.3.3 Determination of the Transition Point Since the consolidation phase typically accounts for majority of the total expression time required to produce a well dewatered cake, it is important to determine the transition point between filtration and consolidation. The filtration phase will terminate in the consolidation phase in an expression process when the whole sludge suspension forms a filter cake. According to Eq.(41) (V + V ) 2 = k(t + t ) (41)
Acknowledging that V = AL and taking the square root of Eq.(40) results in the following:
A(L + Lm ) = ,/ k(t + tm ) (66)
Differentiating Eq.(66) and rearranging
dL _,/k (67) al t + tm A
30 The term - dL/d/ t + tm is constant for constant-pressure
cake filtration as Eq. (40) is valid. The transition point
L is determined as the term - dL/d/ t + tm starts to deviate
from a constant. It may also be determined graphically. 2.4 Compressibility of Sludge Suspension Compressibility of a sludge suspension is very significant to its filtration and consolidation behavior. It is a measure of the degree of cake structural collapse resulting from compressive stresses. Deformation of solids particles which are subjected to both form and frictional drags and failure of the particle structure are the principal elements of consolidation. Particle deformation depends on the nature of surface stresses and the elastic properties of the solid. Degradation of particle aggregates with movement of particles into open spaces constitutes the major non-elastic mechanism during cake formation. For purposes of this study, compressibility was defined as the change of average specific resistance per unit increase in effective pressure and was typically calculated using the following empirical equation:
a- = a PS (68) where a = an empirical constant, which equals the specific o resistance value for pressure of unity S = compressibility index A log-log plot of average specific resistance versus applied
31 pressure differential yields constants a t:, and S.
The validity of the empirical approach is verified if the plot is linear. For municipal waste water sludges, S has been found to range between 0.4 to 0.85 (WPCF, 1969). Water treatment alum sludges have been found to vary from 0.8 to 1.3 in the compressibility index (Adrian et al.,1968). For a incompressible material, such as sand, S = 0. Increasing applied pressure in filtration operation is commonly used to increase the cake solids and the filtration rate. However, it has been found that high pressure may be unable to achieve this purpose effectively when the cake is highly compressible. If we substitute Eq.(60) into Eq.(24), it can be seen that when S equals unity the flow rate is independent of the pressure drop across the cake; while as S is greater than unity, highly compressible materials react unfavorably to pressure increase. In consolidation, as the cake is compressed, the flow resistance increases and the flow rate of expression gradually drops to zero. Yeh (1985) in his research came to the following conclusions: For highly compressible cakes (S 1), high pressure is beneficial in consolidation but not in filtration due to the adverse effect discussed above; while for moderately compressible cakes (S < 1), moderately high pressure may be appropriate in both filtration and consolidation in order to obtain a compromise between the flow rate and the average cake solids content.
32 CHAPTER 3
EXPERIMENTAL APPROACHES
3.1 Origin of Sludge Samples
Sludge samples examined in this study were from several pulp and paper plants. Manufacturing of paper products consists of several processes including preparation of raw material, pulping, bleaching, and papermaking. A large portion of the waste generated in these processes is in the form of liquid (e.g., spent liquors and wash waters) and solid wastes (e.g., fibers, residues and fillers).
The pulp and paper mill, where a majority of initial sludge samples were collected in this study and with which a majority of the sample protocol was developed, was designated herein as Plant
P which generates approximately 70 to 115 TPD (63.6 to 104.5 metric tons/day) of solids (Kutyna, 1982). A diagram of all sewer lines at Plant P is shown in Figure 3.1. Four main sewers are used to discharge the effluents from various manufacturing processes to the No. 1 lift station (Sta. 25.0). From here, the mixed effluents flow into two settling basins operated in series or parallel. After settling, the effluent enters an aeration basin with a hydraulic detention time of 7 days. The aerated effluent then passes through two polishing ponds and is later discharged to a river. Settled primary sludge from the settling basins is pumped to a sludge holding lagoon referred to as
33 Station 42.0 and allowed to thicken. Supernatant liquid from
Sta. 42.0 is recycled to the settling basins. Thickened sludge
is dredged and landfilled.
Fine Paper Bleach Paperboard Filter Total Pulp Sewer Sewer Sewer Sewer Sewer
Sta. 1.35
Sta. 3.0 Sta. 2.0 Sta. 20.0
Sta. 1.01
Sta. 25.0
ASB Basin Treated Effluent
Dredged Sta. 42.0 Sludge
Fig. 3.1 Primary Sludge Sewer Diagram of Plant-P; ASB = Aerated Stabilization Basin (Ortiz,1988).
Sludge samples from Plant-P were collected at the dredged sludge lagoon Sta. 42.0 by Plant-P personnel at scheduled times and sent to the laboratory by air freight. Additional sludge samples sent from other pulp and paper mills were also examined in the laboratory. The other plants where samples of primary and
34 secondary sludge suspensions came from were designated as Plants
CL, CS, E, L, PA, S and V.
Upon arrival at the laboratory, samples were identified by the date of arrival. For example, sample P-42.0-9157 was a sample from Plant-P, Sta. 42.0, that arrived at the laboratory on day 157 (Julian calendar) or June 6, 1989. This method of identification provided a means of determining the storage time of a sample when analyzed. All descriptive information provided by plant personnel were recorded.
3.2 Sampling Procedures
Because the objective of experimental analysis was to determine the dewatering properties of the sludge samples received, additional thickening of some samples was needed at the laboratory depending upon the experimental situation. This was done by allowing the original suspension to settle overnight when refrigerated. Excess supernatant was removed to generate a thicker sludge suspension. Thickened sludge samples generally had suspended solids concentrations of 50 g/L or higher. Before sampling, all sludge suspensions were mixed thoroughly to ensure maximum homogeneity. One-liter plastic bottles were used to store analytical samples. All suspensions and samples were kept refrigerated at 3-5 °C while not in use to inhibit biological activity.
3.3 Experimental Apparatus
3.3.1 Capillary Suction Time (CST) Apparatus
The capillary suction time (ST) apparatus is a commercial device used extensively in sludge-dewatering practice to rapidly
35 characterize sludge suspensions with respect to dewatering properties (Vesilind, 1979). As shown in Figure 3.2, a CST apparatus consists of a 10-mm diameter cylinder, a plate with one
2 - tce
4 : — e •.er 5 C5 :aze!-
Fig. 3.2 Schematic diagram of CST apparatus
electrode on the inner circuit, measured 1.55 cm from the center of the cylinder, and a pair of electrodes on the outer circuit, distanced 2.25 cm away from the center of the cylinder, and a chronometer which is activated when the liquid travels on a CST paper from the outer edge of the cylinder collar to touch the first electrode. A small volume (approximately 5 mL) of a sludge suspension is placed in the cylinder for each CST measurement. The chronometer is activated after water, extracted from the sledge suspension in the cylinder by capillary forces in the paper, travels, from the outer edge of the cylinder collar and touches the first electrode. The timer is then stopped when the liquid interface travels a distance of 0.70 cm to reach the pair
36 of outer electrodes. The CST paper used was Whatman No.40 Chromatography random-fiber paper. The particular CST apparatus used in this study was manufactured by Triton Electronics Limited (model WPRL Type 92/1). 3.3.2 Pressure Cell Apparatus The pressure cell apparatus used to determine the specific resistance and compressibility index of sludge suspension con- sisted of a 250-mL stainless steel cylinder, 4.7-cm in diameter and 14-cm high (Gelman model 4280); a pressurized nitrogen cylinder with a pressure regulator; a 100-mL volumetric flask for filtrate collection; and an electronic scale (Fisher Scientific XT top loading balance) connected to a personal computer for data acquisition. A schematic diagram of a pressure cell apparatus was presented in Figure 3.3. The filter paper used in the tests was cut from Whatman qualitative No.1 filter paper. 3.3.3 Compression-Permeability Cell (C -P Cell) The C-P cell used in this study was made of stainless steel. The apparatus included a cylinder with a length of 43.2 cm and an inner diameter of 7.55 cm, a cap and a perforated base with filtrate collecting conduits. A detailed diagram of the C-P cell used is shown in Figure 3.4. The overall system consisted of a hydraulic fluid reservoir, a hydraulic ram (Dayton model 4Z449A), a piston with a diameter of 7.5 cm which could be attached to the hydraulic ram, a filtrate collecting jar placed on an electronic scale (Fisher Scientific XT top loading balance) which was connected to a personal computer with program developed to record
37 1 Nitrogen gas cylir,ce - 2 Pressure gauge 3 Three-way valve 4 Pressure cel 5 Volumetric flask 6 Analytical balance 7 Personal computer
-.
Fig. 3.3 Schematic diagram of pressures cell apparatus
38 6 E; ter PerforalE..: 8
Fig 3.4 Normal sectional schematic diagram of C-P cell
39 expression time and corresponding filtrate volume automatically. The driving force for the hydraulic system was gaseous pressure regulated from two pressurized nitrogen cylinders. As schematically presented in Figure 3.5, pressurized nitrogen gas could be regulated into and out the hydraulic fluid reservoir through each of the two three-way valves 5 & 6. When the hydraulic fluid reservoir was subjected to pressure, the pressure was transmitted onto the hydraulic ram by the fluid, and the piston attached to the hydraulic ram was then driven into the C-P cell as the hydraulic ram moved down. Similarly, through the other three-way valve, pressure could be applied upward to create a vacuum in the hydraulic ram, therefore withdrawing the hydraulic ram, subsequently the piston was lifted. The piston also had two 0-rings to provide maximum sealing against C-P cell wall. Upon neglecting the wall friction, the ratio of the output pressure at the bottom of the piston versus the reading gauge pressure was 1.835. Same as in the pressure cell test, the filter paper used was also Whatman qualitative No.1 filter paper. 3.4 Analytical Methods 3.4.1 Sample Characterization Characterization of sludge samples was conducted in accordance to the procedures described in Standard Methods (APHA, 1986) which was developed to provide guidelines for the examination of waters, sludge suspensions and sediments of a wide range of quality. Sludge samples examined during this study were
40
1 N trOcen r:er fOr n: c stoncc...n 2 N trogen gas c%. n:er (cr r .
3 DP .r-Se:ure cause 4 7-"ressure puce 'tree - v6 ay va' .e to r- o.'e
51 6 ' cirr-Nere' -war va ve to r- o.e c Stir LC P- YCr3t.. C f U reset. C' 8 . a .e ate', c : rar- rar- 5 E. 6 I I : stcr I I CCI-- : - ESS
1 .7. • a .E at r: r
17 .rate:: e:t a- a .' :a :a a:t zs erS: 7-, a
1 5
13
1
Fig. 3.5 Schematic diagram of overall C-P cell dewatering and data acquisition system
41 subjected to physical and chemical analysis at Georgia Tech'.
These included pH, suspended solids concentration (SS), volatility of suspended solids, total and soluble chemical oxygen
demand (COD). Other analyses were conducted by Weyerhaeuser -
designated laboratories on selected samples.
3.4.1.1 Suspended and Volatile Suspended Solids
Suspended solids concentrations (SS) and volatile suspended
solids concentrations (VSS) of all sludge suspensions were
determined in accordance to the procedure outlined in Sections
209 C and D of Standard Methods (APHA, 1986), respectively, using
Gooch crucibles. The filter papers used were Fisherbrand G4
Glass Fiber Filters. All determinations were performed in
triplicate to obtain corresponding average values.
3.4.1.2 Total and Soluble Chemical Oxygen Demand
The procedure outlined in Section 508 of Standard Methods
(APHA, 1986) was used in all determinations of chemical oxygen demand (COD). The soluble COD of a sludge suspension was determined by analyzing the filtrate obtained from filtering the suspension through a 0.45 pm membrane filter (Gelman Sciences
Inc., Ann Arbor Michigan, Product #66068). In this study, each sludge sample was diluted 100-fold to determine the corresponding total COD value, and the filtrate was diluted 25-folds for soluble COD determination.
3.4.1.3 pH
Ph measurements for all sludge suspensions were conducted by following the procedure outlined in Section 423 of Standard
Methods (APHA, 1986).
42 3.4.2 Dewatering Properties of Sludge Suspensions 3.4.2.1 CST Determination Each reading of OST was obtained by placing 5 mL of sludge sample into the 10-mm diameter cylinder of the CST apparatus and recording the time required for the liquid to travel 0.67 cm through the Whatman chromatography random-fiber paper. Due to nonhomogeneous and fibrous nature of the sludge suspensions, all CST measurements were run in triplicate to get the average value for a suspension. 3.4.2.2 Specific Resistance and Compressibility Index Prior to determining specific resistance, the average dry mass and average wet mass of filter paper used were obtained. These were determined to calculate the moisture content in the sludge cake excluding any moisture associated with the filter paper. The average dry mass of the filter paper which was previously dried at 103 °C for 24 hours was 0.1362 g with a standard deviation a of 0.004 g. The average wet mass was determined by filtering 100 mL of distilled water at a differential pressure of 50 kPa. The average wet mass determined was 0.3785 g with a a of 0.039 g (Ortiz, 1988). All mass were measured on a Mettler H542 Analytical Balance using Fisherbrand aluminum weighing dishes whose mass were determined to be 1.000 g. Therefore, the true mass of a wet or dry filter cake could be determined by deducting 1.3785 g or 1.1362 g from the measured values, respectively (Ortiz, 1988). The small deviations which resulted in the determination of the average mass for the wet and
43 dry filter papers did not affect the accuracy of determining the mass of wet sludge cakes.
Traditionally, the specific resistance is determined at a differential pressure of 50 kPa. The selection of this pressure was apparently based on the common use of vacuum filtration decades ago when 100 kPa (i.e., one atmosphere) was the maximum pressure achieved. All samples from well-mixed sludges were stored in 1-L bottles and refrigerated. Prior to testing, each sample bottle was shaken to insure uniform solids concentration so that a representative sludge sample could be obtained. For each test, depending upon the ease of filtration, a suspension of
50 mL or greater volume was introduced to the pressure cell.
Temperature of the sludge suspension before each run was recorded for later calculation of the specific resistance. The test consisted of measuring filtrate volume along with time. The suspension was allowed to stand quiescently for two minutes before pressure was applied. Filtrate volume and time were recorded at certain time intervals by means of a computer data acquisition system which consisted of an on-line personal computer connected with a electronic scale. Small time intervals such as 10 sec were used during the first 5 minutes of filtration, while greater time intervals were used thereafter until filtrate flow ceased. The filter cake formed on top of the filter paper was then taken out and weighed along with the filter paper on an aluminum weighing dish. After being placed in a 103
°C oven for 24 hrs and allowed to cool for 3 hrs in a desiccator,
44 the dish was weighed to determine the dry mass of the cake.
Calculations of specific resistance were done on personal
computer using a program developed at the Georgia Institute of
Technology (Johns, 1987).
The compressibility index of a sludge suspension can be determined by running specific resistance tests at various pressures. Plotting specific resistance values versus corresponding pressures in logarithmic scale, the slope of the best-fit line determined by linear regression is the compressibility index for the suspension, and the intercept equals to the specific resistance value at unit pressure.
Because a pressure range of 150-300 psi (1035-2070 kPa) was commonly adopted in industrial practice of mechanical dewatering, a comparable pressure range of 50 kPa, 600 Kpa, 800 kPa and 1300 kPa were used in this study for determination of compressibility index.
3.4.2.3 C-P Cell Test
C-P cell test was designed to examine sludge dewatering properties over the complete cycle of expression, both cake filtration phase and consolidation phase. Pressure levels selected in this study were 1101 kPa, 1468 kPa, 2385 kPa and 3303 kPa, broad enough to simulate what is actually used in industrial dewatering applications. This pressure range (e.g., approximately 160 psi to 480 psi) covers projected operating ranges for belt presses, filter presses and screw presses used in pulp and paper mills. The range furthermore was selected to
45 clearly demonstrate the benefit, or lack there of, of elevated
pressures in dewatering processes. In the test, mechanical
pressure was conveyed through the piston to the sludge
suspension. To generate a consolidated cake with a thickness no
less than 1.0 cm and considering the variations among feed
suspension solid concentrations, 800 g of a suspension was used
as a measuring reference for each C-P cell test. After pressure was applied to drive the piston into the cell, the air entrapped between suspension and the piston was released through an air
exhaust conduit built internal to the piston. The air exhaust valve was closed after a small amount of sludge suspension jetted out which was collected for later mass balance calculation.
Timing was initiated as soon as the desired pressure equilibrium across the total thickness of the sludge suspension was established, this usually took around 5 minutes. The filtrate volume and time were recorded by the computer data acquisition system described above at an interval of 1 minute for the first hour of each test and an interval of 3 minutes thereafter until the end of the test. Test duration depended on filtration rate and varied for sludge samples. To determine final cake solids content, consolidation was continued until the flow rate decreased below 0.3 mL/min, which was regarded for the purpose of this study as the experimental completion of consolidation phase.
Similar to the pressure cell test, wet and dry cake mass were determined to calculate final cake solids content. In addition, final cake thickness and total filtrate volume were recorded.
46 The transition point between cake filtration and consolidation phases for each C-P cell test could be determined by following the graphical method outlined in Chapter 2 (Eq. 67). Using the personal computer program Symphony, recorded filtrate volumes were converted into the corresponding thickness of sludge cake in the cell with respective time. After a few steps of data conversion and rearrangement, the value of dL/dt" was determined. The moment when dL/dt" started to deviate from a constant value was then determined to be the transition from cake filtration into cake consolidation.
47 CHAPTER 4
DATA ANALYSIS AND DISCUSSION
4.1 Characterization of Plant-P Sludge Samples
A total of twenty-one samples were examined, as provided by personnel at plants throughout the industry.
• Six samples (P-42) from the Plymouth mill were
examined. These samples were all obtained from a
dredge operation within the sludge-holding ponds at the mill;
• Six samples (L) from the Longview primary clarifier underflow were examined;
• Two samples (V) from the primary clarifier underflow at the Valliant mill were examined;
• One sample (S) from the Springfield plant was examined; • One sample (E) from the Everett primary settling basin was examined;
• Two samples (CL) from the Columbus plant were examined; • Two samples (PA) from the settling basin influent at the Prince Albert plant were examined, and • One sample (CS) of activated sludge from the Cosmopolis plant was examined. Because of the various origins of the samples, certain characteristics of these sludge samples varied between samples, which could result in different dewatering behavior. Results of pH, suspended and volatile solids concentration determinations are listed in Table 4.1.
4R
Table 4.1 pH, Suspended and Volatile Suspended Solids Concentrations of Sludge Samples
pH SS VSS VSS/SS Sludge Sample (g/L) (g/L) (g/L) (%)
P42-9157 6.9 58.16 38.77 67 Primary
P42-9166 6.5 90.18 41.38 46 Primary
P42-9178 6.4 53.06 37.21 70 Primary
P42-9208 6.6 56.89 39.20 69 Primary
P42-9212 6.6 55.35 38.87 70 Primary
P42-9213 6.5 55.87 41.12 74 Primary
L-9339 6.2 37.98 30.03 79 Primary
L-0263A 7.9 55.80 41.94 75 Primary
L-0263B 8.4 51.78 39.20 76 Primary
L-0264A 9.1 56.11 42.98 76 Primary
L-1011A 7.1 61.75 37.10 60 Primary
L-1011B 7.1 60.59 36.96 61 Primary
S-0005 11.5 218.90 27.68 13 Primary
E-0073 6.6 479.20 45.60 10 Primary
V-0234A 6.3 6.02 5.67 94 Primary
V-0234B 7.1 10.51 9.82 93 Primary
CL-0305A 6.6 (8.58%)* (5.1%)* 60 Secondary
CL-0305B 6.9 (11.02%) * (7.2%)* 66 Secondary
PA-1039A 9.8 302.52 41.56 14 Primary
PA-1039B 10.6 55.80 41.94 10 Primary
CS-1039A 9.4 28.82 25.81 90 Secondary
*Total solids and volatile solids concentrations (not "suspended" solids) are presented as mass/mass basis.
49 Values of pH among all sludge samples examined ranged from 6.32 to 11.5. Since effect of pH on dewatering properties was not among the primary objectives of this study, no efforts were made to determine the optimum pH values for best dewatering of the sludge samples. Nevertheless, the pH of a sludge suspension could affect properties such as degree of ionization and particle surface charge which are important for the formation of a filter cake lattice with suitable porosity for effective dewatering. For P42 sludge samples, suspended solids concentrations ranged from 53 to 90 g/L, while volatilities of suspended solids (VSS/SS) were fairly consistent and close to 70% with exception of sample P42-9166 whose volatility was only 45.9%. Because the detention time of sludge samples dredged from the holding lagoons at Plant P could vary from months to years, and mud from the bottom of the lagoon could be included in the sample during the collecting process, certain deviations in volatility found among samples received at different times should be considered normal. As mentioned before, some of the P42 samples, and both CS samples, were concentrated by gravity in the laboratory upon arrival. Plant L samples had suspended solids concentrations ranging from 38 to 62 g/L with volatilities between 60% and 80%. Suspended solids concentrations for Plants S, E and PA were very high, while their volatilities were very low (around 10%). In comparison, Plant V and CS had low suspended solids concentrations and very high volatilities (around 90%). The two samples from Plant CL were exceptionally thick and could not be filtered in the traditional suspended solids tests. Therefore,
50 Fig. 4.23 Fig. 4.22
dljdt0- 5 (cm /s0 . 5) dL/dt0• 5 (cm /s0. 5) 0.01 0.1 0 1 .00 1000 testimmagamllaillirmul4 Pressure of1468kPa Plot Pressure of Plot Slope =0.04 Filtration phase of of - -dL/dt" vst dL/dt 1101 kPa
m — 81 vstfor b
\ t (sec) t (sec) 1E4 Consolidation: t=5760s. for 42.0-9213-1468 kPa 0 Sample 42-9213 Sample 42-9213 at at 1E5
— 1.00 Filtration phase
42.0-9213-2385 kPa
— 5) , Slope = 0.04 Consolidation: t = 5040 s — 0. /s
esemars~11111Mili-Nst
(cm 0.10 5
. 0 0 9) dt 46 dLi
0.01 1000 1E4 1E5
t (sec) Fig. 4.24 Plot of -dL/dt m vs t for Sample 42-9213 at Pressure of 2385 kPa
1.00
. Filtration phose 42.0-9213-3303 kPo
5) Slope = - 0.02 Consolidation: t = 5520 s 0. /s CAStiAilaPINIMM
(cm 0.10 5 • 0 dt dLi
0.01 1000 1E4 1E5
t (sec)
Fig. 4.25 Plot of -dL/dt m vs t for Sample 42-9213 at Pressure of 3303 kPa
82 Table 4.9 Slopes of Plots -dL/dt" vs t In Cake Filtration Phase of Plant-P Samples
Slope of Plot (cm/sec15 ) Suspension 1101 kPa 11468 kPa 2385 kPa 3303 kPa
42-9157 -0.10 -0.03 0.01 -0.10
42-9166 0 0 0.03 0.05
42-9178 0.04 0.10 0.04 0.09 42-9208 -0.02 0 -0.02 0 42-9212 0.03 -0.05 -0.05 0 42-9213 0.03 0.04 0.04 -0.02
filtration rate increases with pressure. Both input sludge volume and time to begin data collection after the initiation of expression on each C-P cell expression test were difficult to maintain consistent (see Table 4.10). Therefore, the elapsed time before cake consolidation began (obtained from each C-P cell expression process) should not be used for absolute comparison between one and another but merely serve as a reference. For parabolic filtration phase, a plot of -dIldt" vs t should exhibit a straight line with a slope of zero, corresponding to a constant average specific resistance over the filtration phase. However, in most cases with the samples examined, slope of the plot was slightly less or greater than zero. For negative slope, clogging of the pores in a developing cake could occur due to migration of fine particles, which would
83 Table 4.10 Elapsed Time Before Cake Filtration Enters Consolidation in C-P Cell Expression of Plant-P Samples
Elapsed Time (sec) Suspension 1101kPa 1468kPa 2385kPa 3303kPa
42-9157 7500 6900 5100 5400 42-9166 3900 3540 2940 3000 42-9178 3540 7200 5760 9000 42-9208 5580 5220 4320 5040 42-9212 4320 4320 3960 4140 42-9213 6660 5760 5040 5520
lead the average specific resistance to increase with time while positive slopes could possibly be attributed to the effect of compressible solids during filtration. The layer closest to the filter media was subjected to the greatest pressure and, therefore, compressed to a greater degree. Each added layer of solids would have a local specific resistance slightly less than the preceding layer, and the average specific resistance decreased with the filtrate volume (Novak et al., 1988). In addition, the fibrous aggregates of the sludge samples could have made the solids deposition during filtration very nonuniform. These would have caused uneven distributions of the interstices in cakes through which the filtrate flowed, and Darcy's law would not hold under the circumstances. As for the plot of -dL/dt m vs t in consolidation phase, there is no particular pattern in terms
84 of its shape simply because Darcy's law does not apply for cake consolidation. The plot of log(t) versus log(V) for the overall expression process is a line which should be linear in the filtration phase and non-linear after expression enters into the consolidation phase. Based upon the transition points determined, the slopes for the filtration phase were calculated by linear regression and are given in Table 4.11. For samples examined, excellent regression coefficients were obtained in calculating the slopes (r2 was greater than 0.95 in all cases). The plots for sample P42-9213 at pressures of 1101 kPa, 1468 kPa, 2385 kPa and 3303 kPa are presented in Figs. 4.26 to 4.29. The respective slopes were 1.94, 1.90, 1.98 and 2.00, very close to the theoretical value of 2 based on Darcy's law. However, for some of the P samples, there were deviations for the slope from a value of 2, such as in the case of sample P42-9166 at pressure of 3303 kPa where the slope was only 1.46. Reasons for such deviations could be related to the fibrous nature of the sludge solids as discussed earlier. Figs. 4.30 to 4.49 are plots of log(t) vs log(V) for the remaining Plant-P samples. Cake solids contents obtained from C-P cell expressions at various operating pressures and temperatures were included in Table 4.12. In order to determine the ultimate cake solids content achievable by C-P cell expression, plots of dV/dt vs V were employed to project ultimate filtrate volumes. Degree of completion for each expression process was then expressed as the
85
Table 4.11 Slopes of Plots log(V) vs log(t) in Cake Filtration Phase of Plant-P Samples
Slope of Plot Suspension 1101kPa 1468kPa 2385kPa 3303kPa
42-9157 1.73 1.57 1.62 1.57
42-9166 1.64 1.48 1.64 1.46 42-9178 1.57 1.52 1.60 1.55 42-9208 1.87 1.90 1.91 1.83
42-9212 1.94 2.03 2.05 2.00
42-9213 2.00 1.94 1.90 2.00
Table 4.12 Cake Solids Contents Achieved and Degree of Completion with C-P Cell Expression of Plant-P Samples Cake Solids Content(%) (Degree of Completion (%)) Suspension 1101kPa 1468kPa 2385kPa 3303kPa
42.9157 34.88 38.31 39.93 57.51 (82%) (79%) (72%) (80%) 42.9166 49.66 55.42 52.97 56.13 (92%) (97%) (91%) (92%)
42.9178 39.80 39.48 39.50 40.12 (88%) (81%) (80%) (76%)
42.9208 38.98 40.21 40.22 43.23 (91%) (93%) (92%) (83%) 42.9212 41.10 44.69 51.52 47.36 (93%) (97%) (92%) (93%)
42.9213 41.10 44.69 51.52 47.36 (77%) (85%) (76%) (82%)
86 iy+ i 0 J
Logy
Fig. 4.26 Plot of logt vs logy for Sample 42-9213 at Pressure of 1101 kPa
1E5
42.0-9213-1468 kPa
Filtration phase: slope = 1.90
IEA' 1E4 0 _1
1000 100 1000
Logy
Fig. 4.27 Plot of logt vs logy for Sample 42-9213 at Pressure of 1468 kPa
87
1E5
42.0-9213-2385 kPa
Filtration phase: slope = 1.98
I; 1E4 0 ....1
1000 100 1000
LogV
Fig. 4.28 Plot of logt vs logy for Sample 42-9213 at Pressure of 2385 kPa
1E5
42.0-9213-3303 kPa
Filtration phase: slope = 2.00
T:; s 1E4 0 i
1000 100 1000
LogV
Fig. 4.29 Plot of logt vs logy for Sample 42-9213 at Pressure of 3303 kPa
88 LogV
Fig. 4.30 Plot of logt vs logy for Sample 42-9157 at Pressure of 1101 kPa
LogV
Fig. 4.31 Plot of logt vs logy for Sample 42-9157 at Pressure of 1468 kPa
89 LogV
Fig. 4.32 Plot of logt vs logy for Sample 42-9157 at Pressure of 2385 kPa
LogV
Fig. 4.33 Plot of logt vs logy for Sample 42-9157 at Pressure of 3303 kPa
90 Logy
Fig. 4.34 Plot of logt vs logy for Sample 42-9166 at Pressure of 1101 kPa
LogV
Fig. 4.35 Plot of logt vs logy for Sample 42-9166 at Pressure of 1468 kPa
91 LogV
Fig. 4.36 Plot of logt vs logy for Sample 42-9166 at Pressure of 2385 kPa
LogV
Fig. 4.37 Plot of logt vs logy for Sample 42-9166 at Pressure of 3303 kPa
92 LogV
Fig. 4.38 Plot of logt vs logy for Sample 42-9178 at Pressure of 1101 kPa
1E5
42.0-9178-1468 kPa
Filtration phase: slope = 1.52
1 5'I 1E4 t 0
1000 100 1000
LogV
Fig. 4.39 Plot of logt vs logy for Sample 42-9178 at Pressure of 1468 kPa
93 II% 0 -J
LogV
Fig. 4.40 Plot of logt vs logy for Sample 42-9178 at Pressure of 2385 kPa
LogV
Fig. 4.41 Plot of logt vs logy for Sample 42-9178 at Pressure of 3303 kPa
94 0
LogV
Fig. 4.42 Plot of logt vs logy for Sample 42-9208 at Pressure of 1101 kPa
LogV
Fig. 4.43 Plot of logt vs logy for Sample 42-9208 at Pressure of 1468 kPa
95
1E5
42.0-9208-2385 kPa
Filtration phase: slope = 1.91
1E4
1000 100 1 000
LogV
Fig. 4.44 Plot of logt vs logy for Sample 42-9208 at Pressure of 2385 kPa
LogV
Fig. 4.45 Plot of logt vs logy for Sample 42-9208 at Pressure of 3303 kPa
96 0 ...1
LogV
Fig. 4.46 Plot of logt vs logy for Sample 42-9212 at Pressure of 1101 kPa
Logy
Fig. 4.47 Plot of logt vs logy for Sample 42-9212 at Pressure of 1468 kPa
97 LogV
Fig. 4.48 Plot of logt vs logy for Sample 42-9212 at Pressure of 2385 kPa
LogV
Fig. 4.49 Plot of logt vs logy for Sample 42-9212 at Pressure of 3303 kPa
98 ratio of total collected filtrate volume and the ultimate filtrate volume. In Figs. 4.50 to 4.53, degrees of completion for sample P42-9213 are from 76% to 85%. Results for other sludge samples can be found in Table 4.12 and through Figs. 4.54 to 4.73. As can be seen clearly from the shape of the plots, a transition point exists between the filtration phase and the consolidation phase, which matches with the one in corresponding -dL/dtm plot; and linear relationships between dV/dt and V in the consolidation phase is confirmed by excellent regression coefficients (r 2 was greater than 0.95 in all cases). An ultimate filtrate volume can be determined by extrapolating the linear slope until dV/dt reached zero. Theoretically, the absolute value of the slope should also imply the rate of consolidation, the greater the value, the less time it would take for consolidation to complete. The slopes for Plant-P samples are tabulated in Table 4.13. For sample P42-9213 (Figs. 4.50 to 4.53), the absolute values of the slope increased as the applied pressure increased. However, this was not obvious for other samples examined, and some even exhibited the opposite trend. As in the case of sample P42-9166 (Figs. 4.58 to 4.61), the absolute values of the slope decreased as the pressure increased from 1101 kPa to 3303 kPa. This simply indicates that for the sludge suspensions examined (moderately compressible with compressibility indexes of 0.57 to 0.88), increase of pressure in the range as applied in this study could hardly affect the rate of consolidation substantially.
99
) ec l/s (m dt dV/
V (mL)
Fig. 4.50 Plot of dV/dt vs V for Sample 42-9213 at Pressure of 1101 kPa
) L/sec (m dV/dt
V (m f..)
Fig. 4.51 Plot of dV/dt vs V for Sample 42-9213 at Pressure of 1468 kPa
100 Fig. 4.53Plotof dV/dtvsVforSample42-9213 at Fig. 4.52PlotofdV/dtvsVforSample42-9213at
dV/dt (m l/sec ) dV/dt (m L/sec ) 0.10 0.20 0.00 0.30 0.40 0 Pressure of3303 kPa Pressure of2385kPa 200 101 V (mt.) V (mL) 400 600 800
Fig. 4.55PlotofdV/dtvsVfor Sample42-9157at Fig. 4.54PlotofdV/dtvsVforSample42-9157at
dV/dt (m l/sec ) dV/dt (mL/sec ) 0.00 0.10 0.20 0.30 0.40 0.10 0.00 0.20 0.30 0.40 0 0 Pressure of1101kPa Pressure of1468 kPa 0 0 0 o o ii.M4Nuititalwiloolp Slope=—3.85x10 200 200 102 V ( V (mL) Degree ofcompletion:82% Degree ofcompletion:79% 400 400 etooam mL 42.0-9157-1101 kPa 42.0-9157-1468 kPa Slope =—3.21x10 ) tottibitt 600 600
-4 -4 " 800 BOO 000 0.40
42.0-9157-2385 kPa
0.30 -o ) Degree of completion: 72% 0 L/sec 0.20 dt (m dV/ 0.10 Slope = — 3.53 x 10 -4 006 0o0
0.00 0 200 400 600 800
V (m i.)
Fig. 4.56 Plot of dV/dt vs V for Sample 42-9157 at Pressure of 2385 kPa
0.40
0.30 ) L/sec 0.20 (m dt
dV/ 0.10
0.00 0 200 400 600 800
V (mi.)
Fig. 4.57 Plot of dV/dt vs V for Sample 42-9157 at Pressure of 3303 kPa
103 Fig. 4.59Plotof dV/dtvsVforSample42-9166 at Fig. 4.58PlotofdV/dtvsVforSample42-9166at
dV/dt (mL/sec) dV/dt (m L/sec ) Pressure of1468 kPa Pressure of1101kPa 104 V (mL) 400 600 800 Fig. 4.61PlotofdV/dtvsVfor Sample42-9166at Fig. 4.60PlotofdV/dtvsVforSample42-9166at
dV/dt (mL/sec ) dV/dt (m L/sec ) 0.20 0.10 0.00 0.30 0.40 0.00 0.10 0.20 0.30 0.40 0.50 0 0 Pressure of3303 kPa Pressure of2385kPa 200 200 105 V (ml.) V (m 400 400 i.) 600 600 800 800 0.40 0 42.0-9178-1101 kPo
0.30 ) o Degree of completion: 88% 0
l/sec 0 0.20 (m dt Slope = — 4.39 x 10 -4 dV/ 0.10 0 0
0.00 0 200 400 600 800
V ( mL)
Fig. 4.62 Plot of dV/dt vs V for Sample 42-9178 at Pressure of 1101 kPa
0.40
0.30 ) l/sec 0.20 (m dt
dV/ 0.10
0.00 0 200 400 600 800
V (mL)
Fig. 4.63 Plot of dV/dt vs V for Sample 42-9178 at Pressure of 1468 kPa
106 Fig. 4.65PlotofdV/dtvsVfor Sample42-9178at Fig. 4.64PlotofdV/dtvsVforSample42-9178at
dV/dt (mL/sec) dV/dt (ml/sec) 0.00 0.20 0.30 0.40 0.10 Pressure of3303 kPa 0 Pressure of2385kPa 200 107 V (mL) V (mt..) 400 600 BOO 0.40
0.30
)
l/sec 0.20 (m t d
dV/ 0.10
0.00 0 200 400 600 BOO
V (mL)
Fig. 4.66 Plot of dV/dt vs V for Sample 42-9208 at Pressure of 1101 kPa
0.40
0.30
) c
L/se 0.20 (m t d
dV/ 0.10
0.00 0 200 400 600 800
V (mi.)
Fig. 4.67 Plot of dV/dt vs V for Sample 42-9208 at Pressure of 1468 kPa
108 Fig. 4.69PlotofdV/dtvsVfor Sample42-9208at Fig. 4.68PlotofdV/dtvsVforSample42-9208at
dV/dt (m L/sec ) dV/dt (m L/sec ) 0.00 0.10 0.20 0.30 0.40 0 Pressure of3303 kPa Pressure of2385kPa 200 109 V (mL) 400 600 800 0.40
0.30 ) c L/se 0.20 (m dt
dV/ 0.10
0.00 0 200 400 600 800
V (mt.)
Fig. 4.70 Plot of dV/dt vs V for Sample 42-9212 at Pressure of 1101 kPa
0.40
0 42.0-9212-1468 kPa
0.30 0 ) Degree of completion: 97% 0 o
L/sec o 0.20 0 (m t d
dV/ 0.10
0.00 0 200 400 600 800
V (mL)
Fig. 4.71 Plot of dV/dt vs V for Sample 42-9212 at Pressure of 1468 kPa
110 Fig. 4.73PlotofdV/dtvsVfor Sample42-9212at Fig. 4.72PlotofdV/dtvsVforSample42-9212at
dV/dt (m L/sec) dV/dt (mL/sec ) 0.00 0.10 0.20 0.30 0.40 0.00 0.10 0.20 0.30 0.40 Pressure of3303 kPa 0 0 Pressure of2385kPa 0 0 0 0 co 200 200 0 111 V (mL) V (ml.) Degree ofcompletion:92% 400 400 42.0-9212-2385 kPo Slope =—3.70x10 600 600 -4
800 800 Table 4.13 Slopes of Plots dV/dt vs V in Cake Consolidation Phase of Plant-P Samples
4 Slope of Plot ( - 10 sec") Suspension 1101kPa 1468kPa 2385kPa 3303kPa
42-9157 3.21 3.85 3.53 3.49 42-9166 6.50 5.85 5.30 5.28 42-9178 4.39 3.60 4.00 3.72
42-9208 3.47 3.45 3.22 3.06
42-9212 4.39 4.25 3.70 4.06
42-9212 4.39 4.25 3.70 4.06
42-9213 2.95 3.15 3.22 3.50
Therefore, such variation of the slope values should be regarded as normal scattering and not used for the purpose of data interpretation in this study. Discussion of pressure effects on consolidation will be conducted later. After obtaining the ultimate filtrate volume for each individual C-P cell expression, the maximum filtrate volume which can be generated from consolidation is predictable and the time required for consolidation to reach a specified cake solids content is known from either plot -dIJ/dtm vs t or plot dV/dt vs V. In addition, knowing the ultimate filtrate volume, the difference of ultimate filtrate volume and actually collected filtrate volume is subtracted from the mass of wet cake; therefore, the ultimate cake solids content achievable for each
112 expression process can be calculated. The ultimate cake solids contents determined for C-P cell expression of Plant-P samples are presented in Table 4.14. The term "ultimate" cake solids refers to a projected cake that is formed under constant pressure to a point where no additional water (at the indicated pressure) can be extracted from the cake. Hence, ultimate cake solids is the maximum achievable solids content that can be achieved for a particular suspension at the indicated pressure. Theoretically, cake solids content should increase as expression pressure increases. By viewing Tables 4.12 and 4.14, some of the results failed to show the trend clearly. This could be attributed to the temperature differences, different degrees of consolidation at which each particular C-P cell test was terminated, and possible experimentally associated processing errors. Figures 4.74 and 4.75 graphically presented the cake solids data from Tables 4.12 and 4.14, respectively. 4.3.3 Results of Plant-L Samples Figures 4.76 to 4.94 are the plots of -dL/dt" vs t of six Plant-L samples. In comparison to the same plots of Plant-P samples, it is evident that the time to reach the transition point from the filtration phase to consolidation phase (see Table 4.15) was approximately twice as long for Plant-L samples (except for L-1011A and L-1011B which were similar to Plant-P). The transition points also occurred more abruptly for the Plant-L samples. The slopes of the filtration phase of the plots were close to zero (i.e., 0.02, 0.02, 0.03 and 0.02 for L-9339),
113 Table 4.14 Ultimate Cake Solids Contents Achievable with C-P Cell Expression of Plant-P Samples at Various Pressures and Temperatures
Ultimate Cake Solids Content (%) Temperature ('C) Suspension 1101kPa 1468kPa 2385kPa 3303kPa
42-9157 42.62 48.46 54.44 72.05 (21°C) (11°C) (22°C) (24°C)
42-9166 53.91 57.03 57.93 61.18 (22°C) (22°C) (22°C) (22°C)
42-9178 45.36 48.60 49.27 52.47 (10°C) (19°C) (25°C) (25°C)
42-9208 42.79 43.37 43.72 52.08 (13°C) (23°C) (25°C) (23°C)
42-9212 41.21 45.96 55.76 50.93 (24°C) (25°C) (25°C) (25°C)
42-9213 43.90 45.30 48.58 51.06 (11°C) (17°C) (21°C) (22°C)
Table 4.15 Elapsed Time Before Cake Filtration Enters Consolidation in C-P Cell Expression of Plant-L Samples
Elapsed Time (sec) Suspension 1101kPa 1468kPa 2385kPa 3303kPa
L-9339 27720 26280 27720 L-0263A 12060 9000 L-0263B 13320 10260 L-0264A 5580 12960 8100 L-1011A 3600 3360 3781 3000 L-1011B 3420 3360 2940 3060
114 Fig. 4.75UltimateCakeSolidsContents AchievableByC-P Fig. 4.74MeasuredCakeSolidsContentsAttheEndofC-P 5 '5 al7 70 • • 0
Coke Solids Fraction . 20 50 30 40 60 70 80 20 30 40 50 60 80 1000 1000 Pressures Cell ExpressionofPlant-PSamples atVarious ' : Pressures * Cell ExpressionofPlant-PSamplesatVarious 7° 1:;. ...... a• . ....,;,-,,..::
... • "*; A. 0 • ..• A o •
AI 42., • . .•••• ...... — ... a • 0 42-9157 ...... :::,,,...... A 0 42-9157 • 42-9166 ... 42-9178 42-9166 42-9178 ' .•• 2000 2000 Pressure (kPo) Pressure (KPo) ...... ..:::.: ..... 115 :11 ...... . f.'
a w • ..::,:...... e ..::::: :...... :::...... :.:: . ...... '''' v • v • A A .:: ..:.::...... 1 .
: .,....- 3000 3000 . :::::;;:: .•• 1 • v 42-9213 11 • • 7 . ::: .•• 42-9213 42-9208 42-9208 42-9212 42-9212 .. ..: ■ 4 .0 1 1 4000 4000 . . . . t (sec)
Fig. 4.76 Plot of -dL/dt" vs t for Sample L-9339 at Pressure of 1101 kPa
1.00
Filtration phase L-9339-1468 kPa
5) Slope = 0.02 Consolidation: t=27720 s 0. /s
0.10 (cm 1 5 oveceeetell".141°-0 . 0 t d —dLi
0.01 , - a 100 1000 1E4 1E5
t (sec)
Fig. 4.77 Plot of -dL/dt" vs t for Sample L-9339 at Pressure of 1468 kPa
116 1.00
Filtration phase L-9339-2385 kPa
5) , Slope = 0.03 Consolidation: t=26280 s 0. /5
0.10 (cm 5 . 0 dt —dL/
0.01 100 1000 1E4 1E5
t (sec)
Fig. 4.78 Plot of -dL/dt(1 ' 5 vs t for Sample L-9339 at Pressure of 2385 kPa
1.00
L-9339-3303 kPa
5) Consolidation: t=27720 s 0. /s
0.10 (cm 5 . 0 dt —dV
0.01 100 1000 1E4 1E5 t (sec)
Fig. 4.79 Plot of -dLidt" vs t for Sample L-9339 at Pressure of 3303 kPa
117
,_-0263A-1101 kPa S'ope = 0.C'2 C 3^,salidaton:. t=1.2C x C 4
0.010 103 10E10 1E4 1E5
Fig. 4.80 Plot of -dL/dt m vs t for Sample L-0263A at Pressure of 1101 pKa
1 COO Fitration phase L-0263A-3303 kPc
0 Slope = —0.03 Consolida:ion: t = 9001 s
1
U
00'0 ICC 1303 1E4 1E5 t (sec)
Fig. 4.81 Plot of -dL/dt m vs t for Sample L-0263A at Pressure of 3303 kPa
118 L-02633-1101 icPc
AAA,. I. • e•s/..•• A tv
Er!
vim` Lf) d
Filtration phase S!cps =
0 01 0 100 1000 1E4 1E5
t (sec)
Fig. 4.82 Plot of -dL/dt m vs t for Sample L-0263B at Pressure of 1101 kPa
L-02633-3303 Conseidcfor: t = x 10 4 s
Or,
t 0 r. e";
C — 1
c • 100 1000 1E4 1E5 t (sec)
Fig. 4.83 Plot of -dL/dt m vs t for Sample L-0263B at Pressure of 3303 kPa
119
1.000 FIltration phase L-0264A-1101 kPa Slope = 0.02 6 Con so!:dation: t = 5880 s
U 0.100
6
C 100 1000 1E4 1E5
t (SEC)
Fig. 4.84 Plot of -dL/dt m vs t for Sample L-0264A at Pressure of 1101 kPa
1.000 , 7,,tratior, phase L-0264A-1488 kPa S.:ope = 0.01 Consc!idctioh..: t=1.295 x 1C 4
• 0 0.100 --e—e–c---e-e-993;eaRYesigingraniglimiralar - st6 6
C 010 100 1000 1E4 1E5 t (sea)
Fig. 4.85 Plot of -dL/dt m vs t for Sample L-0264A at Pressure of 1468 kPa
120
1 .000 Filtration phase L-0264A-3303 kPa 5) Slope = 0.01 Consolidation: t = 8100 s
-0. 0 ec /s i
rr 0--s—e-e-eeeteammenalleMilmwarft, 0 1100 5 (c
0. r -
t r d —dV
CP coic 100 1000 1E4 1E5
t (sec)
Fig. 4.86 Plot of -dL/dt m vs t for Sample L-0264A at Pressure of 3303 kPa
1 C'Di; L-1011A-1468 kPc Consolidation: t = 3360 s 6 C10C 0 Filtration phase
Slope = 6
0010r
7 61D°
001 0. 100C 1E4 1E5 t (sec)
Fig. 4.87 Plot of -dL/dt m vs t for Sample L-1011A at Pressure of 1468 kPa
121
L-1011A-1101 kPa 4 Consolidction: t = 3600 s O o 0,1= Filtration phase Slope = 0.02
Colo J
0.001 1000 1E4 1E5
t (sec)
Fig. 4.88 Plot of -dL/dt m vs t for Sample L-1011A at Pressure of 1101 kPa
1 000 L-1C11A-2365 kPa
Consolidation: t = 3781 s 5) rixmm=ammmammo -0. 0.100
/s Filtration phase
rn 6 Slope = 0.01
(e db 5 Gt.
dr0. czio ozo 0 iL/ *.,!) —c
3 0 001 1000 1E4 1E5
t (sec)
Fig. 4.89 Plot of -dL/dt m vs t for Sample L-1011A at Pressure of 2385 kPa
122 1 000 L-1C11A-3303 kPc 0 Consolidation: t = 3000 s 0 manszmaisitimakt., 0.100 1 3111;3 o Filtration phase
U c54 Li 4t- Slope = 0 65'
0 g13 9) 0
0 . 001 1000 - 1E4 1E-5
t (sec)
Fig. 4.90 Plot of -dL/dt 0h5 vs t for Sample L-1011A at Pressure of 3303 kPa
1 CDC L L-1C113-11C1 kPc
,-...- 0 Consolidation: t = 3421 s 0 6 :1===trA c'-"c,Q < El i_ o 31 0 ...., o loo E c 4 E ;I Filtration phase u r 0 En Slope = 0.02 6< ic '64 c OIG -■ 0
0
0001 1000 1E4 1E5
t (sec)
Fig. 4.91 Plot of -dL/dtm vs t for Sample L-1011B at Pressure of 1101 kPa
123 L-1011B-1468 kPa 0 Consolidation: t = 3360 6 0:003==elenitZ7z 0 0
0100 - Filtration onase
1.1")
0010
0
0001 1000 1E4 1E5 t (sec)
Fig. 4.92 Plot of -dL/dt" vs t for Sample L-1011B at Pressure of 1468 kPa
tax L-10118-2385 kPa i o Consolidation: t = 2940 s 1 r-z :ri:111422233221.11%14:3 0 I c:too 't- '..- Filtration 7 nose F r o o i Q 0 ..o Slope = -0.01 1 Ln % o f 0 < I - ooso t- rtt..o ''.-- Ft C% C S i I 0 001 I 1000 1E4 1E5
t (sec)
Fig. 4.93 Plot of -dL/dt" vs t for Sample L-1011B at Pressure of 2385 kPa
124
1 .0 X1 L— 1011B-3303 kPo t = 3060 s tr) 6 0 0 OC O F Fitrctio- cncee
Si^ce = 02
r
1E4 1E5
t (sec)
Fig. 4.94 Plot of -dL/dt m vs t for Sample L-1011B at Pressure of 3303 kPa and are presented in Table 4.16. Also, plots of log(V) vs log(t) were not presented for Plant-L samples; however, the slopes are included in Table 4.17 and match closely to the theoretical value of 2.0 based on Darcy's Law.
Table 4.16 Slopes of Plots - dLides vs t in Cake
Filtration Phase of Plant - L Samples
Slope of Plot (cm-sec") Suspension 1101kPa 1468kPa 2385kPa 3303kPa
L-9339 0.02 0.02 0.03 0.02 L-0263A 0.02 -0.03 L-0263B 0 0 L-0264A 0.02 0.01 0.02 L-1011A 0.02 0 0.01 0 L-1011B 0.02 0 -0.01 -0.01
Table 4.17 Slopes of Plots log(V) vs log(t) in Cake Filtration Phase of Plant-L Samples
Slope of Plot Suspension 1101kPa 1468kPa 2385kPa 3303kPa
L-9339 1.99 2.08 2.00 2.04
L-0263A 1.92 1.98 L-0263B 2.24 2.06
L-0264A 1.97 1.94 1.97
L-1011A 1.94 1.93 1.96 1.97
L-1011B 1.95 1.96 1.99 1.99
126 A minor problem was encountered in determining the ultimate filtrate volume from the dV/dt vs V plots of samples L-1011A and L-1011B. These C-P cell expression runs proceeded past the 0.2- 0.3 mL/min stopping-point stated earlier. Figure 4.95 shows the data clustering near the x-axis where dV/dt is very close to zero. A linear regression of the consolidation phase data gave an ultimate filtrate volume less than the final filtrate volume collected and recorded. To stay within the range of experimental procedures and equipment, dV/dt vs V data below about 0.25 mL/min were deleted for purposes of consistent analysis (Fig. 4.96). A linear regression was then run on the truncated consolidation- phase data to give an acceptable ultimate filtrate volume. This correction was acceptable and valid for comparing dewatering characteristics between samples. It should also be noted that more conservative ultimate cake solids concentrations resulted. The remaining Plant-L plots of dV/dt vs V are presented as Fig. 4.97 to Fig. 4.115. Cake solids contents are tabulated in Table 4.18, for samples L-0263A, L-0263B and L-0264A. Slopes of the dV/dt vs. V plots are included in Table 4.19. Ultimate cake solids contents are given in Table 4.20 for all six Plant-L samples and range from 32.45% to 50.19%. Figures 4.116 and 4.117 graphically present the cake solids data from Tables 4.18 and 4.20. The slopes of the consolidation phase of the dV/dt vs V plots are contained in Table 4.19.
127
0-4C0 L-1011A-1101 kPa
03:0 0
) 0
O /sec l O t (m d dV/
0 000 C 20C 40: 500
V ()-n! )
Fig. 4.95 Plot of dV/dt vs V for Sample L-1011A at Pressure of 1101 kPa
0400 L-1011A-1101 kPa
C3.00
)
ec 0
0 1Js 0 C.2:0 (m dt
dV/ Siooe = —8.68 X 10 -4 0:100
o 00C 0 200 400 600
V (mL)
Fig. 4.96 Plot of dV/dt vs V for Sample L-1011A at Pressure of 1101 kPa: Truncation of Terminal Rate Data in Fig. 4.95 for Purpose of Analysis
128 0.40
L-9339-1101 kPa 0.30
) c
L/se 0.20 0 (m
dt 0
dV/ 0.10
0.00 0 200 400 600 800
V (mL)
Fig. 4.97 Plot of dV/dt vs V for Sample L-9339 at Pressure of 1101 kPa
0.40
L-9339-1468 kPa 0.30
) Degree of completion: 97% ec
L/s 0.20
(m 0
dt 0
dV/ 0.10 Slope u= — 1.95 X 10 -4 '1111Nalb 0.00 Im. 0 200 400 600 BOO
V ( m )
Fig. 4.98 Plot of dV/dt vs V for Sample L-9339 at Pressure of 1468 kPa
129
0.40
L-9339-2385 kPo 0.30
) Degree of completion: 99%
L/sec 0.20 (m t d
dV/ 0.10 Slope = — 1.85 x 10 -4
0.00 Aloft. 0 200 400 600 800
V (mL)
Fig. 4.99 Plot of dV/dt vs V for Sample L-9339 at Pressure of 2385 kPa
0.40
L-9339-3303 kPa 0.30
) Degree of completion: 100%
l/sec 0.20 (m
dt 0
dV/ 0.10 Slope = — 1.83 x 10 -4
0.00 -4•46. 0 200 400 600 800
V (mL)
Fig. 4.100 Plot of dV/dt vs V for Sample L-9339 at Pressure of 3303 kPa
130 Fig. 4.102Plotof dV/dtvsVforSampleL-0236A at Fig. 4.101PlotofdV/dtvsVforSampleL-0236Aat
dV/d1 (m l/sec ) 0.000 0 100 C 400 0.200 0.300 0 400 .3.00 Pressure of3303 kPa 0 Pressure of1101kPa 0 0 0 0 0 200 V (mL) V (mL) Degree ofcorrpietion:96% 131 Degree ofcompletion:96% 400 Slope =—2.17x10 L-02653A-3303 IkPc Slope =—2.53x10 L-0263A-1101 kPa 600 -4 -4
600 4-00 L-02638-1101 kPa Degree of completion: 96% 0 300
) 0 L/sec 0.220 r 0 (m
it 0
dV/c Slope = —2.26 x 10" 0 1 00 1
0 000 200 400 60c 500
V (mL)
Fig. 4.103 Plot of dV/dt vs V for Sample L-0236B at Pressure of 1101 kPa
C 400 L—C2638-3303 kPa Degree of completion: 97% 0 300 I-
J
) 0 lisec 0200 1 0 (m
dt 0 Slope = —1.88 x 10" dV/ 0.100
V (mL)
Fig. 4.104 Plot of dV/dt vs V for Sample L-0236B at Pressure of 3303 kPa
132 Fig. 4.106Plotof dV/dtvsVforSampleL-0264A at Fig. 4.105PlotofdV/dtvsVforSampleL-0264Aat
dV/dt (rn ilsec ) 0 100 C 43Z. C00-0 0. 0.200 C 300 ❑ 300 4-00 , 00 Pressure of1468 kPa Pressure of1101kPa 0 0 0 0 0 2CC V (mL) V (mL) Decree Degree ofcompletion:97% 133 400 1.00 L-0254A-4S5kPc Slope =—1.98x10 L—C264A-1101 kPa of - - • c..cmpletion: 92% :9 600 600
-4 "
800 600 1 0,400 L-0264A-3303 kPa Degree of completion: 96% 0300 0
) c
0 L/se 0.200 0 t (m d dV/ 0.100
0.000 0 200 400 60C
V (rrL)
Fig. 4.107 Plot of dV/dt vs V for Sample L-0264A at Pressure of 3303 kPa
400 L-1011A-1101 kPa
C 300 0
) 0
C lisec i 0 0.200 0 0 (rr t. d
dV/ Slope = —8.68 X 10 -4 o
0 000 0 200 400 600 6C0
V (mL)
Fig. 4.108 Plot of dV/dt vs V for Sample L-1011A at Pressure of 1101 kPa
134
0.400 L-1011A-1468kPo
0 0300E a
0 0 c o 0
= —5.91 X 1 C 0 100 1
"UKt
0 000
V •-•1 1
Fig. 4.109 Plot of dV/dt vs V for Sample L-1011A at Pressure of 1468 kPa
O 4::
0.100 r
C CDC E.::
rn I
Fig. 4.110 Plot of dV/dt vs V for Sample L-1011A at Pressure of 2385 kPa
L-1317A--303 kPa
C
)
ec 0 /s l 0 Siope = —5.22 X 10 -4 (m
dt O dV/
V (mL)
Fig. 4.111 Plot of dV/dt vs V for Sample L-1011A at Pressure of 3303 kPa
C 400 0 L-1011E-1101 kPa
aoc
) 0 ec 0
L/s 0 0.200 0 (m t d dV/ 0,100
0.000 200 400 600 800 V (mL)
Fig. 4.112 Plot of dV/dt vs V for Sample L-1011B at Pressure of 1101 kPa
0 40C L-1C11B-1458 kPc
0 C 300
) 0 0 L/sec 0 Slope = —7.21 X 10 -4 0.203 0
(m 0 0 dt dV/ C 100
0.0DC 0 0 230 400 630 633 V 'sr L)
Fig. 4.113 Plot of dV/dt vs V for Sample L-1101B at Pressure of 1468 kPa
4:-%2 L-1011'-'-23P5 kPc
0 .3D0 C
cicoe = —5.7.7 X .0 4 0 0. 2 30 0
033 403 600 WO V (r-,,L)
Fig. 4.114 Plot of dV/dt vs V for Sample L-1101B at Pressure of 2385 kPa
137 Fig. 4.115PlotofdV/dtvsVforSampleL-1101Bat
ciVbit (rn ijsec ) 0 000 0. 0.200 C 4:Z 300 100 0 Pressure of o O O O o o 200 3303 kPa V (mL) Degree ofcompletion:100% 400 Slope =—1.02x10 L-1C118-3303 kPa O 800 -3
800
JJ
LC; L
2f` L.
0 0 L-0263A 20 • ••• • L-02632 L-026 4A
r, : 1000 2000 3000 4000
Pressure (kPa)
Fig. 4.116 Measured Cake Solids Content at end of C-P Cell Expression of Plant-L Samples
60
50 X) ( ion t c Fra
ids l 30 1- J
So 0 0 L-0263A • • L-9339 ke • -• L-02639 o c L-1011A 20
Ca a ■ J 4, L 0264A ■ L-10118
10 1000 2000 3000 4000
Pressure (kPc)
Fig. 4.117 Ultimate Cake Solids Contents Achievable by C-P Cell Expression of Plant-L Samples
139 Table 4.18 Cake Solids Contents Achieved and Degree of Completion with C-P Cell Expression of Plant-L Samples
Cake Solids Content (%) Degree of Completion (%) Pressure (kPa) 1101 1468 2385 3303
L-02633A 36.74 ---- 31.12 (96%) (96%)
L-0263B 33.56 ---- MN. MID ONN. 39.45 (96%) (97%)
L-0264A 36.63 28.39 ■■•■ ■■••=. 39.69 (97%) (92%) (98%)
Table 4.19 Slopes of Plots dV/dt vs V in Cake Consolidation Phase of Plant-L Samples
Slope of Plot (-10 -4 x sec- ) Pressure (kPa) 1101 1468 2385 3303
L-9339 1.95 1.85 1.83
L-0263A 2.53 2.17
L-0263B 2.26 1.88
L-0264A 1.98 1.39 3.65
L-1011A 8.68 5.91 7.67 5.22 L-1011B 3.95 7.21 6.37 10.20
140 Table 4.20 Ultimate Cake Solids Contents Achievable with C-P Cell Expression of Plant-P Samples at Various Pressures and Temperatures
Ultimate Cake Solids Content (%) Temperature (°C) Pressure (kPa) 1101 1468 2385 3303
L-9339 37.56 32.45 39.96 44.38 (8°C) (10°C) (8°C) (8°C) L-0263A 48.06 40.26 L-0263B 42.90 50.00 L-0264A 45.28 44.98 45.37
L-1011A 38.31 40.52 42.21 46.38 (9.5°C) (8.5°C) (8.5°C) (8.5°C) L-1011B 43.90 45.30 48.58 51.06 (8.5°C) (8.5°C) (8.5°C) (8.5°C)
4.3.4 Results of Plant S, E, V, CL, PA and CS Samples
Figs. 4.118 to 4.146 are the plots of -dL/dt °5 vs t for samples S-0005, E-0073, V-0234A, V-0234B, CL-0305A, CL-0305B, PA- 1039A, PA-1039B and CS-1039A, respectively. All of these plots reflect the sharp move from the filtration phase to the consolidation phase as did the Plant-L samples. The samples with the highest suspended solids concentrations (S-0005, E-0073, PA-
1039A and PA-1039B) had very low times to complete the filtration phase. The elapsed times of filtration for all the samples are presented in Table 4.21. The slopes of the -dL/dt °-5 vs t plots in the filtration phase are given in Table 4.22. Samples V- 0234A, PA-1039A and PA-1039B have slope values which deviated
141 1.00
Filtration phase S-0005-1101 kPo '
5)
0. Slope = 0.1 Consolidation: t =.- 1980 s /s
(cm 0.10 . ,,-4eGGaso 5 • o 0
dt 0 o dLi 0 — 0 0 .8 0.01 10 100 1000 1E4 1E5
t (sec)
Fig. 4.118 Plot of -dL/dt.°•5 vs t for Sample S-0005 at Pressure of 1101 kPa
10.00
5) 1.00 0. /s
(cm 0.10 5 • 0 d1
dL/ 0.01 —
1.00E-3 10 100 1000 1E4 1E5
t (sec)
Fig. 4.119 Plot of -dL/dt m vs t for Sample S-0005 at Pressure of 3303 kPa
142 1.00
0
5) 0--43-43-0400 0 0. 0.10 o q) /s Filtration phase 0 m 0
(c slope = 0.08 5 . 0
dt 0.01 o -. E-0073-1101 kPo o , dlj oho — Consolidation: t = 540 s —,Q2 o715 o 1.00E-3 o. 10 100 1000 1E4
t (sec)
Fig. 4.120 Plot of -dL/dtm vs t for Sample E-0073 at Pressure of 1101 kPa
1.00
5)
0- 0 0.10 /s Filtration phase 0
m 0 Slope = 0.02
(c 0 5
- 0
0 0 0.01 ea E-0073-1468 kPo
—dL/dt Consolidation: t = 480 sec
1.00E-3 10 100 1000 1E4
t (sec)
Fig. 4.121 Plot of -dL/dtm vs t for Sample E-0073 at Pressure of 1468 kPa
143 1.00
5)
0- 0.10 /s m (c 5 . 0
dt 0.01 E-0073-2385 kPa
—dL/ Consolidation: t = 420 s
1.00E-3 10 100 1000 1E4 t (sec)
Fig. 4.122 Plot of -dL/dt" vs t for Sample E-0073 at Pressure of 2385 kPa
1.00
) o 5
. o 0 0.10 0 /s Filtration phose Slope = 0.2 0 (cm 0 5 .
0 00 dt 0.01 0 E-0073-3303 kPa —dli Consolidation: t = 300 s oo cz5) co o 1.00E-3 10 100 1000 1E4 t (sec)
Fig. 4.123 Plot of -dL/dt° vs t for Sample E-0073 at Pressure of 3303 kPa
144
1 OX V-0234A-1468 kPc 0 Ins u Fi
Ln° C.100 -
0 U Corso elation: t = 1.12 x 10 4 s O
6 0E10_ Fitration anase 0 S!cpe = 0.1 1
0 001 100 1000 1E4 1EE
t c e c)
Fig. 4.124 Plot of -dL/dt°3 for Sample V-0234A at Pressure of 1468 kPa
V-023 4A-2385 kPc
U - ui [ Cchsc,ect'on: t = 4320 s 0 0 r.'trcl ■ on phase 0 = 0.35 0
Polo' 100 1000 1E4 1E5 t (sec)
Fig. 4.125 Plot of -dL/dt m for Sample V-0234A at Pressure of 2385 kPa
145 V-0234A-3303 kPc
0.100 O
C,onsalidation: t = 4500 s O
Filtration phase C
S;ope = 0.21 O
C 01C 100 1000 1E4 1E5 t (sec)
Fig. 4.126 Plot of -dL/dt1:3 •5 for Sample V-0234A at Pressure of 3303 kPa
1 000 V-02343-1101 kPa
r
O 2.100 Consolidation: t = 7021 s O
O Filtration phase S:ope = 0.04 O
C 2 1 0 1C3 1000 1E4 t (sec)
Fig. 4.127 Plot of -dL/dt m for Sample V-0234B at Pressure of 1101 kPa
146 1 CCC V - 0:134 -7 - 33C:3 kFc
0 t = 6301 s
Flitration phase 0 ' - - —-
1 C C
S e C
Fig. 4.128 Plot of -dL/dtm for Sample V-0234B at Pressure of 3303 kPa
1 C X CL-0305A-110', KPa 0 Cansatdat;oh: t = 2. 484x1 C 4 5
oloc 0 0 vaiesinvaimowitaih-_-.4j
6 G 01 3 it Eltrction phase Slope = —0.01 '75 0 0 0 0.00 . 100 1000 1E4 1E5 t (sec)
Fig. 4.129 Plot of -dL/dt 0-5 for Sample CL-0305A at Pressure of 1101 kPa
147 1.000 CL-0305A-1468 kPa
0 5) 0
^0. Consoiication: t = 2.754 x 104 s 0.100 /sec -i
70:PWR561 .0 (cn 6-0-7F55- 'AL4otgeld005 5
0 010
dr0. Fiitrationphase v cb Slope = —0.03
—dL/ G 21, 0 001 100 1000 1E4 1E5 t (sea)
Fig. 4.130 Plot of -dL/dtm for Sample CL-0305A at Pressure of 1468 kPa
1 000 • • 0L-0305A-2385 klPa a L) Consolidation: t = 2.538 x 10 4 s 6
0.100 0
-41 larimr" 0 6 0010 r. 0 Fiftration phase 0 0 Sicpe = —0.02 0 0
0.001 1 100 1000 1E4 1E5 t (sec)
Fig. 4.131 Plot of -dL/dt m for Sample CL-0305A at Pressure of 2385 kPa
148
1 000 ( CL-0305A-3303 kPa o
5) Consolidation: t = 2.448 x 10 4 s -0. 0.100
/sec o
1 cI—cr-,-ro-Ges c;P° 5 (cm r0.
d Filtration phase r Slope = –0.02 —dL/
0 001 100 1000 1E4 1E5 t (sec)
Fig. 4.132 Plot of -dL/dtm for Sample CL-0305A at Pressure of 3303 kPa
1.CX CL-0305B-1101 kPo U Consolidation: t = 1.512 x 10 4 s
0 0.100
°—°—.-j-e'ereG)2€111.4elig6"4514111" tr.
C 010 Filtration phase Slope = –0.02
0.001 1C0 1000 1E4 1E5 t (sec)
Fig. 4.133 Plot of -dL/dt m for Sample CL-03058 at Pressure of 1101 kPa
149 1.000 CL-0305B-1468 kPa Consolidation: t = 9900 s 0
0 0.010 Filtration phase Slope =
0 0.001 100 1E4 1E5 t (sec)
Fig. 4.134 Plot of -dL/dtm for Sample CL-0305B at Pressure of 1468 kPa
1.000 CL-03058-2385 kPa
5) Consolidation: t = 7920 s
-0. 0
ec 0.100 /s r m r (c 5 0. - 0 010 1 d1 Filtration phase 1 / Slope = —0.01 1 —dl
0.001 100 1000 1E4 1E.S. t (sec)
Fig. 4.135 Plot of -dL/dt m for Sample CL-0305B at Pressure of 2385 kPa
150
1.000 rl - n pp - C L- v....J....) Mr- 0 Consolidation: t = 7741 s
U 0.100 P.
l O I F C OUDr Filtration phase
S'ope = —0.01
0. 0 01 100 1000 1E4 t (sec)
Fig. 4.136 Plot of -dL/dtm for Sample CL-0305B at Pressure of 3303 kPa
' 000 PA-10,79A-1101 kPa Consolidation: t = 130 s OLD c., 1,::,:.• t- ‘4,..4,44. Y F V4-7-Q0 C.CC L FTtrction Phase 00— [ ct 9,,,,0 S'ooe = C.C7 0 ,..%; 000-7,,-; :., c0 ,,,4,-444: I. o 6 ' 0.001 00 0 cc [L 0 0 I' r , 0:TE. 4 i 10 100 1000 1 Ed
t (sec)
Fig. 4.137 Plot of -dL/dt m for Sample PA-1039A at Pressure of 1101 kPa
151 1.000 PA-10398-1468 kPa --Q-0-49-5 0°c36 0 Consolidation: t = 50 s CD cp 0
63 0 O o so oo,,c8 oo
DIN . 0 e(b00 00 moo Fi,tration phase c p Slope = 0.35
100 1CDO 1E4 t (sec)
Fig. 4.138 Plot of -dL/dt c13 for Sample PA-1039A at Pressure of 1468 kPa
PA-1039A-2385 kPc Consolidation: t = 135 s 1
1 oc F-71troton 27ose. C C Sione = 0.' 4 0 L2 • G"
Fig. 4.139 Plot of -dL/dt m for Sample PA-1039A at Pressure of 2385 kPa
152
PA-107.:13A-'3:2 -7 k 7c . :cri--41...7,- v Co! `-' COrS'0!;CGZIOrl: t = 145 5 310- (...' I ^"Y. '- It/0 : E 0 i r-. 1 1 r ea 1 cb '.):.01 t FTtratlon prase o 0 0 7., 0 0 0 Slope = 0.11 0 0 apS,- t 0 a- a- — 0 1 czoli-
] 1 L .
' 000E 4. 10 100 1000 1E4 t (sec)
Fig. 4.140 Plot of -dL/dtm for Sample PA-1039A at Pressure of 3303 kPa
1.000 b-0--Q-crecoc° PA-10399-1101 kPc 0 Consolidation: t = 46 s OD 6 0100 0 0 O o U [ :7.010 k Fitra ,..ion phaseo 0 f c 0 ocz o ° 0 Slope = 0.24 o ( 0 . 001 L..- O r. I.
1 00 0 E 4 10 100 100C 1E4 t (sec)
Fig. 4.141 Plot of -dL/dt c/ " 5 for Sample PA-1039B at Pressure of 1101 kPa
153
COO PA-1039A-1468 kPa Consolidation: t = 161 s
0 C9
Fitretion ohasa
0 O
r-o 103 1000 1 :4
t (sec)
Fig. 4.142 Plot of -dL/dt" for Sample PA-1039B at Pressure of 1468 kPa
cr-Q-°-cre;P:P3') fl PA-1 039B-23551 kPa Consolidation: t = 65 s O 0100 c
c.cio O O Filtration phase 0 c58 0,, o 0 0 0 e.00i Slope = 0.04 0c
r
1 000E 4 10 100 1000 1E4
t (sec)
Fig. 4.143 Plot of -dLidt" for Sample PA-1039B at Pressure of 2385 kPa
154
1:000 :4474i—Tr000loo PA-1039E-3303 kPa amo Consolidation: t = 39 s 5) o cta. 0 1 00 -0. oni• /s 6,,eippo 0'0 1 0.010 5 (cm o=0
0. 0 - 11 - o 0 0 o o L/I 0.001 Filtration phase -d Slope = 0.17 o
1.000E4 10 100 1 000 1E4 t (sec)
Fig. 4.144 Plot of -dL/dt" for Sample PA-1039B at Pressure of 3303 kPa
lox
Filtration phase CS —1039A-1101 kPc = —G.04 Consolidation: t=1.008 x 10 5 s
E 0 C. L
•
0 01 0 100 1 000 1 E4 1 M I E6
t (sec)
Fig. 4.145 Plot of -dL/dt" for Sample CS-1039A at Pressure of 1101 kPa
155
1.000
Filtration phase CS-1039A-3303 kPa Slope = —0.04 Consolidation: t=1.513 x 10 5 s
0.100
C 010 . 1000 1E4 1E.5 1E6
t (sec)
Fig. 4.146 Plot of -dL/dtm for Sample CS-1039A at Pressure of 3303 kPa Table 4.21 Slopes of Plots -dL/dt m vs t in Cake Filtration Phase of Plants S, E, V, CL, PA, CS Samples
Slope of Plot (cm/sec'•, ) Pressure (kPa) 1101 1468 2385 3303 S-0005 0.10 0.08
E-0073 0.08 0.02 0.20 0.20
V-0234 0.10 0.36 0.21
V-0234B 0.04 0.08
CL-0305A -0.01 -0.03 -0.02 -0.02
CL-0305B -0.02 0 0.01 -0.01
PA-1039A 0.07 0.13 0.14 0.11
PA-1039B 0.24 0.38 0.04 0.17
CS-1039A -0.04 -0.04
Table 4.22 Elapsed Time Before Cake Filtration Enters Consolidation in C-P Cell Expression of Plants S, E, V, CL, PA, CS Samples
Elapsed time (sec) Pressure (kPa) 1101 1468 2385 3303 S-0005 1980 4680
E-0073 540 4802 420 300
V-0234 11160 4320 4500
V-0234B 7020 6301
CL-0305A 24840 27540 25380 24480
CL-0305B 15120 9900 7920 7740
PA-1039A 130 160 135 145
PA-1039B 46 50 65 39
CS-1039A 100800 151300
157 substantially from zero (0.1 to 0.38); all other slopes are approximately zero. Also, slope values from log(V) vs log(t) plots are given in Table 4.23. All samples, except for PA-1039A and PA-1039B, match the theoretical slope of 2 by Darcy. Plant PA samples have slope values close to one and, as stated earlier, could be explained by the high fiber content of the sludge.
Table 4.23 Slopes of log(V) vs log(t) in Cake Filtration Phase of Samples S, E, V, CL, PA, CS Samples Slope of Plot Pressure (kPa) 1101 1468 2385 3303 S-0005 0.92 1.92 E-0073 1.28 1.67 1.81 1.95
V-0234 1.66 1.40 1.46
V-0234B 1.73 1.54 CL-0305A 1.83 1.85 1.88 1.84
CL-0305B 1.79 1.80 1.81 1.80
PA-1039A 0.77 1.16 11.22 1.21 PA-1039B 0.95 1.04 1.56 1.06 CS-1039A 2.31 2.36
Plots of dV/dt vs. V are given as Figs. 4.147 to 4.175.
Generally, cake consolidation of Plants S and E sludge samples were very thorough, with calculated degrees of completion all greater than 97%. Therefore, the actually-collected filtrate volume for each individual C-P cell expression was almost equal
158 0.40 ,
S-0005-1101 kPo 0.30
) Degree of completion: 100% 0 l/sec 0.20 0 a■ 0 (m
dt 00 Slope = — 3.30 x 10 -3 dV/ 0.10
0.00 0 100 200 300 400
V (mL)
Fig. 4.147 Plot of dV/dt vs V for Sample S-0005 at Pressure of 1101 kPa
) L/sec (m dt dV/
Fig.4.148 Plot of dV/dt vs V for Sample S-0005 at Pressure of 3303 kPa
159 0.60
0.50 E-0073-1101 kPa
Degree of completion: 100% ) 0.40 0
L/sec 0.30 0 0 0 (m 0
dt 0 0.20 0 dV/ 0.10 Slope = —4.63 x 10 -3 °
0.00 0 50 100 150 200 250 V (ml_)
Fig. 4.149 Plot of dV/dt vs V for Sample E-0073 at Pressure of 1101 kPa
0.60
0.50 E-0073-1468 kPo
Degree of completion: 100% ) 0.40 0
l/sec 0.30 0 (m dt 0.20 0
dV/ 0 0.10 0 Slope = — 1.46 x 10 -3 o 0.00 cito 0 50 100 150 200 250
V (mL)
Fig. 4.150 Plot of dV/dt vs V for Sample E-0073 at Pressure of 1468 kPa
160 Fig. Fig. 4.152
dV/d t (m l/sec ) 4.151 dV/dt (mt../sec ) 0.60 0.00 0.20 0.10 0.30 0.40 0.50 0.10 0.20 0.30 0.00 0.40 0.50 0.60 0 0 Pressure of2385kPa Plot ofdV/dtvsVforSampleE-0073at Pressure of3303kPa Plot ofdV/dtvsVforSampleE-0073 at
E-0073-3303 kPa Degree ofcompletion:100% 50 50 0 Slope =—3.47x10 Slope =—6.73x10 o Degreeofcompletion:100% 100 100 161 V (mL) E-0073-2385 kPa V (mL) 0 0 0 150 150 0 0 -3 0 0 0 0 -3 0 200 0 200
' 0 0 lio
250 250 • O
6C0 63C
Fig. 4.153 Plot of dV/dt vs V for Sample V-0234A at Pressure of 1468 kPa
0 4-00 V—C234A-2385 kPc
Degree of com.,-,, letion: 99% 0.300 I-
) ec L/s C.20: - F:ope = —1.35 x 10 -3 (m dt
0 00 Q dV/ 0 100 !-
Lvv
Fig. 4.154 Plot of dV/dt vs V for Sample V-0234A at Pressure of 2385 kPa
162 Fig. 4.155PlotofdV/dtvsVforSampleV-0234Aat Fig. 4.156Plotof dV/dtvsVforSampleV-0234B at
dV/tit (rn t/:, ec ) dV/dt (rn L/sec) 0.000 0.10 0.2X O COO 0.100 0 3001- 0 300F- 4-Cr0 400 0 Pressure of3303kPa 0 Pressure of1101 kPa I 1
0 0 0 o 0 0 0 030 C 0 200 200 V (rnL) V (rnL) Degree ofcompletion:98% Degree ofcompletion:100% 163 400 400 Slope =—7.62x10 V-0234A-3303 kPa V-02348-1101 kPa = —1.69x10 600 -4 -3
600 C_400 V-0234B-3303 kPa Degree of completion: 100% 0.300
) L/sec 0.200
(rn S'ope = —3.83 x 10 -3 dt dV/ 0.100 ocoapozoc b 0.000 6 0 200 400 V (rnL)
Fig. 4.157 Plot of dV/dt vs V for Sample V-02348 at Pressure of 3303 kPa
0-100 C — C3 05A — 1 101 kPa Degree of completion: 97%
0
Slope = —1.28 x 10 -4
Fig. 4.158 Plot of dV/dt vs V for Sample CL-0305A at Pressure of 1101 kPa
164 0100 CL-0305A-1468 kPa Degree of completion: 94% 0.075
)
L/sec O 0.050 (m dt V/ d Slope = —1.29 x 10 -4 0 025
0.0" 0 10C 200 300 400 V (MO
Fig. 4.159 Plot of dV/dt vs V for Sample CL-0305A at Pressure of 1468 kPa
0.1 00 1 CL-0305A-2385 kPa Degree of completion: 99% 0 075
) O O O
L/sec O 0.050 0
(m O
dt 0
dV/ Slope = —1.28 x 10 -3 0 025
0
0.000 0 100 200 300 400 V(ML)
Fig. 4.160 Plot of dV/dt vs V for Sample CL-0305A at Pressure of 2385 kPa
165 0.100 CL-0305A-3303 kPa Degree of completion: 96% 0 075
) ec 0 /s l_ 0.050 0 0 t (rn
d 0.7 Slope = —1.38 x 10 -4 dV/ 0 025
0:000 C 100 200 300 400
V (MO
Fig. 4.161 Plot of dV/dt vs V for Sample CL-0305A at Pressure of 3303 kPa
0 100 CL-0305B-1101 kPa Decree of completion: 91% 0 075 0
) c
e 0 0 /s
l_ 0 0-050 0
(rn qb dt et, Slope = —1.37 x 10 -4 dV/ 0.025 [
CCM C 100 200 300 400
V ( mL)
Fig. 4.162 Plot of dV/dt vs V for Sample CL-0305B at Pressure of 1101 kPa
166
0.100 CL-030513-1468 kPa o Degree of corrIp!eti ,--.1: 97% 075 I-
) 0 c 0 s(! / t. 0 m 0.050 /-
t ( 1 d 1 S:ope = —5.05 x 10 -4 dV/ 0.025
A414Amm R om c 100 200 300 430
V (MO
Fig. 4.163 Plot of dV/dt vs V for Sample CL-0305B at Pressure of 1468 kPa
C 100 CL-03053-23E5 kPa 0 Degree of corroeticrl: 97% 0 075 0 )
0 0
L/sec 0 0.050 r t (m
d 0 Slone = —2.80 x 10 -4 V/
d 0 0,025 ‘C.4k' iktr
0.000 C 100 200 300 400
V (mL)
Fig. 4.164 Plot of dV/dt vs V for Sample CL-0305B at Pressure of 2385 kPa
167
0.100
0 CL-03C5B-3303 kPa Degree of completion: 98% 0 075
) L O
0 L/sec 0.050
On Mope = —3.75 x 10 -4 dt
dV/ 0 J 025 0
300 400
Fig. 4.165 Plot of dV/dt vs V for Sample CL-0305B at Pressure of 3303 kPa
1.030 PA-1039A-1101 kPa
0 0 0 750 L
0 0 0 dope = -1 .08 x 10 -2 o 0
0.500
0.250
0.000 0 50 100 150 2CC v (mL)
Fig. 4.166 Plot of dV/dt vs V for Sample PA-1039A at Pressure of 1101 kPa
168 1.000 00 0 PA —1039A —1468kPa 0 o 00 00 0.750 0 Slope = —8.33 x 10 -3 ) 0 Acn 0 0-- 0 o co
L/sec o 0 0 0 p.5.. 0 (m dt dV/
0:250 r 0
0.000 C 50 100 150 200 V (mL)
Fig. 4.167 Plot of dV/dt vs V for Sample PA-1039A at Pressure of 1468 kPa
1.300 IV o PA-1039A-2385 kPa o 0 000 0
0.750 ) 0 o°
0 L/sec 0.500 0 (m dt dV/ 0.250 Slope = —1.32 x 10 -2
0.000 0 50 100 150 200 V (mL)
Fig. 4.168 Plot of dV/dt vs V for Sample PA-1039A at Pressure of 2385 kPa
169 1.000 O
0 0 PA-1039A-3303 kPo 0 0 o°0 0
0 750
) 0 0 00 c /se . l o)(:) 0.500 cbo dt (m qb o dV/ 0.250 +- Slope = —3.75 x 0-3
4 0 0 0.000 0 50 100 150 200 V (mL)
Fig. 4.169 Plot of dV/dt vs V for Sample PA-1039A at Pressure of 3303 kPa
4 PA-10398-1101 kPa
0
3 ) O O O /sec
t. O 2 o dt (m O O dV/
Slone = —8.79 x 10 -2
c 0 50 100 150 200
V (ML)
Fig. 4.170 Plot of dV/dt vs V for Sample PB-1039B at Pressure of 1101 kPa
170 PA-10398-1468 kPa
3f-
)
0 0
/sec 0 0 n _
0 (1 t. i Vb i t 0 Slope = —4.76 x 10 -2
C 0 50 100 150 200
V (mL)
Fig. 4.171 Plot of dV/dt vs V for Sample PB-1039B at Pressure of 1468 kPa
4 PA-10398-2385 kPa
3 O
0 0 0 0 0 0 0 0 0 0
Slope = —4.16 x 10-2
0 50 100 150 200 V (mL)
Fig. 4.172 Plot of dV/dt vs V for Sample PB-1039B at Pressure of 2385 kPa
171
PA-1039B-3303 kPa 0
3 L O ) O
c 0
O /se
l 0 2 O 0 (m t d dV/
Sicpe = —3.14 x 10-2
0 0 100 150 200 V (mL)
Fig. 4.173 Plot of dV/dt vs V for Sample PB-1039B at Pressure of 3303 kPa
0 043
CS-1039A-1101 kPa C 0030
O
0 0.020 O
-o 0.010
0.000 200 400 800 800
V (mL)
Fig. 4.174 Plot of dV/dt vs V for Sample CS-1039A at Pressure of 1101 kPa
172 040
CS - 1C.,39A - 3303 kPa
C 03f)
00:0 &CO
Fig. 4.175 Plot of dV/dt vs V for Sample CS-1039A at Pressure of 3303 kPa to the projected ultimate filtrate volume. Consequently, the experimentally-determined final cake solids content could be regarded as the corresponding ultimate cake solids content. Plant CL samples had similar high consolidation (greater than 90% for all samples), but ultimate cake solids content was about 10% to 20% higher than final cake solids. Sample V-0234A had ulti- mate cake solids content values around 80-90% (approximately 40% higher than its respective final cake solids contents). These numbers are misleading since very small cake masses were gene- rated from C-P cell runs, allowing experimental error to be a substantial factor. Also, Plant-PA samples were over-run (like L-10111A and L-10118) and were corrected as shown earlier. Appropriate final cake solid contents and ultimate cake solid contents are presented in Table 4.24 and Table 4.25, respec- tively. It should also be noted that the two Plant-CS samples just reached consolidation after over 48 hours of C-P cell running time. Therefore, no consolidation data were available. Finally, slopes of the consolidation phase of the dV/dt vs V plots are given in Table 4.26. 4.4 Determination of Sludge Devaterability Based on Filtration Data Generated with C-P Cell Having the filtration data of each C-P cell expression, average specific resistance could be calculated in the same manner as was done with the pressure cell data. Comparing results of dewaterability for all the sludge samples examined
174 Table 4.24 Cake Solids Contents Achieved with C-P Cell Expression of Samples V, CL, CS at Various Pressures and Temperatures
Cake Solids Content (%) (Temperature ( °C) Pressure (kPa) 1101 1468 2385 3303 V -0234A 47.28 53.85 44.92 V -234B 38.70 50.77 CL-0305A 58.97 52.75 50.77 70.39 (8°C) CL-0305B 62.67 66.82 64.42 65.98 (8°C) CS-1039A 13.05 8.2 (8 °C) (8 ° C)
Table 4.25 Ultimate Cake Solids Contents Achieved with C-P Cell Expression of Samples S, E, V, CL, PA at Various Pressures and Temperatures Ultimate Cake Solids Content (%) (Temperature ( °C) Pressure (kPa) 1101 1468 2385 3303 S-0005 62.78 66.441 (10 °C) (8 °C)
E-0073 64.59 67.28 69.70 72.14 (9 °C) (9 °C) (8 °C) (14 °C)
V-0234A 96.18 84.20
V-0234B 41.23 51.05
CL-0305A 72.50 75.58 54.85 85.97 (8 °C) CL-0305B 95.70 72.99 76.63 71.30 (8 °C)
PA-1039A 61.96 59.97 65.14 65.54 (8 °C) (8.5°C) (8.5°C) (8.5°C)
PA-1039B 62.02 67.12 68.14 69.17 (8 °C) (8.5°C) (8.5°C) (9.5°C)
175 Table 4.26 Slopes of s dL/dt vs V Plots in Cake Consolidation Phase of Samples S, E, V, CL, PA
Slope of Plot (-10' x sec') Pressure (kPa) 1101 1468 2385 3303
S-0005 33.0 23.3 E-0073 46.3 14.6 34.7 67.3 V-0234 8.1 13.5 7.6 V-0234B 16.9 38.3
CL-0305A 1.3 1.3 12.8 1.4
CL-0305B 1.4 5.0 2.8 3.8 PA-1039A 108.0 83.3 132.0 37.5 PA-1039B 879.0 476.0 416.0 314.0
with both the pressure cell (Table 4.5) and the C-P cell (Table 4.27). It was found that the characterizations were generally consistent, although for most of the data, values of the same parameter determined in these two cases were different. Possible reasons for the differences were wall effects and the cake solids content at the end of filtration determined for calculating the average specific resistance. In the C-P cell expression test, certain wall effects would be created as the piston moves in the cell to compress the sludge suspension. As the velocity of the piston keeps decreasing during filtration, the wall friction would change which makes the actual pressure on sludge solids a variable. In C-P cell expression, the cake solids content at the
176 Table 4.27 Data of Average Specific Resistance and Compressibility of Sludge Samples As Determined with C-P Cell for Plant P and Three Samples from Plant L, S and E
Avg. Specific Resistance a. (Tm/kg) (Tm/kg)
Pressure 1101 kPa 1468 kPa 2385 kPa 3303 kPa
42-9157 9.38 12.66 16.48 22.75 1.54 0.76
42-9166 3.63 4.57 6.96 8.83 0.51 0.82 42-9178 4.66 14.02 23.67 47.89 0.05 1.95
42-9208 7.38 10.64 17.43 20.61 0.81 0.94
42-9212 8.96 11.40 19.64 25.69 0.83 0.99 42-9213 9.63 11.18 21.10 30.83 0.64 1.10 L-9339 34.90 59.20 87.90 137.00 2.24 1.17
S-0005 2.26 4.17 0.59 0.56 E-0073 0.09 0.30 0.40 0.77 0.00 1.72
end of cake filtration could only be estimated from mass balance rather than direct weighing measurement as in the case of pressure cell test.
For each of the sludge samples examined, the constant a, which is equivalent to the average specific resistance value at unit pressure (1 bar) and compressibility index, S, as obtained from regression analysis over the full pressure range of 50 kPa to 3303 kPa for combined pressure-cell test C-P cell expression data are presented in Table 4.28. If based on the data obtained,
177 Table 4.28 Compressibility of Sludge Samples Determined Based on Combined Data From Both Pressure Cell Test and C-P Cell Expression
Sample r2 a. (-) Tm/kg (-)
P42-9157 0.93 2.49 0.64 P42-9166 0.97 0.62 0.79 P42-9178 0.83 1.88 0.80 P42-9208 0.60 5.56 0.38 P42-9212 0.98 1.54 0.81 P42-9213 0.89 3.30 0.60 L-9339 0.99 6.32 0.82 S-0005 0.94 0.97 0.38 E-0073 0.89 0.02 1.01
values of a. and S in Table 4.28 to correlated well with the corresponding values determined with the pressure cell. To assess this, the average specific resistance versus pressure with separate data from pressure cell dewatering test and C-P cell expretsion were plotted on log-log scale, for initial project samples, in Figs. 4.176 through 4.184. Samples include only C-P cell data in Figs. 4.185 through 4.196. Additional visual examination of each of the plots indicated that the data point at low pressure (the average specific resistance value at 50 kPa) would significantly affect the overall regressional
178 Fig. Fig. ..- Y E 31
Average Specific Resistance (Tm/kg) 4.177 4.176 100.0 100 10 1 1 Average SpecificResistancevsPressure ForData Generated WithBoth PressureCellandC-P 1 For Sample42-9166 Average SpecificResistancevsPressureForData For Sample42-9157 Generated WithBothPressureCellandC-P • • 42-9157 • • with C—Pcell with pressurecell with C—Pcell with pressurecell 10 1 0 179 Pressure (kPa) Pressure (kPa) 100 100 1000 1000 1E4 1E4
) 100 kg /
Tm 42-9178 ( • with pressure cell • with C—P cell tonce is 10 Res ific c e Sp
e rog 1 Ave 1 10 100 1000 1E4
Pressure (kPa)
Fig. 4.178 Average Specific Resistance vs Pressure For Data Generated With Both Pressure Cell and C-P Cell For Sample 42-9178
) 100 kg / Tm
( • with pressure cell
nce • with C—P cell ta is 10 Res ific ec Sp e rag 1 Ave 1 1 0 100 1000 1E4
Pressure (kPa)
Fig. 4.179 Average Specific Resistance vs Pressure For Data Generated With Both Pressure Cell and C-P Cell For Sample 42-9208
180
) 100.0 kg /
Tm 42-9212 ( • with pressure cell 10.0 • with C—P cell tance is Res
ific 1.0 ec Sp e rag 0.1 Ave 1 10 100 1 000 1E4
Pressure (kPo)
Fig. 4.180 Average Specific Resistance vs Pressure For Data Generated With Both Pressure Cell and C-P Cell For Sample 42-9212
) 100 kg / Tm
( • with pressure cell
nce A with C—P cell ta is s 10 Re
ific ec Sp e
1 Averag 1 10 100 1000 1E4
Pressure (kPo)
Fig. 4.181 Average Specific Resistance vs Pressure For Data Generated With Both Pressure Cell and C-P Cell For Sample 42-9213
181 Fig. Fig.
Average Specif ic Resistance (Tm/ kg ) 4.183 Averag e Specific Res istance (Tm/kg) 4.182 1000 10.0 100 0.1 1.0 10 1 Generated WithBoth PressureCellandC-P Average SpecificResistancevsPressure ForData For SampleS-0005 1 Generated WithBothPressureCellandC-P Average SpecificResistancevsPressureForData For SampleL-9339 1 • • with C—Pcell with pressurecell 10 10 182 Pressure (kPa) Pressure (kPo) 100 100 1000 1 0 0 0 1 E4 1E4 Fig.
Averag e Sp 4.184 ec ific Resis tance (Tm/kg) 0.001 0.010 0.100 1.000 1 Average SpecificResistancevsPressureForData For Sample Generated WithBothPressureCellandC-P A • withpressurecell with C—Pcell 10 E-0073 183 Pressure (kPo) 100 1000 1E4 E L-0263A A wTh C—P cefl a)
0
C)
a)
0 L- a) E4 100 1C3
P''c'ecJr -e (kPt.-.)
Fig. 4.185 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample L-0263A
—0263B
100 1000 1E4
Pressure (kPc)
Fig. 4.186 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample L-0263B
184
1000
P L-0264A 1-=
• with C — P celi
C 10, 2 1 . _ _ V 10 a.)
0
100 1000 1E4,
Pressure (kPa)
Fig. 4.187 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample L-0264A
L - 1011A
A With C-P cell a)
1 00 111
1 0 a) I a 1 a)
a)
100 1000 1 E4
Pressure (kPa)
Fig. 4.188 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample L-1011A
185 100C Cn L-1011B • with C—P cell C) 100 1 401 t.71 C) 1
147: 10 •
C) O C)
100 1000 1E4
Pressure (kPc)
Fig. 4.189 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample L-10118
1:00 7
E V-0234A • with C—P cell C) A U • 00 O
Fri CC
10 c.r) C) a C)
100 1000 1E4
Pressure (kPc)
Fig. 4.190 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample V-0234A
186 V-02348 • with C—P ceil
r 1
1 1C0 1000 1 E4
PressJre (kPa)
Fig. 4.191 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample V-0234B
187 1 :100
E CL-0305A • with C-P cell C) 0 C 100 0
Of U
10
C. 0 > 100 1000 1E4
Pressu-e (kPa)
Fig. 4.192a Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample CL-0305A
1E4 0 CL-0305A
A with C-P cell co U C 0 t.r1 ai 10::
100 100 1000 1E4
Pressu-e (kPc)
Fig. 4.192b Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample CL-0305A
188 1 330 1 CL-03058
• with C — P ce:1
100 I-
10
100 lox 1E4
Pressure (kPa)
Fig. 4.193 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample CL-0305B
PA - 1039A
with C-P cek
0 tr,cl
1.000
c.3 1 a 1
0 co 0.100 100 1000 1 E4
Pressure (kPc)
Fig. 4.194 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample PA-1039A
189
10 CDC
PA-1039B
• w:th C—P cell
0 100 1C0 1 000 1E4
P-ess,;re (kPc)
Fig. 4.195 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample PA-1039B
1E4
CS -1C3GA
ti
td-;
0 a) 100 100 1003 1E4
Pressu-e(kDa)
Fig. 4.196 Average Specific Resistance vs Pressure for Data Generated with C-P Cell for Sample CS-1039A
190 result. Therefore, it is preferred statistically to exclude this dominant data point while the accuracy of its value remains unknown. By doing so, it was found that the remaining data points were much better correlated to each other, indicating the average specific resistance determined from the cake filtration phase in C-P cell expression process were in agreement with those obtained with the more commonly used pressure cell apparatus.
Subsequent analysis of a was done with the filtration-phase data from C-P cell.
4.5 Assessing Dewaterabilities of Plants P, L, S, E„ V, CL, PA and CS
Collected at different paper mills, sludge samples from all plants exhibited certain characteristic differences, such as pH, suspended solids concentration and solids volatility, which could have affected their dewatering properties.
The range of pH values for all of the sludge samples was between 6.3 and 11.5. Most of the samples were near neutral pH of 7, or slightly alkaline in the 9-11 pH range. Although the impact of pH on sludge dewatering properties was uncertain,
Samples S-0005, PA-1039A and PA-1039B had the highest pH values and were found to have very good dewaterability during expression with the C-P cell.
Having suspended solids concentrations as high as 218.9 g/L,
479.2 g/L, 302.52 g/L and 337.40 g/L, respectively, Samples 5-
0005, E-0073, PA-1039A and PA-1039B were easiest to dewater, with average specific resistances between 0.09 Tm/kg and 2.26 Tm/kg at
191 1101 kPa from C-P cell expressions. In addition to high solids concentration and possible pH impact, good dewaterabilities of these samples were consistent with their low solids volatilities (VSS/SS from 9.5% to 13.7%) indicating an inert fraction with higher density and lower compressibility. At a pressure range of 1101 kPa to 3303 kPa, the final cake solids contents (or ultimate cake solids contents for Plant-PA samples) were 63% to 66% for Samples S-0005; 65% to 72% for Samples E-0073; 62% to 66% for PA- 1039A; and 62% to 69% for PA-1039B. Plant CL, V and CS samples showed moderate dewaterability when compared to Plants S, E and PA. Suspended solids concentrations were very low (except Plant CL) with very high volatilities, around 90%. At a pressure of 1101 kPa, average specific resistance values were very high as well, with values of 277.10 Tm/kg, 87.79 Tm/kg, 53.04 Tm/kg and 810.1 Tm/kg for samples CL-0305, CL-0305B, V-0234B and CS-1039A, respectively. Finally, cake solids content were 59% to 70% for CL-0305A; 63% to 66% for CL-0305B; 47% to 45% for V-0234A; 39% to 51% for V-0234B; and 18% to 13% for CS-1039A. The variation of dewaterabilities among Plant P samples were moderate, as were dewaterabilities of Plant L samples. Average specific resistance values at 1101 kPa for Plant P samples (Table 4.27) ranged from 3.6 Tm/kg to 9.6 Tm/kg, where sludge compressibilties ranged from 0.76 to 1.95. The final cake solids achieved by expression of Plant P samples, at a pressure range of 1100 kPa to 3300 kPa were 34% to 57%. Dewatering of Plant L
192 sample was found to be more difficult as compared to dewaterability of Plant P samples. Average specific resistance values for Plant L samples at a pressure of 1101 kPa ranged from 8.3 Tm/kg to 25.1 Tm/kg with compressiblities from 0.73 to 1.17. Final cake solids concentrations for Plant L samples are lower than those values of Plant P, and ranged from 28% to 44% with pressures between 1100 and 3300 kPa. In terms of compressibility, Sample E-0073 was determined to be most compressible with an S value of 1.12 and Sample S-0005 the least compressible with an S value of 0.39. Table 4.29 contains the average specific resistance data of sludge samples at 100 kPa (1 bar) and 1000 kPa. The data also confirm that the general order of ease of dewatering among the four groups of sludge samples examined was E, S, P and L. For sample L-9339, the advantage of increasing applied pressure in expression is to be offset by the significant increase in the average specific resistance subsequently. Therefore, increasing pressure in expression of Sample L-9339 would not be beneficial as for the remaining sludge samples.
193 Table 4.29 Comparison of the Average Specific Resistance of Sludge Samples With Different Origins at Pressures of 100 kPa and 1000 kPa
Sample Pressure Cell C-P Cell Origin a, a a. a (100 kPa) (1000 kPa) (100 kPa) (1000 kPa)
P 0.60-5.53 4.55-20.5 0.05-1.54 4.46-8.86 L 3.66 9.85 2.24 33.13 S 1.04 2.55 0.59 2.14 E 0.02 0.26 0.002 0.10
Note: The units of a, and a are Tm/kg. The values of a at 1000 kPa were obtained by using Eq. (68) based on experimentally determined a, and S values.
194 CHAPTER 5
SUMMARY AND CONCLUSIONS
Understanding the fundamental expression mechanisms of filtration and consolidation as employed in dewatering pulp and paper sludges will provide valuable insights towards selection of mechanical dewatering equipment, as well as determining cost- effective operating pressures for final cake solids content desired. As a result of the research, the following observations are summarized:
1) Expression, as defined herein, is the combined process of cake filtration and consolidation. The filtration phase terminates in the consolidation phase when the whole sludge suspension forms a filter cake.
2) Dewatering by consolidation is distinguished from cake filtration by the fact that the hydraulic pressure in a filter cake is sustained due to the continuous liquid flow, whereas
the hydraulic pressure in a consolidating cake decreases continuously. 3) The transition point between cake filtration and consolidation phases can be well determined for pulp and paper suspensions,
based on Ruth's equation.
4) The specific resistance to filtration (i.e., resistance of sludge cake to passage of filtrate and expressed as a headloss per unit dry cake solids) is a function of solids compressive pressure P, which is zero at the cake surface and reaches its
195 maximum which equals the pressure drop across the cake at the
septum. In the filtration phase, the sum of P. and hydraulic
pressure P, in a compressible cake equals the total applied
pressure. The concept of specific resistance is invalid for
the consolidation period simply because the relationship of P.
and PI, is not applicable. In a consolidating cake, the liquid
flow is entirely from compressing voids in the cake and is no
longer in continuity.
5) Theoretically, specific resistance value of a sludge does not
change with its solids concentration, while capillary suction
time (CST) does. Therefore, when compared between sludges,
the CST must be related to the solids concentration and the
specific resistance value to evaluate sludge dewaterability.
Because of the highly nonuniform and fiberous nature of solids
particles presented in the paper waste sludge, CST seems to be
an inappropriate measure for dewaterability.
6) For some of the sludge samples examined, filtrate volume and
time was not parabolic, which implied the average specific
resistance of the developing cake was non-constant. For
compressible solids filtration, the average specific
resistance is likely to decrease as filtration proceeds and as
the cake compresses and consolidates during filtration-
dewatering; while it will increase when blinding occurs in
which migration of fine particles clogs cake interstices.
Under the circumstances where highly nonuniform-sized fiberous
aggregates are present for filtration, as encountered in this
study, the validity of Darcy's equation is questionable
because of the highly non-uniform nature of the resulting
196 cakes.
7) Having assume the septum resistance negligible, experimental
reading from the initial period of cake filtration should be
excluded in the data analysis.
8) Experimental data revealed that plot of dV/dt versus V
exhibits a linear relationship in the consolidation phase.
This has bene proved mathematically based on conventional
Terzaghi theory of consolidation. In addition, the slope of
the plot indicates rate consolidation. The greater the
absolute value, the less time it would take for consolidation
to complete.
9) The maximum volume of filtrate obtainable from cake
consolidation can be predicted by extrapolating the
consolidation portion of plot dV/dt vs. V to get the ultimate
filtrate volume. Therefore, the ultimate cake solids content
that could be achieved by cake consolidation is predictable.
Using mass balance, cake solids content at any time during
expression can be estimated.
10) here is no particular pattern how the term -dL/dt °5 , used to
examine the length of the filtration phase, should exhibit in
the consolidation phase.
11) In the filtration phase, a pressure increase has favorable
effect on moderately compressible materials (Compression index
S < 1), while it has adverse impact on highly compressible
materials (S > 1).
12) For the sludge suspensions examine, it was found from
experimental results that increase of cake solids content with
pressure was only moderate.
197 13) During consolidation period, it seems that an increase of
expression pressure in a modest range can not substantially
increase the cake solids content subsequently for less or
moderately compressible materials. However, increase of
pressure has very favorable impact on the consolidation of
highly compressible materials.
14) The procedures developed and data presented in this study can
be used by Weyerhaeuser facilities considering changes in
sludge dewatering facilities as follows:
• predict maximum cake solids content that can be achieved
with a sludge suspension, thereby allowing for a
preliminary economic analysis of sludge-dewatering and
sludge disposal options.
• determine design pressures for pilot-scale dewatering
studies and for evaluation of utility of changing
pressures in, for example, existing belt presses, screw
presses, centrifuges and pressure filters.
• determine the most appropriate sludges for consideration
for use with high pressure dewatering systems and
avoiding the expense of these high-pressure systems with
those for which there are limited benefits.
• assess performance of existing equipment and processes
compared to theoretical best performance as developed
with a batch compression permeability cell experiment.
198 REFERENCES
Adrian, D. D. et al., " Source Control of Water Treatment Waste Solids", Dept. of Civil Engineering, University of Massachusetts, Amherst, Massachusetts (1968). APHA, "Standard Methods for the Examination of Water and Wastewater", 16th. Edition., American Public Health Association, American Water Works Association, Water Pollution Control Federation, Washington, D.C. (1986). Bierck, B. R., "An Investigation of Fundamental Mechanisms of Compressible Cake Filtration", Cornell University, Ithaca, New York (1988). Edde, H., "Environmental Control for Pulp and Paper Mills", Noyes Publications, Park Ridge, New Jersey (1984). EPA, "Design Manual Dewatering Municipal Wastewater Sludges", U.S. Environmental Protection Agency, Washington, D.C. EPA-625/1- 82-014 (1982). Grady, C. P. L., and Lim, H. C., "Biological Wastewater Treatment Theory and Applications", Marcel Dekker, Inc. New York (1980). Johns, P. J., "Design and Operation of Fixed-Volume Filter Presses", Special Research Problem, School of Civil Engineering, Georgia Institute of Technology, Atlanta, Georgia (1987). Leu, W. F., "Cake Filtration", Ph.D. Dissertation, University of Houston, Houston, Texas (1981). Novak, J. T. et al., "The Blinding of Sludges During Filtration", Journal WPCF, Vol.60, No.2, pp. 206-268 (1988). Ortiz-Juan R. E., "Effects of Variations in Waste Components on Solid-Liquid Separation in the Pulp and Paper Industry", Special Research Problem, School of Civil Engineering, Georgia Institute of Technology, Atlanta, Georgia (1988). Risbud, H. M., "Mechanical Expression, Stresses at Cake Boundaries and New Compression-Permeability Cell', Ph.D. Dissertation, University of Houston, Houston, Texas (1975). Sambuichi, M., "Theoretical and Experimental Analysis for Constant Pressure Filtration", Ph.D. Dissertation, Nagoya University, Nagoya, Japan (1964).
199 Schwartzberg, H. G., pp. 423-470, "Engineering Properties of Food", Edited by Peleg, M. and Bagley, E., AVI Press, Westport, Connecticut (1983). Shirato, M. et al., "Internal Flow Mechanism in Filter Cakes", AIChE Journal., Vol. 15, pp. 405-409 (1969). Shirato, M. et al., pp. 299-423, "Filtration: Principles and Practices", Edited by Matteson, M. J. and Orr, C., Marcel Dekker, Inc. New York (1987). Springer, A. M., "Industrial Environmental Control Pulp and Paper Industry", John Wiley & Sons, New York (1986). Tiller, F. M. and Yeh. S., "The Role of Porosity in Filtration", AIChE Journal, Vol.33, No.8, pp. 1241-1256 (1987). Tiller, F. M. et al., "Compressibility of Particulate Structures in Relation to Thickening, Filtration, and Expression - A Review", Separation Science and Technology, 22(2&3), pp. 1037- 1063 (1987). Vesilind, P. A., "Treatment and Disposal of Wastewater Sludges", Ann Arbor Science, Ann Arbor, Michigan (1979). Yeh, S. H., "Cake Deliquoring and Radial Filtration", Ph.D. Dissertation, University of Houston, Houston, Texas (1985).
200 APPENDIX
201 LIST OF TABLES
Table Page 4.1 pH, Suspended and Volatile Suspended Solids Concentrations of Sludge Samples 49 4.2 Oxygen Demand Coefficient (0) for Various Carbonaceous Compounds and Materials 51 4.3 COD Data and Oxygen Demand Coefficients of Sludge Samples 53
4.4 CST Values of Sludge Samples 55 4.5 Data of Average Specific Resistance and Compressibility of Sludge Samples as Determined with Pressure Cell 56 4.6 Data of Average Specific Resistance and Compressibility of Sludge Samples As Determined with C-P Cell 57 4.7 Total Material Balance on C-P Cell Expression of Plant-P Sludge Samples 64 4.8 Mass Balance on Dry Solids of C-P Cell Expression of Plant-P Sludge Samples 67 4.9 Slopes of Plots -dL/dt as vs t in Cake Filtration Phase of Plant-P Samples 83 4.10 Elapsed Time Before Cake Filtration Enters Consolidation in C-P Cell Expression of Plant-P Samples 84 4.11 Slopes of Plots log(V) vs log(t) in Cake Filtration Phase of Plant-P Samples 86
4.12 Cake Solids Contents Achieved and Degree of Completion with C-P Cell Expression of Plant-P Samples 86
4.13 Slopes of Plots dV/dt vs V in Cake Consolidation Phase of Plant-P Samples . . 112
202
List of Tables (continued)
Table Page
4.14 Ultimate Cake Solids Contents Achievable with C-P Cell Expression of Plant-P Samples at Various Pressures and Temperatures . . 114 4.15 Elapsed Time Before Cake Filtration Enters Consolidation in C-P Cell Expression of Plant-L Samples 114 4.16 Slopes of Plots -dL/dt °5 vs t in Cake Filtration Phase of Plant-L Samples 126 4.17 Slopes of Plots log(V) vs log(t) in Cake Filtration Phase of Plant-L Samples 126
4.18 Cake Solids Contents achieved and Degree of Completion with C-P Cell Expression of Plant-L Samples 140
4.19 Slopes of Plots dV/dt vs V in Cake Consolidation Phase of Plant-L Samples . . 140
4.20 Ultimate Cake Solids Contents Achievable with C-P Cell Expression of Plant-P Samples at Various Pressures and Temperatures 141 4.21 Slopes of Plots -dL/dt °5 vs t in Cake Filtration Phase of Plants S, E, V, CL, PA, CS Samples 157
4.22 Elapsed Time Before Cake Filtration Enters Consolidation in C-P Cell Expression of Plants S, E, V, CL, CS Samples 157 4.23 Slopes of log(V) vs log(t) in Cake Filtration Phase of Samples S, E, V, CL, PA, CS Samples 158 4.24 Cake Solids Contents Achieved with C-P Cell Expression of Samples V, CL, CS at Various Pressures and Temperatures 175
4.25 Ultimate Cake Solids Contents Achieved with C-P Cell Expression of Samples S, E, V, CL, PA at Various Pressures and Temperatures . . 175
203 List of Tables (continued)
Table Page
4.26 Slopes of dL/dt vs V Plots in Cake Consolidation Phase of Samples S, E, V, CL, PA 176 4.27 Data of Average Specific Resistance and Compressibility of Sludge Samples as Determined with C-P Cell for Plant P and Three Samples from Plant L, SS and E 177 4.28 Compressibility of Sludge Samples Determined Based on Combined Data from Both Pressure Cell Test and C-P Cell Expression 178
4.29 Comparison of the Average Specific Resistance of Sludge Samples With Different Origins at Pressures of 100 kPa and 1000 kPa 194
204 LIST OF FIGURES
Figure Page
2.1 Schematic Diagram of Sludge Suspension Under Cake Filtration 9 2.2 Schematic Pressure Profiles in a Filter Cake 17 3.1 Primary Sludge Sewer Diagram of Plant-P (Ortiz, 1988) 34 3.2 Schematic Diagram of CST Apparatus 36 3.3 Schematic Diagram of Pressure Cell Apparatus 38
3.4 Normal Sectional Schematic Diagram of C-P Cell 39
3.5 Schematic Diagram of Overall C-P Cell Dewatering and Data Aquisition System . 41 4.1a Plot of CST vs Suspended Solids for PlantP Samples 59
4.1b Plot of CST vs Suspended Solids Concentration for Plant-L Samples 59
4.2 Plot of -dL/dt' s vs. t for Sample 42-9166 at Pressure of 1101 kPa 71 4.3 Plot of -dL/dt °5 vs. t for Sample 42-9166 at Pressure of 1468 kPa 71
4.4 Plot of -dL/dt °5 vs. t for Sample 42-9166 at Pressure of 2385 kPa 72
4.5 Plot of -dL/dt °5 vs. t for Sample 42-9166 at Pressure of 3303 kPa 72
4.6 Plot of -dL/dt' s vs. t for Sample 42-9157 at Pressure of 1101 kPa 73 4.7 Plot of -dL/dt °5 vs. t for Sample 42-9157 at Pressure of 1468 kPa 73
205 4.8 Plot of -dL/dt °.5 vs. t for Sample 42-9157 at Pressure of 2385 kPa 74 4.9 Plot of -dL/dt °5 vs. t for Sample 42-9157 at Pressure of 3303 kPa 74
4.10 Plot of -dL/dt °5 vs. t for Sample 42-9178 at Pressure of 1101 kPa 75 4.11 Plot of -dL/dt °5 vs. t for Sample 42-9178 at Pressure of 1468 kPa 75
4.12 Plot of -dL/dt °5 vs. t for Sample 42-9178 at Pressure of 2385 kPa 76 4.13 Plot of -dL/dt °5 vs. t for Sample 42-9178 at Pressure of 3303 kPa 76 4.14 Plot of -dL/dt °5 vs. t for Sample 42-9208 at Pressure of 1101 kPa 77 4.15 Plot of -dL/dt °5 vs. t for Sample 42-9208 at Pressure of 1469 kPa 77
4.16 Plot of -dL/dt °-5 vs. t for Sample 42-9208 at Pressure of 2385 kPa 78 4.17 Plot of -dL/dt c5 vs. t for Sample 42-9208 at Pressure of 3303 kPa 78
4.18 Plot of -dL/dt °5 vs. t for Sample 42-9212 at Pressure of 1101 kPa 79 4.19 Plot of -dL/dt °5 vs. t for Sample 42-9212 at Pressure of 1469 kPa 79
4.20 Plot of -dL/dt °5 vs. t for Sample 42-9212 at Pressure of 2385 kPa 80 4.21 Plot of -dL/dt °5 vs. t for Sample 42-9212 at Pressure of 3303 kPa 80 4.22 Plot of -dL/dt °5 vs. t for Sample 42-9213 at Pressure of 1101 kPa 81 4.23 Plot of -dL/dt °5 vs. t for Sample 42-9213 at Pressure of 1468 kPa 81
206
4.24 Plot of -dL/dt °5 vs. t for Sample 42-9213 at Pressure of 2385 kPa 82
4.25 Plot of -dL/dt °5 vs. t for Sample 42-9213 at Pressure of 3303 82 4.26 Plot of Logt vs. LogV for Sample 42-9213 at Pressure of 1101 kPa 87 4.27 Plot of Logt vs. LogV for Sample 42-9213 at Pressure of 1468 kPa 87
4.28 Plot of Logt vs. LogV for Sample 42-9213 at Pressure of 2385 kPa 88
4.29 Plot of Logt vs. LogV for Sample 42-9213 at Pressure of 3303 kPa 88 4.30 Plot of Logt vs. LogV for Sample 42-9157 at Pressure of 1101 kPa 89 4.31 Plot of Logt vs. Logy for Sample 42-9157 at Pressure of 1468 kPa 89 4.32 Plot of Logt vs. LogV for Sample 42-9157 at Pressure of 2385 kPa 90
4.33 Plot of Logt vs. LogV for Sample 42-9157 at Pressure of 3303 kPa 90 4.34 Plot of Logt vs. LogV for Sample 42-9166 at Pressure of 1101 kPa 91
4.35 Plot of Logt vs. LogV for Sample 42-9166 at Pressure of 1468 kPa 91 4.36 Plot of Logt vs. LogV for Sample 42-9166 at Pressure of 2385 kPa 92 4.37 Plot of Logt vs. LogV for Sample 42-9166 at Pressure of 3303 kPa 92 4.38 Plot of Logt vs. LogV for Sample 42-9178 at Pressure of 1101 kPa 93 4.39 Plot of Logt vs. LogV for Sample 42-9178 at Pressure of 1468 kPa 93
207
4.40 Plot of Logt vs. LogV for Sample 42-9178 at Pressure of 2385 kPa 94 4.41 Plot of Logt vs. LogV for Sample 42-9178 at Pressure of 3303 kPa 94
4.42 Plot of Logt vs. LogV for Sample 42-9208 at Pressure of 1101 kPa 95 4.43 Plot of Logt vs. LogV for Sample 42-9208 at Pressure of 1468 kPa 95 4.44 Plot of Logt vs. LogV for Sample 42-9208 at Pressure of 2385 kPa 96 4.45 Plot of Logt vs. Logy for Sample 42-9208 at Pressure of 3303 kPa 96
4.46 Plot of Logt vs. LogV for Sample 42-9212 at Pressure of 1101 kPa 97
4.47 Plot of Logt vs. LogV for Sample 42-9212 at Pressure of 1468 kPa 97 4.48 Plot of Logt vs. LogV for Sample 42-9212 at Pressure of 2385 kPa 98
4.49 Plot of Logt vs. LogV for Sample 42-9212 at Pressure of 3303 kPa 98 4.50 Plot of dV/dt vs. V for Sample 42-9213 at Pressure of 1101 kPa 100 4.51 Plot of dV/dt vs. V for Sample 42-9213 at Pressure of 1468 kPa 100 4.52 Plot of dV/dt vs. V for Sample 42-9213 at Pressure of 2385 kPa 101
4.53 Plot of dV/dt vs. V for Sample 42-9213 at Pressure of 3303 kPa 101
4.54 Plot of dV/dt vs. V for Sample 42-9157 at Pressure of 1101 kPa 102 4.55 Plot of dV/dt vs. V for Sample 42-9157 at Pressure of 1468 kPa 102
208 4.56 Plot of dV/dt vs. V for Sample 42-9157 at Pressure of 2385 kPa 103 4.57 Plot of dV/dt vs. V for Sample 42-9157 at Pressure of 3303 kPa 103 4.58 Plot of dV/dt vs. V for Sample 42-9166 at Pressure of 1101 kPa 104 4.59 Plot of dV/dt vs. V for Sample 42-9166 at Pressure of 1468 kPa 104 4.60 Plot of dV/dt vs. V for Sample 42-9166 at Pressure of 2385 kPa 105 4.61 Plot of dV/dt vs. V for Sample 42-9166 at Pressure of 3303 kPa 105 4.62 Plot of dV/dt vs. V for Sample 42-9178 at Pressure of 1101 kPa 106 4.63 Plot of dV/dt vs. V for Sample 42-9178 at Pressure of 1468 kPa 106
4.64 Plot of dv/dt vs. V for Sample 42-9178 at Pressure of 2385 kPa 107 4.65 Plot of dV/dt vs. V for Sample 42-9178 at Pressure of 3303 kPa 107 4.66 Plot of dV/dt vs. V for Sample 42-9208 at Pressure of 1101 kPa 108 4.67 Plot of dV/dt vs. V for Sample 42-9208 at Pressure of 1468 kPa 108 4.68 Plot of dV/dt vs. V for Sample 42-9208 at Pressure of 2385 kPa 109 4.69 Plot of dV/dt vs. V for Sample 42-9208 at Pressure of 3303 kPa 109 4.70 Plot of dV/dt vs. V for Sample 42-9212 at Pressure of 1101 kPa 110
4.71 Plot of dV/dt vs. V for Sample 42-9212 at Pressure of 1468 kPa 110
209
4.72 Plot of dV/dt vs. V for Sample 42-9212 at Pressure of 2385 kPa 111 4.73 Plot of dV/dt vs. V for Sample 42-9212 at Pressure of 3303 kPa 111 4.74 Measured Cake Solids Contents at the End of C-P Cell Expression of Plant-P Samples at Various pressures 115 4.75 Ultimate Cake Solids Content Achievable by C-P Cell Expression of Plant-P Samples at Various Pressures 115
4.76 Plot of -dL/dt p.5 vs. t for Sample L-9339 at Pressure of 1101 kPa 116 4.77 Plot of -dL/dt °5 vs. t for Sample L-9339 at Pressure of 1468 kPa 116 4.78 Plot of -dL/dt °5 vs. t for Sample L-9339 at Pressure of 2385 kPa 117 4.79 Plot of -dL/dt °5 vs. t for Sample L-9339 at Pressure of 3303 kPa 117
4.80 Plot of -dL/dt °5 vs. t for Sample L-0263A at Pressure of 1101 kPa 118
4.81 Plot of -dL/dt °5 vs. t for Sample L-0263A at Pressure of 3303 kPa 118 4.82 Plot of -dL/dt °5 vs. t for Sample L-0263B at Pressure of 1101 kPa 119
4.83 Plot of -dL/dt °5 vs. t for Sample L-0263B at Pressure of 3303 kPa 119
4.84 Plot of -dL/dt °5 vs. t for Sample L-0264A at Pressure of 1101 kPa 120 4.85 Plot of -dL/dt °5 vs. t for Sample L-0264A at Pressure of 1468 kPa 120
4.86 Plot of -dL/dt °5 vs. t for Sample L-0264A at Pressure of 3303 kPa 121
4.87 Plot of -dL/dt °5 vs. t for Sample L-1011A at Pressure of 1468 kPa 121 210
4.88 Plot of -dL/dt ps vs. t for Sample L-1011A at Pressure of 1101 kPa 122 4.89 Plot of -dL/dt °.5 vs. t for Sample L-1011A at Pressure of 2385 kPa 122
4.90 Plot of -dL/dt °5 vs. t for Sample L-1011A at Pressure of 3303 kPa 123 4.91 Plot of -dL/dt °.5 vs. t for Sample L-1011B at Pressure of 1101 kPa 123 4.92 Plot of -dL/dt °5 vs. t for Sample L-1011B at Pressure of 1468 kPa 124
4.93 Plot of -dL/dt' s vs. t for Sample L-1011B at Pressure of 2385 kPa 124
4.94 Plot of -dL/dt' s vs. t for Sample L-1011B at Pressure of 3303 kPa 125
4.95 Plot of -dL/dt c5 vs. t for Sample L-1011A at Pressure of 1101 kPa 128
4.96 Plot of -dL/dt c-5 vs. t for Sample L-1011A at Pressure of 1101 kPa: Truncation of Terminal Rate Date in Fig. 4.95 for Purpose of Analysis 128
4.97 Plot of dV/dt vs V for Sample L-9339 at Pressure of 1101 kPa 129
4.98 Plot of dV/dt vs V for Sample L-9339 at Pressure of 1468 kPa 129 4.99 Plot of dV/dt vs V for Sample L-9339 at Pressure of 2385 kPa 130 4.100 Plot of dV/dt vs V for Sample L-9339 at Pressure of 3303 kPa 130
4.101 Plot of dV/dt vs V for Sample L-0236A at Pressure of 1101 kPa 131 4.102 Plot of dV/dt vs V for Sample L-0236A at Pressure of 3303 kPa 131
4.103 Plot of dV/dt vs V for Sample L-0236B at Pressure of 1101 kPa 132 211
4.104 Plot of dV/dt vs V for Sample L-0236B at Pressure of 3303 kPa 132 4.105 Plot of dv/dt vs V for Sample L-0264A at Pressure of 1101 kPa 133 4.106 Plot of dV/dt vs V for Sample L-0264A at Pressure of 1468 kPa 133 4.107 Plot of dV/dt vs V for Sample L-0264A at Pressure of 3303 kPa 134 4.108 Plot of dV/dt vs V for Sample L-1011A at Pressure of 1101 kPa 134
4.109 Plot of dV/dt vs V for Sample L-1011A at Pressure of 1468 kPa 135 4.110 Plot of dV/dt vs V for Sample L-1011A at Pressure of 2385 kPa 135 4.111 Plot of dV/dt vs V for Sample L-1011A at Pressure of 3303 kPa 135 4.112 Plot of dV/dt vs V for Sample L-1011B at Pressure of 1101 kPa 136 4.113 Plot of dV/dt vs V for Sample L-1011B at Pressure of 1468 kPa 137 4.114 Plot of dV/dt vs V for Sample L-1011B at Pressure of 2385 kPa 137 4.115 Plot of dV/dt vs V for Sample L-1011B at Pressure of 3303 kPa 138 4.116 Measured Cake Solids Content at End of C-P Cell Expression of Plant-L Samples . 139 4.117 Ultimate Cake Solids Contents Achievable by C-P Cell Expression of Plant-L Samples 139
4.118 Plot of -dL/dt p.5 vs. t for Sample S-0005 at Pressure of 1101 kPa 142 4.119 Plot of -dL/dt 0-5 vs. t for Sample S-0005 at Pressure of 3303 kPa 142
212
4.120 Plot of -dL/dt °5 vs. t for Sample E-0073 at Pressure of 1101 kPa 143 4.121 Plot of -dL/dt °-5 vs. t for Sample E-0073 at Pressure of 1468 kPa 143
4.122 Plot of -dL/dt °5 vs. t for Sample E-0073 at Pressure of 2385 kPa 144 4.123 Plot of -dL/dt °5 vs. t for Sample E-0073 at Pressure of 3303 kPa 144
4.124 Plot of -dL/dt °.5 for Sample V-0234A at Pressure of 1468 kPa 145 4.125 Plot of -dL/dt °5 for Sample V-0234A at Pressure of 2385 kPa 145 4.126 Plot of -dL/dt °5 for Sample V-0234A at Pressure of 3303 kPa 146 4.127 Plot of -dL/dt °5 for Sample V-0234B at Pressure of 1101 kPa 146
4.128 Plot of -dL/dt c5 for Sample V-0234B at Pressure of 3303 kPa 147 4.129 Plot of -dL/dt cs for Sample CL-0305A at Pressure of 1101 kPa 147 4.130 Plot of -dL/dt c ' for Sample CL-0305A at Pressure of 1468 kPa 148 4.131 Plot of -dL/dt °5 for Sample CL-0305A at Pressure of 2385 kPa 148
4.132 Plot of -dL/dt °.5 for Sample CL-0305A at Pressure of 3303 kPa 149 4.133 Plot of -dL/dt °5 for Sample CL-0305B at Pressure of 1101 kPa 149 4.134 Plot of -dL/dt °5 for Sample CL-0305B at Pressure of 1468 kPa 150 4.135 Plot of -dL/dt °5 for Sample CL-0305B at Pressure of 2385 kPa 150
213
4.136 Plot of -dL/dt °. ' for Sample CL-0305B at Pressure of 3303 kPa 151 4.137 Plot of -dL/dt °5 for Sample PA-1039A at Pressure of 1101 kPa 151 4.138 Plot of -dL/dt °5 for Sample PA-1039A at Pressure of 1468 kPa 152
4.139 Plot of -dL/dt °5 for Sample PA-1039A at Pressure of 2385 kPa 152
4.140 Plot of -dL/dt °.5 for Sample PA-1039A at Pressure of 3303 kPa 153 4.141 Plot of -dL/dt °5 for Sample PA-1039B at Pressure of 1101 kPa 153
4.142 Plot of -dL/dt °5 for Sample PA-1039B at Pressure of 1468 kPa 154 4.143 Plot of -dL/dt °5 for Sample PA-1039B at Pressure of 2385 kPa 154
4.144 Plot of -dL/dt °5 for Sample PA-1039B at Pressure of 3303 kPa 155 4.145 Plot of -dL/dt °5 for Sample CS-1039A at Pressure of 1101 kPa 155 4.146 Plot of -dL/dt °5 for Sample CS-1039A at Pressure of 3303 kPa 156 4.147 Plot of dL/dt vs. V for Sample S-0005 at Pressure of 1101 kPa 159 4.148 Plot of dL/dt vs. V for Sample S-0005 at Pressure of 3303 kPa 159 4.149 Plot of dL/dt vs. V for Sample E-0073 at Pressure of 1101 kPa 160
4.150 Plot of dL/dt vs. V for Sample E-0073 at Pressure of 1468 kPa 160 4.151 Plot of dL/dt vs. V for Sample E-0073 at Pressure of 2385 kPa 161
214
4.152 Plot of dL/dt vs. V for Sample E-0073 at Pressure of 3303 kPa 161 4.153 Plot of dL/dt vs. V for Sample V-0234A at Pressure of 1468 kPa 162
4.154 Plot of dL/dt vs. V for Sample V-0234A at Pressure of 2385 kPa 162
4.155 Plot of dL/dt vs. V for Sample V-0234A at Pressure of 3303 kPa 163 4.156 Plot of dL/dt vs. V for Sample V-0234B at Pressure of 1101 kPa 163
4.157 Plot of dL/dt vs. V for Sample V-0234B at Pressure of 3303 kPa 164
4.158 Plot of dL/dt vs. V for Sample CL-0305A at Pressure of 1101 kPa 164
4.159 Plot of dL/dt vs. V for Sample CL-0305A at Pressure of 1468 kPa 165 4.160 Plot of dL/dt vs. V for Sample CL-0305A at Pressure of 2385 kPa 165 4.161 Plot of dL/dt vs. V for Sample CL-0305A at Pressure of 3303 kPa 166 4.162 Plot of dL/dt vs. V for Sample CL-0305B at Pressure of 1101 kPa 166 4.163 Plot of dL/dt vs. V for Sample CL-0305B at Pressure of 1468 kPa 167 4.164 Plot of dL/dt vs. V for Sample CL-0305B at Pressure of 2385 kPa 167
4.165 Plot of dL/dt vs. V for Sample CL-0305B at Pressure of 3303 kPa 168 4.166 Plot of dL/dt vs. V for Sample PA-1039A at Pressure of 1101 kPa 168
4.167 Plot of dL/dt vs. V for Sample PA-1039A at Pressure of 1468 kPa 169
215
4.168 Plot of dL/dt vs. V for Sample PA-1039A at Pressure of 2385 kPa 169 4.169 Plot of dL/dt vs. V for Sample PA-1039A at Pressure of 3303 kPa 170 4.170 Plot of dL/dt vs. V for Sample PA-1039B at Pressure of 1101 kPa 170 4.171 Plot of dL/dt vs. V for Sample PA-1039B at Pressure of 1468 kPa 171 4.172 Plot of dL/dt vs. V for Sample PA-1039B at Pressure of 2385 kPa 171 4.173 Plot of dL/dt vs. V for Sample PA-1039B at Pressure of 3303 kPa 172
4.174 Plot of dL/dt vs. V for Sample CS-1039A at Pressure of 1101 kPa 172 4.175 Plot of dL/dt vs. V for Sample CS-1039A at Pressure of 3303 kPa 173
4.176 Average Specific Resistance vs. Pressure for Data Generated with Both Pressure Cell and C-P Cell for Sample 42-9157 179 4.177 Average Specific Resistance vs. Pressure for Data Generated with Both Pressure Cell and C-P Cell for Sample 42-9166 179
4.178 Average Specific Resistance vs. Pressure for Data Generated with Both Pressure Cell and C-P Cell for Sample 42-9178 180
4.179 Average Specific Resistance vs. Pressure for Data Generated with Both Pressure Cell and C-P Cell for Sample 42-9208 180
4.180 Average Specific Resistance vs. Pressure for Data Generated with Both Pressure Cell and C-P Cell for Sample 42-9212 181 4.181 Average Specific Resistance vs. Pressure for Data Generated with Both Pressure Cell and C-P Cell for Sample 42-9213 181
216
4.182 Average Specific Resistance vs. Pressure for Data Generated with Both Pressure Cell and C-P Cell for Sample L-9339 182 4.183 Average Specific Resistance vs. Pressure for Data Generated with Both Pressure Cell and C-P Cell for Sample S-0005 182 4.184 Average Specific Resistance vs. Pressure for Data Generated with Both Pressure Cell and C-P Cell for Sample E-0073 183 4.185 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample L-0263A 184 4.186 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample L-0263B 184
4.187 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample L-0264A 185 4.188 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample L-1011A 185 4.189 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample L-1011B 186
4.190 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample V-0234A 186
4.191 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample V-0234B 187 4.192a Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample CL-0305A 188 4.192b Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample CL-0305A 188
217
4.193 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample CL-0305B 189 4.194 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample PA-1039A 189 4.195 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample PA-1039B 190 4.196 Average Specific Resistance vs. Pressure for Data Generated with C-P Cell for Sample CS-1039A 190
218