Biological Treatment of Landfill Leachate
BIOLOGICAL TREATMENT OF LANDFILL LEACHATE
b~ Julie-Marie Pouliot
Department of Civil and Environmental Engineering Faculty of Engineering Science
Submitted in partial fulnllment of the requirements for the degree of Master of Engineering Science
Faculty of Graduate Studies The University of Western Ontario London, Ontarîo, Canada September 1999
O Julie-Marie Pouliot 1999 National Library Bibliothèque nationale du Canada Acquisitions and Acquisitions et Bibliographie Senrices senrices bibliographiques 395 Wellington Street 395. rue Wellington OîCawaON K1AûN4 OrrawaON KIAW canada canada
The author has granted a non- L'auteur a accorde une licence non exclusive licence allowing the exclusive permettant à la National Lïbraxy of Canada to Bibliothèque nationale du Canada de reproduce, Ioan, disbiiute or sell reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/nlm, de reproduction sur papier ou sur format électronique.
The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantid extracts tiom it Ni la thèse ni des extraits substantiels rnay be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Aerobic reactors were used in the cunent research to study the effects of Merent additives on the biological treatment of lanm leachate. These additives were phosphoric acid, powdered activated carbon (PAC), polyethylenimine and BOD
~a.Iance~~mdactured by NEXTEQ Limited, Toronto. Synthetic and naturd 1andfïI.l leachates were investigated The latter was collected at a Iandf3l site near London,
Ontario. Two different bioreactors were used: a 3-L batch bioreactor and a 20-L continuous stirred tank reactor (CSTR).
From the batch bioreactor study, it was observed that the addition of phosphonc acid clearly increased the chernical oxygen demand (COD) utikation rate and decreased the effluent COD of the synthetic leachate. The other additives, especiaiiy BOD
ala an ce^^, seemed to influence more specincaily the COD utiiization rates. COD reduction data for the most efficient combinations of additives were modeled and found to follow the logistic decay mode1 fairly weU. The eEciencies of glass fiber and
Versapor fïiters were compared using total suspended solids (TSS) as a parameter. It was found that the TSS measured with glass fiber filters represented 66 % of that measured with Versapor nIters. Ammonia and biochernical oxygen demand (BOD) levels were also monitored during the study. Ak stripping was believed to be the main mechanism for ammonia removal. It was also observed that the comrnonly used technique to evaluate BOD of domestic wastewater has to be modified when testuig landfill leachate.
For the continuous stirred tank reactor (CSTR) study, synthetic leachate supplemented with phosphoric acid was used. Several dinerent hydraulïc retention times were investigated to evaluate their influence on effluent quality. Biomass growth on the inner wail of the bioreactor was fomd to greatly improve the treatment efnciency regarding COD removal. About 95 % COD reduction was observeci. The efficiencies of glass fiber and Versapor filters wae ako studied and compared with the results obtained with the batch bioreactors. Tt was found that for the CS% both nIters gave similar TSS, most Iikely due to a d.erentmicrobial population. The COD of the volatile suspended solids (VSS) was fomd to be 0.64 mg COD/mg VSS. It was compared with the commonly assumed vdue of 1-42 mg CODfmg VSS.
Key words: lannfill leachate, biological treatment, batch reactors, continuously stirred tank reactors (CSTR), phosphorus, powdered activated carbon (PAC), polyethylenimine
(PET),BOD ala an ce^. 1 would like to îhank my supervisors, Dr. Ernest Yanfbl and Dr. Amarjeet S. Bassi for their the and expertise during this research endeavour. Scholarship provided by
Natural Sciences and Engineering Research Council (NSERC PGS A) and AMWAY of
Canada a.&O gratefûiiy acknowledged.
Sincere apprecÏation is expressed to the Stan and fellow graduate students at The
University of Western Ontario for their support and fiendship. Je voudrais aussi remercier ma mère Louise, mon père Ides et ma soeur Catherine pour leurs multiples encouragements et le support qu'ils m'ont offert tout au long de ma maîtrise. J'ofEe aussi des remerciements tout spéciaux à Leila pour les nombreuses heures qu'elle a bien voulu me consacrer. Page -. Ceaificate of examkation ll --- Abstract Ill
Acknowledgements v
Table of contents VI
List of tables ix
List of figures X
List of Appendices XV
CWTER1: INTRODUCTION
1.1 Background
12 Objectives and scope of present study
CHAPTER 2: LITERATURE REVIEW
Municipal landfill Ieachate 2.2.1 Characteristics 2.2.2 Water quality indicators . 2.2.2.1 Chemical oxygen demand (COD) 2.2.2.2 Biochemical oxygen demand (BOD) 2.2.2.3 Solids . 2.2.2.4 Nitrogen
Treatment of leachate 2.3.1 Biologicai treatment techniques 2.3.1.1 Recirculation 2.3.1 2 Activated sludge 2.3.1.3 Trickling filters (TF) 2.3.1.4 Rotating biological contactors (RBC) 2.3.I .5 Stabilization ponds 2.3-1-6 Wetlands 2.3.1.7 Sequencing batch reactors (SBR)
2-32 PhysicaL I chemicd treatment techniques 2 -3-2- 1 Filtration 2.3 2.2 Activated carbon adsorption 2.3 -2.3 Coagulation / floccdation 2.3 -2-4 Ozonation
CaAPTER 3: MATERIALS AND METHODS
3.1 Feed Characterization 42
3-2 Batch Bioreactor Experimental Set-Up 45
3.3 Continuous Stùred Tank Reactor (CSTR) Experïmentd Set-Up 46
3.4 Analytical Methods 46 3.4.1 pH 46 3.4.2 Solids 46 3 -4.3 Chemical oxygen demand (COD) 47 3-4.4 Biological oxygen demand (BOD) and total phosphorus (TP) 47 3.4.5 Ammonia(NH3-N) 48 3.4.6 Nitrate (NO3--N) and nitrite (N0pN) 48
CHAPTER 4: BATCH STUDIES RESULTS ANS DISCUSSION
4.1 Batch treatment of synthetic leachate 54
4.2 Batch treatment of synthetic leachate with additives 4.2.1 Addition of phosphoric acid 4.2.2 Addition of powdered activated carbon @AC) 4.2.3 Addition of polyethylenimine (PEI) 4.2.4 Addition of BOD 13alanceTM 4.2.5 Comparison of additives efficiency 4.2.5-1 COD utilization rates 4.252 Peak solids concentration 4-2-53 Monod kïnetics
4.3 Batch treatment of London W12A lannfill leachate 69
4.4 Comparison of batch treatment for synthetic and London landflil leachates 70
4.5 Total suspended solids (TSS) analysis 72 4-6 Biological orrygen demand @OD) analysis
4.7 Nitrate @O3? and nitrite (Na)analysis
4.8 Conclusions
CHAPTER 5: CONTINtTOUS STIRRED TANK REACTORS (CSTR)
5.2 Continuous stined tank reactor (CSTR) results 5.2.1 liiitialstudy 5.2.2 Effect of hydraulic retention times 5.2.3 Effect of waü growth
5.3 Chernical oxygen demand (COD) of the biomass
5.4 Total suspended soli& (TSS) analysis
5.5 Conclusions
CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS
6.1 Summary and conclusions
6.2 Recommendations
APPENDICES
REFERENCES
VITA Table Description Page
CHAPTER 2: LITERATURE REVIEW
2.1 Characteristics of young and o1der leachates.
2.2 Advantages and disadvantages of different lancifill Ieachate treatment techniques.
2.3 ExampIes ofcomponents separated by MF, UF and HFRO processes.
CHAPTER 3: MATERIALS AND METHODS
3.1 Synthetic leachate composition.
3.2 Trace metal solution composition.
3.3 Characteristics of W12A landfiIl leachate, London, Ontario.
CEUPTER 4: BATCH BIOREACTORS
4.1 Absorbance peaks reached with different additive combinations.
4.2 Batch bioreactor treatment of London W12A landfil1 Ieachate,
4.3 Average COD reduction in synthetic and real landfill leachate batch treatment.
4.4 Cornparison of giass fiber and Versapor filters for TSS measurement in batch bioreactors.
4.5 BODs and COD before and after batch biological treatment of synthetic and natural leachates. Figure Description Page
CHAPTER 2: LITERATURE REVIEW
2.1 Bankdesign involving a leachate collection system, a natural clayey deposit and downward advective-diffusive transport.
2.2 Barrïer design involving a leachate collection system, a natural clayey deposit, upward advection and downward diffusion - a hydraulic trap.
2.3 A compacted clayey prlmary berused in conjunction with an engineered hydraulic control laye and hydraulic trap to minimize contaminant impact together with a composite secondary liner (geomembrane and clayey liner) used to minimize volume of fluid needed to maintain the hydraulic trap. By pumpkg the hydraulic control layer, this can also be used as a secondary leachate collection system.
2.4 London W12A landfiIl leachate voIume during 1996.
2.5 Changes in organic matter during biological oxidation of polluted waters under aerobic conditions,
2.6 (a) Normal BOD cuve for oxidation of organic matter. (b) Influence of nitrification,
2.7 Pathways for aerobic microbial degradation of organic wastes.
2.8 Activated sludge process for secondary treatment of wastewater.
2.9 Schema of a trîckling mter.
2.10 Schema of osmosis and reverse-osmosis phenornena-
2.1 1 Solute removal from water by reverse-osmoàs.
2.12 Dead-end filtration with cake formation and crossflow cake-fkee filtration,
2.13 Typical formulas of coagulant polymers. Figure Description Page
CHAPTER 3: MATERIALS AND METHODS
3.1 Schema of the batch bioreactor experimental set-up.
3.2 Batch bioreactors experimental set-up. Lefi: test with addition of PAC; right: test with addition of BOD ala an ce^^.
3.3 Continuous stùred tank bioreactor set-up. Content volume: 20 L; nmber of baffles: 4; number of blades per impeIler: 4; P :penstdtic mini-pump.
3.4 Continuous stirred tank reactor expetimental set-up.
3.5 Close-up on the biomass growth on the inside wall of the reactor.
CaAPTER 4: BATCE STUDIES RESULTS AND DISCUSSION
Average absorbance (at 600 nm), total suspended solids (TSS) and chemical oxygen demand (COD) of two batch tests during biological treatment of synthetic leachate (no additives).
Average chemical oxygen demand (COD) of two batch tests during biological treatment of synthetic leachate (no additives).
Average absorbance (at 600 nm) of three batches during biological treatment of synthetic leachate (addition of phosphorus).
Average chemical oxygen demand (COD) of three batch tests during biological treatment of synthetic leachate (addition of phosphorus).
Average absorbance (at 600 nm) during batch biological treatment of synthetic leachate showing Muence of phosphorus addition.
Average chemical oxygen demand (COD) during batch biological treatment of synthetic leachate showing influence of phosphorus addition-
Average absorbance of five batch tests showing the influence of difrent PAC concentratiom on the biodegradation of synthetic leachate (addition of phosphorus), Figure Description Page
Average COD of five batch tests showing the influence of different PAC concentrations on the biodegradation of synthetic leachate (addition of phosphonis). 86
Powdered activated carbon (MC) adsorption test showing measured residual chemical oxygen dmand (COD) at difTerent PAC concentratiom.
Contaminant removal trends in PACT~systems.
Average absorbance of batch tests showing the influence of different PEI concentrations and phosphoric acid on the biodegradation of synthetic leachate.
Average chemical oxygen demand (COD) of batch tests showing the infiuence of different PEI concentrations and phosphoric acid on the biodegradation of synthetic leachate.
Average ammonia (Ml3)durîng batch tests showing the influence of different PEI concentrations and phosphoric acid on the biodegradation of synthetic leachate-
Measured absorbance of four batch tests during biolo 'cal treatment of synthetic leachate contahing 5 ppm of BOD Balance& and phosphoric acid.
Measured chemical oxygen demand (COD) of four batch tests during biological treatment of synthetic leachate containing 5 ppm of BOD ala an ce^ and phosphonc acid.
Measured amrnonia (NH3-N) of three batch tests during biologkd treatment of synthetic 1andfi.U leachate containing 5 ppm of BOD al an ce^^ and phosphoric acid-
Influence of additive concentration on measured utilization rate of chemical oxygen demand (COD) during batch biologicd treatment of synthetic leachate.
Relationship between growth rate of a bacterhm and the concentration of the substrate supporthg its growth.
Disappearance curves for chernicals that are mineralized by diffierent growth related kinetics- Figure Description Page
Logistic decay modeling of substrate disappearance in the treatment of synthetic leachate supplemented with phosphorus and 150 pprn of PAC. 98
Cornparison of substrate disappearance in the treatment of synthetic leachate supplemented with phosphonis and 150 ppm of PAC and phosphorus only (average of individual batches modeled with logistic decay), 98
Logistic decay modehg of substrate disappeamce in the treatment of synthetic leachate supplemented with phosphonis and 15 ppm of PEI, 99
Cornparison of substrate disappearance in the treatrnent of synthetic leachate supplemented with phosphorus and 15 ppm of PEI and phosphonis only (average of individual batches modeled with Iogistic decay). 99
Logistic decay modeling of substrate disappearance in the treatment of synthetic leachate supplemented with phosphonis and 5 ppm of BOD ala an ce^. 100
Cornparison of substrate disappearance in the treatment of synthetic leachate supplemented with phosphorus and 15 ppm of BOD ala an ce^ and phosphonis only (average of individual batches modeled with logistic decay). 100
CHAPTER 5: CONTFNUOUS STUDIES RESULTS AND DISCUSSION
5.1 Initial study with continuous stirred tank reactor (CSTR) showing the effects of biomass washout on absorbance at hydraulic retention &es (HRTs) of5 to 6.5 days. 114
5.2 Initial study with contuiuous stirred tank reactor (CSTR) showing the effects of biomass washout on solids concentrations at hydraulic retention times (HRTs) of 5 to 6.5 days. 115
5.3 Initial shidy with continuous stirred tank reactor (CSTR) showing the effects of biomass washout on COD at hydraulic retention times (HRTs) of 5 to 6.5 days. 116 Figure Description Page
Continuous stirred tank reactor (CSTR) studies showing the influence of hydraulic retention time (HRT) variations on absorbance. 117
Continuous stirred tank reactor (CSTR)studies showing the influence of hydrauIic retention time WT) variations on total and volatiie suspended soli&. 118
Continuous stirred tank reactor (CSTR) studies showing the influence of hydraulic retention time (HRT) variations on COD- 119
Continuons stirred tank reactor (CSTR) studies showing the influence of waU growth on absorbance. 120
Continuous stiiTed tank reactor (CSTR)studies showing the influence of wall growth on total and volatile suspended solids. 121
Continuous stirred tank reactor (CSTR)studies showing the ineuence of wall growth on COD. 122
Comparison of glass nber and Versapor nIters on the measurement of total suspended solids (TSS) in a CSTR. 123
xiv APPENDIX Page
Appendix A 130
A- 1 13 1
A-2 132
Appendix B
Appendix C 1.1 BACKGROUND
For years people have died fiom plagues without understanding the cause of their propagation. London England, is a city among many others that has suffered greatly fiom drhkhg water epidemiology. In the 19& centmy, the source of diseases such as cholera and typhoid fever was a mystery, since they were believed to be the consequences of evil behaviour. In 1854, Dr. John Snow suggested that the cholera epidemic might be countered by removing the drinking water pump situated on Broad Street, which was drawing water from under a major sewage outfall. The intuition of Dr. Snow was strongly criticized and it took thirty yean for the cholera microbe to be identined.
However, he brought awareness of the importance of separating domestic wastewater discharges kom drinking water sources. By the beginning of the 20" cenwthe world's fïrst activated sludge process was developed in England @avey, 1999).
As a result, for many yeas now, the more industrialized corntries have been treating theïr domestic wastewater before discharging it into a receiving water body.
Government regdations regarding point source discharges have become more stringent and therefore, different techniques have been developed to meet these requirements.
Extensive research amund the world is being performed to find new treatment methods,
Mprove existing ones and make aU of them hnancially feasible.
Even though domestic sewage seems to be the most apparent source of surface and groundwater poilution, there are many others with similar effects. For years, municipal solid waste landfills have not been considered as a possible source of
groundwater contamination. PrÏor to the early 1970s, landfill design did not include any
form of barrîer system to prevent leakage of contaminants hto the surrounding
environment. Following major Ieakage incidents such as the Love Canal episode
(Niagara Fails, New York), the importance of bamîers and Ieachate collection systems
was recognized and incorporated into landfill designs. Foliowing these developments,
the treatment and disposal of leachates generated fkom landfUs became an important
focus of waste management-
Several factors can affect the chatacteristics of a IandfilI leachate. Initiaily, the
ongin and the nature of the solid wastes are the major factors of influence. Then, as
chemical and biological processes occur, the age of the landfill and environmental
conditions such as the amount of precipitation have an important role. A young leachate,
Le. in the acidogenic phase, contains a high concentration of volatile fatty acids (VFA)
due to anaerobic fermentation. On the contrary, a leachate in the methanogenic phase is
characterized mainly by refkactory organic compounds or humic Like substances. These
latter cornpounds are formed when the VFAs are converted to biogas, composed of
methane and carbon dioxide (Welander and Henrysson, 1997). Consequently, as a
leachate ages and organics are being degraded, the BODKOD ratio decreases and the pH
and amnonia concentrations increase. The latter can reach very high values (2700 mg/L
NI&-N, Henderson and Atwater, 1995) and if converted to nitrate, could result in
eutrophication of the receiving water body. It is therefore desirable to achieve complete nitrogen removal before discharge of the treated effluent. Landfill leachate dso contains heavy metals. It is one of the reasons why regdatory bodies do not favor the treatment of leachate with municipal sewage. It is much harder to dispose of sludge fiom a biological treatment when it can not be used for agriculturee Another reason to justify separate treatment is that conventional municipal treatment processes do not efficiently remove many refiactory organic compounds (Zenon Environmental systems hc. 1989). Some of these compounds are hydrophobie and may accumulate in organisms (Welander and
Henrysson, 1997)-
Many ciiffirent methods have been investigated for treating leachate generated ikom municipal sanitary wastes. Since leachate contains both biodegradable and non- biodegradable components, the methods studied can be divided into two major groups: biological and physicaVchemica1 treatments. Some of the important biological treatment methods include recirculation, activated sludge, sequencing batch reactors, aerobic lagoons and constructed wetiands- Physica1,chernical techniques are oxidation, coaguiation/floccu.iation, activated carbon, rnicrofEItration, ultrafi1tration and reverse- osmosis (van Dijk and Roncken, 1997; Bressi and Favali, 1997; Luning and Notenboom,
1997).
The City of London, Ontario, is one among others concemed about municipal landfïll leachate treatment. The City disposes of its solid wastes in landfïll site W12A located at the southern end of the city. This site comprises two leachate collection systems, one for the older section of the site and the other for the newer section. There is no on-site facility to treat the collected leachate, neither is there any piping system to co~ectthe landfil1 to the sewage treatment plant. Consequently, the leachate needs to be hauled by tanker truck to a pumping station where it is transported by gravity sewers to the Greenway Pollution Control Center for treatment. About 10 miilion imperid galions per year of leachate are hauled at a cost of $3.50 per 1000 ImperÎal gallons. This corresponds to a total cost of $135 000 per year (Van Rossum, 1997). The process is quite expensive and the treatment not ideal for the above mentioned reasons. Consequentiy, there is a need for effective and inexpensive methods of leachate treatment.
1.2 OBJECTIVES AND SCOPE OF PRESENT STUDY
Low concentrations of powdered activated carbon (50-200 ma)(Metcalf and
Eddy, 1991) have been added to activated sludge tanks in PACT (powdered activated carbon treatment) process. This process allowed an existing wastewater treatment plant to operate at a hi& influent flow rate and stabilized the treatment during shock loads of
BOD or toxic organics in the innuent (Sayles and Suidan, 1993). In the current study, it was also expected that the addition of low concentrations of PAC wodd favour the attachent of biomass to the inside wall of the reactor and provide a support surface for its growth. Polyethylenimine (PEI) has been previously shown to be a potent permeabilizer of the outer membrane of Gram-negative bacteria in a previous study
@elander et al-. 1997). At concentrations of less than 20 mg/L, its effect was comparable to that of EDTA. PEI was added to a batch bioreactor to detennine if it would increase the biomass activity and hence, accelerate the breakdown of organics.
BOD Balancem (supplied by NEXTEQ Limited, Toronto) is a novel flocculant containing natural surface active agents. There is no available data related to its use in the treatment of landnll leachate, hence its efficiency was compared to that of phosphoric acid, PAC and PEI. The objectives of the present study were twofold: (i) examine the effects of four different additives on the efficiency of biological landfùl leachate treatment (phosphoric acid, powdered activated carbon (PAC), polyethyleniuüne (PEI) and BOD ala an ce^) and (5) investigate the effects of hydraulic retention the variations and biomass waIl growth on the efficiency of a continuous stirred tank reactor (CSTR). Chapter 2 provides general information on the chamcterÏstics of Iaanfill leachate and a review of the most commonly used biological and physicaVchemica1 treatment tec&ques. In Chapter 3, the batch bioreactor and continuous stirred tank bioreactor (CSTR) used to treat the landfiil leachate are presented together with the analytical procedures. The redts obtained for synthetic and London landfiil leachates batch studies are detailed and discussed in
Chapter 4 and the efficiencies of the various additives are compared. Chapter 5 presents the results obtained for continuous treatment of synthetic leachate as well as a discussion on the effects of residence the variations and wall growth. Finally, conclusions and recomrnendations for Merresearch are summarized in Chapter 6. 2.1 LANDFILLS
Since the early 1970s, the design of landfill sites for disposa1 of municipal,
industrial and commercial refuses include barrier systems as weii as leachate collection
systems to prevent contamination of the surrounding environment- Barriers usually
include one or more of the following components: (i) natural clayey soils such as
lacrustine clay or clayey tîll, (ii) recompacted clayey liner, (iii) cut-off walls, (iv) natural
bedrock or (v) geomembranes in composite liner systems (powe et al.. 1997).
Figure 2.1 shows a landfïll with a simple barrïer design, Le. a natural clayey
deposit and a leachate collection system. The potentiometric surface in the aquifer is
undemeath the base of the lanW which causes downward flow fiom the landiill. In
Figure 2.2, there is upward fiow fiom acquifer to landfill since the potentiometric surface
in the acquifer is above the base of the landfill. This phenornenon is called an hydraulic
trap. Figure 2.3 shows a more complicated barrier design with two clay liners. As can be
seen in the previous figures, many different techniques are available to contain the contaminants and coilect the leachate- Many considerations have to be taken into account
when choosing a specific design, including: the regdatory penod over which a landfill is required to have no, or negligible, effect on groundwater quality, the waste composition, the location of the site, the hydrogeological characteristics of the site, the service Me, the amount of precipitation, etc. LancEll leachate is formecl by the percolation of rainwater through domesi refuses. The water causes leaching of soluble saits and partly biodegraded organic compounds, responsibe for a fod-smelling, dark-colored leachate. It may also contain fine particles of soil fiom the daily cover. Bacterid degradation starts under aerobic conditions as swn as the wastes are deposited m the landfill, generating high temperatura. The system becomes anaerobic following rapid depletion of oxygen, much cooler and far Iess reactive (Rowe et al., 1997).
Several factors affect the composition of lanm leachate. These include the age of the landfill, the nature of the waste (solid or liquid), the source of the waste
(municipal, industrial, commercid, mining) and the amount of precipitation. A young leachate in the acidogenic phase is characterized by a high organic fiaction and a
BODJCOD ratio greater than 0.4. It can be easily biodegraded and it is weakly acidic, consequently mobilipng heavy metals. An older leachate in the methanogenic phase is not as easily biodegraded as a young leachate. It contains refiactory organic compounds, high concentrations of ammonia and is characterized by higher pH values. Table 2.1 presents characteristics of typical young and older leachates. Table 2-1: Characteristics of young- and older Ieachate. [Rowe et al,, 1997-1 Corn~onents/ Characteristics Younpr leachate older leachate Water 95 % 99 % Dissolved and suspended inorganics 3% 1 % Dissolved and suspendecl organics 2% 0.5 % COD 23 000 ppm 3 000 ppm BOD, 15 000 ppm 180 ppm DH 5.2 - 6.1 7.2 - 8
The volume of Ieachate produced in a 1andfi.U varies greatly dependuig on the
amount of precipitation it receives, which in tum is dependant on location and season
changes. For example, in the city of London, Ontario, the volume of leachate coIlected at
landfill W12A in 1996 varied fiom 5110 m3 in April to 1885 m3 in September. Figure 2.4
presents the monthly leachate volume during 1996 (Van ROSSU~,1997).
2.2.2 Water Quality Indicators
2.2.2.1 Chernical oxygen demand (COD)
Chernical oxygen demand is used to evaluate the organic strength of domestic and
industrial wastewaters. It measures the amount of oxygen necessary to completely oiùdize d organic matter. One limitation of the test is that it does not differentiate between biologically oxidîzable and biologically inert organic matter, neither does it indicate the rate at which the biologicaily active material would be oxidized under natural conditions. However, COD can be measured rapidly (3 hours) and this is why it is often used instead of the BOD, test.
There are tbree methods to evaluate COD: Open Reflux, Closed Reflux
(Titrirnetrïc), Closed Reflux (Colorimetric) (Standard Methods, 1992) . The Open Reflux method is based on the prùiciple that a boiiing mixture of chromic and sulfunc acids oxidizes most types of organic material. The sample is added to the mixture with a
known excess of potassium dichromate (K,CrO,). Mer reaction, the remaining amount
of K2Cr20, is measured by titration with ferrous ammonium sulfate and the oxidizable
organic materiai is calculated in terms of oxygen equîvalent. For the Closed Reflux
(titrimetric) method, a closed system is used to dow longer contact the with the
oxidant- Fuially, for the Closed Reflux (colorimetric) method, the vessels used are seded
glas ampoules or capped culture tubes. The amount of oxygen consmned is measmed
againçt standards at 600 nm using a spectrophotometer(Standard Methods, 1992).
2.2.2.2 Biochemical oarygen demand (BOD)
Biochemical oxygen demand (BOD) is defined as the quantity of oxygen required by bacteria while stabilizing decomposable organic matter under aerobic conditions, Le. organic matend is used as food by the bacteria Energy is derived fiom oxidation reactions, producing carbon dioxïde, water and ammonia The BOD test is used to determine how polluted a domestic or industrial waste is, in terms of the amount of oxygen it will require if it is discharged in a natural watercourse (Droste, 1997)-
The test consists in the measurement of oxygen consumed by living organisms
(bacteria) when they are oxidizing organic matter in a waste, as weil as oxygen used to oxidize inorganic materid such as suifides and ferrous iron. For the results to be rneaningful, samples have to be protected fiom air to ensure that no reareation occurs as oxygen is consumed. Since the maximum solubility of oxygen in water is around 9 mgK at 20 OC, strong wastes have to be diluted to maintain the oxygen concentration above
O methroughout the testing period A quantitative relationship exïsts between the oxygen needed to convert organic compounds inîo CO, H20and NH, (Sawyer et aL.
1994):
Biomass concentration and temperature are the main factors gove&g the rate of reaction, which is why the tests are usuaily conducted at a constant temperature of 20°C.
In theory, an Uifinite the is required to completely oxïdize the organic matter. However, for practical purposes, a 5-day incubation period is chosen during which a reasonably large percentage of the total BOD is exerted. The 5-day penod aiso minimizes interference nom oxidation of ammonia, usually observed after 10 days. For domestic and many industrial wastewaters, the BOD, represents 70-80 % of the total BOD. The reactions are usuaily of the fïrst order, i.e. the rate of reaction is proportional to the amount of organic matter remaining at any time in solution @oste, 1997).
A plot of the amount of organic matter oxidized in the is show in Figure 2.5 and the oxygen utilized in time is presented in Figure 2.6. For the fust ten days, as cm be seen in Figure 2.6, the curve for the oxidized organic rnatter and the oxygen utilized are similar- However, after ten days, the cuves Her if the nitrification is taken into account. This is due to aitrifyùig bactena (autotrophic) which oxidize noncarbonaceous matter for energy. In domestic wastewater, these are only present in srnaU numbers and reproduce quite slowly at 20 OC. Therefore, their population is usuaiiy not important enough before ten days to influence the oxygen utilization rate. The foiIowing equation cmbe used for the caIcuIation of BOD (poste, 1997):
Where:
BOD, : Biochemical oxygen demand after t days (mg/L) DOi : Initial dissolved oxygen concentration (mg/L) DO, : Final dissolved oxygen concentration (mg&) DO,, : hitial dissolved oxygen of the seed control (mg/L) DO, : Final dissoLved oxygen of the seed control (m*) vss : Volume of seed added to sample (mL) v, : Volume of seed in the seed control (mL) Y, : Volume of the bottle (mL) vs : Volume of sample added to the bottle (mL) DF : V&
For a Long time, the ultimate BOD and the theoreticai oxygen demand were thought to be equal. However, it was reaiized when studying the oxidation of glucose that the uItimate BOD was about 85 % of the theoretical value, implying that only a fiaction of the glucose was transfomed to carbon dioxide and water. This phenornenon is caused by a hction of the organic matter which is transformed to ceIi tissue and remains unoxidized until lysis occurs (living ceUs feeding on dead ceils). Eventually, living ceiis as weli as dead ceus will become food for higher organisms like protozoaos.
At the end, organic matter that is very resistant to Merbiological attack remah. It is called humus and represents the discrepancy between the total BOD and the theoretical oxygen demand (Droste, 1997). 2.2.2.3 Sofids
Solids refer to the suspended or dissolved materid in water and wastewater.
Usually, a hi& concentration of dissoIved solids diminishes the quality of the taste, which is why an upper huit of 500 mfi is recommended for drinking water. Soiids analyses are very important in a wastewater treatment plant, in order to control the physical and biological steps.
Different kinds of soIids can be measured m a sample. 'Total solids" (TS) are defked as the material lefi in a container once the IIquid phase has evaporated and the leftovers have been dried at a deked temperature. TS includes suspended solids (SS)
(which would be retained by a filter) as well as dissolved solids @S) (which would pass through the filter). The separation of dissolved solids fiom suspended solids depends on the type of filter (pore size, porosity, area, thickness) as well as the material deposited on the filter (physicd nature, particle size). The ignition of total, suspended or dissolved solids for a specinc period of the at a specific temperature represents the fied solids.
The substances lost during ignition are called volatile solids (Standard Methods, 1992).
2.2.2.4 Nitrogen
Nitrogen is present in many dinerent foms in water and wastewater. Nitrate
(NOi), nitrite (NO;), ammonia (MI3)and organic nitrogen (N) can be found and all of them are interconvertible. A functional definition of organic nitrogen is "organically bound nitrogen in the trinegative oxidation state" and it does not uiclude all of the organic nitrogen compounds. Total kjeldahl nitrogen (TKN) includes both organic nitmgen and ammonia The name cornes nom the technique used in their determination. Organic nitrogen includes a lot of mirent materials such as proteins, peptides, nucleic acids and urea, as weil as numerous synthetic organics. Typical concentrations Vary fimu a few hundred micrograms per Liter in naturai lakes to 20 mg/L or more in raw sewage. "Total oxidized nitrogen" corresponds to the sum of nitrate CNO;) and nitrite (NO;). Nitrate is usually found in trace quantities in surface waters but it ca.reach high concentrations in some groundwaters. Oniy a maximum of 10 meis allowed in drinking water because excessive amounts contribute to the disease known as methemoglobmemia m infants-
Nitrate is also an essential nutrient for a lot of photosynthetic autotrophs. Arnmonia is a natural component of surface water and it is also found in wastewaters. On the other hancl, it is not found in important concentrations in groundwaters, because it adsorbs to soi1 particles and it does not leach very easily. Ammonia concentrations encountered in water can Vary fiom 10 CIgn for surface water to 30 mafor some municipal wastewaters (Standard Methods, 1992).
2.3 TREATMENT OF LEACEIATES
Many different techniques are currently in use to treat lanW leachates. The majority of them are adaptations of wastewater treatment techniques and can be divided in two main categories: biological treatments and physical / chernical treatments. Table
22 presents the most commonly used treatment methods with associated advantages and disadvantages and the fouowing sections describe different techniques in more details. Table 2.2: Advantages and disadvantages ofdifferent 1andii.UIeachate treatment techniqu& (references aven in Section 2.3)- Treatment Advantages Disadvantages techniques Activated shdge - Effkctke nmovai of Iow MW compounds- - Not efficient on compounds with MW - ReIatnrcIy cheap in campvison with other higfirr than 5000- biologicd processes- - Susceptibleto trpset - Chnonstrateci fiill-de performance in - Piutriens additions may be required. Ontario (Sarnia) -Sensitive to seasonal volume variations
- Long residence Cime produce a more higbly - Requires a clarifier for sloughed off soIi&- mindized sludge. - Oxygen transfer is a Iimiting factor for BOD - No blowers necessary- > 450 mg/i (Adetcaifand Eddy, 1992)- - Synthetic media allows for much Etigher - NaWdraft current of cold air through the loading rate. mter rnay cause it to fÏeeze,
- Remove SS which are not eady sectIed- - Render Mersenimg unne~essiuy~ - Non-susceptible to upset
- Removes orgaIücs which are di5cult to - Necessitate regeneration of carbon or it is Activated carbon degrade biologically- wasted with the sludge- adsorption - Can efficientiy be combbed with another biological process- - UsefuI for poIishing. - ReIariveIy m-e- Primary treatment - Good to reduce memi concentrations and - Large footprlntc colour. - Produce important amounts of sludge- arecipitation / - Removes compounds with MW higher than clarification) 5000-
Primary treatment - Assured mvalof al1 suspendeci soli&- - More expensive than conventiond - Smaller fwtprint than conventiond clarification- (precipitation / darXcation microûitration) - Usefiil if immediate start-up of mamient is required - Useh1 where voIume of Ieachate must be reduced for off-site disposal,
- Remove high concentration of inorpicand Necessitate treafed infIuent organic matter hmpretreated Ieachate, Membrane fouImg. - FiItratÎon range of les than 0.002 microns- - Smaller fmtprint than convenuonal treamt Rotating biological - Quite diable because of large amount of Requires a clarifier for sloughed off soli&. biomass- Potential for scahg caused by iron and contactors - Withstand hydraulic and organic surges. - Low power requirements and can operate at higher BOD / Phosphow ratio. - Dernonstrated full-scaIe performance in ûnm-O(MissiSsauga).
Recirculation and - VoIume reduced by evaporation- - Limited by climatic conditions- - Organics reduced by nattual biologiul - MetaIs and refiactory organics do not Land (spray) activity and sunlight. degrade. irrigation - Strong odour. - ~l~uidvolume mcfeases in landdiII. 2.3.1 Biological Treatment Techniques
2.3.1 .i Recircuiation
Recircdation is the simplest option for biological treatment It involves rehming collected leachate to a IancEU, which acts as an anaerobic reactor. When combined with spraying, the volume of leachate might be reduced by evaporation. However, buildup of excess water usually occurs evenhially and heavy metds and toxic organics may hinder biological activity.
Recircdation has been investigated by Diamadopoulos (1994) and Townsend et al. (1996). Diamadopoulos investigated the characterization and treatment of recirculation-stabilized sanitary landnll leachate. Leachate fiom recently deposited waste was recirculated through older areas of a landfiil. The stabilized leachate was characterized by 90 % COD reduction, 98 % BOD reduction and lower heavy metal concentrations than the fiesh leachate. Townsend et al- (1996) studied the effects of leachate recycling on landfil1 stabilization. Samples of leachate, biogas and landfilled wastes were coLiected and analyzed over a four year period. They observed that a greater degree of stabilization occurred in the leachate recycle area relative to the untreated area.
2.3.1.2 Actîvated sludge
The activated sludge process was developed in England in 1914 (Metcalf and
Eddy, 1991) and it is one of the most common wastewater treatment processes. Organic material in the waste is converted to microbid mas and carbon dioxide by microorganisms, A fiaction of the biomass is recycled fkom a secondary sedimentation tank sludge and retumed to an aeration tank to maintain a high biomass concentration. There are two main pathways for aerobic microbial degradation and they are shown in
Figure 2.7. The activated sludge process is schematued in Figure 2.8.
Activated sludge usually reqyhes addition of nutrients and might be affêcted by seasonal variations in the leachate composition. However, as demomtrated at a treattnent plant in Sarnia, Ontario (Lagowski and Poisson, 1990), use of activated sludge is an effective way of treating leachate, even when it contains high concentrations of refkactory organics.
2.3.1.3 Trïckliog filters (TF)
The trickling filter is the most commonly used attached-growth biological treatrnent process. The ktone was operated in England in 1893 (Metcalf and Eddy,
1991). The modem system is made of a highly permeable medium through which wastewater is trickled. This medium, made of rocks or plastic, is a support dacefor the growth of microorganisms. The rocks diameter varies Eom 25 to 100 mm and the depth of the bed, îÏom 0.9 rn to 2.5 m. 'The shape of the reactor is usually circular. A rotary distributor pours the wastewater fiom the top and an underdrain collects the treated effluent to bring it to a settling tank. The separation of suspended solids hmthe efnuent is not as important as in the activated sludge process, since the majority of the biomass is attached to the filter media, but a clarifier is usudy used to remove the sloughed off solids (Metcalf and Eddy, 1991). A scheme of the tricklùig filter is shown is Figure 2.9.
The grânular activated carbon-biological fluidized bed is a diEerent version of the trickhg filter, aIso ushg attached biomass. It has been found very efficient in reducing
COD, especialiy rekctory organics, and high concentrations of ammonia. Iwami et al. (1992) and Imai et al. (1993) used two fluidized bed in series. The fïrst bed was
anaerobic and the second one was aerobic. They were abIe to remove 60 % of the
dissolved organic carbon @OC) and 70% of the total nitrogen (T-N) consktently over
700 days. Horan et al. (1997) conducted similar studies with a Lime softening pre-
treatment to remove toxic and heavy metals that couId inhiiit biological growth. They
achieved 55% COD and 93% ammonia removal, It was demonstrated that a conventional
activated sludge process with shdar mania loading was conçiderably less efficient for both nitrification and COD reduction.
2.3.1.4 Rotating biological contactors (RBC)
A rotating biological contactor is made of a series of closely spaced circular disks mounted together on a shaft and approximately 40% submerged in the influent. The disks are usually made of Styrofoam or hi&-density plastic, their diameter varies fiom 2 to 3.2 m and they are rotated at about 1 or 2 rpm. The constant rotations allow a thin film of biornass to grow on the surface of the disks. The contact time with air maintains the system in aerobic conditions that allow the mîcroorganisms to degrade organic matter in the sewage (Metcalf and Eddy, 1991). A final clarifier is required for the sloughed biomass and other suspended solids. The advantages of such a system are high biomass concentration and Low power input required to supply oxygen. There is no need for recycle since the biomass is attached to the medium and maintenance is minimal. On the other hand, units have been prone to problems with shafts and disks and the reactors must be covered in cold climates proste, 1997). Rotating biological contactors have been studied for the biological treatment of landfiil leachate (Zenon Envkonmental Systems Inc., 1994)- The system included primary and final clarification and the solids generated were retumed to the landhll site.
The cost analysis for the treatment of a ditute leachate favored the use of revene-osmosis over that of RBC. A Mirent study was conducted to treat a high ammonia lancEU leachate in Taiwan. A pre-denitrifjrhg anaerobic filter, a RBC and a final clarifier were combined to remove more than 95 % ammonia-N, 92 % BOD and 49 % COD (
Henderson and Atwater, 1995)-
2.3.1.5 Stabiiization ponds
Stabilization ponds, also called lagoons or oxidation ponds. are the oldest form of wastewater treatment. Their ecosystem is quite complex since both aerobic and anaerobic processes occur, but the operation is simple and inexpensive because the influent is usually not pretreated and the flow through the pond is by gravity. The Mie required for treatment can Vary nom a few days in warm weather to six months in colder regions. The major expense in the construction of a stabilization pond being the land, they are often chosen as wastewater treatment technique in remote areas where the terrain is cheaper.
Their minimal operational demand and efficiency in warm temperature render them an excellent solution for treating sewage in develophg countries (Droste, 1997)-
Mechanical aeration can be provided when reduced treatment tirne are required.
Aerobic lagoons have been used in Great Britain to render landfïll leachate dischargeable to domestic sewers and proven to be an efficient treatment method. PhosphorÏc acid addition was required to ensure proper nutnent availabiIity and costs and attention were minimal (Robinson and Grantham, 1988).
2.3.1.6 Wetlands
Wetlands are naturai wet ecosystems, at least intennittently flooded with water, and they cover 14% of the surface in Canada @reste, 1997). Vegetation in a wetland is very diversified and the most common species are: caW, reed, sedges, burnishes, &es and grasses (Mitsch and Gosselink, 1992; USEPA, 1988). For wastewater treatment, the most extensively used floating aquatic plants are water hyacinth and duckweed.
Wetlands are most commonly utilized for polishing of secondary effluents. They are designed to remove biochemical oxygen demand (BOD), suspended solids (SS), nutrients and heavy metals. Two différent types of systems can be designed: surface or subsurface flow. The fïrst one is similar to a naturai wetiand since a fiee water surface is rnaintained. Plants have to be able to survive in anoxic conditions for extended period of times since anaerobic conditions wiU often develop in the upper layer of the water covered soil. For the second one, water flows through a permeable medium supporting vegetation. It usually offers a better treatment than the surface flow systern and it prevents mosquito problems.
Constructed wetlands have been investigated for the treatment of leachate by
Martin and Johnson (1999, Martin and Moshiri (1994), Maehlum (1995), Cossu et aL
(1997) and Grove and Silberman (1995). This relatively new application seems very promising, even if more data are necessary to confirm its efficiency, especialiy under seasonal variations of the Ieachate characteristics and temperature. 2.3.1.7 Sequencing batch reacton (SBR)
The sequencing batch reactor process is an activated sludge process, but is designed to operate dernon-steady state conditions. It operates in a true batch mode, providing for flow eQualization and blending and reducing operator ski11 and attention requirements (Nomoss, 1992). There are usually six cycles to complete a true batch: anoxic fÏU, aerated iïll, reaction, settling, decantation and waste sludge.
Sequencing batch reactors (SBR) have been studied by many scientists ail over the world (Timur and Ozturk, 1997; Robinson et al-,2997; Norcross, 1992; Hosomi et aL,
1989; Diamadopouios et aZJ997). In the United Kingdom for example, many full-scale plants are currently operational, sometimes combined with reed bed treatment systems to provide polishing of the efnuent. The instdations require a large surface area, but the
SBR is efficient enough for the effluent to be discharged to high quality surface watercourses (Robinson et al., 1997)- Hosomi et al. (1989) have studied the SBR for the removal of nitrogen and rehctory organic compounds. Methanol was used as an hydrogen donor. Nitrogen removai of 95 % and COD removal of 50 % were achieved.
Timur and Ozturk (1997) were working with anaerobic SBR at mesophilic conditions.
2.3.2 PhysicaI / Chetnical Treatment Techniques
2.3.2.1 Filtration
There are man-- different types of filtration in use for the separation of undesirable substances nom a Liquid. Among these are microfiltration (MT), ultrafiltration (UF) and hyperfiltration (HF) or reverse osmosis (RO). What distinguishes them is the nature of the membrane and the application of hydraulic pressure to speed up the transport procases (Cheryatl, 1986). Table 2.3 shows which components can be separated by
mIcrofiItration, ultrafiltration and reverse osmosis,
Table 2.3: Examples of components separated by MF, UF and RF/RO processes. [Cheryan, 1986.1 SIZE EXAMPLE MEMBRANE PROCESS 100 pm Pokn Microfiltration
O. 1 p.m (1 O00 A) DNk -es7 Microfiltration
The microfiltration process is designed to retain particles in the micron range, Le.
suspended particles with diameter nom 0.1 p to 10 p. Particles larger than 10 j.m
will be best handled by conventional filtration processes. As can be seen nom Table 2.3,
the smallest bactena can be separated fiom a solution by microfiltration and the driving
force is the pressure. Therefore, in a membrane bioreactor, separation of biomass f?om
the effluent stream cmbe achieve with a microfiltration membrane.
Ultrafiltration started at the beginning of the 1970s as a mean of concentrating macromolecules in dilute solution (McGregor, 1986). The membrane is ofien made of cellulose acetate (Moore, 1976) and it retains particles larger than 0.001 to 0.02 pm, Le. macromolecuies. The driving force is the pressure and it counterbalances the natural process called osmosis, which tends to reduce the clifference in concentration on each side of the membrane. The minimum pressure necessary is the osmotic pressure- Since the
particles dealt with are fàirly large, the osmotic pressures involved a& low in cornparison
with the ones encountered in reverse-osmosis.
Reverse-osmosis is the opposite of a natural process caed osmosis. It is usea to remove high concentrations of dissolved solids (Droste, 1997). The technique consists in
forcing water through a semi-permeable membrane and only the passage of pure water is allowed. Figure 2-10 shows the ciiffierence between osmosis and reverse-osmosis,
Pressures rauging f?om 35 to 100 atm rnight be required to overcome the high osmotic pressure of small solutes (Cheryan, 1986). The whole process depends on the preferential sorption of water on the surface of the membrane, usually made of porous ceildose acetate, as can be seen in Figure 2.1 1.
Cake formation, concentration poIarization, secondary or dynamic membranes, gel forxning solute, deposited Iayer and clogging are ail terms referrîng to membrane fouling. This phenornenon is a quite serious problem in rnicxofiItration, ultrafiltration and reverse osmosis.
Iiiitially, filtration was a dead-end process. The slurry could be filtered as a batch or a contuiuous mode, but the f3ow rate through the membrane was decreasing very rapidly with time. This was due to the accumulation of macromolecules and colloids at the surface of the membrane, clogging the pores. Different methods were investigated to minimize the flux reduction through the filtering media One of the most effective ones was cross-flow filtration, a process where the liquid flows parallel to the mter medium,
Figure 2.12 shows the Merence between dead-end and crossflow filtration. Tanny (1977) desmi the fouIing phenornenon: 'In almost every filtration process hvolving coiloids or mammolecules, a dynamic membrane will be obtaîned.
The only question is how to attempt to control and optimize the system. There are, in fact, vVtually always colloids in liquids in sufncient quantity to forrn a secondary membrane.''
In order to reduce fouling, new techniques creating very high shear forces (hi@ velocity gradient close to the surface)), have been studied. The high shear prhciple can be applied using centrifiigal force. Another way to minimize membrane fouling is by trying to control the resistance of the filter cake, which can be very high when fine particles are filtered. This can be done by altering the particle size distniution or the state of aggregation of those same particles. In order to alter the particle size distribution, it is possible to add another soiid in solution, called a Eilter aid (Orr, 1977). On the other hand, the alteration of the state of aggregation of the particles cm be achieved by coagulation and flocculation. The particles are forced to form into relatively large open flocs of irregular shape and consequently, the filter cake permeability is much increased.
Coagulation / floccdation is described in more details in section 2.3.2.3.
Dinerent types of filters and membranes have been studied for the treatment of landfill leachate. Zenon Environmental Systems Inc. (Burlington, Ontario) has conducted studies for the Ontario Ministry of Environment to assess the application of reverse- osmosis technology for the treatment of lmdfill leachate as weil as different pretreatment options such as precipitation and microfiltration. Zenon has also developed the
~eno~ern~~and the ZeeweedM processes which have been applied to both domestic wastewater in PoweI Rfver, BC @ïU, 1998) and iandnll leachate in Milton, Ontario,
successfûlly.
2.3.2.2 Activated carbon adsorption
In wastewater secondary treatment like activated sludge, the totality of the organic
compounds is not oxidized, which is why the effluent often needs to be polished. It is
somettixnes passed over a bed of activated charcoaI to remove the undesired substances
(dissolved or in colloidal suspension). The suface area of the charcoal is so large that it
has the capacity to adsorb a wide variety of molecules. Chernical reactions and
precipitation also occur on the carbon sudace. The efficiency of activated carbon has been investigated for the removal of COD, colloids, particulates, taste, odour and residual
chlorine proste, 1997).
Sometimes, a process called PACT (Powdered Activated Carbon Treaûnent) is used and it involves the continuous addition of PAC to the activated siudge bioreactor to
adsorb toxic organics (Sayles and Suidan, 1993). The PACT was deveIoped and patented by engineers at DuPont (WEF and ASCE, 1998). It allows to operate the treatment facilities at higher influent flowrate and help stabilizing the process to shock loads of
BOD and toxic organics. After the activated sludge tank, the PAC and adsorbed substances settle in the clanfier with the sludge. The sludge carbon mixture can be incinerated (1225 K) to destroy the sorbed organics and to regenerate the medium or it can be treated by anaerobic digestion (Levin and Gealt, 1993). In the latter, many of the sorbed organics are destroyed by methanogenic mîcrobial activity and the carbon is disposed of with the digested sludge. Strong acids or bases also regenerate PAC (Droste, 1997). Concentrations of 20-200 mg& of carbon are udyutilized in the PACT process (Metcalf and Eddy, 1991). The medium is also used to remove odor and taste fkom drinking water, especialîy chlorine.
The PACT process was investigated for the treatment of lanaIeachate by Lebel et ai. (1989) and compared with the conventionai activated sludge process. The sanitary
1ancifil.l used in this study accepted municipal and hazardous wastes, both liquids and soli&. Leachate, gas condensate and contaminated groundwater were ali treated by the 1 process. The study concluded that the PACT process was more suitable for the treatment of that specific leachate because it produced a higher quaiity effluent and maintained a very stable operation. Activated carbon cm also be used as a polishing step after biological treatment Morawe et aL, 1995).
2.3.2.3 Coagulation / flocculation
From the dennition of La mer and Healy (1966), coagulation and flocculation are quite different even ifboth processes can be induced by the same reagent. Coagulation is the consequence of a reduction in the zeta potential of a particle suspended in an electrolyte. This is accomplished by a modification of the nature and the concentration of the ions present in solutions. Flocculation is the process involved when particles are caused to aggregate. However, those two words take a Merent meaning in water and wastewater treatment. Coagulation is used to descnbe the addition of reagents to the water in order to induce the reaction and fiocculation is the subsequent slow agitation to allow floc growth (On, 1977). Zn the coagulation / floccdation process, used in both water and wastewater treatrnent, the particles are coated with a chemicdy sticky layer and it allows them to settie rapidly (Droste, 1997). Naturally occurring compounds can be used to obtain coagulation, as well as synthetic polymers. Among the namal compounds, the most commonly used are AI,(S04), and F~((s0~)~and they are usudy cheaper than the synthetic ones. These latter are very effective coagulants and the flocs they produce is not as voluminous and geIatinous as that of their inorganic counterparts (Droste, 1997)-
They are separated in three main categories: cationic, anionic and nonionic.
Polyethylenimine is an example of cationic polymer, with molar masses less than one million. Their chains have amine, imine or quatemay ammonium groups producing the positive charge. Figure 2.13 gives typical formulas of coagulant polymers (Droste,
1997). The effectiveness of coagulants as well as required doses for a specinc wastewater are evaluated with jar testing machines.
Coagdation/floccuIation has been studied in order to remove coiloidal particles in landfill leachate (Ho et al., 1974; Welander and Hemysson, 1997). Some of the chernicals utilized were alun 4-(so4)3and femc chloride FeCl,. Welander and
Henrysson (1997) used FeCl, and obtained 52 % COD removal with 500 ppm of coagulant. Polyethylenimine has been studied in the past, mauily in biochemistry, and used for many diEerent purposes: filter aid (Preston et al., 1989), immobilizer for yeast and bactena (D'Souza, 1990), flocculant (Gill and Herrïngton, 1987), adsorbant (Alince,
1988), stabilizer (Gianfkeda et al., l989), surfactant (Feigenbaum, 1995) and permeant
(Yoon et al, 1995; Helander et al., 1997). Helander et al. (1997) studied the effects of
PEI on the permeability properties of the outer membrane of Gram-negative bacteria. Their target organisms were Eschmcliia coli, Psetidomonas amgrnosa and Salmmellea lyphimmkm and they observeci increased hydrophobic penneation of the outer membrane, The effect of PEI was close to that of EDTA but was found to be slowed down by millimolar concentrations of Mgch- In the wastewater field, Nunez et al.
(1999) studied the effects of a mixture of PEI and PACl CpolyaIiIminium chloride) on the coagdation~flocculationprocess of a slaughterhouse wastewater treatment. Milstein et al. (199 1) studied the effécts of a mixture of PEI and modified starches to precipitate the bu& of organic matter from spent bleaching effluent. They obtahed 75 % reduction in adsorbable organic chlorine (AOX), 59 % in COD and 80 % in color.
2.3.2.4 Ozonation
Ozone (O3)is a very powemù oxïdizing agent and biocide. It has been used for drinking water treatment since 1906 in Nice, France (Singer, 1990). Nowadays, more than 2000 water treatment plants in Europe and approximately 90 in North America use ozone for disinfection and taste and odour control (Tatey1991).
Ozone is created by an electric discharge in a gas that containç oxygen or ultraviolet irradiation of the same gas at wavelengths lower than 200 m. The rate of ozone production is dependant on the oxygen concentration and the amount of impurities contained in the gas. Equation 2.3 details the formation of ozone proste, 1997).
30, -20, (2-3)
Ozone reacts with the majority of organics and it destroys most of halogenated byproducts formed by subsequent chlorination. However, some of ozonation byproducts are of signincance for human health, among which are organic peroxides and unsatmated aldehydes. More readily biodegradabIe compormds are formed by partial oxidation of organic matter, which is why ozonation is sometimes used in the treatment of recalcitrant organic containhg wastes. Ozone is aIso effective in oxidizing inorganic compounds and removing Werent tastes and odour fiom chlorhated, coagdated or sand Htered water.
One possible way to improve the efficiency of ozonation to oxidize humic acids is to combine the treatment with ultraviolet irradiation,
Ozone has been studied for the treatment of Iandfill Ieachate by Beaman et al,
(1997) and Fettig et al. (1996). Fettig et al. (1996) investigated the adsorption behaviour of a leachate organic components with and without preoxÏdation by different quantitïes of ozone. It resulted that the fiactions of non-adsorbable or weakly adsorbable species increased after preoxidation and about 40 % of the remaining organics were biodegradable. Consequently, ozonation decreased the carbon's potential for adsorption and increased the biotreatability of the landf?il leachate. Beaman et al (1997) conducted similar studies on whether ozone treatment can increase the biodegradability of a landfill leachate. They used bench-scale landfill lysimeters and recirculated ozonated leachate.
They observed that increased ozone dosage produced higher BOD, / COD ratios and improved COD reductions. Laachat. Iwo1 in luidfiil Luchare oolt.diorr ryr1.m W8t.r P utnbk
Potonti~mr~c ------d surfam in rquifor
Domw.rd tkw Niturai iquitird from kndfill
* C ------_ ------*------.-----J----*--
Figure 2.1: Barrier design involving a leachate collection system, a natural clayey deposit and downward advective-diflbsivetransport. bweet al., 19971 Upwud flaw from .quifor Nituml aquitird to luidfill 1
Figure 2.2: Barrier design involving a leachate collection system, a natural clayey deposit, upward advection and downward difision - a hydraulic trap. [Rowe et al., 19971 (b) Secondary leachate Natuml aquitard coîktion system
Figure 2.3: A compacted clayey primary liner used in conjmction with an engineered hydraulic control layer and hydraulic trap to minimize contaminant impact together with a composite secondary liner (geomembrane and clayey liner) used to minimize volume of fldd needed to maintain the hydraulic trap. By pumping the hydraulic control layer, this can also be used as a secondary leachate collection system. mowe et al, 19971 Jan Feb March ApriI May Iune Suly August Sept Ocr Nov Der: Months of the year
Figure 2.4: London W12A IandfiIl leachate volume during 1996. Figure 2.5: Changes in organic matter during bio Iogical oxidation waters under aerobic conditions. [S awyer, 1992 .] (0) 4 value Curve for CO~~~~QCCOUSdemand Ut 20°C y=~(l-IO-&+)
Time, days
Figure 2.6: (a) Normal BOD curve for oxidation of organic matter. @) Influence of nitrification. [Sawyer, 1992.1 Oxidation A Approximately + 0, + CO, + H,O + energy 40 % ofC
Organic matter Eneray
V
+ N, P and trace elements New cells
Synthesis
Figure 2.7: Pathways for aerobic microbial degradation of organic wastes. [Redrawn fiom Manahan, 1984.1 Aeration tank Settling tank Emuent hm Emuent hm prÎmary marnent secondary ueaûnent
- Waste sludge
Figure 2.8: Activated sludge process for secondary treatment of wastewater. Rotating influent distributor t
Underdrain .L Effluent to clder
Figure 2.9: Schema of a tnckling filter Osmosis
Dimtïoir of w8t.r fIow through somi-potmmablm mombrana
Reverse osmosis
Figure 2.10: Schema of osmosis and reverse osmosis phenomena. [pedrawn fiom Cheryan, 1986.1 H20 M+ M1' X- x- x- Hz0 x- X- Water contaminated EL0 Eh0 with saIts Hz0 Mt M+ M+ X- ET20 x- H20 M* X- M+ mo Adsorbed water
Purïfiëd water purifiGd water
Figure 2.1 1: Solute removal from water by reverse-osmosis. [Redrawn f?om Manahan, 1984.1 Dead-end filtration
suspeniion Crossflow filtration
filtrate
Figure 2.12: Dead-end filtration with cake formation and crossflow cake-free filtration. [Redrawn fÏom Murkes, 1988.1 Pol y ethy lenimines Polyvinylamiaes Cationic
Figure 2.13: Typical formulas of coagulant polymers. [Droste, 1997. After Degrémont Innlco, 1979.1 3.1 FEED CHARACTERIZATION
For the first set of experiments, a synthetic leachate solution was used. This
synthetic solution was chosen because it was well characterized. The composition of the
synthetic Ieachate was based on three dineent sources: (0 Ieachate used in the
Department of Civil and Environmental Engineering, UWO (Personal communication with L. bpovic), (ii) analysis of leachate samples collected at the London W12A
1andfi.U during the swlzmer of 1998 and (iü) series of data acquired fkom the City of
London on leachate composition nom 1977 to 1996. The synthetic leachate composition is presented in Table 3.1 and that of the trace metal solution (TMS) is given in Table 3.2.
Table 3.1 : Synthetic leachate composition. Constituents Concentration ( IL) Acetic acid 3.5 mL Propionic acid 2.5 mL Butyric acid 0.5 rnL NaHCO, 1.506 g CaClz or 1.441 g CaC12 x 2H20 1.674 g MgC12 x 6 H,O 1.557 g MgSO, or 0.078 g MgSO, x 7 H,O 0.16 g NH,HCO, 1.22 g CO(NH3, : urea 0.348 g NaNQ 0.025 g KzC03 0.162 g KHCO, 0.156 g K,HPO, 0.015 g TMS 0.5 g NaOH to pH 7 Table 3.2: Trace metals solution (TMS) composition- Constituents Concentration (mg/L) FeSO, x 7 H,O 2000 HP03 50 ZnSO, x 7 H,O 50 CuS04 x 5 H20 40 MnSO, x 4 H20 500 W4)6M07O24 50 A(so4)3x 16 H20 30 CoS04x 7 H20 150 NiSO, x 6 40 500 96% concentrated &SO, 1mL
The theoretical chernical oxygen demand (COD) of the synthetic leachate was found to be 7745 ppm and was calculated based on the folIowing assumed stoichiometric reactions:
Acetic acid: CH,COOH + 2 O = 2 H,O + 2 COz (1)
Propionic acid: CH,CH2COOH + 3-5 O = 3 H20+ 3 CO2 (2)
Butyric acid: CH,CH,CH2COOH + 5 O2 = 4 H,O + 4 CO2 (3) Details of the calculations are given in Appendix A-1.
Appropriate addition of phosphoric acid (H,POJ, powdered activated carbon
(PAC), polyethylenimine (PEI) and BOD ala an ce^^ is descnbed as foilows.
It is hown that the phosphorus content of landnil leachate is too low for adequate growth of microorganisms. The theoretical optimum ratio for the influent degradable matter which applies to an activated sludge process, as detailed by Droste (1997), is as follows:
(on a mass basis) In the present study, the nitrogen sources were WHCO, ,CO(NQ and Nam, which corresponds to 382 ppm of N. The only phosphorus source was K,-HPO, available at a concentration of 3 ppm. Thus the ratio of available nutnents on a mass basis was: COD:N:P=7745:382:3=100:4.9:0.04
Nitrogen requirements were satisfied, but not those for phosphorus. This deficiency was compensated by the addition of 0.44 xnL of H3P04per L of synthetic leachate- A synthetic leachate sample containhg phosphorus was also sent to a commercial laboratory for independent BOD, analysis and the result was found to be 4450 ppm. Therefore, the
BOD,/COD ratio in the present study was 0.57. PAC was added as per the guidelines in
Metcalf and Eddy (1991) at concentrations varying nom 50 to 200 ppm.
Polyethylenimine was added to the bioreactors at concentrations varying fkom 5 to 30 ppm and, fïnaIly, BOD t al an ce^ was added at a concentration of 5 ppm, in accordance with the recommendation of the manufacturer.
For the second set of experiments, reai leachate was obtained fiom London landfill W12A and treated in batch bioreactors. The leachate was collected on two different days: April 2gmand May 17" 1999. The characteristics of the leachate on those two specific days are shown in Table 3.3. The data for the composition of the landfill leachate throughout the year 1996 is given in Appendix A-2.
The initial content of the bioreactors was 90% of synthetic or natural leachate and
10% of inoculum. The inoculum represents the initial microbial population in the bioreactors and it Uiitiafly came fiom a sample of natural landfil1 leachate that was collected at W12A in August 1998. The muted population of microorganisms in that sample was then fed with synthetic leachate. Table 3.3: Characteristics of W12A Iandfill leachate, London, Ontario. Parameters 29 Aprü 1999 17 May 1999 PH 7.54 8-0 Absorbance 0.683 0.486 TSS WL) 0.38 0.48 COD (PP@ 2975 4260 BOD5 (PP@ 1585 2290 BODICOD 0.53 0.54 NH, @Pm) 508 835 NO3 @Pm) 0.1 0.15 @P@ 642 930 P (ppm) - 5.56
3.2 BATCH BIOREACTORS EXPERLMENTAL SET-UP
A schema of the batch bioreactor used in the current study is shown in Figure 3.1
and a picture, in Figure 3.2. A 3-L working volume, stirred, air sparged conical flask was
used. The ody additions to the bioreactor were air and dphuric acid (1 M) for pH
control. The air flow rate was d3icient to maintain the solution saturated with oxygen
and the sulphuric acid was added on a daily basis to keep the pH at 7. A magnetic stker
was used to ensure homogeneity of the solution and proper distribution of the oxygen
throughout the reactor. The air coming out of the reactor went through a water condenser to prevent water loss, 3.3 CONTINUOUS STIRRED TANK REACTOR (CSTR) EXPERIMENTAL SET-UP
The continuous stirred tank reactor used ih the cunent study is show in Figures
3.3,3 -4 and 3-5. The working volume of the reactor was 20 L and it had three impeliers
of four blades each, as well as four bafnes to ensure homogeneity of the solution.
Aeration fiowrate was maintained at approximately 20 Umin and addition of sulfure acid
was required daily to maintain the pH around 7. Two peristaltic mini-pumps with
variable flowrate (VWR) were used for the innuent and the effluent The synthetic
leachate fed to the CSTR was mked continuously to ensure proper distribution of
nutrients and the hydraullc retention time of the solution was varied fiom 5 to 15 days.
3.4 ANALYTICAL METHODS
3.4.1 pH
The pH was measured using a Fisher ScientSc Accumet Mode1 25 pH meter,
ROSS Sure-Flow pH Electrode and Orion b@er solutions. Sodium hydroxide and sulphuric acid solutions (1M) were used to adjust the pH of the synthetic and natural leachates as weU as the soIutions in the bioreactors du~gthe reactions.
3.4.2 Soiids
The solids were evaluated by two different methods: the absorbance of culture at
600 nm with the HACH DR12000 Spectrophotometer and solids concentration (TSS and
VSS). The absorbance of a sample measures the quantity of light absorbed by a sample and consequentiy, it is related to the amount of solids in the sample. The higher is the absorbance, the higher is the quantity of soliàs in suspension in the sample. It is the converse of transmittance moste, 1997). Total suspended solids (TSS) was measured
using two Werent types of fiiters: Geiman type IVE glass mer filter (Standard Methods,
1992) and Gelman type 45 Versapor supported membrane atm. The sample size used
was 5 mL, which led to a dried residue of more than 2.5 mg (Standard Methods, 1992).
Volatile suspended solids (VSS) was measirred on the residue fiom the TSS analysis
(glass fiber filters) ignited at 550 OC, as per Standard Methods (1992).
3.4.3 Chernicd Oxygen Demand (COD)
In the present study, COD was measured on the Htered samples with the HACH
D/R 2000 Spectrophotometer. The method used was the colorimetrïc determination of
COD at high range (O to 1500 ma)and high range plus (O to 15 000 mg/L). The
readings were done at a wavelength of 620 nm. The oxidizing agent used consisted of
chromic acid, mercuric sulphate, silver sulphate, sulphuric acid and demuieralized water.
The total reaction time required for the oxidation was 2 hours.
3.4.4 Biological Oxygen Demand (BOD)and Total Phosphorus
BOD and total phosphorus were analyzed at a commercial laboratory (Philip
Andytical Senices Corporation, London) using test procedures outlined in Standard
Methods, 19' edition. Total phosphorus was evduated with a Skalar Segrnented
Continuous Flow Analyzer by ascorbic acid / antimonyI-molybdate colourimetry. 3.4.5 Ammonia (NH3-N)
The concentration of ammonia as nitrogen in a sample was also measured with the
HACH D/R 2000 Spectrophotometer. The salicyate method was used for concentrations
between O and 0.50 me. The readings were done at a wavelength of 655 nm. The reagents were ammonia cyanurate and ammonia salicyate powder pillows. The samples were diluted by a factor of 500 or 1000 to bring the analytical concentrations within the range of the spectrophotometer- The reaction time for the ammonia salicyate was 3 minutes and that for the ammonia cyanunte was 15 minutes-
3.4.6 Nitrate (NO;-N) and Nitrite (NOL-N)
The concentration of nitrate and nitrite as nitrogen in a sample was also measured with the HACH DR 2000 Spectrophotometer. The cadmium reduction method was used for concentrations between O and 0.40 ma. The readings were done at a wavelength of
507 nm and the reagents were Nitriver 3 Nitrite Reagent and Nitraver 6 Nitrate Reagent
Powder PïlIows. The samples were diluted by a factor of 10 or 100 to bring the andytical concentrations within the range of the instrument. The reaction heswere 3 minutes for the Nitraver 6, foilowed by a 2-minute settling period and 10 minutes for the Nitriver 3. FZask capacily: 4 L Content volume: 3 L
RPM
Figure 3.1 : Schema of the batch bioreactor experimental set-up. Figure 3.2: Batch bioreactors experimentai setup. Lefi: test with addition of PAC;nght: test with addition of BOD ala an ce? Air 1I I 7-
Synfhetic leachate Wate container
Figure 3.3: Continuous stirred tank bioreactor set-up. Content volume: 20 L; number of baffles: 4; number of blades per impeiier: 4; P: peristaltic mini-pump. Figure 3.4: Continuous stimd tank reactor experimentd set-up (CSTR). Figure 3.5: Close-up photograph ofthe biomass pwthon the inside w aU of reac BATCHSTUDIES: RESULTS AND DISCUSSION
4.1 BATCH TREATMENT OF SYNTHETIC LEACHGTE
Batch studies were conducted on synthetic leachate and the following parameters were evaluated once a day for the duration of the tests: absorbance of cuIture, total suspended solids (TSS) and chernical oxygen demand (COD). These resuits are shown in
Figures 4.1 and 4.2.
Figure 4.1 shows the average values obtained for absorbance, TSS and COD.
Overall, biodegradation processes were fdyslow. In 400 h of treatment, the COD was reduced to ody 20 % of its initial value. Figure 4.1 aiso shows that the absorbance curve at 600 nm follows closely that of the total suspended solids- Since absorbance required less time to measure than TSS, absorbance could be used as an approximate indicator of
TSS. Figure 4.2 shows the COD results obtained for individual batch tests. It can be observed that even when the initial COD was varied (5605 and 8125 ppm), the rates of
COD utilization were fond to be similax (22 and 15 ppm/h). Calcdation details are presented in Section 4.2.5.1 and Appendur B.
4.2 BATCH TREATMENT OF SYNTHETIC LEACHATE WI'ïEI ADDITIVES
4.2.1 Addition of Phosphoric Acid (P)
Since a typical sludge formula is close to C,H,N02P,, (Hoover and Porges
1952), the microorganisms require the solution they are in to contain certain amounts of each of those elements to grow and reproduce. It was noted fiom Tables 3.1 and 3.2 that the synthetic landfiu leachate used was deficient in phosphorus. This could be one of the reasons why the COD reduction rate was low k the tests discussed in the previous section. Consequently, in order to increase biodegradability, the synthetic leachate was supplemented by 0.44 mUL (744 mgII,) of phosphoric acid and three batch tests were conducted. The resuIts are presented in Figures 4.3 and 4.4.
Figure 4.3 shows that the absorbance reached a maximum of 1.4 after approlcimately 90 h (in cornparison with 200 b without additives in Figure 4.1) and then diminished considerably- Ali curves displayed similar trend and in las than 250 h, the biomass went through lag phase, exponential growth (or log growth) (Droste, 1997), stationary and death (or decay) phases. These observations are consistent with typical microorganisms growth curves (Blanch and Clark 1997). Consequently, the solids reduction observed after 100 h is due to lysis (endogenous decay). Figure 4.4 shows the
COD results obtained for the same three batches- The COD was reduced to 20 % of its initial value after approximately 155 h, reaching a value as Iow as 320 ppm in one of the batches, which is noticeably faster than the treatment without phosphorus (P), where it took nearly 400 h to reach 20 % of initial COD (Figure 4.1). Accordingly, the COD utilization was increased fiom 18 ppm/h to 55 ppmh with phosphonis addition
(discussion on COD utilization rates in Section 4.2.5-1 and Appendk B).
Figures 4.5 and 4.6 present the average absorbance and COD with and without addition of phosphoric acid, clearly illustrating the hprovement in the treatment. In
Figure 4.5, the cuve for treabnent with phosphorus addition is representative of that of a
pica al batch growth and iu Figure 4.6, typical fkst order klnetics for substrate disappearance is observed after the initial lag phase. In both Figures, the batches containing no phosphorus were slower than those with phosphonis and probably hdered because of a lack of nutrients.
4.2.2 Addition of Powdered Activated Carbon (PAC)
Powdered activated carbon @?AC)was next added to the batch bioreactors at concentrations of 50, LOO, 150 and 200 pprn to assess how it wouid affect the efficiency of the treatment. One senes of studiw was conducted with synthetic Ieachate containing no phosphorus and two with phosphoric acid added.
For the batches containhg no phosphorus, the absorbance varied fkom 1.0 to 1.4 and the growth peak was reached after 150 h. The COD utilization rates were 18,2424 and 32 ppmh for PAC concentrations of 0, 50, 100 and 150 pprn respectively (discussion on COD utilization rates in Section 4.2.5.1 and Appendix B). It was observed that an increase in PAC concentrations produced higher COD utilization rates, but not as high as when phosphorus was added to the reactors. AU graphs are shown in Appenduc C.
The average absorbance fkom the two series with phosphorus is presented in
Figure 4.7. The highest absorbance (1 -4) was reached with PAC concentrations of 50, 100 and 150 pprn after approximately 140 h and the lowest with a PAC concentration of 200 pprn after 170 h. The average COD obtained nom the two series with phosphorus are presented in Figure 4.8. AU cunres displayed first order decay after initial lag phase. The
COD utilization rates for PAC concentrations of O, 50, 100, 150 and 200 pprn were 52,
54, 65, 79 and 53 ppmh respectively (discussion on COD utilization rates in Section
4.2.5.1). The batch containing O¶ 50 and 200 pprn of PAC produced the slowest reduction in COD, while the one containhg 150 pprn gave the fastest reduction in COD. PAC concentrations of 100 and 150 ppm produced higher COD utilkation rates than phosphorus alone (55 ppm/h).
To ensure that the increased COD reduction was not due to adsorption onto carbon sites in the PAC, a separate adsorption test (isotherm) was performed. The leachate was iaitially autoclaved at 120 OC for 20 minutes to minimize the inauence of biologicd reactions. The 3-L reactors were stirred for 24 hours which was the the required to obtain stable COD readings. Powdered activated carbon @AC) concentrations were varied fkom O to 100 g/L. The measured residual COD is presented in Figure 4.9. Adsorption began to afFect residuai COD in solution at a PAC concentration of 5 g/L and higher. Concentration of PAC Iower than 5 glL were also investigated (0.05, 0.15,0.30 and 1.0 &). The results showed that the amount of COD removed was very small (c 200 ppm) and within the error of the spectrophotometer readùigs. Figure 4.9 shows that approximately 2000 ppm of COD was removed with 100 g/L of PAC. In cornparison, the highest concentration of PAC used in the bioreactors for the treatment was only 0.2 g/L. It can therefore be concluded that at this concentration, adsorption of organics was not high enough to account for the better treatment observed with PAC addition. It is believed that depending on the concentration it is added at in a bioreactor, PAC can have positive or negative effects on the biodegradation of the organic cornpounds. These effects are dlscussed below.
A lot of research has been done concerning the use of activated carbon in the treatment of water and wastewater. The PACT process, briefly discussed in the iiterature review, is used relatively ftequentiy nowadays to enhance the performance of activated sludge and removal of organics- The process has demonstrateci beneficiai properties,
including (WEF and ASCE, 1998) (Cheremisinoff and Cheremisi~off~1993):
- Suppressed foaming in aerators; - Improved hydraulic capacity; - Impmved solids-settling characteristics; - Increased dewaterability of waste sludge; - Ability of PAC to adsorb biorehctory materials and toxic compounds to improve effluent quality and lessen shock Ioaduig effects; - Improved nitrification rates of activated sludge systems receiving industriai wastewater; - Reduction in odor, foaming and bullcing problems; and - Improved color and BOD, removaL
The main disadvantage of the PACT process is the need for regeneration or purchase of virgin PAC. Most successfûl applications have occurred in industries with cases without regeneration. Figure 4.10 and ASCE, 1998) shows that an augmentation in PAC concentration addition results in nIst order decay of the majority of the residual contafninants. It shows that 200 ppm of PAC reduce the effluent TOC by 40 ppm. This result strengthens the observations made fkom Figure 4.9 regarding the range of COD removal at PAC concentration of 200 ppm. No observations were made on the efEects of
PAC concentrations on oxygen transfer rates. The granda- activated carbon-biological fluidized bed was also used efficiently to remove refiactory organics nom lanâfiii leachate, as detailed in Section 2.3.1.3. However, since the system was operatcd under anaerobic conditions, PAC concentrations did not influence the quality of oxygen tram fer. From this information it is believed that in the current çtudy, the treatment's improvement at PAC concentrations lower tha. 200 ppm codd be related to the attachment of the micro~rg~smson the carbon particles, in suspension or on the inner daceof the bioreactor. This phenornenon would render the conditions more propitious for growth (Droste, 1997) and may increase microbid cell density. Also, one of the reasons why a PAC concentration of 200 ppm resulted in poorer COD utilization could be that it affected the oxygen transfer fkom the bulk of the soIution to the biomass. From
Figures 4.9 and 4-10, it is known that higher concentrations of PAC are responsïbIe for lower final contaminant concentrations. However, in an aerobic system, efficiency of the biomass plays a key role in the quality of the effluent and if not properly aerated, diminution of biodegradation rates rnay occur,
4.2.3 Addition of Polyethylenimine (PEI)
Polyethylenimine (PEI) was added to the batch bioreactors at concentrations of 5,
15,20 and 30 ppm. The treatment of synthetic leachate without phosphorus was studied in one batch test containing 15 pprn of PEI, whereas the treatment with phosphorus was studied in many different batch tests: one batch with 5 ppm, 3 batches with 15 ppm, 2 batches with 20 ppm and 1 batch with 30 ppm of PEI.
Absorbante, COD and ammonia (M&-N) concentrations were measured during the treatment of synthetic leachate without addition of phosphoric acid and with a PEI concentration of 15 ppm. It took approximately 200 h for the solids to reach a peak absorbance of 1.2, 190 h to reduce COD to 20 % of its original value and 200 h to reduce ammonia (NH3-N) to 20 % of its original value. The COD utilization rate was 3 1 ppa characterizing relatively slow biodegradation reactions. The COD utilization is faster with PEI than without additive at all, but denniteIy s10wer than with the addition of phosphonc acid AU graphs are shown in Appendix C.
The absorbance, COD and NH,-N resuIts obtained for mirent concentrations of
PEI and phosphonis contaking leachate are presented in Figures 4.11 to 4.13. The curves obtained with the addition of phosphonis only are also plotted in Figures 4.1 1 and
4.12 for cornparison. The highest absorbame (1.3) was obtained with addition of phosphonis only after 100 h and the lowest COD was produced with a PEI concentration of 5 ppm, while the lowest atnmonia concentration was attained with 15 and 20 ppm of
PEI. It took approximately 135 h for the COD to be reduced to 20 % of its initial value
(final COD were very similar, regardless of PEI concentration). Based on the calculated
COD utilization rates, the most effective treatment was found to involve 15 ppm of PEI, which reached an average of 75 ppdh and maximum of 90 ppd. PEI concentrations of
5,20 and 30 ppm resulted in COD utiIization rates of 56,66 and 55 ppmh (discussion on
COD utilization rates in Section 4.2.5.1 and Appendix B)- Addition of PEI seemed to improve the effectiveness of the treatment, on the basis of organic substances degradation, although it did not appear to have increased biomass growth.
These results seem to be in accordance with those obtained by Helander et al.
(1997). They observed that the addition of polyethylenimine permeabilized the outer membrane of three diEerent Gram-negative bacteria, consequently accelerating the rate of transfer of nutrients fiom the solution to the microorganisms. The results obtained in the curent study indicate that PEI did not have an effect on the biomass growth, but did influence the rate of utiIization of COD positively. It is believed that PEI influenced not only the target organisms in EIelander7s study, but ais0 the mixed culîure of
microorganisms utrlized in this research.
4.2.4 Addition of BOD ala an ce^
According to the manufacturer, BOD dan ce^^ shouid be used for: wastewater
colfkction, lift stations, sewer lines and holding tanks. Its features are that it controis
odours, degreases, reduces sludge deposit and cleans sudaces including sewer pipe walls
and wet waUs. It is desded as a product containing naturd daceactive agents that
improve ce11 waiI peafzeability, acceelerate the breakdown of biological materials and
reduce BOD levels. There was no data related to its use in the treatment of landfill
leachate,
BOD BalanceTMwas added to the batch bioreactors at a ked concentration of 5
ppm, in accordance with the manufacturer's recommendation. In ail, five batch tests
were conducted: four with addition of phosphoric acid to the synthetic leachate and one
without.
Absorbante, COD and ammonia (NH3) were measured for the synthetic leachate
with BOD al an ce^^ and without phosphorus addition- The absorbance increased until
250 h. It took approximately 190 h for the COD to be reduced to 20 % of its initial value,
resulting in a COD utilization rate of 3 1 ppdh. The ammonia concentration was reduced to less than 5 ppm after 250 h. These trends indicate a more efficient treatment than for the case with no additives at aU. However, the changes in absorbance, COD and ammonia were slower than in the treatment involving addition of phosphoric acid. AU
graphs are shown in Appendùc C. The resuits fiom the four batches obtained with the addition of BOD ala an ce^
and phosphoric acid are presenteâ in Figures 4.14 to 4J6, Maximum absorbance (1 -4)
occurred around the same time (about 80 h) in al1 four batches. COD also foilowed the
same trend in aii four batches and the fïrst order decay after initial lag phase ended der
approxhately 100 h. On average, it took 110 h for the COD to be reduced to 20 % of its
initial value. Individual COD utikation rates were calcdated to be 108, 104, 80 and 66
ppmh for batches 1 to 4 respectiveIy, with an average of90 ppa(discussion on COD
utilization rates in Section 42.5.1 and Appendix B). These rates are largely supenor to
that obtained with phosphorus only (55 ppmlh). As for the ammonia, the nrst order
decay ended &et approximately 100 h and the average final value was 27 ppm.
From the results obtained in the current research, it seems that BOD ala an ce^
did have an effect on ceil wdpermeability during the aerobic biological treatment of
synthetic lanW leachate. The rate of organica breakdown has been increased, as can be
concluded fiom the COD utilization rates.
4.2.5 Cornparison of Additives Effïciency
In order to compare the efficiency of ail additives studied in the current research, three d.erent analysis were conducted. The additives were compared regarding COD utilization rates, peak absorbance and logistic decay model. These cornparisons are presented in the foilowing sub-sections, 4.2.5.1 COD utilization rates
COD utilization rates were caiculated for each batch test (see Appendix B), averaged for each additive combinations and plotted in Figure 4.17. From this Figure, it cm be seen that the addition of increasîng concentrations of PAC done up to 150 ppm, improved the rate of degradation, but only to approximately 30 ppm/h, which roughly corresponded to the rates obtained with the addition of BOD ala an ce^^ and PEI done, without phosphorus. The combination of PAC with phosphorus was found to be a more efficient treatment option, the best one being a PAC concentration of 150 ppm plus phosphorus for which the COD utilization rate was 79 ppm of CODh. It is postuiated that the addition of PAC to the bioreactor facilitated the attachment of the biomass on the inside wall of the container and offied the biomass a support surface and growth while in suspension. These conditions would have been favorable to the microorganisms, which wodd explain why the biomass was more effective in reducing the COD. From
Figure 4.17, it wodd seem that a PAC concentration higher than 150 ppm may not be favorable. The COD utilizittion rate went down to 53 ppdh which was very similar to the 52 ppdh obtaïned in the bioreactor containing on& phosphorus, It wouid seem bat this higher concentration of PAC somehow slowed down the breakdown of organic matter- One explanation for this phenornenon could be limitations in oxygen transfer to the biomass film due to increased PAC concentrations.
The addition of 15 ppm of PEI in combination with phosphorus also yielded improved treatment. The average COD utilization rate obtained was 75 ppmh with the highest value being 90 ppd. As noted by Helander et al. (1997), polyethylenimine
(PEI) is a penneabilizer of the outer membrane of Gram-negative bactena, which could explain the hcreased rate of breakdown of organic matter. The nutrients transfer across
the ceU wdmay have been accekrated, Based on the results of the present experiments,
it would seem that PEI concentrations of 5,20 and 30 ppm would not be as efficient as 15
ppm in the biolo@caLtreatmmt of leachate.
The most efficient combination of additives was BOD BalanceTMat 5 ppm and
phosphorus. COD utilization rates as high as 108 ppdh were observed with the average
being 87 ppm.5. There is no published information on the nature of BOD ala an ce^, but
it is apparently a flocculant containhg nahiral surface active agents that tend to improve
cell wall permeability- From the results obtahed in this study, it wodd seem that BOD
Balancem has a positive infiuence on the biodegradation of synthetic leachate when
coupled with phosphonis. Higher concentrations of BOD Balancem were not tested.
4.2.5.2 Peak absorbance
When comparing the peak absorbance for each additive combination, it appears that other than phosphonis, the additives did not have a strong influence on solids concentration or ceU gcowth. The average absorbance peaks attained, for all additive combinations, are presented in Table 4.1. The fïrst column is a List of the Merent combinations studied, the second column show the redts obtained for the batches without phosphorus and the third column, the results obtained for the batches with phosphorus. From this Table, it cm be seen that the addition of phosphorus increased the peak absorbance, since the average for the batches without phosphonis is 88 % of that for those with phosphorus. The other additives did not seem to have a marked influence on the peak absorbante. From these results, it can be concluded that treatment efficiency
can not always be comlated with biomass concentrations
Table 4-1: Absorbance peaks reached with different additive combinations. Additive combinations No phosphorus Phosphoms No additive [PACI = 50 ppm [PAC] = 100 ppm [PAC] = 150 ppm CpAC] = 200 ppm Pn]=5ppm LpErJ = 15 ppm PET1 = 20 pprn CpElJ = 30 ppm POD ala an ce^] = 5 pprn Average 1-19 1-36
4.2.5.3 Monod kinetics and logistic decay
Different models have been used to represent the kinetics of biodegradation under
a number of assumptions: there exists a pure culture of single bacterial population, the culture is growiog and degrading a single and soluble organic compound and there are no barriers between the substrate and the cells (Alexander and Scow, 1989). When microorganisms are degrading a particular substrate, three possible situations may occur:
(i) the biomass is growing at the expense of that subshte and is using it as a carbon source, an energy source or as another nutrient required for growth, (ii) the biomass is growing at the expense of another nutrient but is metabolizing the particular substrate,
(iii) the biomass is not growing as it rnetaboiizes the chernical of concem (Alexander and
Scow, 1989). In the current research, the ktcase applied since the biomass was feeding on the VFAs of the synthetic leachate and growth was obsewed. Udy, if the concentration of carbon source is Iow, the pwth rate of microorganisrns will be Limited. However, as the carbon source increases, the growth rate also increases, up to a maximum value at very high substrate concentration (Monod,
1949). Equation 4.1 is illustrateci in Figure 4-18.
where: p : specinc growth rate of the mked population of microorganisms (h-') : maximum specinc growth rate @-') S : limiting substrate concentration (mg/') : substrate concentration at &2 representing the aflhity of the bacterium for the limiting substrate (the lower the value, the greater the afflnity) (6)
When the initial substrate concentration S, is far in excess of K, (Sm,the majority of the growth cycle occurs without being afkcted by the reduction in the carbon source. Consequently, a semi-log plot of ceil number vs time or substrate metabolized vs time gives a straight line. However, a semi-log plot of substrate remaining vs time does not give a shaight line, since the shape of the curve reflects logarithmk growth, as cmbe seen in Figure 4.19. At the beginning, very little substrate disappearance is showing because of the low biomass population. As the population doubles, rapid loss becomes evident and the last few doubling in the population are responsible for much of the substrate disappearance. The integral fom of the equation representing this curve is given in Equation 4.2 (Simkiris and Alexander, 1984):
S=S, +x0(1-ed) where:
S, : initia1 substrate concentration (me) X, : amount of substrate required to produce the initid population (ma)
When the initial substrate concentration is much below (So4Q, the kinetics of substrate disappearance are much different- The growth rate deches with the because of lack of substrate. This is called logistic growth and a typicai cuve can be seen in Figure 4-19. The integrid form of the equation is @en in Equation 4.3. The period dwhg which the majority of the growth occurs can be closely approximated by a straight line (Alexander and Scow, 1989).
where: k:HF,,IK,
In the curent research, only one initial concentration was studied, which is that representhg the London Wl2A lanâfill leachate. Thus, the relationship between the biomass growth rate and the substrate is not known. The initial substrate concentration being relatively high (theoretical COD of 7745 mg/L), one would have expected to see the substrate disappearance curve foilow logarithmic kinetics. However, the experimental data were found to foilow logistic kinetics much better. The data for the best additive combination (150 ppm of PAC, 15 ppm of PEI and 5 ppm of BOD
ala an ce^^) were fitted usuig the logistic model. Individual test cuves were averaged to obtain a representative curve for each additive. The generated curves were then compared with the curves obtained with the addition of phosphorus only. Figure 4.20 shows the COD reduction dtsobtained for 2 batches contauimg
phosphorus and 150 ppm of PAC. These data were averaged and plotted together with
the results obtamed for phosphorus only, as shown in Figure 4.21. The emx bars,
representing standard deviatims, overlap in the first section of the curve and show
relatively hi& varïability between the batches. This was expected in the present study,
since a mixed culture of microorganisms was used for the treatment, inducing variable
inocdurn quality- As shown in Eption 43, the k values obtained nom the modeling
represent m. Consequentiy, the higher the k values the better the treatment, since
kXis the maximum specific growth rate of the biomass and K, represents the affinity of
the biomass to the substrate (the lower the &, the higher the ety). The average k
value obtained for the batches containing phosphorus only was 1-84x 104 ilmg, where
as that obtahed for a combination of PAC and phosphorus was 4.99 x 10 " Umg. From these results, it appears that the addition of a concentration of 150 ppm of PAC to the bioreactors improved the rate of biodegradation of the organic content.
Figure 4.22 shows the COD reduction results obtained for 3 batches containing phosphorus and 15 ppm of PEI. These data were averaged and plotted together with the results obtained for phosphorus only in Figure 4.23. The error bars slightly overlap, again indicating the influence of inoculum quality and the need to repeat the tests as many times as possible to obtain a good approximation of the expected results. The average k value obtained for a combination of PEI and phosphorus was 3.63 x lo4 L/mg, which is slightly higher than the k value for phosphorus alone (1.84 x 104 Umg ). Thus, it appears that the addition of 15 ppm of PEI to the bioreactors improved the rate of biodegradation of the organic content in the synthetic leachate. FinaiIy, Figures 424 and 4.25 show the results obtained for a combination of 5 ppm of BOD BalanceTM and phosphorus. Four different batches were nui as indicated in
Figure 4.24 and the resuits were averaged and compared with the addition of phosphorus alone in Figure 4.25. The error bars are overlapping, rendering the dib-tinction between the two combination of additives more diflïcult, However, the k dueobtained for the treatment with BOD Balancem addition (3-54 x 104 Umg) was slightly hîgher than that obtained for phosphorus alone. It seems that BOD BalanceTMalso had a positive efféct on the treatment efficiency.
In conclusion, fiom the logistic decay modeling redts, it is believed that 150 ppm of PAC, 15 ppm of PEI or 5 ppm of BOD BalanceTM combined with phosphorus increased the biodegradation rate of synthetic lana leachate more than phosphorus alone di& However, as was seen in Figures 4.21, 423 and 4.25, the data obtained had relatively high standard deviations and error bars overlapped. This signifies that a higher amount of batches should be nur with the various additive combinations to provide a
Larger database, fiom which reliable conclusions on COD utilization and maximum specinc growth rate could be drawn-
The reactors used in wastewater treatment are complex environments and the application of existing models is n;ff;cult. A few of the factors complicating the applicability of the models are as follows: many species may be metabolking the same organic substances simultaneously and these may have different E& value; protozoa or species parasitizing the biodegrading populations may be governing the activity and the size of the latter and finally, the majority of the models ignore the acclimation period (Alexander and Scow, 1989). These fictors could explai.why the logistic model fitted
the data better than the logarithmic model.
4.3 BATCH TREATMENT OF LONDON W12A LANDFLLL LEACHATE
Two series of four batch biological treatment tests were conducted with leachate
collected at the W12A landfill site near London, Ontario. The best combinations of
additives obtained in the synthetic leachate tests were reproduced. These were [PAC] =
150 ppm, POD ~alancey= 5 ppm and [PEI]= 15 ppm. The first series included
addition of phosphorus to aiI set-ups, while the second series had no phosphorus. The
data obtained for final COD are given in Table 4.2. In both series, initial COD values were Lower than that of the synthetic leachate. The third colurnn lists ail additive combinations for the fïrst and the second series and the last column presents the redts for final COD,af€er batch treatment.
Table 4.2: Batch bioreactor treatment of London W12A landfill leachate. Series Initial COD [Additives] Final COD (PP~ (PP@ 1 2975 Phosphorus (P) 875 P +- 150 ppm of PAC 810 P + 5 ppm of BOD ala an ce^ 505 P + 15 ppm of PEI 470 2 4260 None 1100 150 ppm of PAC 1045 5 ppm of BOD ala an ce^ 1020 15 ppm of PEI 1100
Two key observations can be made f?om these results. Fkstly, it is apparent that the bioreactors containing phosphorus were more efficient, based on the fial COD values- The results hmseries t show that all reactors reached lower haI COD concentrations than those in series 2. Secondly, among the reactors in series 1, those containing BOD ~aIance~and polyethylenimine reached even lower final COD values.
The reactors were run for approximately 120 h in the first series and 150 h in the second, which would account for the higher initial COD values for the second senes.
4.4 COMPARISON OF BATCH TREATMENT FOR SYNTaETIC AND LONDON LANDFILL LEACEALE
The effluent COD values obtained in the treatment of the synthetic and natural leachates were averaged and expressed as percentage of the Initial values. This was done for both synthetic and real leachate, with and without phosphorus, for all additive combinations studied in the current research. These percentages are show in Table 4.3, which shows a cornparison of the effectiveness of the additives regardless of the time required for the treatment. The fkst column lists the different additive combinations, the second column presents the percentage of COD reduction for the synthetic leachate and the third column, the percentage of COD reduction for the London leachate.
Table 4.3: Average COD reduction in synthetic and natural lanm leachate batch treatment. Additives % COD reduction Synthetic Leacbate London Leachate None 83 74 150 ppm of PAC 87 75 5 ppm of BOD BdanceTM 92 76 15 ppm of PEI 91 74 Phosphorus (P) 92 71 P + 150 ppm of PAC 92 73 P + 5 ppm of BOD danc ce^ 93 83 P + 15 ppmofPE1 93 84 As expected, the synthetic leachate was eask to biodegrade than the naturai
leachate. The latter contained a wide range of compounds that can inhriit the growth of
microorganisms. The addition of phosphorus facilitated the reduction of COD in the
synthetic leachate. This is especiatly obvious when the data for no additives (83 %) and
phosphorus only (92 %) are compared For the naturai lanaleachate, the nnal COD
values were aIl very similar when no phosphorus was added. With the addition of P,
however, the reactors containhg BOD ~a~ance~and PEI yielded 9 % increase in COD
reductions. The positive influence of PEI and BOD Balancem observed for the treatment
of synthetic landiili leachate is dso noticed for the treatment of London leachate-
4.5 TOTAL SUSPENDED SOLIDS QSS) ANALYSIS
In environmental engineering, TSS is measured using different types of filters. In the curent study, the efficiency of two dif%erent filters was compared: Gelman type AIE glass fiber filter and Gelman type 45 Versapor supported membrane filter. The use of glass fiber filter is recommended in Standard Methods (1992) and it is described as a standard filter for dissolved and suspended solids testing in sanitary water analysis procedures. The particle retention is 1 pm and it is binder and organic-fiee. Knowing that the diameter of the srnallest bactena is approximately 0.4~(see Chapter 2), it was to be expected that not aU the microorganisms would be retained on the fltter. The
Gelman type 45 Versapor filter has a pore size of 0.45 p. It is made of acrylic copolymer on a non-woven support and is described as a general purpose laboratory filter that can repIace glass fiber filters. In order to compare the filters efficiency, two batch reactors (synthetic leachate
supplemented with phosphorus) were sampled on three consecutive days and TSS was
analyzed after filterhg with glas fiber and Versapor nIters. The results are shown in
Table 4.4. The fkt column indicates the reactor, the second the type of filter used, and
the last three present the TSS results for the three days of testing.
Table 4.4: Cornparison ofglass Ber and Vmapor filters for TSS measurement in batch bioreactors. - Reactor Type of nIter TSS (a/L) Day 1 Day 2 Day 3 1 Glass fiber 1.12 1.O3 0.92 Versapor 1.65 1.5 1.3 2 Glas fiber 0.92 0.97 0.78 Versapor 1.59 1-42 1.23
The average glass fiber to Versapor TSS ratio was 0.661 with a standard deviation of 0.047. It is obvious fiom those results that, for a 5-mL sample sue, the Versapor filter retained a more sipifkant fkction of the suspended solids than the giass fiber filter. It is seems likely that a fairly important fiaction of the biomass had a diameter ranging from
0.45 pto 1 pm and subsequently, was not filtered by the glass fiber filter having a pore size of lp.
4.6 BIOLOGICAL OXYGEN DEMAND (BOD) ANALYSIS
Samples fiom the batch bioreactors, collected before and after treatment of synthetic and natural leachate supplemented with phosphorus, were sent to a local commercial laboratory for BOD, analysis. The results for BOD, COD and BOD, / COD ratio before and after treatment are given in Table 4.5. The ktcolumn specifies the type of leachate as weD as the parameters evaluated, the second column presents the results for
the synthetic Leachate, and the last two the results for the two London W12A landfiIl
leachates-
Table 4.5: BOD, and COD before and after batch biological treatment of synthetic and na& Leachates. Type of leachate Synthetic Naturd #l Natural#2 Before treatment: BOR Cppm) 4450 1585 2290 COD (PP~) 7745 2975 4260 BOD&OD 0.57 0-53 0.54 After treatmeoe BOD, @pm) 23 23 - COD @~m) 53 1 470 1020 BOD,/COD 0.04 0.05 - COD reduction (ppm) 7214 2505 3240
The BOD, obtained f5om the commercial laboratory represented 62% (synthetic
leachate), 63% (Naturai leachate #1) and 71% (Natural leachate #2) of the total COD reductions. The majority of the COD reduction occurring during the treatment period should be due to biological degradation, since it was verifïed that no significant
adsorption occurred onto the powdered activated carbon (see Section 4-2-21 and air stripping should not contribute to organic carbon reduction (Evans, 1987). Consequently, these results show that the 5-&y biological oxygen demand @OD& was not a good indicator of the biodegradable hction of organic matter in the leachate.
The BOD, tests represent the amount of dissolved oxygen consumed by a controlled population of microorganim while biodegrading organic matter contained in a wastewater. This controlled biomass usualiy cornes fiorn a sample of fiesh sludge taken at a municipal wastewater plant. It is usually not acclimatized to landnll leachate, whose composition is very Mirent hmthat of a municipal wastewater, Therefore, the
biomass used in BOD, analysis might not be as efficient in biodegradùig the lana
leachate as that used in the cment study. This codd explain why the BOD, values were
lower than expected. Serra et al. (1997) studied this phenornenon and drew similar
conclusions on the precision of BOD memement for IandfilI leachates-
Wastewater BOD analysis is influenced by many different factors including the
availability of nutrients, the bacteriai population present in the feed and in the seed and
the presence of hazardous substances. Sena et al. (1997) studied how the variability of
landfiIl leachate characteristics influence B OD test results. They showed the necessity of
modifying the composition of dilution water used for BOD testing, which is usually prepared according to Standard Methods (1992). Their tests showed that factors such as phosphorus content, dilution ratio and pH can compiicate the Uiterpretation of BOD
results. They found the following: (i) lag phases were generaiiy longer with leachate than with municipal wastewater, (ii) there was oha lack of phosphorus for the development of aerobic biological processes, (iii) preparation of buf5er solution to guarantee neutrd pH at the begimiing of the BOD measurement test is important, (iv) higher dilution factor for methanogenic leachate gives higher BOD and (v) seeding will strongly influence an acidogenic leachate. TheH conclusions showed that reliable BOD analysis for landfill leachate would require special preparation and some modifications to the Standard
Methods. These various factors Bely affiected the BOD results presented in the curent study. 4.7 MTRATE @O) AND NITRIT''(NO;) ANALYSIS
Ammonia @H3-N),nitrate (NO;) and nitrite (NO;) were monitored in spthetic
leachate batch tests involving BOD Balancem and PEI. The initial ammonia
concentrations varied hm160 ppm to 200 ppm. The reduction of ammonia foilowed
very closely that of COD as previously discussed Nitrate plus &rite was also monitored
but found to be present only in low concentrations tbroughout the tests and it reached an
average nnal value of 0.1 ppm. It seems that no nitdication was occucTiIIg and that
ammonia was being utilized in a dLfferent process. Since aeration was high enough to
keep the bioreactor satunited with dissolved oxygen, air stripping probably played a key
role in NH, removal.
4.8 CONCLUSIONS
This part of the research was initiated to characterize the biodegradability of
landfill leachate in the presence of additives, when using batch reactors. Results were
obtained for a synthetic leachate and natural leachate fkom a Id11site near London,
Ontario. The synthetic leachate had a theoretical oxygen demand of 7745 pprn while the
London leachate was more methanogenic and had a COD that ranged fiom 2900 pprn to
43 00 ppm. The additives studied were phosphoric acid, powdered activated carbon
(PAC), polyethylenimine (PEI) and BOD ala an ce?
The addition of phosphorus to the batch bioreactors containhg synthetic leachate significantly lowered the final COD values and increased the COD utilization rates.
Phosphorus is a necessary nutrient for microorganisms and its addition allowed the biomass to become more efficient and accelerate the breakdown of the biodegradable fiaction of organic matter. The shape of the absorbante, total suspended solids (TSS) and
chernical oxygen dernand (COD) cmes seemed to ùidicate that biological growth was
not hindered to the same extent as in a system containing no phosphorus. The addition of
PAC concentrations up to 150 ppm to e phosphorus containhg leachate also increased the
COD utilization rate. It is believed that this additive helped the formation of wail growth
and gave a support surface to the mi~roorga~smsin suspension. However, the addition
of 200 ppm of PAC seemed to hinder both ceU growth and COD utilizatlon rate- From
these results, it is believed that the addition of too much PAC to an aerobic batch
bioreactor might have a negative effect on biodegradation efficiency, which could be
caused by poorer rate of oxygen transfer to the biomass. A concentration of 15 ppm of
polyethylenimine had a similar effect to that of 150 ppm of PAC regarding COD
utilization rate. It is likely that in the present study involving biomass acciimatized to
1andfi.U leachate, PEI permeabilized the microorganisrns cell waU, which is consistent
with the observations made by Helander et al. (1997). With a combination of phosphorus
and BOD ala an ce^^, COD utilization rates as high as 108 ppdwere obtaùied,
compared to less than 20 ppdfor a system without additive. The BOD Balancem
apparently accelerated the breakdown of biologicai matter in the synthetic landfill
leachate. For a phosphorus containhg leachate, other additives did not seem to have an influence on the effluent COD, but had a positive effect on COD utilization rates, thereby reducing the thne required for treatment. From the statistical analysis, it also appeared that PAC, PEI and BOD ala an ce^ improved the rates of biodegradation. However, there was insufficient information to quanti@ the improvement, as more repeats of the same tests would be required. For the treatment of the London 1andfi.U leachate, the best combination of additives obtaïned with synthetic Ieachate were reproduced, Le. 150 ppm of PAC, 15 ppm of PEI and 5 ppm of BOD BalanceTM.The addition of phospho~lowered ha1COD values and the improvement was Merenhanced by a supplementary addition of BOD
ala an ce^^ or PEI. COD reductiom up to 84 % wexe obsenred. When the real leachate was not supplemented with phosphorus, the other additives did not seem to have a signincant influence.
From ammonia (N&-N) and nitrate @O3-) plus nitrite (NO;) analysis, it is believed that no nitrification / denitrification occurred- However, ammonia removal up to
98 % was observed, implying a dinerent utilization process. It is believed that air stripping was the main removal mechanism.
Finally, observations were made regarding the precision of two parameters analyzed during the cunent study, Le. total suspended solids (TSS) and biological oxygen demand @OD). Regarding TSS, it was observed that the results obtained with the
Gelman type 45 Versapor supported membrane filter were more precise than those obtained with Gelman type A/E glass fiber filter (recomrnended by Standard
Methods,l992). As for the BOD,, it was noticed that the method descnbed in Standard
Methods (1992) should be modifïed when the wastewater studied is lanm leachate. A numerous amounts of factor are likely to affect the BOD, results, rendering them meaningless. O 100 200 300 400 Tirne (h)
Figure 4.1: Average absorbance (at 600 nm), total suspended soiids (TSS) and chemical oxygen dernand (COD) of two batch tests during biological treatment of synthetic leachate (no additives). O! I I 1 t O 1O0 200 300 400 Time (h)
Figure 4.2: Measured chexnical oxygen demand (COD) of two batch tests during biological treatment of synthetic leachate (no additives). O 50 1O0 150 200 250 300 Time (h)
Figure 4.3: Measured absorbance (at 600 nm) of three batch tests dlrring biological treatment of synthetic leachate (addition of phosphorus). Batch#l Ci Batch #2 A Batch #3
-
O 50 100 150 200 250 300 Time (h)
Figure 4.4: Measured chernical oxygen demand (COD) of three batch tests during biological treatrnent of synthetic leachate (addition of phosphorus). O P addition I Ci No adddiion
O 50 1 O0 150 200 250 300 350 Time (h)
Figure 4.5: Average absorbance (at 600 nm) during batch biologicd treatment of synthetic leachate showing influence of phosphorus addition. O Addiion of P a NOaddiin
O 50 IO0 150 200 250 300 350 Time (h)
Figure 4.6: Average chernical oxygen demand (COD) during batch biological treatment of synthetic leachate showing influence of phosphorus addition. O FAC] =SO pprn A [pAC]=100 ppm O [PACJ = 150 ppm v [pACI=ZOOppm
O 50 100 150 200 250 300 Time (h)
Figure 4.7: Average absorbance of two senes of batch tests showing the influence of different PAC concentrations on the biodegradation of synthetic leachate (addition of phosphorus). [PACI =O ppm [PAC] = 50 ppm A [PAC] = 100 ppm
O 50 100 150 200 250 300 Time (h)
Figure 4.8: Average COD of two series of batch tests showing the influence of different PAC concentrations on the biodegradation of synthetic Ieachate (addition ofphosphorus). Figure 4.9: Powdered activated carbon (PAC) adsorption test showing measured residual chemicai oxygen demand (COD) at different PAC concentrations. Figure 4.10: Contamùiants removal trends in PACT~~systems. @?romWEC and ASCE, 1998.1 O [PEI] = 5 ppm, P [PEI] = 15 pprn, P A [PEI] = 20 pprn. P [PEI] = 30 ppm. P O Poniy
O 50 1O0 1 50 200 250 300 Tirne (h)
Figure 4.1 1: Average absorbame of batch tests showing the influence of phosphoric acid and dinerent PEI concentrations on the biodegradation of synthetic leachate. O PEIJ= 5 ppm, P O [PEI] = 15 ppm, P A [PEI]: = 20 pprn. P O [PEI] = 30 ppm. P
O 50 1 O0 150 200 250 300 Time (h)
Figure 4.12: Average chernical oxygen demand (COD) of batch tests showïng the influence of different PEI concentrations and phosphorïc acid on the biodegradation of synthetic leachate. O [PEU = 5 ppm, P [PEI1 = 15 ppm, P A (PEU = 20 ppm, P O (PEI1 = 30 ppm, P
O 50 100 150 200 250 Time (h)
Figure 4.13: Average ammonia (NH3-N) of batch tests showing the influence of different PEI concentrations and phosphoric acid on the biodegradation of synthetic Ieachate. O BatchM - O Batche A Batch #3 r0 Batch #4
O 50 1O0 150 200 250 Time (h)
Figure 4.14: Measwed absorbance during four batch tests d&g biological treatment of synthetic leachate containing 5 ppm of BOD ala an ce^ and phosphoric acid. O Batch #l O Batch #2
Time (h)
Figure 4.15: Measured chernical oxygen demand (COD) during four batch tests during biological treatment of synthetic Leachate containing 5 ppm of BOD al an ce^^ and phosphonc acid, O Batch #î A Batch #3 Batch #
O 50 1 O0 150 200 250 Time (h)
Figure 4.16: Measured ammonia N3-N)during three batch tests du~gbiological treatment of synthetic landfül leachate containing 5 ppm of BOD ala an ce^ and phosphoric acid. +[PEU 4th P A [BOD Balance1 with P + [BOD Balance1 no P D [PEU no P [PACI with P [PAC] no P
O 50 100 150 200 250 [Additive] (p p m)
Figure 4.17: Idluence of additive concentration on utilization rate of chernical oxygen demand (COD) during batch biological treatment of synthetic Ieachate. Figure 4.18: Relationship between growth rate of a bacterium and the concentration of the substrate supporting its growth. [Alexander et al., 1989.1 Figure 4.19: Disappearance curves for chernicals that are mineralized by different growth related kinetics. [Alexander etaL, 19891 O 50 100 150 200 Time (h)
Figure 4.20: Logistic decay modehg of substrate disappearance in the treatment of synthetic leachate supplemented with phosphorus and 150 ppm of PAC.
'O-..
700 120 140 Erne (h)
Figure 4.21 : Cornparison of substrate disappearance in the treatment of synthetic leachate supplemented with phosphorus and 150 ppm of PAC and phosphorus only (average of individual batches modeled with logistic decay). O 50 100 150 200 250 TÏme (h)
Figure 4.22: Logistic decay modeling of substrate disappearance in the treatment of synthetic leachate supplemented with phosphorus and 15 ppm of PEI.
100 120 140 Time (h)
Figure 4.23: Cornparison of substrate disappearance in the treatment of synthetic leachate supplemented with phosphorus and 15 ppm of PEI and phosphorus only (average of individual batches modeled with Iogistic decay). LOO
100 150 Tïme (h)
Figure 4.24: Logistic decay modehg of substrate disappearance in the treatment of synthetic leachate supplemented with phosphonis and 5 ppm of BOD ala an ce^^.
O 50 100 150 200 250 Tirne (h)
Figure 4.25: Cornparison of substrate disappearance in the treatment of synthetic leachate supplemented with phosphonis and 15 ppm of BOD ala an ce^ and phosphorus ody (average of individual batches modeled with logistic decay). Pnor to discussing the experiments, the theory of continuous treatment is
presented The rate of substrate removal in a biological treatment process can be
descriied by the Monod equation (Droste, 1997):
Where:
r, : Rate of substrate removal (mfld) k and K :Maximum and haE-velocity constants (mgNd and mg/L) S : Substrate concentration (mg/L)
The two constants are hctions of many different factors such as dissohed oxygen (DO)
concentration, pH, temperature, inbi'bitory substances, nutrients available and
degradability of the substrates. Since wastewater treatment processes usually produce
efauents containhg low substrate concentrations, the Monod equation cmbe reduced to
a first-order mode1 (&oste, 1997):
r, =kS (5-2)
Where k does not have the same value as in Equatïon 5.1- The production of biomass
fiom substrate removai is described in Equation 5.3 (Droste, 1997):
rXp= - Y rs (5-3) where: r, : Production of VSS (biomass) fiom substrate removai (mg/L/d) Y : Yield factor (mas of microorganisms produced pamass of substrate removed) r, : Rate of substrate removd (mwd)
Endogenous decay also has to be taken into account when expressing the biomass production. It is a consequence of substrate Eted conditions and biomass decay
+hou& mation, death, predation and autoo'udation. Endogenous decay can be rnodeled by a fksî-order expression oroste, 1997):
rx. =-KeXV
r,, : Rate of decrease of VSS caused by endogenous decay (mg/L/d) y : Rate coristant (mas removed through endogenous decay / mass presedd) y. : Volatile suspeoded solids (VSS) concentration (mg/L)
Finally, the net growth rate of microorgm-sms is a combination of Equations 5.3 and 5.4, as shown in Eqwtion 5.5 @reste, 1997):
r, = - Yr, - K,X, where: r, : Net growth rate of microorganisms (mgNd)
Two other parameters are also very important in the activated sludge process.
These are the food to microorganisms ratio (FM)and the sludge age. The F-M ratio, U, is dehed in Equation 5.6 (Droste, 1997). It describes the degree of starvation of the microorganisms. Where:
Q : Volumetrk flowrate (Ud) S, : Influent substrate concentration (m&) S, : Enluent substrate concentration (ma) V : Reactor volume (L) 0, : Hydraulic retention time @RT) (d)
The sludge age (83 or sludge residence the (SRT) is def5ned as the average residence
time the sludge stays in the aeration basin. If there is no sludge recycling, SRT will be
the same as HRT, the average amount of tune a particle of water spends in the aeration basin. The equation for the sludge age is (Droste, 199'7): mv 0, = solids removal rate from the system
In the current study, a CSTR witbout recycle was use& meaning that the biomass withdrawn f?om the reactor with the effluent was wasted. Substrate and biomass balances for this reactor are detailed below. SUBSTRATE BALANCE @coste, 1997)
In - Out + Grneration = Accumulation
From Equation 5.8 :
Er, is substituted by a Monod mode1 of the second orderr
(S. 10)
Solving for Se:
where: a=l, b=kB,-S,+K and c=-KS,
From Equation 5.1 1, it can be seen that influent and effluent subsîrate concentrations and
HRT fiom at least two operating conditions must be known in order to determine the kinetic coefficients. BIOMASS BALANCE (Oroste, 1997)
In - Out + Generation = AccurnuIation
(S. 14)
In Equation 5-14 X,, represents the influent VSS. However, influent biomass is usually assumed to be negiigible and the mass balance becomes:
QX, =r,V
Substituting r, for equation 5.5:
As mentioned above, sludge age 0, (SRT) and 0, (LIRT) are the same for the reactor studied in the cunent study, since there is no recycle. Consequently:
Combining Equaîions 5.1 6 and 5.17 gives:
since: -rs = -s* and U=- SO 4 4xv
Equation 5.18 relates the F:M ratio to the sludge age. Another useful parameter in the design of activated sludge process is the minimum sludge age (Lawrence et al., 1969,
1970). It is determined by the tiighest rate at which the bion;ass can grow, which in tum is dependent on the maximum rate of substrate removal. Ceiis will be washed out of the system if they are removed hmthe reactor at a rate faster than the minimum sludge age.
The highest rate of substrate removal wiU occur at the highest substrate concentration in the reactor, which is S,. Consequently, fiom Equation 5.18, it is possiile to express the minimum sludge age 8:, as shown in Equation 5.19:
5.2 CONTINUOUS STIRRED TANK REACTOR (CSTR) RESULTS
Three different experiments were conducted with the same continuous reactor.
The purpose of the first experiment, or the initial study, was to determine an approxhate minimum sludge age. In the second experùnent, the effects of hydraulic retention the
(HRT) variations were studied. Finaily, the last experiment conducted was to observe the effects of wall growth. ALI experiments were conducted in a 20-L CSTR with synthetic leachate containing phosphoric acid and the results of these experiments are discussed in the following sub-sections.
5.2.1 Initid Study
The initial study was conducted at hydraulic residence times @T) of 5, 6 and
6.5 days. The experiments were started as a batch for 3 days to allow for a sufncient biomass to grow. During those three days, air and mixing were provided, but there was no nutrients addition. Then, the batch bioreactor was converted hto a continuous bioreactor (CSTR)with two mini-pumps to control the influent and the effluent flowrates. nie duration of the experiment was 12 days and absorbance, total suspended solids
(TSS), volatile suspended solids (VSS) and chernicd oxygen demand (COD) were measured daily. These results are presented in Figures 5.1 to 5.3. 107
Figure 5.1 shows the rdts obtahed for absorbance. As can be seen, the
absorbance decreased fkom an initial value of 0-917 to 0-291 after 290 hours. This
indicates that with a HRT up to 6.5 days, ceii washout occurred. This observation can
also be made fkom Figure 5.2, showhg TSS and VSS. The initial and ha1 TSS were
0.93 g/L and 0.37 g/L, where as the initial and hai VSS were 0-92 g/L and 0.3 g/L.
Moreover, the average VSS:TSS ratio was found to be 0.87 with a standard deviation of
0-07. Consequentiy, it codd be approximated that the biomass used in the treatment of
synthetic leachate in this study represented 87 % of the TSS. The typical VSS to TSS ratio in mixed liquor gîven by Droste (1997) is slightly lower, Le. 0.75 to 0.80. The higher ratio observed in the present study was expected since the feed used was synthetic and contained much Iess inorganic suspended solids than a real wastewater. Figure 5.3 shows that COD was not at steady state either. The CSTR was started with an initial
COD concentration of 2605 ppm. After 12 days, the COD had increased by 100 % to
5295 ppm. It can be concluded fiom these resdts that sludge age must be maintained higher than 6.5 days to avoid cell washout.
5.2.2 Effect of Hydrauiic Retention Times (HRT)
For the second experiment, the continuous stirred tank reactor (CSTR) was also started fiom a batch set-up, but at a higher hydraulic retention time WT) of 10 days.
The experiment was conducted for a total of 1100 h- Absorbance, TSS, VSS and COD of non-nltered and filtered samples were measured. After 550 h, HRT was increased to 12.5 days for 400 h and in addition, ammonia (MX3-N)was monitored. Mer 950 h, HRT was increased Merto 15 days uniil the end of the experiment- The rdts obtained for
absorbance, TSS ,VSS and COD are presented in Figures 5-4to 5.6.
From Figure 5.4, it can be seen that during the IO day HRT period, the absorbance
slowly decreased and stabibed at 1.00 i0.06- After 700 h, it stabilized again at 0.66 4
0.05, at HRT of 12.5 days. Another change of HRT to 15 days did not further affect the
absorbance. Similar observations cm be made fiom Figure 5.5 showing TSS and VSS
and Figure 5.6 showing COD. VSS stabilized at 0.75 + 0.09 g/L and 0.53 f 0-1 g/L at
HRT of 10 and 12.5 days respectively. Another HRT change to 15 days had no innuence
on the steady state. From Figure 5.6, two steady States cm also be observed. COD
stabilized at 992 + 60 ppm and 605 pprn +131 ppm at HRT of IO and 12.5 days
respectively. As was the case for solids, an increase in HRT to 15 days did not disturb
the steady state. The VSS:TSS ratio was found to be 0.64 f 0.13.
It was observed that even though there was a solids reduction in the first haif of
the testing penod, the breakdown of the organic matter was not affected, since the quality
of the effluent împroved over tirne. A HRT of 10 days gave an effluent COD of 992 ppm
where as HRTs of 12.5 and 15 days gave an effluent COD of 605 ppm. From these
results, it appears that an increase in HRT fkom 10 to 12.5 days had a positive effect on
the quality of the effluent. However, another hcrease fkom 12.5 to 15 days did not
Merimprove the final effluent. The suspended solids reduction in the first part of the
testing period may be related to biomass attachment to the inside waii of the reactor, as well as HRT augmentation. This could explain the reduction in the VSS to TSS ratio
fiom 0.87 to 0.64. The attachment would have allowed for higher sludge age, more endogenous decay, dinerent distrïïution of microorganisms types and consequently, a more efficient biodegradation of the volatile fatty acids in the synthetic leachate. From the cdcdated average ofthe effluent COD for retidence times of 12.5 and 15 days, it was found that the efficiency of the treatment, based on COD removal, reached 92 %.
5.2.3 Effect of WaU Growth
FolIowing the observations made in the second experiment regarding wall growth, the effect of biomass attachent on the inner waif of the bioreactor was investigated in the third expeziment. The CSTR was left as a batch for 350 h, Le. the mini-pumps for the influent and the efflumt wtre stopped. The stirrer was also tumed off and oniy aeration was left to maintain the system in aerobic conditions. This dowed for a thicker biomass film to form on the inner wail of the reactor since there was no more shear force fkom the stirrer to prevent build-up. As was shown in Figure 3.5 in a close-up photograph of the reactor, the biomass film virtually covered the whole wail. Then, the CSTR was started again for 400 h. The initial hydraulic retention time (HRT) was 13.5 days, but was changed to 7.5 days after 240 h. Absorbance, TSS (measured with gIass fiber and
Versapor mters), VSS, COD and NH,-N were measured.
As can be seen fiom Figure 5.7, the absorbance seerns to have stabilized at 0.93 +-
O. 10. Similar obsewations can be drawn fiom Figure 5.8 (TSS and VSS) and Figure 5.9
(COD), where the data is representative of a continuous bioreactor. The TSS and VSS averaged 1.08 f 0-17 and 0.77 f 0.13 g/L with a TSS:VSS ratio of 0.68 + O. 13. This ratio is very similar to that observed for the second experiment (0.64 & 0.13). As for the COD, it stabilized at 561 f 197 ppm. This is lower than what was observed in the second experiment (605 f 131 ppm) as was shown in Figure 5.6. There is evidence to believe that treatment was more efficient dera thicker biomass fïim was dowed to fonn in the reactor, since higher effluent quafity was achieved at a Iower HRT. In the third experhnent, the 1st HRT studied was 7.5 days and the average effluent COD was 408 k
111 ppm, whexeas the best treatment obtained in the second experiment was with a HRT of 12.5 and 15 days and the efBuent COD was 605 + 131 ppm. Furthexmore, in the nrst experiment, ceii washout occuned at a HRT of 6.5 days. Consequently, with a dinerence of ody one day in the HRT, the treatment went hmceii washout to best emuent qaaIity because of the formation of a biomass fïim on the inner waU of the reactor. With a residence time of 7.5 days, the efficiency of the treatment for COD removai reached 95
%.
5.3 CHEMICAL OXYGEN DEMAND (COD) OF THE BIOMASS
In the second experiment with the CSTR, the COD of non-filtered samples was rneasured. The purpose was to evaluate the COD of the VSS. The analyses were done on
8 consecutive days. The average fltered COD, non-filtered COD and VSS were 1100 +
236 ppm, 1572 + 189 ppm and 0.73 1: 0.08 g/L, resulting in 0.64 mg COD/mg VSS.
Frorn the chemicd equation for the oxidation of biomass (C&NOJ, 1.42 mg CODlmg
VSS is obtained (Droste, 1997). However, this theoretical value is too often assumed to be appropriate and does not always reflect reality. The chernical formula of the biomass may Vary and affect the theoretical COD. The results of the present study show the importance of filtering samples before COD analysis. 5.4 TOTAL SUSPENDEID SOLIDS WSS) ANALYSIS
In the third experiment with the CSTR, TSS was analyzed with both glas fiber and Versapor fllters. Redts hmboth analysis are presented in Figure 5.10. From these rd&,it does not seem that the TSS values obtained with the Versapor nIters are higher than those obtained with the glas fiber füters. The average ratio for the TSS measured with glass fiber filters to the TSS meanned with Versapor filters gave 0.96 with a standard deviation of 0-19- Th,no signincant dBierence was observed between the amount of solids retained by the two flters, which is a different conclusion than the one drawn for the batch treatment results. One possible explmation is that the biomass population in the CSTR was different fkom that in the batch bioreactors, since the sludge retention times (SRT) were different. It is known that high SRT and highly stawed conditions are responsible for poor settleability due to pinpoint floc formation (Droste,
1997). This could be amibuted to the presence of larger microorganisms, Le. solids retained with a larger pore size filter.
5.5 CONCLUsIONs
This part of the research was initiated to characterize the biodegradability of synthetic landf3.i leachate in a continuous stirred tank bioreactor (CSTR). The synthetic leachate used was supplemented with phosphoric acid to ensure the biomass would not lack essential nutrïents. The reactor was aerated and stirred to ensure proper oxygen distribution. DBerent hydraulic retention times (HRT) were iavestigated to observe their effect on effluent quaiity. The first expdent was conducted at HRTs of 5, 6 and 6.5 days, Within 12 days, the solids concentration was decreased to approximately 35 % of its initial vaiue and the effluent COD increased by 100 %. It is conchded that ceii washout occurred as the sludge age was not maiatained hi& enough. In the second expehent, HRT of 10,
12.5 and 15 days were investigated It was observed that the treatment was improved when increasing the mTfiom 10 to 12-5days, but the COD remained the same &er chmging it hm 12.5 to 15 days. This showed that an optimum COD removal of 92 % was achieved at those specifÏc conditions. Wail growth formation was also observed towards the end of this experhent, which could explain the reduction in VSS to TSS ratio in cornparison with the nrSt experiment. Mer the second experiment, wdgrowth was allowed to thicken for 350 h in order to observe attachment effects. Then, HRTs of
13.5 and 7.5 days were hvestigated. The quaIity of the effluent was better at a HRT of
7.5 days than it was before wall growth at a HRT of 15 days. The positive effect of waii growth was evident and 95 % COD removal was achieved.
The efficiency of glass fiber and Versapor filters was studied and cornpared with the results fkom the batch bioreactors. It was obsemed that with the CSTR, Versapor filters did not retain more solids than the glass fiber faters, as was observed with the batch bioreactors. One possible explmation is that higher sludge age in the CSTR was responsible for a ciiffirent biomass population. This could have resulted in larger size microorganisrns which are more easily retained on the glas fiber fikers. Also, the COD of the biomass was evaluated and found to be lower than that obtaïned fkom the chemical equation for the oxidation of the biomass. This observation emphasized the importance of calculating the COD of the VSS for each bioreactors instead of assuming the commody used value of 1.42 mg COD/mg of VSS. 150 200 Time (h)
Figure 5.1: Initial study with continuous stirred tank reactor (CSTR)showing the effects of biomass washout on absohance at hydraulic retention tixnes (HRTs) of 5 to 6.5 days. O 50 100 150 200 250 300 350 Time (h)
Figure 5.2: Initial study with contuiuous stirred tank reactor (CSTR)showing the effects of biomass washout on solids concentrations at hydrauiïc retention times (HRTs) of 5 to 6.5 days. O 50 1O0 1 50 200 250 300 350 Tirne (h)
Figure 5.3 :initial study with continuous stirred tank reactor (CSTR)showing the effects of biomass washout on COD at hydraulic retention times WTs) of 5 to 6.5 days. 0-0 O Average = 1.00 5 0.06
O 200 400 600 800 1000 1200 Time (h)
Figure 5.4: Continuous stirred tank reactor (CSTR) studies showing the influence of hydraulïc retention time (HRT) variations on absorbance. O TSS a VSS
Average VSS =0,75 2 0.09 g&
Average VSS = 0.53 5 O. 10 glL
600 Time (hl
Figure 5.5: Continuous stirred tank reactor (CSTR)studies showing the influence of hydraulic retention time (EIR'I') variations on total and volatile suspended soli&. O Average = 992 2 60 pprn
Average = 605 2 13 1 pprn
600 Tirne (h)
Figure 5.6: Continuous stined tank reactor (CSTR) studies showing the influence of hydraulic retention time (HRT) variations on COD. HRT = 13-5d HRT = 75d 1.6
200 300 Time (h)
Figure 5.7: Con~uousshed tank reactor (CSTR) studies showing the influence of waIi growth on absorbance. HRT = 135 d HRT=75d E
Figure 5.8: Continuous stirred tank reactor (CSTR) shidies showing the influence of wall growth on total and volatile suspended solids. Average = 56 1 + 197 ppm ------O O O O O
200 300 Time (h)
Figure 5.9: Continuous skedtank reactor (CSTR)showing the influence of wail growth on COD O Glass fiber filters I O Versapor filters
O 100 200 300 400 500 Tirne (h)
Figure 5.10: Cornparison of glas fier and Versapor filters on the measurement of total suspended solids (TSS)in a continuous stirred tank reactor (CSTR). CONCLUSIONSAND RECOMMENDATIONS
6.1 SUMMARY AND CONCLUSIONS
The principal objective of this study was to examine the effects of four different additives on the efficiency of biological IandfiU leachate treatment under aerobic conditions. These additives were: phosphoric acid, powdered activated carbon (PAC), polyethylenimine (PEI) and BOD ala an ce^^. Both naturd and synthetic landflIl leachates were used in the study. The naturd leachate was collected at W12& a landnll site near London, Ontario. Two different types of bioreactors were utilized to study the biodegradation of leachate: a batch bioreactor and a continuous stirred tank bioreactor (CSTR).
From the batch studies with synthetic leachate, it was observed that the addition of phosphoric acid greatiy improved the efficiency of the treatment. It was added at a concentration of 0.44 mUL of synthetic leachate, to obtain a C0D:N:P ratio of 100:5:1.
Phosphoric acid was found to accelerate cell growth and lower effluent chemicd oxygen demand (COD). It also increased the COD utilization rate fÏom 18 ppdh (no additives) to 55 ppmm.
DifXerent concentrations of powdered activated carbon (PAC) were investigated to optimize the efficiency of the biodegradation: 50, 100, 150 and 200 ppm. Both the synthetic leachate with and without phosphorus were tested respectively with different
PAC concentrations. Without addition of phosphorus, average COD utilization rates of
18,24,24 and 32 ppmh were obtained for PAC concentrations of 50, 100, 150 and 200 pprn respectively. With addition of phosphorus, much higher average COD utilkation rates were attained: 52, 54, 79 and 53 ppm/h. The best combination for optimizing the treatment was phosphorus with 150 ppm of PAC. It is believed that addition of PAC up to 150 pprn improved the treatment by rendering the conditions more propitious for growth. Attachment of biomass on the inner wall of the bioreactor and on the PAC in suspension may have favored the biodegradation It was aiso vaedthat improvement in effluent COD was not due to adsorption with a series of batch tests containing PAC concentrations up to 100 g/L. On the other hand, addition of more than 150 pprn of PAC hindered the breakdown of organic substances. The poorer COD utilization may have been related to a reduction in the oxygen transfer rates fiom the bulk of the solution to the biomass.
DBerent concentrations of polyethylenunine were also been investigated to optùnize the efficiency of the biodegradation: 5, 15, 20 and 30 ppm. Wïth a synthetic leachate containing phosphorus, average COD utilization rates attained were 56, 75, 66 and 55 ppmh for PEI concentrations of 5, 15, 20 and 30 pprn respectively. The combination of additives optimizing the treatment was phosphorus and 15 pprn of PEI. It is believed that addition of PEI may have penneabilized the outer membrane of the mixed culture bacteria, accelerating the rate of transfer of nutrients fiom the solution to the microorganisms.
BOD ala an ce^ was added to the batch bioreactors at a fixed concentration of 5 ppm, in accordance with the manufacturer's recommendation. A combination of phosphorus and BOD BalanceTMyielded an average COD utilization rate of 90 ppm/h. It is believed that the naîural surface active agent in the product affecteci cell waH pemeability which resulted in improved rates of biodegradation.
From the modeling to logistic kinetics, it was also observed that additive combinations of PAC, PEI or BOD ala an ce^^ with phosphorus improved the rate of biodegradation more than phosphonis aloae. However, more batch tests are necessary to justiQ fuaher these conclusions.
For the batch studies with naturd leachate, the best combinations of additives obtained wîth synthetic leachate were reproduced with and without phosphorus addition
(150 ppm of PAC, 15 ppm of PEI and 5 ppm of BOD Balancem). Better results were obtained with the leachate supplemented with phosphork acid, especidly in the bioreactoa containing PEI and BOD BalanceTM.For these two specific cases, an average
84 % COD removal was attained for an initial COD of 4260 ppm.
Synthetic leachate total suspended solids (TSS) analyses were conducted with two different nIters (giass fiber and Versapor) to compare their efficiency. 1t was found that the solids retained by the glas fiber filter represent 66 % of those retaîned by the
Versapor filter. Biological oxygen demand (BOD) analysis were also conducted on both synthetic and natural leachates- It was observed that BOD, obtained fiom a commercial
Iaboratory was not a good indicator of the biodegradable fiaction of organic matter in the leachate. This is probably because the biomass used in BOD, analysis was not as efficient in biodegrading the leachate as that used in the curent study. Reliable analysis for lanaleachate would require some modincation of the standard method commonly used for domestic wastewater analysis. Finaily, it is believed that the main mechanism for ammonia removal was air stripping. The continuous studies were conducted with synthetic Ieachate supplemented wÏth phosphoric acid Three different tests were nui, all having différent purposes. The first test was to determine the minimum sludge age of the bioreactor- It was fond that ceU washout occurred at hydraulic retention &es @lKi"ï up to 6.5 days. In the second test, the HRT was varied fiom 10 to 15 days to observe how the effluent was being affected-
At a HRT of IO days, the average effluent COD was 992 ppm. The same efflaent quality was observed for ARTS of 12.5 and 15 days, Le. 605 ppm. It was concluded that no f.urther improvement in effluent quality could be obtained by another increase in HRT.
The third test was conducted to observe the influence of biomass growth on the inner wall of the bioreactor. The reactor was !eA for two weeks as a batch bioreactor to allow for a thicker film to grow. HRTs of 13.5 and 7.5 days were investigated The quality of the effluent was superior at a HRT of 7.5 days (561 ppm) than ii was before wail growth at a
HRT of 15 days. The positive effect of wali growth was evident and 95 % COD removal was achieved.
The efficiency of glass fiber and Versapor filters was studied and compared with the results obtained with the batch bioreactors. It was observed that with the CSTR,
Versapor filters did not retain more solids than the glas fiber filters, as was observed with the batch bioreactors. Also, the COD of the biomass was evaluated and found to be lower than that obtained fiom the chernicd equation for the oxidation of the biomass.
This observation ernphasized the importance of calculating the COD of the VSS for each test instead of assuming the commonly used value of 1.42 mg COD/mg of VSS. 6.2 RECOMMENXDATIONS
Some recommendations cmbe offered for fhture research and are as follows:
- The use of an automatic pH controIler for both batch and contmuous reactoa wodd
minimize pH changes and consequently, disturbance of biomass.
The content of a CSTR with biomass acclimatized to landfiIl leachate should be used
as the source of inoculum for the batch bioreactors. This would mhimke the variations
in inoculum quality and the results obtained fiom repeats of same testing conditions
would probably vary to a much lower extent.
A wider concentration range of the various additives should be investigated. Adding
more than 200 ppm of PAC to a batch bioreactor would help verify if there is oxygen
transfer hindrance at higher PAC concentrations. Studying higher concentrations of both
PEI and BOD ala an ce^ would allow to obtain a better understanding of the relationship
beîween the additive concentration and its inauence on a mixed culture of
microorganisms.
More batches of each additive combinations should be conducted to aliow for more
conclusive logistic decay modeling and statisticd analysis.
With the CSTR, effluent COD should be measured at various hydraulic retention time
(HRT) after the thickness of the biomass film on the inside wall of the bioreactor has
stabilized. This would allow to mode1 the system with Monod kinetics and find the
kinetic constants,
Depending on sludge age, domestic wastewater acclimatized biomass is relatively weil
characterized. It would be interesting to characterize landfill leachate acclimatized
biomass for means of cornparison. After modeling of the CS= kinetic constants could be compared with those obtained firom a CSTR with recycling. The recycling could be accomplished ai a conventional activated sludge with settling tank process or a membrane bioreactor-
As the advantages of wall growth were evident in the current study, it wodd be intereshg to run some experiments with attached biomass (e-g- trîckluig filter) and compare the efficiency of the nxed biomass with that of a conventional activated sludge system. APPENDIX A Calculation of the synthetic Ieachate theoretical chemicd oqgen demand.
1 Organic acid 1 1 Density ( Quantity of acid 1 COD 1
Acetic 60.05 LOS0 3.5 0,061 2 O. 1224 3917 Propionic 74.08 990 2.5 0.0334 O. 1169 3741 APPENDIX A-2
W12A Landfill, London, On tario LEACHATE #l [older section of the land fill) Date pH Conductivity BOD Phenols Chlorld Hardne TKN Fe Mn 504 NH3 Ca Mg Cd Cr Cu Ni Zn Pb es ss (umhoslW (mglL) (uglL) (mW (mglL) (mglL) (mgll) (msll) (mM-1 (mglL) (ML) (WC) (mW (WU (mlL) (mgU QU (WL) 16.01.95 6.8 138 11 0.66 203 0.01 < 0.04 0.07 0.24 0.13 0.04 21.02.95 7.2 10520 383 161 1178 1450 757 24 0.74' 743 149 262 0.02 0.06 0.06 0.19 0.620.18 20.03.95 7.3 43 1 17 0.72 04.05.95 4 11460 666 223 1178 1498 26 0.86 15.06.95 7.6 13820 543 244 1313 1517 19 0.61 < 2 931 136 286 0,02 0.09 0.05 0.24 0.54 0,26 10.07.95 7.4 14030 430 1540 1514 20 0,34 170 125 292 0,03 0.14 0.06 0,35 0.81 0,35 1 1,08.95 7.7 391 13 0.40 1030 0,Ol 0.08 0.08 0.29 0.68 0.22 18.09.95 7.5 14510 545 361 1450 1557 18 0.49 <2 573 149 288 0.02 0,08 0,07 0,32 0.65 0.29 24.10.95 7,8 13870 306 269 1540 944 13 0.20 20 62 86 177 0.02 0.09 0.04 0,26 0.70 0,24 20.11.95 7.0 6980 248 903 1268 12 0.81 403 145 220 0,01 0.06 0.06 0.14 0,42 0.17 05,12.95 7.1 23 1 20 0,18 425 0,02 < 0.04 0,13 0.59 0,29 0.04 22.01.96 7.2 261 10 0.96 429 0,02 0.06 0.06 0.22 0,45 0.19 19.02.967.1 13610 306 212 1250 1489 21 0.34 c 2 989 153 269 0.02 0,08 0.07 0,27 0.67 0,25 11 ,03.96 7.3 240 24 0.39 920 0.02 0.08 0,07 0,24 0,65 0.25 19.04.96 7.0 318 136 9 0.96 27 310 0.02 0,05 0.06 0.17 0.54 0.15 23.05.96 7.0 8020 375 182 1150 1655 22 0.87 16 404 183 291 0.03 0.05 0,05 0.16 0,33 0.16
. 03.06.96 7.1 11640 324 , 260 1250 1567 14 0.39 97 700 164 281 0.02 0.07 0.05 0.21 0.33 0.20 04.07.967.4 12960 615 154 1450 1761 23 0.31 11 513 173 323 O,02 0.09 0.14 0,29 2.00 0.22 15.08.96 7.3 724 14 0.26 641 - 0.02 0.07 0.07 O, 19 0.48 0.24
APPENDIX B
In this appendix are presented examples of COD utilIzatim rates cdculations.
One batch without any additives, shown in Figure B-1, and one batch with 5 ppm of BOD
ala an ce^ plus phosphorus, shown in Figure B-2, were chosen to represent the slowest and the fastest COD utilization rates observed-
O 50 100 150 200 250 300 350 400 450 500 Time (h)
Figure B-1 : COD utilization rate calculation for a batch without any additives. 75 100 125 150 175 200 225 250 Time (h)
Figure B-2: COD utilization rate calculation for a batch without any additives. Figure C-1: Measured absorbance (at 600 nm) of four batch tests during biological treatment of synthetic leachate showing the influence of different PAC concentrations (no addition of phosphorus). O 100 200 300 400 500 Time (h)
Figure C-2: Measured chernical oxygen demand (COD) of four batch tests during biological treaûnent of synthetic leachate showing the influence of different PAC concentrations (no addition of phosphorus). O 50 100 150 200 250 300 Time (h)
Figure C-3 :Measured absorbance (at 600 nm), chemiral oxygen demand (COD)and ammonia (NH3) during biological treatment of synthetic leachate containhg 15 ppm of polyethylenimuie (PEI) (no addition of phosphorus). Time (h)
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