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Reports Utah Water Research Laboratory

January 1982

Reverse Osmosis in the Treatment of Drinking Water

R. Ryan Dupont

Talbert N. Eisenberg

E. Joe Middlebrooks

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Recommended Citation Dupont, R. Ryan; Eisenberg, Talbert N.; and Middlebrooks, E. Joe, "Reverse Osmosis in the Treatment of Drinking Water" (1982). Reports. Paper 505. https://digitalcommons.usu.edu/water_rep/505

This Report is brought to you for free and open access by the Utah Water Research Laboratory at DigitalCommons@USU. It has been accepted for inclusion in Reports by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. Reverse Osmosis In The Treatment Of Drinking Water

R. Ryan Dupont Talbert N. Eisenberg E. Joe Middlebrooks

Utah Water Research Laboratory Utah State University Logan, Utah 84322 WATER QUALrry SERIES December 1982 UWRL/Q-82/05 REVERSE OSMOSIS IN THE TREATMENT

OF DRINKING WATER

by

R. Ryan Dupont, Talbert N. Eisenberg, and E. Joe Middlebrooks

WATER QUALITY SERIES UWRL/Q-82/05

Utah Water Research Laboratory Utah State University Logan, Utah 84322

December 1982 ABSTRACT

An extensive review of the literature was conducted and results were evaluated for the use of the, reverse osmosis process in the treatment of drinking water supplies. All aspects of reverse osmosis technology, including pretreatment requirements; membrane type and configuration; membrane cleaning and mainten­ ance; and reverse osmosis removal of organics, inorganics, and microbial contaminants were incorporated into the literature evaluation.

A survey (Appendix E) of existing full scale reverse osmosis installations was also carried out and results of the survey are discussed.

In light of data presented in the literature and results of the survey conducted, the following recommendations were made to prevent catastrophic membrane fouling occurrences and costly plant shutdowns in the future.

1) Conduct a comprehensive raw water quality evaluation.

2) M,aintain cont inuous feed and product water qual ity monitoring.

3) Incororate process automation and system upset warning provisions in future installations.

4) Provide greatly improved training for reverse osmosis installation operators.

The reverse osmosis system is particularly well suited for the treatment of water supplies which contain a number of con­ taminants that would otherwise require a combination of treatment processes for their removal, due to the ability of the reverse osmosis process to remove salts, organics, and a number of microbial contaminants. Effective pretreatment and routine backwashing, membrane cleaning, and disinfecLion must be carried out; however, if adequate system operation is to be assured.

iii TABLE OF CONTENTS

Chapter Page

I INTRODUCTION . 1

Fundamental Considerations 1

General Principles • 1 Operating Principles 2

Historical Development 4

II PRETREATMENT • 7

Particulate Removal • 7

Filtration • 7 Coagulation-Flocculation­ Sedimentation 7

Scale Prevention 8

pH Control • 8 Scale Inhibitors 8 Iron and Manganese Removal 8 Disinfection 9 Oxidants 9

III MEMBRANES 11

Cellulosic Membranes 11 Polyamide Membranes • 12 Composite Membranes • 13 Summary . 15

IV MODULE CONFIGURATION • 17

Plate and Frame Modules • 17 Tubular Modules • 17 Spiral Wound Modules 19 Hollow Fiber Modules 21 Summary • 23

V MEMBRANE CLEANING AND MAINTENANCE 25

Operational Considerations 25

v TABLE OF CONTENTS (Continued)

Page

Organic Foulants 26 Bacterial Growth 26 Hardness Scale 27 Inorganic Colloids and Metal Oxides • 28 Membrane Rejuvenation 28

VI REMOVAL OF INORGANICS USING REVERSE OSMOSIS 31

Single Component Systems 31 Multicomponent Systems 35 Ionic Charge Relationships 37 Water and Wastewaters 38 Summary • 42

VII REVERSE OSMOSIS REMOVAL OF THE INORGANIC CONTAMINANTS CONTROLLED BY THE NATIONAL INTERIM PRIMARY DRINKING WATER REGULATIONS 43

Arsenic • 43

Barium . , 45 Cadmium • 45 Chromium 46 Fluoride 47 Lead 48 Mercury • 48 Nitrates 49 Selenium 50 Silver 51 Radiation 51 Summary • 52

VIII REMOVAL OF ORGANICS USING REVERSE OSMOSIS 53

Single Components Systems 53 Multicomponent Systems 56 Chlorinated Organics/Pesticides • 57 Drinking Water Treatment 59 Wastewater Treatment 60 Summary • 61

IX REMOVAL OF MICROORGANISMS 63

Bacteria 63 Viruses • 64 Summary • 64

vi TABLE OF CONTENTS (Continued)

Page

x PERFORMANCE EVALUATION OF REVERSE OSMOSIS INSTALLATIONS 65

Water Sources and Treatment Objectives 65 Pretreatment 65 System Operation 66 Operators 66 Operating Problems and Recommendations 67 Recommendations For Future Reverse Osmosis Installations • 67

XI SUMMARY, CONCLUSIONS, AND RECOMMENDA­ TIONS 69

Summary and Conclusions • 69 Recommendations • 70

REFERENCES 73

APPENDICES 83

Appendix A: Chemical Cleaning Reagents for Reverse Osmosis Membranes • 85 Appendix B: Reverse Osmosis Membrane Cleaning Procedures 89 Appendix C: Reverse Osmosis Membrance Rejuvenation Procedures 91 Appendix D: Reverse Osmosis Installations Included in Operational Survey 93 Appendix E: Operational Survey 98

vii LIST OF FIGURES

Figure Page

1. Simple osmosis. 1

2. Simple reverse osmosis • 3

3. Asymmetric structure of typical reverse osmosis membranes (Johnston and Lim 1973) 3

4. Plate and frame configuration of (a) first generation and (b) second generation design (Nielsen et ale 1980) 18

5. Second generation plate and frame configuration (OWRT 1979) 18

6. The tubular module element (OWRT 1979) • 19

7. The spiral bound module element (OWRT 1979). 20

8. The hollow fiber module (DuPont 1977a) • 22

9. Flow characteristics of selected solution systems (Sourirajan 1964b) • 33

ix LIST OF TABLES

Table Page

1. Effects of membrane foulants (DuPont 1977b) • 27

2. Separation of some related solutes aqueous solution under identical experimental conditions using S & S cellulose acetate membranes (Sourirajan 1964b) 32

3. Metal removal efficiencies by reverse osmosis (Johnston and Lim 1973) • 34

4. Reduction ratios of sodium and magnesium salts (Burns and Roe 1979 35

5. Reduction ratios of metal chlorides (Burns and Roe 1979) 36

6. Rejection of various compounds by reverse osmosis at 400 psi (2800 kN/m2) , pH 6, and membrane type ROGA #4101 (Nusbaum and Riedinger 1980) • 39

7. Separation of selected water pollutants by reverse osmOS1S (Hauck and Sourirajan 1969) 40

8. Average percent reductions of constituents by various reverse osmosis configurations treating secondary wastewater effluents (Boenand Johannsen 1974) 41

9. National Interim Primary Drinking Water Standards for selected inorganic con- taminants 44

10. National Interim Primary Drinking Water Standards for fluoride 44

11. A summary of operator training and experience 67

12. A summary of operator maintenance training and experience . 67

x CHAPTER I

INTRODUCTION

Fundamental Considerations 7T, and is related to the solution's vapor pressure and temperature as shown General Principles 1.n Equation 1.

0 Osmosis is defined as the spontane­ RT PA ous movement of a solvent through a 7T = - In- (1) semipermeable membrane from a less VA PA concent rated to a more concent rated solution. The ideal semipermeable where membrane impedes solute movement but allows solvent flow. Solvent will pass 7T = osmotic pressure, atmosphere through the membrane in both directions; however, it will pass more rapidly in R = 0.0882 l-atm/mole oK the direction of the more concentrated solution until a hydrostatic pressure T = oK develops that produces equilibrium conditions of equal flow of solvent in VA = l/mole of solvent both directions across the membrane, 0 Figure 1. This hydrostatic pressure, PA = vapor pressure of sol vent in ~h, is defined as the osmotic pressure, dilute solution

SOLUTION WI LL RI SE TO THIS POINT WHERE Ah= 7r T SEMI- PERMEABLE MEMBRANE

MORE CONCENTRATED LESS CONCENTRATED SOLUTION SOLUTION

WATER FLOW

Figure 1. Simple osmosis.

1 PA = vapor pressure of solvent in structure of this layer. Two distinct concentrated solution descript ions of surface morphology are supported by distinct transport theories Raoult's law relates the vapor labeled the solution diffusion theory pressure of a dilute solution to the and the pore theory_ The solution concentration of particles in the diffusion theory characterizes the solution. From this relationship, passage of molecules and ions across Equation 1 can be used to express the nonporous membrane boundary layers as osmotic pressure in terms of the solute occurring through a solution diffusion molar concentration as: mechanism with surface pores being regarded as membrane imperfections that allow largely nonselective transport 'IT = CRT (2) through them. The pore theory on the other hand proposes that materials are preferentially adsorbed onto the where membrane surface and that their trans­ port through the membrane occurs through C = solute concentration, gm/mole the surface pores while no transport is assumed to occur by diffus ion through Equation 2 is valid only for dilute the polymer matrix. solutions where Raoult's law remains true. Both the solution diffusion theory and the pore theory have strengths The osmotic pressure of a solution and weaknesses. The appl ication of increases with solution concentration as either theory depends upon the specific shown in Equation 2 and a rule of thumb problem at hand and the conceptual based on sodium chloride is a 0.01 psi simplicity either theory has in quanti­ osmotic pressure increase for each tatively explaining experimental results mg/l increase in solution concentration (Johnston and Lim 1973). While an exact (Culp et a1. 1978>' High molecular understanding of the mechanisms of flow weight organics produce much lower through reverse osmosis membranes is not increases shown by sucrose producing a required for everyday utilization of the 0.001 psi increase for each mg/l in­ process, a general understanding of the crease in solution concentration (Culp possible transport mechanisms may allow et a1. 1978). for the expansion of reverse osmosis applications. Further explanations of The spontaneous movement of solute the proposed mechanisms of flow through to the more concentrated solution can be reverse osmosis membranes may be found ove rcome through the appl icat ion of in Hodgson (970), Reid and Breton pressure on the more concentrated (1959) and Lonsdale and Podall (1972). solution side of the semipermeable membrane, Figure 2, in excess of the Operating Principles osmotic pressure of the solut ion. The reversal of the osmostic flow is the The rate of transport of solvent basis behind the reverse osmosis process through the semipermeable membrane used for water and wastewater treatment. in the reverse osmosis process is a function of the applied pressure, the Reverse osmosis membranes are differenti;:il osmotic pressure between asymmetric films with a macroporous solutions, the area and characteristics substructure underlying a dense surface of the membrane, and the temperature of layer, Figure 3. While there is agree­ the solution. ment that separation occurs at the dense surface layer, there still re­ The behavior of semipermeable mains some question as to the specific membranes can be expressed by two

2 PRESSURE

SEMI-PERMEABLE MEMBRANE

MORE CONCENTRATED LESS CONCENTRATED SOLUTION SOLUTION

WATER FLOW

Figure 2. Simple reverse osmosis.

---1 ~ 0 0.25 -4JL ------"J r-- < 100 A ~ CD .. -. ·...... -...... -...... T ::':~::i:::';: ::i::~~;:'; ~i::~. .: ~.~~.;:::.; 0: 0: 0: 0: 0: 0l!:':';:; T ®

® ~ 100JL WATER 1

G) Dense Surface Layer, 0.25- 4 JL ® Transition Region, Intermediate Density and Porosity, Vaiable Thickness ® Macroporous Substructure

Figure 3. Asymmetric structure of typical reverse osmosis membranes (Johnston and Lim 1973).

3 basic equations, one describing the osmotic pressure which in turn reduces solvent or product water flow through the water flux through the membrane. the membrane and the other describing The net result is a lower water flux and the salt flux through the membrane. reduced water quality as the percent of The product water flow, Fw, is described feed water recovered is increased. as follows: The exact operating conditions for a particular application will generally (3) depend upon the raw water quality, the final product water quality require­ where ments t and the required water flux rate. 2 Fw = product water flow t gm/cm -sec Historical Development A = water permeability constant, g/cm2-sec-atm The phenomenon of osmosis has been studied for over 200 years. Nolet,

~p = pressure different ial appl ied in 1748 t was the first to observe across the membrane, atm the passage of a solvent through a semipermeable membrane (Williams and ~'IT = osmot ic pressure di fferent ial Williams 1967). Dutroelot, Vicrordt, across the membrane, atm and Traub cont inued the early reverse osmos is work with animal membranes and The salt flux is described by Equation 4 artificial membranes during the 19th as: century (Burns and Roe 1979).

(4 ) Pfeffer measured the osmostic pressure of solutions with varying where concentrat ions in 1877 and showed that the product of the osmotic pressure Fs = salt flux, gm/cm2-sec and volume of a solution was constant at a constant temperature. He also B = salt permeability constant, observed that for a given solution, the cm/sec osmotic pressure increased with an increase in temperature while the ratio concentrat ion gradient across of osmotic pressure to temperature 3 the membrane t gm/cm remained constant (Williams and Williams 1967). Both the water and salt permeability constants depend upon t he membrane Van't Hoff built from Pfeffer's and the procedures used in its manu- observations to show that the osmotic fact ure. pressure, 'IT, is equal to the product of the solute concentration, C, the These equations indicate that absolute temperature, T, and the uni­ the water flux is dependent upon the versal gas constant, R, as was shown in applied pressure while the salt flux is Equation 2. Once again, this relation­ not. This results in an increase ship holds true for dilute solutions in both the quantity and quality of where Raoult's law is valid. produc t water as the appl ied pressure is increased. However, this improved The first application of osmosis performance is countered by an increased was proposed by Ostwald in the late feed water salinity as the water flux is 19th century (Williams and Williams increased. The higher feed water 1967) in the form of a perpetual motion salinity increases the salt flux through mach ine based on the di fference in the membrane, and increases the solution osmotic pressure caused by different

4 membrane types. Osmotic pressure is some 500 times greater than that of independent of membrane type, however, the earlier films while still retaining and as expected, the machine did not a high degree of salt rejection. With work. their significant contribution, reverse osmosis technology began to leave the Direct osmos is has had pract ical research stage. use in determining molecular weights and in studying the thermodynamic Advancements in membrane technology properties of solutions. It was have continued with the expansion not until the 1950s, however, that of the reverse osmos is proces s for the scientists recognized the practical solution of water quality problems. In appl icat ions of reversing the process. an inventory of desalination plants In 1953, the U.S. Department of the with treatment capacities of 95 m3 /d Interior, through the Office of Saline (25,000 gpd) or more, EI-Ramly and Water, sponsored an investigation at the Congdon (1981) listed 447 reverse University of Florida of desalination by osmosis plants in the United States with reverse osmosis. Reid and Breton a total treatment capacity of approxi­ conducted this study and found that mately 757,000 m3/d (200 MGD). Of the cellulose acetate exhibited permeability total, 119,000 m3/d (31.4 MGD) or 16 to water with semipermeability to salts percent was for domest ic use. As raw (Goff and Gloyna 1970). water quality deterioration continues with increased domestic, industrial, and agricultural use and as high quality In 1960 Loeb and Sourirajan devel­ water resources dwindle, the use of oped a modified cellulose acetate reverse osmosis as a water treatment membrane whose water permeability was option can be expected to increase.

5 CHAPTER II

PRETREATMENT

The purpose of pretreatment is to efficient filtration and long filter provide feedwater and brine streams with runs (Burns and Roe 1979). Other media, the physical and chemical properties such as granular nonhydrous silicate necessary to prolong membrane life. (Adams and Brant 1977), activated carbon Pretreatment steps are utilized to (Luttinger and Hoche 1974), and macro­ prevent premature deterioration of reticular res ins, may be used depending membranes, to minimize clogging of upon the particular application and the membranes due to part iculate loading or corresponding economic considerations. chemical precipitation on the membrane surfaces, and to prevent bacterial Cartridge filters are usually growth on and within the membranes. ins taIled pr ior to reverse osmos is systems as an addit ional prefilter to Speight and McCutchan (1979) protect the unit's membranes (Burns suggested that to avoid cos tly system and Roe 1979). The cartridge filter failure, pretreatment should be designed me d i a ma t e ria 1 is e i the r c e llu los e , for the worst case raw water quality rayon, wool, or acrylic fibers with expected. The exact pretreatment , recomme nded effect ive sizes vary ing requirements depend upon the quality of with the membrane configuration (Burns the raw water used and would include and Roe 1979). either physical or chemical processes or a comb i nat ion of the two to reach the Coagulation-Flocculation­ required pre-reverse osmosis water Sedimentation quality. If feedwater with a high concen­ Particulate Removal tration of suspended material of a colloidal nature is to be treated using Reverse osmosis systems are not reverse osmosis, suspended solids particulate removal devices and will removal prior to filtration may be clog rapidly during high particulate required. Coagulation causes the loadings. Proper operation of reverse neutralization of charges on the sur­ osmosis systems requires a feedwater f ace of the suspended colloids and turbidity of less than 1 JTU (Buckley destabilizes the suspension so that the 1975) and various physical and chemical slow mixing in the flocculation step processes can be utilized for feedwater allows particle aggregation and enhances particulate removal pretreatment. particle removal through sedimentation and filtration. Filtration Aluminum or iron compounds such as Filtration is the most common aluminum sulfate, sodium aluminate, pretreatment step to reduce membrane ferric sulfate, and ferrous sulfate are fouling from particulate matter. Dual used as coagulants. These compounds are media filtration, using sand and anthra­ acidic in nature and react with the cite, allows deep penetration of solids alkal inity of the feedwater to form into the filter bed and results in sulfates of magnesium, calcium, or

7 sodium as well as hydroxide precipi­ keep calcium, magnesium, and iron salts t ates. in solution. Sodium hexametaphosphate is widely used in reverse osmosis Scale Prevention installation especially for the inhibi­ tion of calcium sulfate precipitation. A number of chemical process options are available to control the Iron and Manganese Removal formation of chemical precipitates that may clog and coat the reverse The oxidized forms of iron and osmosis membranes. manganese can be deposited on r~verse osmosis membranes in the form of partic­ pH Control ulate, colloidal, or slime layers and may cause serious damage to the mem­ The adjustment of feedwater pH branes. between 5.0 and 6.5 is used to prevent hydroxide and carbonate scaling based on Aeration. Aeration may be used for the solubility product of the scale the oxidation of iron and manganese to forming compounds. When the pH of the insoluble ferric hydroxide and manganese feedwater is controlled between 4 and oxide. The oxidation of 1 mg/l of iron 1, protection of membrane deterioration requires 0.14 mg/l of oxygen while 1 via hydrolysis is an added benefit. mg/l of manganese requires 0.24 mg/l of oxygen (EPA 191]). Soluble iron is For most applications, sulfuric oxidized readily through aeration, acid is recommended for pH reduction however, manganese oxidation requires (Osmonics 1915). Sulfuric acid is the catalytic effect of contact with economical, is less corrosive than previously precipitated manganese hydrochloric acid, and the sulfate ion oxide to be effective. results in a lower salt flux than monovalent ions. Phosphoric acid is not Ion exchange. Iron and manganese recommended for pH control due to the can be removed by sodium zeolite ion low solubility of calcium phosphate. exchange in which the exchange bed may When the concentration of calcium and be either green sand or high capacity sulfate ions are high in the feedwat"er, resin (Burns and Roe 1919). With the hydrochloric acid may be necessary. use of ion exchange removal of iron and manganese, care must be taken to prevent When acidification is used to oxidation of the soluble iron and reduce the alkalinity of the feedwater, manganese forms in order to limit dissolved carbon dioxide diffuses fouling of the ion exchange bed. through the membrane making the corro­ s ion potent ial high in the product Softening. Iron and manganese water. Consequently, some pH adjustment can also be removed by lime-soda-ash of the product water is also required softening. The iron is oxidized to ei ther through decarbonat ion and/or ferric hydroxide while the manganese lime or caustic soda addition. is oxidized to manganic hydroxide (Burns and Roe 1919). Flocculation and Scale Inhibitors sedimentation are then employed to remove the softening sludge prior to The adjustment of feedwater pH reverse osmosis treatment. is not effective against CaF2 and CaS04·2H20 scaling (Takahashi and Potassium permanganate/manganese Ebara 1918) and a scale preventing dioxide greensand treatment. For small agent is needed. Sodium hexameta­ plants or forfeedwater containing 1 phosphate functions as a sequestering mg/l or less of iron and manganese, the agent to form soluble complexes that use of potassium permanganate as an

8 oxidizing agent followed by filtration chlorine and other oxidizing agents. through manganese dioxide greensand is Zero chlorine residual is recommended an economic alternative for iron and for these membranes and disinfection is manganese removal. The potassium accomplished using a flushing solution permanganate oxidizes the iron and of 0.75 percent by weight of a 30 manganese which then precipitates on percent formaldehyde solution (Burns and the filter. If too little potassium Roe 1979). permanganate is used, the filter itself oxidizes the iron and manganese, while Oxidants when the potassium permanganate is in excess of the feedwater iron and Chlorine 1S present in most mun1C1- manganese, the excess will regenerate pal waters and is usually the most the greensand filter. Due to the high import ant oxid iz ing agent in water cost of potassium permanganate and (Osmonics 1977), however, other oxidants the zeolite bed, preaerat ion is some­ such as chromic acid, ozone, and other times used to preoxidize the iron and halogens will affect reverse osmosis manganese. membranes 1n a similar manner.

Cellulose acetate membranes are the Disinfection most res istant to oxidation with these membranes ab Ie to tolerate cont inuous Bacterial slimes may form during an free chlorine concentrations up to 5 extended shutdown of a reverse osmosis mg/l and periodic free chlorine concen­ unit (DuPont 1977b). Microbial enrich- trations of 50 to 100 mg/l with little ment, or the movement of cellulosic membrane oxidat ion (Osmonics 1977). degrading bacteria through the reverse Chromic acid at feedwater pH values of osmos is membrane to colonize and pro­ greater than 2.2 has also been used liferate within the membrane, can also without membrane deterioration. Al­ occur during the operation of reverse though cellulose acetate membranes are osmosis systems (Hinterberger et al. resistant to oxidation, some manu­ 1974). To counteract this microbial facturers are conservative in the growth and biological membrane fouling, allowable chlorine dosages they recom­ some form of feedwater disinfect ion is mend, i.e., 0.5 mg/l continuous free required. chlorine concentration (Saltech 1978) and 1 mg/l (Burns and Roe 1979) to Hinterberger et al. (1974) showed 5 mg/l (Saltech 1978) maximum free that to reduce bacterial growth on chlorine residuals. reverse osmosis membrane surfaces, chlorination of the feedwater to a point Polyfuran and polyamide membranes of free chlorine residual was necessary. are generally intolerant to oxidative Disinfection of cellulose acetate degradation as stated above and oxidant membranes with the use of slug chlorine removal is required in these reverse dosages at regular intervals is recom­ osmosis installations. When dechlorina­ mended, while continuous chlorine t ion of the feedwater prior to reverse addition should generally be limited to osmosis treatment is required, sodium 1 mg/l free chlorine residual (Burns and bisulfite is normally used at a dosage Roe 1979). of 1.4 mg/l per mg/l of chlorine resid­ ual. Dechlorination can also be carried Polyamide and polyfuran membranes out using activated carbon adsorption are susceptible to degradation from (Speight and McCutchan 1979).

9 CHAPTER III

MEMBRANES

Membranes are the critical com­ be produced thin enough to provide ponent of a reverse osmosis system. reasonab Ie water flux rates, however. For effective operation, the membrane material must be highly permeable Research conducted at the Univer­ to water, highly impermeable to solutes, sity of California, Los Angeles, during and able to withstand high feedwater the late 1950s was concerned with im­ pressures. Water recovery should be proving the water flux of the cellulose high to minimize both feed pumping costs acetate membrane while maintaining its and brine disposal costs. Membranes are high salt rejection properties. Loeb a significant fract ion of the capital and Sourirajan (1961) succeeded in costs of a reverse osmosis system and to increasing the water flux through these be economical, the water flux rate must membranes without a decrease in their be large enough to produce a reasonable salt rejection through the addition of a volume of product water per unit time pore producing agent. (Lonsdale and Podall 1912). High flux rate requirements demand thin membrane This anisotropic membrane had an walls. For long life, the membranes asymmetric structure consisting of a must be resistant to physical, chemical, 0.2 to 0.5 ~m thick dense surface layer and biological attack and to pH and underlain by a porous substructure and temperature extremes (Kellar 1979). was a major breakthrough in the develop­ Finally, because pressure vessel costs ment of the reverse osmosis process. are also high, the membranes should be The thin, dense surface layer provided capable of being cast into shapes with minimal resistance to flow and necessary high packing densities, i.e., high solute retention characteristics, while membrane surface area to pressure vessel the porous substructure provided struc­ volume ratios (Lonsdale and Podall tural support for the thin surface layer 1972). Unfortunately these requirements with little additional resistance to are often incompatible as one would flow. expect and t radeof fs are i nevi tab ly made in the production and use of Chemically, cellulose acetate is a commercial membranes. hydroxylic polymer of long chains of S-glucoside units with molecular weights Cellulosic Membranes of 25,000 to 65,000 that have been acetyl. ated with ace tic anhydride and Research began in the early 1950s hydrolyzed to reduce acetyl at ion to to deve lop a reverse osmosis membrane between 38 and 43 percent. Cellulose with sufficient strength and product acetate membranes are prepared from a water flux to be of commercial interes t solution consisting of the polymer in desalinat ion applications (Chan and di sso 1 ved in an appropriate so 1 vent McCutchan 1978). Cellulose acetate was (usually acetone) along with a non­ the first material found to provide solvent (water or formaldehyde) and an significant electrolyte rejection from appropriate salt, both of which function aqueous solutions (Reid and Breton as swelling agents. Membranes may be 1959). Initial membranes could not cast in either sheet or tubular form by

11 physically spreading a desired thickness high and low pH and elevated temperature of this solution on an appropriate operating conditions, and improved support under controlled atmospheric resistance to membrane compaction as conditions. Evaporation is allowed to compared to cellulose acetate membranes. take place for a controlled period of Membranes produced from a blend of time to permit solvent diffusion through cellulose triacetate and cellulose the polymer and the membrane surface to diacetate have also been developed produce the characteristic membrane (Burns and Roe 1979) that resul t in asymmetry. This structure is gelled by improved performance and operating immers ing the film in a bath of water stability over the Loeb-Sourirajan near O°C. cellulose acetate membranes.

In the as-cast state, these mem­ branes reject only a small amount of Polyamide Membranes sodium chloride, although they are relatively impermeable to high-molecular Since the development by Reid and weight materials. The semipermeability Breton (1959) of cellulose acetate as a is markedly improved by annealing the desalination membrane and the improve­ membranes in a water bath at tempera­ ments in its water flux by Loeb and tures between 60° and 90°C. During the Sourirajan (1961), there has been a annealing process, the permeability to continuous search for new and better water decreases by about an order of membrane materials. In 1967 DuPont magnitude while the permeability to introduced the asymmetric aromatic sodium chloride decreases by more polyamide fiber. The polyamide materi­ than three orders of magnitude. By als are described by Burns and Roe accurately controlling the temperature (1979) as synthetic, organic, nitrogen­ during annealing, a range of different linked aromatic, substantially linear salt rejecting membranes can be pro­ condensation polymers. Although the duced. Water permeability of the water permeabilities through these membrane is inversely, al though not membranes are about an order of magni­ linearly, related to the salt rejection. tude less than through cellulose acetate membranes, their packing density is Although cellulose acetate has about an order of magnitude higher excellent permeability character­ (Belfort 1977). The inexpensive, com­ istics with productivity rates on the pact area of the hollow fiber geometry order of 0.5 to 0.7 m3 /m2 /d, it is makes these membranes compet it ive with limited in some applications because of the high flux cellulose acetate mem­ poor chemical resistance to hydrolysis branes. at a pH below 4 and above 8 and because of inadequate res istance to therma 1 As manufactured, the fibers have induced hydrolysis above 38°C (Porter poor monovalent ion rejection capabili­ 1978). These membranes are also subject ties. A coating of tannic acid is to deterioration by cellulase producing appl ied to the fibers to improve mono­ organisms (Burns and Roe 1979). valent rejection. Productivity rates for this membrane material is in the In an effort to improve the stabil­ range of 0.04 to 0.08 m3 /m2 .d (1 to ity and usefulness of cellulose acetate 2 gal/ft2 .d). Bicarbonate ion re­ membranes, several modified membrane ject ions are low at low pH conditions types have been developed. Dow Chemical but improve with increasing pH. Low has developed cellulose triacetate molecular weight organics are separated hollow fiber membranes (Burns and Roe effect ively by the polyamide membranes 1979) that result in improved salt with the efficiency decreasing rapidly rejection, improved resistance to at a molecular weight of approximately microbial attack, improved stability to 100 (Spatz and Friedlander 1978).

12 Shields (1979) reported that membranes can be increased without a polyamide membranes are physically and decrease in their salt rejection by chemically stable· and consequently long reducing the dense film thickness. membrane lives can be expected from Belfort (1977) reported that composite them. Certain aromat ic polyamides are membranes are able to desalinate sea­ stable during continuous operation over water at a high flux rate of 1.02 a pH range of 4 to 11 while this oper­ m3/m2.d (25 gal/ft2.d) at 10.3 MPa ating range may be broadened to between (1500 psig). 2 and 12 for 1 imi ted time periods. Extended usage at the extreme pH values Even with clean feedwater, the may cause irreversible modifications to water flux through an anisotropic the membrane material and alter its membrane decreases wi th time. Th is separation ability however, and Kosarek phenomenon is apparently the result of a (1979b) suggested a narrower permissible creep process in which the dense surface operating pH range of 3 to 9 with an layer grows in thickness by amalgamation optimum pH value cited of 5.5. with the porous substructure immediately beneath it. The effect of compaction is Polyamide membranes are capable of more pronounced with high flux membranes operating at higher temperatures than and at high temperatures. A major cellulose acetate membranes (Burns benefit of composite membranes is an and Roe 1979) and Kosarek (1979b) improvement in their resistance to this indicated a safe operat ing range to compaction phenomenon (Porter 1978). 49°C. Polyamide membranes have an added advantage over cellulose acetate The composite membrane is similar membranes in that they are essen­ in configuration to the asymmetric t ially immune to biological degradation Loeb-Sourirajan cellulose acetate (Shields 1979) as microorganisms have membrane. An ultra thin film of a not yet developed enzymes that react semipermeable polymer is formed upon the wi th synthetic polymers (Burns and Roe finely porous surface of a highly water 1979). permeable support membrane. The water permeability of the thin film material, The major disadvantage of the the thin film thickness, and the pore polyamide membranes is their extreme characteristics on the surface of the sensitivity to oxidants. Warranty support membrane defermine the water requirements specify 0 mg/l feedwater flux through these composite membranes. chlorine concentration (Kosarek 1979b). The thin film thickness ranges from 0.01 Spatz and Friedlander (1978) suggest to 0.10 l1m and can be varied and con­ that whenever oxidants, especially trolled with reproducibility. The chlorine, will be in the feedwater, composite membrane is greatly improved polyamide should be carefully scruti­ over the classical asymmetric membrane, nized and probably avoided, unless the however, by eliminating the ill defined pH is such that the oxidation potential area between the thin film and the is low. porous substructure (Burns and Roe 1979) • Additional freedom is provided Composite Membranes in the preparation of the composite membranes including: independent The thin dense surface film and selection of materials from which to porous substructure of reverse osmosis prepare the ultra thin semipermable membranes need not necessari ly be made barrier and the finely porous supporting from one material. By optimizing the membrane; independent development and formation of each layer and sandwiching preparation of the thin film and the the layers together, a membrane with porous supporting membrane allowing for superior performance characteristics can optimization of each component for its be produced. The permeability of the specific function; reproducible control

13 over the thickness of the thin film as formation in place of toluene diiso­ needed for different applications; and cyanate. The maj or drawback of the improved control over the porosity of PA-100 composite membrane, as with other the thin semipermeable barrier (Burns composite membranes, is its high sensi­ and Roe 1979). Several types of thin tivity to chlorinated feeds which result film membrane composites have been in a rapid deterioration of the mem­ developed; however, polysulfone has been brane. Research studies were conducted used the most in the commercialization to modify the PA-100 system to make the of composite membranes (Sudak et al. membrane more tolerant of chlorinated 1979). feeds and to eliminate the added cost of dechlorination. The efforts led to the North Star Research and Development development of a polyamide composite Institute developed a cross linked membrane referred to as PA-300. polyethyleneimine membrane, designated as NS-IOO (Chian et a1. 1975). The membrane has a dominant active layer of The PA-300 barrier is prepared polyethyleneimine cross lined with from the interfacial condensation of m-toluene 2,4-diisocyanate, coated on a an epichlorohydrin ethylene idamine porous polysulfone support. The NS-100 (epiamine) condensate with isophthaloyl was claimed to be the most promising chloride (Burns and Roe 1979). Although membrane ever developed with respect to the PA-300 membranes remain chlorine pH stability, permeate flux, and the sensitive, compared to the PA-100 series removal of solutes, especially small they are much more stable in chlorinated polar organic compounds (Chian et a1. feedwaters (Burns and Roe 1979). 1975). At 10.3 MFa (1500 psig), this membrane was reported to have a flux of Burns and Roe (1979) described a over 0.8 m3 /m2 .d (20 gal/ft2 .d) with cellulose triacetate composite membrane 99.5 percent salt rejection when used with a 0.025 to 0:050 ~m thick film that with synthetic seawater (Porter 1978). was formed on a finely porous cellulose In addit ion, the membrane was reported nitrate cellulose diacetate support by to have excellent stability when used dipping the latter in a dilute solution for alkaline feed water with pH's of 7 of cellulose acetate (2.83 percent). to 13. Spatz and Friedlander (1978) The film thickness is controlled by suggested that the membrane will fill a the concentrat ion of the cellulose need in many processes for intermediate triacetate polymer in the solution and salt removal at elevated pH values. Its by the film withdrawal rate. major drawback is that it is readily attacked by chlorine. A new type of dry reverse osmosis asymmetric membrane is being developed Burns and Roe (1979) described a and incorporated into sprial elements by furfuryl alcohol thin film compos ite, Chemical Systems, Inc. (Burns and Roe designated as NS-200. The membrane is 1979). The membranes, produced in the prepared on a poly sulfone support and casting from a solution processed from has demonRtrated 99 percent salt rejec­ quaternized cellulose triesters, are dry tion and water fluxes of 0.73 to 0.81 storable and wet-dry stable. Because of m3/m2 .d (18 to 20 gal/ft2 .d) when tested the presence of the quaternary ammonium on a 3.5 percent salt solution at 6.9 groups, the new membranes have greater MFa (1000 psig) for 1000 hr. permeability and permselectivity than cellulose acetate membranes and are also Burns and Roe (1979) described a more resistant to hydrolysis, chlorine polyamide composite membrane, PA-100, oxidation, and biodegradation. Measured prepared in a manner similar to NS-IOO values for water flux and salt rejection except that isophthaloyl chloride is were 0.92 m3 /m2 ·d (22.5 gal/ft2 .d) employed for reverse osmosis barrier and 98 percent, respectively, on a 1

14 percent sodium chloride solution at 6.9 > polyethylene imine > polyfuran > MPa (1000 psig) (Channabasappa and cellulose acetate. The stability of the Strobel 1976). membranes to oxidation by chlorine was in the order of cellulose acetate > Summary polyetheleneimine > polyamide > poly­ furan. The authors concluded that no The relative stability of four one membrane material proved to be the reverse osmosis membrane materials best and the choice of membranes remains subjected to various operating condi­ application specific. Additional tions was investigated by Spatz and membrane materials are expected to Friedlander (1978). The stability of become available in the future that will membranes to low pH was in the order of not only provide improved physical and polyfuran > cellulose acetate > poly­ mechanical durability, but also enhanced ethyleneimine > polyamide, while mem­ chemical and biological stability brane resistance to high pH feedwater while at the same time providing ~m­ solutions was in the order of polyamide pr9ved process reliability.

15 CHAPTER IV

MODULE CONFIGURATION

The membrane module houses the While the plate and frame con­ reverse osmosis membrane so the feed figuration was abandoned in the United stream is sealed from the product States, the Danish Sugar Corporation, stream. The module must have the DDS, continued the development of mechanical s t abi 1i ty to support the plate and frame systems (Nielsen et al. membranes when they are subjected to 1980). Through continual process high pressures of 1.4 to 10.3 MFa (200 improvement, the DDS developed a second to 1500 psig). The module must also be generation plate and frame configuration constructed to prevent pressure leaks shown in Figure 4(b). While the flow be tween feed and produc t s.treams and was conducted by spacer plates sepa­ large pressure drops through the system. rating the membrane support plates in Hydrodynamically the module should be the original design, Figure 4(a), the designed to minimize the buildup of both second generation DDS design eliminated salt and fouling layers on membrane the spacer plates and allowed the surfaces which impede membrane per­ forma t ion of membrane channe Is from formance. The module should also neighboring support plates, Figure 4(b). provide a high membrane packing density to reduce capital costs of the pressure This second generation design does vessels and should accommodate uncompli­ not require a pressure vessel as each cated membrane replacement. The four membrane is individually sealed by most common module configurations used adjacent spacer plates, Figure 5. The are labeled the plate and frame, the new design has increased the operating tubular, the spiral wound, and the efficiency of the plate and frame hollow fiber design. configuration; however, these modules remain susceptible to fouling, are Plate and Frame Modules difficult to clean and replace, and subsequently are still fairly costly. The first module configuration employed in large scale applications Tubular Modules of the reverse osmosis process was the plate and frame sys tem deve loped by The tubular module, Figure 6, is Aerojet General Corporation (1966). The the simplest design of all modules original design was similar in principle used in reverse osmosis and was the to the filter press and became ext inct first of the current commercial modules in the late 1960s due primarily to the to be developed (Kellar 1979). The difficulty and expense in changing membrane is inserted into or coated onto degraded membranes (Belfort 1977). With the surface of a porous tube which is each membrane mounted on an individual designed to withstand high operating support device, the equipment and pressures. Pressurized feedwater is maintenance costs did not justify the introduced into one end of the tube productivity obtained from this original and flows through the tube while the pI ate and frame configuration (Johnston product water permeates the membrane and Lim 1973). rad ially. Tube scan be arranged as

17 Concentrate Concentrate ,...... ,...,;;;---- ..

Permeate

Permeate.. Feed .. __...,..j~""1oiiioI Permeate Permeate Feed

(a) First generation plate (b) Second generation plate and frame configuration. and frame configuration.

Figure 4. plate and frame configuration of (a) first generation and (b) second generation design (Nielsen et al. 1980).

--~----~---- Center bolt

...... ~ ...... "" •••• " .... , t .. End Flange ...... mmmggm1ggmHl::::: , .... . -- ~..•~ ... ~... ~...• ~ ...~ ... ~....~ ...~ .•. ~... - FLOW

...... ~ t ...... ~ .... " ...... ,...... ··~.. ~··~··~···~··~··~.. ~···~ ..~··~··~· 's== MembraneSpacer plate suppor' disc i PERMEATE Neck ring ---::::::-;f/I-- Membrane -..J'.4rl-- Filter paper

~~:.,;'hf--- Membrane support disc

+-=~~~"""C--___ Filter paper ~::====~====~~~~~-----Membrane

Figure 5. Second generation plate and frame configuration (OWRT 1979).

18 Porous Tube

Pressurized

Feed

Multiple tubes norma·lly connected in series or parallel to form complete module

Fiberglass Reinforced Epoxy Tube

-Cellulosic Liner

Detail

Figure 6. The tubular module element (OWRT 1979). series or parallel. The tubular module Spiral Wound Modules was moderately successful during the 1 ate 1960s in appl icat ions such as Spiral wound modules were intro­ chemical separations and food and drug duced in the mid-1960s by Fluid Systems proce ss ing. Division of Universal Oil Products and were a major step forward in producing The advantages of the tubular large packing densities (Kellar 1979). design relate to its ability to treat The spiral wound module, Figure 7, extremely turbid feedwaters and the ease contains two layers of semipermeable by wh ich it can be hyd raul ically or membranes separated by a woven fabric of mechanically cleaned (OWRT 1979). nylon or dacron. A flexible envelope is formed by sealing the edges of the Disadvantages of the tubular membrane on three sides. The open side configuration include high capital is attached to a perforated central costs, high pumping costs related to tube. A sheet of plastic netting, high velocities required to prevent placed adjacent to the membrane enve­ precipitation from forming on membrane lope, separates the membrane layers surfaces, low water production rates per during assembly and promotes turbulence unit of module volume, and low packing in the feed stream during operation. densities. The envelope and netting are wrapped

19 J

Permeate Flow From Other Modules

Feed Flow Through Open Mesh Outside Membrane Envelope Module Core and Permeate Collector Tube

No

Sealed on Edges With Support Fabric Between

Permeate Flows Through Membrane Into Support Mesh Fabric Then Follows Membrane ::= t ~~ Fabric to Permeate Support Fabric' f:', Collector Tube

Figure 7. The spiral bound module element (OWRT 1979). around the central tube in a spiral by semi-skilled labor and variations in configuration similar to a window module quality can be expected. shade. The spiral wound element is then ready for insertion into a pressure Hollow Fiber Modules container for use. Pressurized feed­ water permeates through the membrane The hollow fiber module, Figure 8, into the fabric. Flow channels direct was first developed by DuPont in the the permeate to the perforated central late 1960s and was later also produced tube for collection and removal from the by Dow Chemical (Buckley 1975). DuPont system. uses aromatic polyamide membranes in its units while Dow Chemical uses cellulose The spiral wound module has a high triacetate membranes. The membrane packing density and a low manufacturing material is spun into hair-like hollow cos t • I tea n bee h em i call y 0 r h y­ fibers having an outer diameter of 85 to draulically cleaned easily and enjoys a 200 ~m. The fibers are bundled together broad range of applications (OWRT 1979). in either aU-shape conf igurat ion for The spiral wound modules can be unrolled exterior brine flow or in a straight and examined for defects and the product configuration for interior brine flow. tube can be tested to locate leaks along The fibers are wrapped around a support the full length of the vessel. When frame with their open ends epoxied into membrane or product tube defects are a tube sheet, making sure the fibers are located visually, or with dye, they can not blocked. be remedied prior to rerolling. Spiral wound modules have also been popular With exterior flow modules, the because of their resistance to scale product permeates radially inward formation and fouling. through the unsupported fiber. The product moves ins ide the hollow fiber The pressure vessel can hold up to bore to the product collection chamber. six membrane module elements in series The exterior flow module is very com­ with the module yielding a productivity pact, is low in cost, and can withstand of 0.6 to 1.2 m3/m2/d (15 to 30 gall high pressures of 2.8 MPa (400 psig). ft2/d) . Product recovery ranges from Its disadvantage is that it plugs easily 5 to 15 percent of the feed flow rate, and is difficult to clean because of the while product side pressure drops small spacing between the fibers in a through the module range from 206 to 276 bundle. KPa (30 to 40 psig). The interior flow modules are The main disadvantage of the spiral similar to heat exchangers. The wound modules is their sensitivity feedwater flows into the bore of the to high turbidity feedwaters due to the hollow fibers at one end, moves along small feed flow passages that are the inside of the fibers, and flows out subject to clogging if extensive of the other end of the unit. The pretreatment is not practiced. Dead product permeates radially outward spaces in the area between the element through the fiber walls. The interior and the pressure vessel are susceptible feed design possesses the character­ to biological growth, while the 0 ring istics of the exterior feed design in seals that separate the elements and addition to providing controlled hydro­ the module end caps can be nicked or dynamics of the feed which improves the roughened allowing leakage of reject ease of cleaning. This design is water into the product stream. A relatively new and no operating experi­ portion of the membrane is needed for ence was reported in the literature. adhesive attachment and results in nonproduct ive areas within the module. Pressure vessels normally contain a Finally, element assembly is performed single element. Productivity ranges

21 JI!

''0 11 Ring

N N

Epoxy Tube Sheet

Figure 8. The hollow fiber module (DuPont 1977a). from 0.12 to 0.24 m3 /m2 /d (3 to 6 pressure vessel in which biological gal/ft2/d) (Burns and Roe 1979), The growth can occur (Burns and Roe 1979). elements have high packing densities Additionally, membrane imperfections of 39,400 m2/m3 (12,000 ft2/ft3) and are cannot be visually identified except by resistant to pressure collapse even to destruction and the large O-ring on the 4 • 1 t 0 6. 9 MP a (6 00 t 0 1 00 0 psi g ) outside diameter of the product tube (Porter 1978). Manufacturing costs are sheet is frequently a source of internal relatively low and systems based on this leakage. Up to 20 percent of the configuration are extremely compact hollow fibers may be blocked by manu­ (OWRT 1979). Broken fibers are claimed facturing defects on the face of the to be self healing by collapsing product tube sheet (Burns and Roe 1979) (Burns and Roe 1979). Product recovery and by design, large membrane areas are per module is 50 to 60 percent of the unproductive due to the product tube feed flow rate. Because the fibers sheet necessary to take the thrust from themselves are capable of withstanding the 2.8 MPa (400 psig) pressure drop high pressures, the encasing module is between the feed and product streams. the major mechanical component of the Finally, limited flow velocities may complete unit and no support screens are occur in areas adjacent to the tube required. The result is a comparatively sheet s resul t ing in nonuni form flow low equipment cost requirement (Johnston distribution through the fiber bundle. and Lim 1973). Summary Even though this module con­ figuration is economic, its susceptibil­ As with membrane selection, module ity to fouling and the difficulty in configuration selection becomes a matter cleaning the units requires extensive of appl ication specificity. All mem­ pretreatment even when treat ing rela­ brane configurations described, except tively clean feedwaters (OWRT 1979). the plate and frame design, are present­ The pretreatment requirement severely ly being used for water and/or waste­ limits the range of applications water treatment. The choice for a for this module configuration. particular use will depend greatly upon the raw feedwater quality, the pretreat­ The hollow fiber modules, like the ment requirements and costs, and the spiral wound module, have dead spaces economics of the particular membrane between the product tube sheet and the module designs being considered.

23 CHAPTER V

MEMBRANE CLEANING AND MAINTENANCE

Even with pretreatment to reduce change in the feedwater composition. fouling and scaling of reverse osmosis Cleaning equipment, chemicals, and membranes, reverse osmosis units re­ procedures are required at reverse quire periodic cleaning and flushing. osmosis installations to compensate for Shields (1979) indicated that a regular any of the above conditions. cleaning program will increase membrane life and maintain adequate membrane Operational Considerations performance. Since chemical cleaning costs average less than $0.02 per 1000 Cleaning methods vary according to gallons of product water (Shields 1979), the type of reverse osmosis module being routine cleaning is clearly a sound utilized. In general, cleaning or i nve s tment. flushing is conducted at low system feed pressures and a brine concentrate flow Johnston and Lim (1973) reported rate approximately equal to the feed that product water flux will decline and flow rate to minimize product water membrane permeability wi 11 be reduced flow. Cleaning or flushing should be due to fouling of the membrane surface, performed, as in normal operation, from densification of the polymer sub­ membrane feed side to reject side, as structure from applied pressures, or reverse flow or back flushing may result irreversible chemical and/or physical in permanent damage to the membrane damage to the polymer surface layer. modules. The membrane surface layer can be damaged from hydrolysis of the ester Cleaning solutions may be heated to group in cellulose acetate membranes improve cleaning efficiency and decrease or from physical abrasion by partic­ the required cleaning time. However, ulate materials in the feed solution. the cleaning solution temperature must Colloidal gels or solid precipitates be monitored to ensure that it does not will foul the membrane surface, increase exceed the allowable maximum operating the effect ive osmotic pressure of the temperature of the membrane. Recircula­ feed, and reduce the net driving force tion of the cleaning solution will for flow across the membrane. increase its temperature and Burns and Roe (1979) suggest a maximum cleaning Ina~equate operational procedures solution temperature of 35°C for safe that may contribute to membrane fouling system operation. would include (Burns and Roe 1979): pretreatment upset conditions, 1mproper Cleaning procedures should be equipment selection, inadequate flushing carried out when either the salt passage following shut down, failure of cleaning increases by 50 percent of normal chemical injection systems, a lack of operating levels, brine or product water operator knowledge or proper execution, flow rates decline by more than 5 a low level buildup of precipitates percent at constant temperature and over extended periods of time, 1n­ pressure condi t ions, or membrane adequate interpretation of salt rejec­ module pressure drops increase by 50 tion and productivity data, and/or a percent (Burns and Roe 1979), If one

25 cleaning cycle fails to improve per­ 2,000 to 500,000 with an average of formance, additional cleaning cycles 20,000 to 50,000. Scale format ion is should be performed. If cleaning is due to its ability to form insoluble unsuccessful, reasons for the fouling precipitates with multivalent metal ions should be determined and correct ive such as Fe+3 or Ca+ 2 • Organic colloids measures taken be fore rep 1 ac ing the or proteins may also cause membrane membrane elements. fouling.

In the event of an emergency Johnston and Lim (1973) reported shutdown, flushing the system with that foul ing from adsorbed organics is product water is recommended. This sometimes of a nature that circulation procedure will remove brine from the of clean water through the system may membrane modules and will reduce the be adequate to restore membrane per­ potential for scale formation on the formance. Some organic foulants may membranes (Burns and Roe 1979). Burns also be dissolved using pH adjusted and Roe (1979) suggest providing an water. Regular cleaning of the mem­ emergency flushing system on reverse branes is a necessity, however, and the osmosis systems consisting of an ele­ most effective organic foulant cleaners vated product water storage tank with are enzyme detergents such as Biz, piping from the tank to the main header Tertgazyme, or Bold. of the reverse osmosis unit. A conduc­ t ivity meter can be used to shut a Bacterial Growth flush control valve when the conduct iv­ i ty 0 f the brine stream reaches an The large surface area of reverse acceptable level. osmosis membranes is an inviting en­ vironment for bacterial growth. Dis­ The nature and extent of membrane infect ion is required prior to reverse fouling is dependent upon the raw osmosis treatment as described earlier feedwater quality, the extent of pre­ to limit microbial growth and biological treatment, and the degree of surface fouling of the membranes. If the turbulence within the membrane modules. disinfection step is not successful, Fouling is caused by a number of differ­ if the system is shut down for an ent materials and their effect on extended period of time, or if the system performance is summarized in product brine"becomes contaminated with Table 1. Because a variety of foulants microorganisms, membrane cleaning exist that hamper reverse osmosis for bacterial slime removal will be performance, a range of cleaning tech­ required. niques has been developed. Specific chemical cleaning agents, their applica­ Generally, membrane sterilization tion, source of supply, and cost are and bacterial slime removal using provided in Appendix A. A summary of a 0.75 to 1.0 percent by weight, 30 foulant characteristics and cleaning percent formaldehyde solution is procedures is found below, while specif­ recommended (Burns and Roe 1979). A ic cleaning procedures are located In· thorough flushing of the membrane Appendix B. module banks and piping should be carried out before the plant is returned Organic Foulants to service. The formaldehyde solut ion should be left in the modules if they Humic acid scale is generally the are to be taken out of service. main organic foulant to be dealt with in reverse osmosis installations. Humic If formaldehyde cleaning fails to acid, a brown polymeric constituent of restore membrane performance, flushing soil organic matter, is a polyelectro­ with a chlorine solution of 1 to 5 mg!l lyte whose molecular weight ranges from free chlorine residual is recommended

26 Table 1. Effects of membrane foulants (DuPont 1977b).

Foulant General Symptoms Salt Passage Bundle Product Pressure Drop Water Output

Hydrated oxides Rapid* Marked Rapid* Marked Rapid* Marked (iron, nickel, Increase Increase Decrease copper, etc.) (>2x) (>2x) (20-50 percent)

Calcium Precipates Significant Slight to Moderate Slight (carbonates, sul­ Increase Increase Decrease fates, phosphates) (10-25 percent) (10-50 percent) «10 percent)

Colloids Gradual** Gradual** Gradual** (Mostly aluminum Marked Increase Marked Increase Marked Increase silicates) (>2x) (2x) (>50 percent)

Mixed Colloids Rapid* Increase Gradual** Gradual** (iron, organics, (2 to 4x) Marked Increase Marked Decrease and silicates) (>2x) (>50 percent)

Bacterial Marked Increase Marked Increase Marked Increase Slimes ()2x) (>2x) (>50 percent)

*Within 24 hr **Over several weeks

(Block 1977) only as a last resort. Carbonate scale will res ist mechanical A maximum of one hour flushing is flushing but can be dissolved 1n a suggested to prevent membrane deterior­ warm weak acid solution of one to ation through chlorine oxidation. two percent citric acid. An ammon1a Chlorine cleaning cannot be used with citrate solution may also be used to po lyamide and polyfuran membranes that remove these scales. Calc ium suI fate are extremely chlorine sensitive. scale is less eas.ily dissolved than carbonate scale bu t 1S more eas i ly Hardness Scale removed by flushing. Block (1977) concluded that the EDTA Na4·4H20 (20 Hardness scale consists of precipi­ percent), N~HC03 (7 percent), and Zonyl t ates of carbonate hardness, i. e. , FSA (0.005 percent) solutions adjusted calcium ',and magnesium carbonate; non­ to pH 7 gave the best results for carbonate hardness, i.e., calcium and calcium sulfate dissolution. magnesium sulfate; and other calcium salts such as calcium fluoride and Boen and Johannsen (1974) reported ca lc ium phosphate. Hardnes s sca Ie can that calcium deposits chemically identi­ be avoided by keeping product water fied as tri-calcium orthophosphate recovery below 50 percent, 'by adding could be removed from reverse osmosis antiscale solutions such as sodium membranes by a 15,000 to 30,000 ppm (2 hexametaphosphate, or by controlling the to 4 oz/ gal) solution of EDTA (Ques tex pH of the' feedwater in the acidic range or Versene 100) adjusted to a pH value where precipitation will not occur. of 7 with sulfuric acid. If sulfuric 27 a c i d 1 sus e d for c 1 e ani ng sol uti 0 n checked for deteriorat ion. All defec- preparations, the solubility limit of tive equipment and appurtenances should calcium sulfate may be exceeded and be replaced with bronze, stainless hydrochloric acid would be preferable steel, or fiberglass reinforced materi­ for pH adjustment. als for high pressure elements and PVC for low pressure elements to minimize Takahashi and Ebara (1978) utilized 1ron oxide fouling. sponge ball cleaning and scale pre­ vent ing agents to limi t hardness scale Block (1977) found ammonium bi­ development in their units. Sponge ball fluoride, at 2 percent by weight ad­ cleaning is a physical abrasion method justed to a pH of 4.3, to provide the that 1S appl icable only to tubular best results for silicate scale removal module membrane configurations and from reverse osmosis membranes. A 2 therefore has limited application. percent by weight sodium phosphate solution adjusted to a pH of 12.4 was Inorganic Colloids and the next best silicate scale remover Metal Oxides followed by ammonium fluoride and ROGA cleaning solution B. No chemical agents Scales of clay-like materials have been found to completely remove composed of si, AI, Ca, Mg, and Fe are silica imbedded in membranes, nor are very difficult to dissolve even without complex aluminasilicates, containing the restrict ions imposed by the sens i­ Ca, Mg, and Fe, completely removed with tivity of the reverse osmosis membranes present cleaning solutions. and are only partially removed by some of the better performing cleaners tested A 2 percent by weight citric acid in the laboratory (Block 1977). It was solution, adjusted to a pH of 4 with therefore recommended to prevent the ammonia hydroxide is recommended by formation of these deposits, rather than DuPont (1980a) for iron hydroxide scale to try and remove them after they are removal. Flushing the modules with formed. Pretreatment steps such as product water prior to cleaning is ultrafiltration or polymer coagulation advised since residual calcium and are necessary to remove these fine magnes ium in the water in the modules particulate materials and prevent will reduce the effectiveness of the this form of membrane fouling. cleaning solution by complexing with the citric acid. A green-yellow color is DuPont (1980a) stated that 1n cases present in the cleaning solution when where iron and oxygen are present in the the citric acid content is in excess of feedwater, iron fouling will occur the iron content on a molar basis. When despite the use of high quality filtra­ there is more iron than citric acid, a tion. This iron fouling will result in red-brown color forms indicating that increased systems pressure drops, the cleaning solution should be changed. decreased product water flux, and Block (1977) also found that iron and increased salt passage. Allen and manganese hydroxide scale could be Shippey (1978) recommended that since removed effect ively by a 2 percent by iron materials cause cleaning diffi­ weight sodium dithiorite solution, culties, no iron should be allowed Na2S204, adjusted to a pH of 3.6. in future reverse osmosis system mate­ rials. In existing facilities, analyses Membrane Rejuvenation should be performed for metals in product water samples before and after When a membrane has been subjected c leaning to monitor the presence of to severe cleaning procedures or cellu­ corrosion products. If corrosion lose deterioration, certain polymer products are detected, upstream pumps and colloid solutions are reported to be and hydraul ic components should be effective in restoring membrane salt

28 rejections (Burns and Roe 1979). Two as they are apt to wash out over a rejuvenation procedures are provided in period of several weeks. Membrane Appendix C. These procedures are productivity is reduced by 10 to 15 effect ive only on intact membranes and percent as well due to a loss of mem­ are generally only temporary remedies brane surface area when the rejuvenation especially when using colloid solutions solutions plug membrane defects.

29 CHAPTER VI

REMOVAL OF INORGANICS USING

REVERSE OSMOSIS

The major function of reverse Sourirajan (1964b) illustrated the osmosis systems is the separation general applicability of reverse osmosis of inorganic substances from a waste as a separation technique for aqueous stream. A great deal of work has been inorganic solutions. He also indicated devoted to the analysis of inorganic the possible predictability of the solute rejection by reverse osmosis separation and flow characteristics of membranes, however, general predictive porous cellulose acetate membranes and models for membrane performance, espe­ the concept that separations are similar c ially when treat ing mul t icomponent for ions of the same va lence. The feedwaters, have yet to be developed. applicability of reverse osmosis was tested with several commonly available Single Component Systems inorganic salts in aqueous solutions using different samples of preshrunk Sourirajan (1963) proposed a Schleicher and Schuell cellulose acetate mechanism based on the Gibbs adsorption membranes. The extent of separation equation for the demineralization of depended only on the pore structure and aqueous sodium chloride solutions chemical nature of the membrane with using porous membranes. The technique respect to that of the solution. The is appl icable to inorganic solutes in ability of a cellulose acetate membrane aqueous solutions involving the prefer­ to separate the inorganic Lons Ln ential sorption of substances at inter­ solution was found to be: citrate> faces. The order in which the given tartarate > sulfate> acetate> chloride cellulose acetate membrane separated the > bromide > nitrate > iodide > thio­ various inorganic ions in aqueous cynate, and magnesium, barium, stron­ solution was: strontium> barium> tium, calcium> lithium, sodium, potas­ lithium> sodium> potassium and sulfate sium. This order is once again the same > chloride> bromide> nitrate> iodide. as the lyotropic series with respect to The given order is the same as the both cations and anions, although lyotropic series with respect to both exceptions to the lyotropic series were cations and anions. Sourirajan (1963) found. The lyotropic order with respect concluded that the negative adsorption to bivalent cations is Mg > Ca > Sr > of solutes at liquid solid interfaces Ba; Sourirajan found the corresponding appears to offer a sound basis for the separation order to be Mg > Ba > Sr > Ca development of a practical technique for at certain levels of solute separation. the separation of substances in solu­ tions. While the parameters involved From the data obt ained by Sourir­ in the mechanism of the separation ajan (l964b), Table 2 and Figure 9 technique were clear, they were not were developed to predict the separation sufficiently defined to make it possible and flow characteristics of any cellu­ to predict in detail the most successful lose acetate membrane for all solu­ system for a given separation problem. t ion systems illustrated, given the

31 J

Table 2. Separation of some related solutes aqueous solution under identical experimental conditions using S & S cellulose acetate membranes (Sourirajan 1964b).

Feed solution molality, 0.5M Feed rate, 30 cc./minute Operating pressure, 750 to 1500 p.s.i.g.

Mole % Salt Removed

Sodium NaCl acetate NaBr NaN03 NaI NaCNS LiCI CKI NHL.CI LiN03 KN03 NHL.N03 w 0 O. o. o. O. O. o. O. O. o. o. o. N 10 14. 8.6 6.5 6. 5. 11. 9. 8.5 7. 6.5 5. 20 27. 16.5 13.5 13. 10. 21.5 18. 16.5 14. 13. 10. 30 40. 25. 20.5 19.5 15. 32. 27. 24. 21. 20. 15.5 40 51.5 33. 27.5 26. 20. 42.5 35. 32. 28. 27. 21. 50 62.5 42. 35. 32.5 25. 53. 44. 40. 36. 34.5 27. 60 71. 50.5 44. 40. 30. 62.5 53.5 49. 45. 42.5 34. 70 78.5 60. 54.5 48. 35. 72. 64. 58.5 55.5 52. 42. 80 86. 70. 65.5 58. 43. 81.5 75.5 69. 66.5 62.5 53. 90 93. 82. 80. 73. 59.5 91. 87.5 83. 80. 77. 71. 100 100. 100. 100. 100. 100. 100. 100. 100. 100. 100. 100. II cellulose 2.5-acetate membranes on a ~ .------~ II FEEO SOLUTION MOLALITY' o.e M 10.5 FEEO RATE: 30 co/minute number of solutes important in water 10 10 OPERATING PRESSURE-Ieoo P",I.O. qual i ty. Phosphate and ammoni a re­ SYSTEM 9.5 9 movals were evaluated at two pH values. I [KN03-HZOJ Z[NH4N~ - H2O] .." 8.5 Removal of nitrate and bicarbonate as 8 3[NaN03 - H2O] 0 0 4CKCI-H2Q] 0 well as other salts were also deter­ • 5[NH4 CI-HZ!l] 0 7 • mined. The rejection of most of the C\I S[NaBr- H2Q] 0 r[Nal-H 2O] 0 salts was sufficiently high for both low a e [NaeNS - HZaJ 0 6 9(LIN0 -H 0J flux and high flux membranes that it J:'" 3 2 • .... IOCLICI-H20J ..

ch aracterist ics of the membrane for any Johnston (1975) described the one of the above systems that contain selective rejection of various heavy monovalent cations and anions. metal chloride salts by cellulose acetate membranes. Interaction of Hindin and Bennett (1969) conducted divalent cations with a cellulose a study with cellulose acetate membranes acetate membrane surface were generally dealing with membrane rejections of uniform and were likely largely cou- specific chemical species found in 1 om b i c in 0 rig in. S e 1 e c t i v e sol ute abundance in most treated wastewater reject ion was dependent mainly on the effluents. An order of ionic rejection interactions of the divalent cations by the cellulose acet ate membrane was with water in the bulk solution. found to be: Al+3 > Fe+3 > Cu+ 2 > Johns ton conc 1 uded that the overa 11 Na+ > Nli4+ > K+ > Cd+ > Mg+ > Ca+2 . The controlling criteria for these inter­ authors stated that the trivalent actions appeared to be the partial molar cations reacted like Lewis acids and free energies of hydrat ion and the formed hydroxy complexes while most entropies of the ions 1n solution. other cations formed hydrates. It was indicated that pH might be an Rangarajan et al. (1976) studied important factor as the hydrogen concen­ the reverse osmos is separat ions of tration might dictate the form of the several inorganic salts in aqueous multivalent cation. An order of rejec­ solutions involving polyvalent ions t ion of anions by the membrane was using porous cellulose acetate mem­ formulated as follows: S04 -2 > Cr04-2 branes. Free energy parameters for the > Cl- > HP04-2 > F- = CN- > N02- > Mg+ 2 , Ca+2 , Mn+ 2 , Co+2, Ni+2 , Cu+ 2 , N03- > B407-2 • Zn+2 , Sr+2 , Cd+ 2 , Ba+ 2 , Pb+2 , Fe+3 , Cr+3 and S04-2 ions, and for the MgS04, Lonsdale et al. (1969) measured the CoS04, ZnS04, MnS04, CuS04, CdS04 and reject ion of cellulose triacet ate and NiS04 ion pairs were determined. Free

I 33 energy parameters offered a means of reject ing 90 percent NaCl from a stan­ predict ing reverse osmo.s 1S separat ions dard salt solution was found to reject of inorganic salts in aqueous solutions more than 90 percent of all the metals. involving the above ions and/or ion pairs using porous cellulose acetate membranes. Only membrane specifications Burns and Roe (1979) recognized in terms of a single reference solute that ion rejection values are relatively such as sodium chloride were required to insensitive to membrane rejection predict performance. differences, especially at high rejec­ tion values. They suggested the use of Johnston and Lim (1978) conducted a reduction ratio as being more indica­ both laboratory and pilot plant studies tive of differences in reverse osmosis on the removal of inorganic contaminants proces s pe rf ormance. The reduc t ion by reverse osmosis using cellulose ratio is defined as the ratio of the acet ate membranes. A cellulose acetate solute concentration in the feed to the membrane capable of rejecting 70 percent solute concentration in the product or NaCl from a standard salt solution permeate and is calculated as follows: was found to reject more than 80 percent of each of the metals except Mg+2 as shown in Table 3. A membrane capable of (5 )

Table 3. Metal removal efficiencies by reverse osmOS1S (Johnston and Lim 1978).

Metal pH of Percent Metal Removal* Chloride 10 mg/l Solution NaC170 NaC190

(1) K+ 6.3 88.1 94.0

(2) Ba+2 5.8 88.3 100.0 (3) Be+2 4.3 83.8 97.0 (4) Ca+2 5.9 80.8 94.1 (5) Cd+2 5.5 85.1 98.3 (6 ) Co+2 5.8 81.9 96.0 (7) Cu+ 2 5.4 84.1 98.6 (8) Fe+2 5 .1 82.0 96.2 (9 ) Mg+2 6.1 73.5 90.0 (10) Mn+ 2 5.8 84.2 97.5 (11) Ni+2 5.9 81.8 95.2 (12) Pb+2 5 .2 85.5 97.6 (13 ) Sn+2 4.0 99.3 100.0 (4) Sr+2 5.9 84.1 96.3 (15) Zn+2 5.6 83.4 97.3

(6) Al+3 4.4 97.3 100.0 (7) Cr+3 4.2 99.1 100.0 08 ) Fe+3 3.4 100.0 100.0

*10 mg/l solutions tested at 1724 kPa (250 psi).

separations noted are for metal removals from a 10 mg/l solution when permeated through the reverse osmosis static test cell.

34 ~ where Table 4. Reduction ratios of sodium and magnesium salts (Burns and Roe RR = the reduction ratio 1979). R = percent rejection/100 Sodium Magnesium CF = solute concentration ~n the S04-2 106 670 feed, mg/l OAc- 88 HC03- 60 Cp = solute concentration ~n the product, mg/l F- 58 Cl- 31 190 At 98 percent reject ion, the reduct ion Br- 18 ratio is 50 to 1 while at 99 percent N03- 10 130 rejection, the ratio increases to 100 to CN- 8 1. Reduction ratios for selected sodium SCN- 6 and magnesium salts are shown in Table 4 and selected metal chloride reduction ratios are shown in Table 5. was greater than the reduction of the specific ion singly in aqueous solution, Multicomponent Systems however, changes were not as apparent for anions as for cations. Erickson et al. (1966) studied the desalination properties of membranes Agrawal and Sourirajan (1970) prepared from cellulose acetate-acetone­ developed a simple method for predicting formamide solutions which were cured at the performance of Loeb-Sourirajan type three different temperatures. In porous cellulose acetate membranes for studies of sea water and brackish water, low concentrations of mixed solute with the order of ion rejection was S04-2 a common ion in aqueous feed solution / Ca+2 > Mg+2 > HC03- > Na+ > K+ > systems. The method requires only data Cl- > Br-. When more than two ions on membrane specification and the occurred in solution, the passage or applicable mass transfer coefficient for rejection of one ion by the membrane was the corresponding single solute. strongly influenced by the surrounding ionic environment. In systems con­ Mixon (1973) conducted bench scale taining a mixture of monovalent and studies with cellulose acetate and divalent ions, the divalent 10ns were polyamide membranes to establish re­ preferentially rejected at the expense jection efficiences for barium, cadmium, of the monovalent ions. Alkaline earth chromium, copper, lead, and zinc. metals as well as sulfates were strongly Experiments were conducted using trace rejected indicating that the sign of the levels of the above metals singly, in ionic charge has no bearing on rejec­ combination, and at different concentra­ t ion. Ions normally rejected by cellu­ tions, using potable waters, waste­ lose acetate membranes were rejected to waters, ani brackish waters as feed­ an even greater extent in multisalt waters. Rejections for metals in solutions, while ions which are usually mixtures showed no significant differ­ passed easily were passed to an even ence when compared with rejection for greater extent. metals individually.

Hinden and Bennett (1969) ~n­ Sastri (1977) investigated the vestigated ion rejection by cellulose reverse osmosis characteristics of zinc acetate membranes. The authors found salt solutions using cellulose acetate that, in general, the percent reduction membranes. In general, Sastri found of specific ions in the product water that product rates increased linearly 35 Table 5. Reduction ratios of metal chlorides (Burns and Roe 1979).

Basis: NaCl = 31/1 0.1 Molar Solutions

600 psig t 75°F IIA Hydration Numbers in Parentheses Source: Reverse Osmosis of Single Salt Solutions, Havens Industries (1965) ! Li F 40/1 59/1

(3.4) (1. 8)

Na Mg Cl 31/1 190/1 W 0\ (2.0) (5.1) (0.9) IIIB VIII VIII IB lIB 2 2 2 2 K Ca Co+ Ni+ Cu+ Zn+ Br 22/1 114/1 184/1 110/1 92/1 119/1 17/1

(0.6) (4.3) (5.3) (0.9)

Rb 26/1*

Cs Ba La 32/1 125/1 354/1

(0) (3.0) (7.5)

*Prorated from a bromide test. with increasing operating pressures and prediction technique was experimentally decreased slightly with increase in feed verified from reverse osmos is data for concentrations. For a given operating the feed solution systems NaCl-KN03-H20, pressure, the separation of zinc nitrate NaBr-KC1-H20, and NaCl-NaN03-H20 using was less than zinc chloride which was several cellulose acetate membranes. less than zinc sulfate. This trend was unaffected by feed concentrations of Rangarajan et a1. (1979) extended 100, 500, or 1000 mg/l zinc. A mixture their analytical technique for pre­ of zinc nitrate and zinc chloride dicting reverse osmosis performance, ion showed greater solute separation than separation and product rates of cellu­ a mixture of zinc nitrate and zinc lose acetate membranes of different sulfate. To determine the role of ion surface porosities to aqueous solutions pairs, Sast ri conduc ted experiment s containing two electrolytic solutes adding sodium sulfate to zinc chloride involving a univalent cation, a divalent and zinc nitrate solutions. The result cation, two univalent anions, and a in both cases was increased solute common univalent anion. The validity of separation which Sastri attributed their predict ion technique was experi­ to the format ion of ion pairs in solu­ mentally verified from reverse osmosis t ion which were better separated than data for the feed solution systems hydrated divalent zinc ions. He indi­ NaBr-MgC12-H20, NaCl-Mg(N03)2-H20, and c ated that for so lu t ions containing NaCl-MgC1 2-H20 • metal nitrate or metal chloride, solute separation could be increased by the Sastri (1979) studied the reverse addition of sodium sulfate. osmosis separation behavior of calcium, magnesium, zinc, manganese, copper, Sastri (1978) conducted experiments aluminum, and iron as nitrate, chloride, with nickel salts using cellulose and sulfate salts, and investigated the acetate membranes and found simi lar effect on solute separation of adding results to those given above with zinc sodium sulfate to magnesium perchlorate salts. Sodium sulfate was added to and manganese nitrate solutions. It was nickel chloride and nickel nitrate concluded that ion pairs increase solute so lut ions and resul ted in increased separation, and that for solutions con­ solute separation. Sastri concluded taining metals, nitrates, or chlorides, that nickel ion pairs, Ni+2S04-2, solute separation could be increased by were separated better than divalent adding sodium sulfate. n i c k eli 0 n s as was show n for z inc. Ionic Charge Relationships Rangarajan et al. (1978) presented an analytical technique for predict ing Loeb and Manjikian (1965) reported reverse osmosis performance, ion separa­ the results of experiments with a tion and product rate, of cellulose reverse osmosis cellulose acetate acetate membranes of different surface membrane treating brackish water with a porosities for different aqueous feed total dissolved solids content of 2500 solutions containing two univalent mg/l, mOle than half of which consisted electrolytic solutes with or without a of divalent ions. Divalent ions were common ion. The prediction technique removed more effectively than monovalent requires only a single set of experi­ ions and the authors indicated that mental data on membrane specifications reverse osmosis could be effect ive for given in terms of the pure water perme­ desalinating waters having appreciable ability constant and the solute trans­ concentrations of calcium, magnesium, port parameter for sodium chloride, sulfate, or carbonate ions. and the applicable mass transfer co­ efficient for the chosen feed solu­ Govindan and Sourirajan (1966) ob­ tion system. The validity of their served that solute separation increased 37 with an increase in valence of the ions than those of the monovalent solute, and the effect was more pronounced with sodium chloride. Below pH 2 sodium the variation of the valence of the chloride rejection was low, while anion. For solution systems involving divalent solute rejections remained ions of different valences, the relative high. separation data form unique lines characteristic of the membrane-solution Johnson and Lim (1978) used cellu­ system, similar to those obtained for lose acetate membrane and found that solut ions cont aining ions of the same trivalent ions were better rejected than valence. Product rate data showed a lower valence ions and large ions were wide scatter for feed solutions con­ rejected better than small ions. The taining ions of unequal valences. effect of metal concentration on percent reject ion was examined for a few metal In a study of the desalination chlorides and only metals of lower properties of cellulose acetate-acetone­ valence showed a slight enhancement formamide membranes, Erickson et ala of removal efficiency with increased (1966) found that divalent ions were metal concentration. rejected to a greater extent than monovalent ions with no apparent regard Sastri (1979) found metal salts of to the sign of the charged ions. Com­ trivalent cations to show the greatest plex multicomponent salt solutions separation with the order of salt exhibited the greatest preferential ion rejection once again predictably W 3 > select ivi ty. Calcium, magnesium, and M+2 > M+l. The separation of sulfates sulfate were rejected 10 to 30 percent was greater than chlorides which was better than the average of all ions in greater than perchlorates or nitrates. solution. Sastri attributed the greater increase in sulfates to the presence of highly Sastri and Ashbrook (1976) studied rejected metal-sulfate ion pairs 1n the reverse osmosis separation of solution. various heavy metal salts in the form of CuS04, Cu(N03)2, NiS04, NiC12, Ni(N03)2, Nusbaum and Riedinger (1980) stated Fe2(S04)3, and Al(N03)3. Cations that rejection of individual ions is not of the order of increasing solute meaningful as ions are present in water rejection were M+3 > M+2 > M+1. Sastri as compounds and pass through a membrane and Ashbrook found that metal sulfate as charge balanced combinations. As salts were rejected to a greater extent shown in Table 6, within a chemical than metal nitrate salts, indicating family, rejection generally decreased that the percent separat ion of the with increasing molecular weight. solute increased with an increasing Rejection of an ionized species 1n­ value of the ion-pair equilibrium creased as the charge on the ion in­ constant. Because the cellulose acetate creased. Salts containing only mono­ membrane has a proton aff inity, and in valent ions showed poorer rejection than the case of an ion pair, both size and those containing divalent or trivalent effective charge may prevent approach of anions or cations. Weak acids and bases the ion pair toward the membrane surface that were only slightly ionized were layer, the ion pair shows better separa­ poorly rejected as were dissolved tion than the hydrated cation. gases.

Tan and Davis (978) studied the Water and Wastewaters reverse osmos is propert ies of po ly­ benzimidazole membranes as effected by Hauck and Sourirajan (1969) re­ pH variat ions when treat ing monova lent ported the performance of a few typical and multivalent solute systems. Rejec­ Loeb-Sourirajan type porous cellulose tions of multivalent solutes were higher acetate membranes for the treatment of

38 Table 6. Reject ion of various compounds by reverse osmosis at 400 psi (2800 kN/ m2 ), pH 6, and membrane type ROGA 114101 (Nusbaum and Riedinger 1980).

Rejection Rejection Compound % Compound %

Lici 96.4 Si02 92.3 NaF 97.1 H3 B03 44 NaCI 96.0 N~CI 93.3 NaBr 92.3 CuCl2 98.9 NaI 88.9 CuS04 99.6 NaN03 93.3 NiCl2 99.4 NaHC03 97.4 NiS04 99.9 Kcl 95.5 FeCl2 99.7 NaS04 99.6 AICl3 99.2 MgCl2 98.8 CO2 0 CaCl2 98.8 H25 0 MgS04 99.8 HCN 0 NaH2P04 99.8

polluted waters. Using feed waters buffering system was investigated by containing 300 to 800 ppm hardne~s Milstead et al. (1971) using cellulose expressed as CaC03, product waters acetate membranes. The quality of the containing 2 ppm or less could be product water was dependent both upon obtained with 90 percent product re­ the carbonate-bicarbonate equilibrium covery and an average initial flux of 65 and the membrane permeability of the l/m2 /h (38 gpd/ft 2 ) at 6.9 MPa (1000 species involved in that equilibrium, psig). The average separation of namely C03-2, HC03-, H2C03, C02, OH­ nitrate was 50 percent at an average and H+. The order of the carbonate product rate of 55.6 l/m2 /h (32.7 species rejection was found to be gpd/ft2 ) at 6.9 MFa (1000 psig), while C03-2 > HC03- > H2C03 > C02. At high phosphate was rejected 99 percent at an feed pH values, the product water was average product rate of 31.1 l/m2/h less basic because of the nearly com­ 08.3 gpd/ft2 ) at 3.45 MFa (500 psig). plete rejection of carbonate. At low It was concluded that the reverse feed pH values, the low rejection of osmosis process using the above type of C02 resulted in an acidic product porous cellulose acetate membranes had water. The precise prediction of the potential of becoming an economic bicarbonate rejection and of product means of renovation of wastewaters water pH in brackish water desalination to provide a product of acceptable was found to be complicated bJ the quality for domestic use as well as for effect varying feedwater composition had high pressure boilers. Table 7 shows upon individual ion rejection. that common water pollutants such as nitrates, borates, fluorides, chlorides, To determine if the type of water phosphates, ABS, and ammonium ions can in which a metal ion was dissolved be effect ively removed by the reverse affected rejection results, Mixon (1973) osmosis process. conduc ted bench scale stud ies with cellulose acetate and polyamide mem­ The effect of reverse osmosis branes using potable, brackish and treatment on the natural bicarbonate wastewaters as a feedwater source.

39 Table 7. Separation of selected water pollutants by reverse osmosis* (Hauck and Sourirajan 1969).

Solute Product Concentration. Solute Product in Feed Concentration Rate System ppm ppm gpd/ft2

NaN03-H20 492 87 27.3 Na2 B407-H20 524 16 26.1 NaF-H20 505 26 26.4 NaCI-H20 507 78 27.6 ABS-H20 95 1 20.9 ABS-H20 300 I 19.6 N~N03-H20 487 97 23.2 Na3P04-H20 480 3 20.4

*Film H-4 Operating pressure 1000 p.s.i.g. Product recovery 90% pH of feed = 9.0.

Removal efficiences were essentially and fluoride were due to the acidified the same for barium, cadmium, cromium, nature of the river water. and zinc from all the feedwaters, while copper removal from wastewater was Buckley (1975) treated brackish significant ly less than from potable or well water in San Diego, California, by brackish waters. reverse osmosis. Rejection of 97 percent of the total dissolved solids Boen and Johannsen (1974) conducted was achieved with 75 percent feedwater pilot studies to determine the feas recovery. bility of applying reverse osmosis as an upgrading process for treated and Johnson and Lim (1978) conducted untreated secondary effluents. Six reverse osmosis pilot plant studies for commercially designed reverse osmosis 9 months using chlorine free secondary pilot units with 1.136 to 3.785 m3/day effluent from an extended aeration pilot (3000 to 10,000 GPD) capacities were plant as feedwater. During this time, tested. The mean percent reduction percent rejections for total hardness, of constitutents during the study is TDS, and chlorides fluctuated very shown in Table 8. Wh He secondary little and the sulfate ion concentration effluent is admittedly not the best was constant. Total inorganic carbon source for drinking water, the data removal was consistent, although not show that reverse osmosis consistently as stable as TDS. Neither removal produced product water meeting primary efficiencies nor permeation rates were and secondary regulat ions for those affected by the level of water recovery. parame ters moni tored in the study. Colorado River water was ~lso tested as Glueckstern et al. (1978) described represent at ive of a high TDS, high a 700 m3 /day reverse osmosis plant sulfate water. Rejections were high for operating in Eilat, Israel, using all constituents except boron and brackish water with 6000 ppm TDS as a fluoride. The poor rejections for boron feed source. The plant produced 560

40 J

Table 8. Average percent reductions of constituents by various reverse osmosis configurations treating secondary wastewater effluents (Boen and Johannsen 1974).

Reverse Osmosis Total Diss. Total Ammonia- Configuration TDS COD COD Hardness Ca+ 2 Ortho-P N03-N Nitrogen Cl- S04-2

DuPont Hollow Fiber B-9 Modules Polyamide Fibers 88 90 90 95 96 93 84 91 94

...... +:- Gulf Spiral Wound Cellulose Acetate 94 88 92 98 99 99 55 96 88 99

University Tubular Cellulose Acetate 97 93 96 99 99 99 84 99 97 99 mg/l TDS in the product water. Feed­ Treatment Plant. As expected, the high water and product water analyses indi­ pressure system performed in a superior cated approximately 90 percent rejection rna nner to that of the low pres su re for the cations and anions measured. system. Removal of natural constituents by each system varied with the substance Shields (1979) presented case measured; however, both systems achieved histories of reverse osmos is pI ants the highest reject ion with sulfate and in Europe and the United States using the lowest with sodium. TDS rejection aromatic polyamide membranes. Feedwater by the high pressure system was approxi­ TDS ranged from 200 to 42,000 mg/l and mately twice that of the low pressure produc t water was produced meet ing system indicating the need for high drinking water standards for TDS. pressure operations for adequate system performance.

Sorg et al. (980) reported the Summary results of chemical analyses of effluent from reverse osmosis systems in Sarasota General reverse osmosis performance County, Florida. All of the reverse predict ive models dealing with a wide osmos is systems produced a high degree variety of multicomponent solute systems of treatment and rejection efficiencies have yet to be developed. From a review of specific ions were close to the of the literature related to inorganic ranges reported in the literature. solute removal by reverse osmosis, a Differences in rejection values between number of performance characteristics systems were said to be due to specific can be recognized: design and operational differences and to differences in membrane age. 1. Multivalent ions are rejected more effectively that univalent ions in Huxstep (1981) evaluated low, 1.38 the order M+3 > M+2 > M+1. MPa (200 psig), and high, 2.76 MPa (400 psig), pressure reverse osmosis treat­ 2. Co-ions affect the rejection of ment for the removal of specific con­ particular 10ns due to ion pair forma­ taminants from drinking water. Two 170 t ion. m3/day (45,000 gpd) pilot plant reverse osmosis systems were installed at the 3. Undissociated or poorly dissoci­ Charlotte Harbor Water Association ated compounds are only poorly rejected.

42 CHAPTER VII

REVERSE OSMOSIS REMOVAL OF THE INORGANIC CONTAMINANTS CONTROLLED BY THE NATIONAL INTERIM PRIMARY DRINKING WATER REGULATIONS

On June 24, 1977, the United States 6.5, operating pressure in the range of Environmental Protect ion Agency estab­ 1.2 to 1. 7 MPa (170 to 250 psig), and lished the National Interim Primary feed water TDS concent rat ions. The Drinking Water Regulations (NIPDWR) (EPA a r sen i c MCL 0 f O. 05 mg / I , co u I d be 1976) to protect the health and welfare achieved for a maximum feed water of the American public and to ensure concentration of 6.0 mg/l of arsenic V, them a supply of safe drink ing water. but could be achieved only with a Maximum contaminant levels (MCL) were maximum feed water concentration of 0.13 set for ten inorganics and radio­ mg/l for arsenic I II. I f arsenic I II nuclides, Tables 9 and 10, whose removal were oxidized to arsenic V prior to by reverse osmosis will be discussed reverse osmosis treatment, arsenic below. III removal should be as effective as arsenic V removal. Arsenic Huxstep (1981) presented results of The National Academy of Science pilot plant studies conducted on the (1977) stated that the current MCL for removal of arsenic III and arsenic V by arsenic of 0.05 mg/l provides a meager low 1.4 MPa (200 psig) and high 2.8 MPa margin of safety. Sorg and Logsdon (400 psig) pressure reverse osmosis (1978) reported that arsenic is a common systems. Removal of arsenic III ranged mineral in many western states and is from 63 to 73 percent for the high probably present in many groundwater pressure system and 12 to 42 percent for supplies serving small communities. the low pressure system. Neither system achieved the arsenic MCL for the source There is little data available on water arsenic concentrations in the the removal of arsenic from drinking range of 1.1 to 4.2 mg/l. Assuming water by reverse osmosis. Polymetrics reject ions of 65 percent for the high (1974) estimated a rejection range of 90 pressure system and 30 percent for to 95 percent. Sorg and Logsdon (1978) the low pressure system, a 0.05 mg/l MCL concluded that since reverse osmosis is could be achieved only for source water effective in removing most dissolved concentrations not exceeding 0.14 and solids, it should be effective for 0.07 mg/l, respectively. Arsenic V arsenic remova 1. removals of approximately 94 percent for the high pressure system and approxi­ Fox (1981) conduc ted tes ts on the mately 79 percent for the low pressure removal of arsenic I II and arsenic V, system were recorded. The MeL could be using both spiral wound cellulose achieved for raw water arsenic V con­ acetate and hollow fiber polyamide centrations not exceeding 0.83 mg/l membranes. Fox demonstrated that the for the high pressure system and not removal of arsenic by reverse osmosis exceeding 0.23 mg/l for the low pressure was dependent upon valence and in­ system. A comparison of arsenic III and dependent of pH in the range of 4.6 to V removals again indicates that arsenic

43 Table 9. National Interim Primary Drinking Water Standards for selected inorganic contaminants.

Maximum Contaminant Contaminant Level mg/l (unless specified)

Arsenic 0.05 Barium 1 Cadmium 0.010 Chromium 0.05 Lead 0.05 Mercury 0.002 Nitrate (as N) 10 Selenium 0.01 Silver 0.05 Radium-226 and 228 (combined) 5 pCi/l Gross alpha particle activity 15 pCi/ 1 Gross beta particle activity 4 mi llrem/yr

Based on a 2 l/day drinking-water intake, except for tritium and strontium-90. Average annual concentrations of tritium and strontium-90 assumed to produce a dose of 4 mrem/year or 20,000 and 8 pCi/l, respectively.

Table 10. National Interim Primary Drinking Water Standards for fluoride.

Maximum Temperature Level mg/l

<53.7 <12.0 2.4 53.8-58.3 12.1-14.6 2.2 58.4-63.8 14.7-17.6 2.0 63.9-70.6 17.7-21.4 1.8 70.7-79.2 21.5-26.2 1.6 79.2-90.5 26.3-32.5 1.4

The MCL for fluoride is determined by the annual average of the maximum daily air temperature for the location in which the community water system is situated.

44 v is more effectively removed than problem for water utilities. Minute arsenic III. traces have been discovered in waters where lead, copper, and zinc are mined Barium and processed. A more serious problem exists 1n surface water receiving Sorg and Logsdon (1980) stated that wastewater from industrial plating although barium is often detected in operations, but even here the problem trace amounts in surface waters and should be minimal due to the insolubil­ drinking water, it is not a serious ity of cadmium carbonate and hydroxide problem in most drinking water supplies. comp lexes in waters with a high pH A few areas in the United States do have value. Cadmium is also a contaminant of a barium problem, however. In northern Illinois, concentrations of barium in zinc galvinized iron and corrosive water provides the potential to dissolve groundwaters commonly range from 2 to 7 cadmium from distribution pipes into the mg/l and in one source a level of 19 mg/l was observed. distribution system. Mixon (1973) conducted tests to McCabe et al. (1970) found only 14 determine the effectiveness of reverse out of 967 finished water supplies with osmosis in removing barium from potable, cadmium concentrations exceeding the MCL brackish, and waste waters in solutions of 0.01 mg/l. The source of cadmium was by itself and with five other metal suspected to be the distribution system salts. The overall mean removal of rather than the raw water source. barium from all waters was greater than 90 percent. Mixon concluded that reverse osmosis could meet the MCL of Several studies appear in the 1.0 mg/l of barium for feedwater con­ literature describing cadmium removal by centrations up to 7.7 mg/l. reverse osmos is, however, the dat a 1S conflicting as to the effectiveness of Johnston and Lim (1978) conducted reverse osmosis. Hindin et al. (1968) laboratory studies on the removal of conducted laboratory tests with cellu­ barium by reverse osmosis using cellu­ lose acetate membranes using raw water lose acetate membranes. Barium solu­ with cadmium concentrations of 0.097, tions of 10 mg/l were tested at 1724 kPa 0.950, and 9.250 mg/l in the feedwater. (250 psig) and a pH value of 5.8. Cadmium removals of 69 percent were Remova Is of 88.3 and 100 percent were observed indicating that the MCL of 0.01 reported for NaC170 and NaC190 mem­ mg/l could be met only for cadmium branes, respectively. levels of 0.03 mg/l or lower in the feedwater. Sorg and Logsdon (1980) reported that for two short laboratory experi­ Mixon (1973) reported cadmium ments conducted by the Drinking Water removals of greater than 90 and 97.9 Research Division of EPA for removal of percent for initial feedwater cadmium 7.0 mg/l barium from a northern Illinois concentrations of 0.10 and 0.96 mg/l groundwater, removals of 95 to 99 cadmium, respectively. Cadmium removal percent were achieved. It was stated was not affected when five other metals that since reverse osmosis is very were added to the feed. On selected e f f e c t i v e in r emo val 0 f h a r d n e s s , it source testing, removal efficiencies for should also be very efficient for barium cadmium exceeded 98 percent for all remova 1. potable, brackish, and wastewaters. Long term test ing showed 1 ittle effect Cadmium on rejection efficiency. Mixon stated that reverse osmosis could produce an Sorg et ale (1978) reported that effluent that would meet the MCL of 0.01 cadmium was not expected to pose a mg/l for cadmium when treating influent

45 feed water with concentrations less than Chromium 0.5 mg/l. Sorg (1979) reported that chromium Houle (1974) evaluated a full scale was not expected to be a serious problem reverse osmosis system for recycling for water utilities because it is not wastewater from an electronics manu­ commonly found in either ground or facturing plant. Cadmium rejections surface waters. McCabe et al. (1970) varied from 43 to 83 percent for feed­ found only four finished water samples water cadmium concentrations in the from 967 wate r sup p 1 i e s wit h tot a 1 range of 0.024 to 0.059 mg/l. The mean chromium concentrations exceeding the percent removal of 66 percent was MCL of 0.05 mg/l. Sorg (1979) indicated es sent ially the same as reported by that the principal source of chromium in Hindin et al. (1968). Houle suggested natural waters is industrial in nature. that this low rejection may be due to The greatest potential for a chromium resolution of the analytical technique problem exists with water sources used. containing discharges from metal finish­ Johnston and Lim (1978) reported ing, textile, and leather industries. cadmium removals of 95.1 and 98.3 Hindin et al. (1968) _conducted percent using cellulose acetate mem­ laboratory tests on chromium VI removal branes with NaCl rejections of 70 and 90 using cellulose acetate reverse osmos is percent, respectively. Cadmium solu­ membranes. Removals of 96.7, 95.0, and tions of 10 mg/l were tested at 1724 kPa 93.5 percent were obtained for raw water (250 psig) and a pH value of 5.5. chromium VI concentrations of 0.47, 5.0, Fox (1981) conducted tests with raw and 49.6 mg/l respectively. water cadmium concentrations ranging from 0.05 to 0.30 mg/l. Both spiral Mixon (1973) evaluated chromium VI wound and hollow fiber systems achieved removal using cellulose acetate mem­ rejection rates exceeding 94 percent branes and obtained removals of 95.8 and under all operating conditions. The pH 88.6 percent with raw water concent ra­ values in the feedwater ranged from tions of 0.94 and 9.35 mg/l, respec­ 5.4 to 7.0 and operat ing pressures t ively. No significant difference was ranged from 1.2 to 16 MPa (170 to 230 observed in the rejection of chromium in psig). No not iceab Ie effect on cadmium a mixture with other metals compared rejection was observed with pH or with rejection of chromium alone. For pressure changes. The 94 percent selected source testing of potable, rejection rate would satisfy the MCL for brackish, and wastewater, he found an cadmium of 0.01 mg/l for influent overall removal efficiency greater than feedwaters with cadmium concentrat ions 93.7 percent. Long term runs had no of less than 0.16 mg/l. appreciable effect on chromium removal. Mixon concluded ~hat reverse osmosis Because of the low MCL for cadmium, could meet the MCL of 0.05 mg/l chromium percent rejection becomes significant. for raw water concentrations less than A low rejection rate of 69 percent would 0.7 mg/l. satisfy the MCL for raw water cadmium concent rat ions of only 0.032 mg/l, Johnston and Lim (1978) inves ti­ whereas a 98 percent removal would meet gated chromium III removal using a the MCL for raw water concentrations laboratory static test cell with cellu­ less than 0.5 mg/l. Because of the lose acetate membranes. At initial raw inconsistencies in cadmium removal water concentrations of 10, 100, and data, it is difficult to assess the 1000 mg/l chromium III, removals were effect iveness of reverse osmos is 1n greater than 99,97.3, and 94.8 percent, cadmium removal, indicating that more respectively. On a 4.54 m3 /day (1200 studies are needed in this area. gpd) pilot scale, they reported greater

46 than 99 percent removal for initial raw not be applicable to waters with higher water chromium III concentrations fluoride concentrations. ranging from 0.15 to 7.3 mg/l. Fox (1981) substantiated that Fox (1981) studied chromium III and fluoride removal is pH dependent at chromium VI removal using hollow fiber low fluoride concentrations using and spiral wound membrane systems. hollow fiber and spiral wound membrane Chromium rejection was found to be systems. The fluoride feed concentra­ de pende nt upon valence and pH, and tion was varied from 4.5 to 14 mg/l, the independent of operating pressure pH from 5.1 to 7.0, and the operating and initial raw water concentration. pressure from 1.2 to 1.6 MFa (170 to 230 Chromium III removals ranged from 90 to psig) during the study. Product water 98 percent for feedwater initial concen­ with fluoride concentrations ranging t rat ions from 0.071 to 0.80 mg/l. The from 0.3 to 4.9 mg/l was obtained. The hollow fiber membrane system reduced sp ir al wound membranes produced 73 chromium III concentrations to below the percent removal at pH 5.1 and 95 percent MCL with a maximum initial feed concen­ removal at pH 7. Hollow fiber membranes tration of 0.60 mg/l chromium III. The showed 50 percent removal at pH 5.1 and spiral wound membrane system performed 92 percent removal at pH 6.8. Operating be tter, meet ing the MCL for raw water pressure did not affect fluoride removal chromium III concentrations up to 1.1 for either membrane system. mg/l. Chromium VI removals ranged from 94 to 97 percent for the hollow fiber Reverse osmosis was effective in membrane system and from 82 to 95 removing fluoride at feedwater pH values percent for the spiral wound membrane above 6.5; however, Fox (1981) pointed system. The hollow fiber membrane out that the high pH value could cause system could meet the MCL for initial calcium carbonate precipitation problems feedwater concentrations less than 1.0 with waters of high calcium concentra­ mg/l and the spiral wound system for t ions. Lowering the pH would prevent initial feedwater concentrations less the problem of fouling but at the than 0.58 mg/l chromium VI. expense of fluoride removal. Blending of product water with feedwater to Fluoride maintain the desired fluoride concen­ tration in the effluent was suggested.' Sorg (1978) reported that many small community water suppl ies are Huxstep (1981) presented results of thought to have fluoride concentrations pilot plant studies on fluoride removals exceeding the MCL. Only limited data on by low 1.4 MFa (200 psig) and high 2.8 fluoride removal by reverse osmosis was MFa (400 psig) pressure reverse osmosis found in the literature. Hindin et ale systems. Fluoride concentrations ranged (1968) conducted laboratory studies from 4.7 to 12.5 mg/l. Resul ts showed on flu 0 rid e us i ng cell u 1 os e ace t at e consistent rejections of fluoride by membrane that showed fluoride concentra­ both systems throughout the influent tion could be lowered from 58.5 to 1.0 concentration range. Removals of 90.3 mg/l. to 93.4 percent for the high pressure system and of 58.3 to 62.4 percent for Reverse osmosis equipment manu­ the low pressure system were recorded. facturers report a wide removal range, Product water concentrations for both from 40 to 96 percent. DuPont (I 977 a) systems increased with influent concen­ stated fluoride removal is pH dependent tration due to the unchanging percent ranging from 45 to 90 percent as the pH rejection. The product water fluoride increases from 5.5 to 7.2. Data are concentration for the high pressure based on brackish waters with fluoride system did not exceed 1 mg/l, while the concentrations of 1 to 10 mg/l and may low pressure system product water

47 fluoride concentration increased from than 97 percent for both hollow fiber 1.9 to 4.7 mg/l as the influent fluoride and spiral wound membrane systems. For concentration was raised from 4.7 to raw water concentrations varying from 12.5 mg/l. The high pressure reverse 0.15 to 0.61 mg/l, both membrane systems osmosis system met the fluoride MCL produced product water with less than even at the 12.5 mg/l influent concen­ the minimum detectable resolution t rat ion. The low pressure system would (0.005 mg/U until raw water lead be applicable only for feedwaters with concentrations reached 0.23 mg/l. a fluoride concen~ration of 2 to 6.5 From 0.23 to 0.61 mg/l, the lead concen­ mg/l. trations in the product water increased, but did not exceed the MCL of 0.05 mg/l. Lead Fox (1981) stated that reverse osmosis can be an effective treatment technique Sorg et ale (1978) stated that the for removing lead. Assuming a 97 principal problem with lead in drinking percent removal rate, a single stage water comes from water distribution reverse osmosis unit could achieve the systems and not from lead in natural MCL treat ing water with lead concent ra­ groundwater or polluted surface waters. tions less than 1.6 mg/l. Occasionally, however, lead is present in groundwaters at levels from 0.4 to Mercury 0.8 mg/l. Dutt and McCreary (1970) reported that 6.5 percent of 677 water EPA (1976) added mercury to the samples collected from Arizona ground­ 1975 NIPDWR establishing an MCL of 0.002 waters had lead concentrations exceeding mg/l. Sorg (1979) stated that because the MCL, with the highest level being mercury is one of the least abundant measured at 0.52 mg/l lead. metals in the earth I s crust, it should not be frequently found in natural Mixon (1973) conducted laboratory groundwater. Potential problems are tests to determine the effectiveness seen with surface waters recel.Vl.ng of reverse osmos is in removing lead wastewaters from industrial or manufac­ and found removals greater than 99.5 and turing processes using mercury. 97 percent for initial lead concentra­ t ions of 0.95 and 9.3 mg/l, respec­ There is 1 ittle data available on tively. Tests for lead in combination the removal of mercury from drinking with five other metals resulted l.n water by reverse osmosis. Johnston and removals of 97.8 and 99.9 percent for Lim (1978) investigated the use of initial source concentrations of 1.1 and reverse osmosis for the removal of heavy 4.75 mg/l, respectively. In long term metals, pesticides, and other toxic runs, lead rejections were stable. chemicals from secondary wastewater effluent. One day batch tests, run with Johnston and Lim (1978) recorded feedwater spiked with 5.0 and 9.0 mg/l lead removals of 85.5 and 97.6 percent of inorganic mercury, produced removals using a laboratory static test cell with of 82.4 and 83.3 percent, respectively. cellulose acetate membranes rated at 70 and 90 percent NaCl removal, respec­ Sorg (1979) reported that the tively. Lead solutions of 10 mg/l were Drinking Water Research Division of EPA tested at 1724 kPa (250 psig) and at a performed one day tests on mercury pH value of 5.2. removal using hollow fiber polyamide and spiral wound cellulose acetate membrane The results of studies of lead sy stems. Resul t s wi th a raw water removal by reverse osmosis by Fox source containing 0.008 mg/l inorganic (1981) support the findings by Mixon mercury showed rejections of 25 percent (1973). Rejection rates for lead for the spiral wound system and 79 to 81 removal from drinking water were greater percent for the hollow fiber system.

48 Sorg (1979) stated that even though the hardness was reduced from 280 mg/l to results of these two studies were not as between 8 and 16 mg/1, and the pH was high as the 95 to 98 percent rejection reduced from 7.6 to 6.2 due to removal range for inorganic mercury estimated by of alkaline salts. In other experiments equipment manufacturers (Polymetrics with hard river water at feed rates of 1974 and Osmonics 1974), full scale 20 to 40 l/hr and 50 percent recovery, reverse osmosis systems operated at high nitrates were reduced from 7.6 to 2.9, pressure and high recovery should 9.6 to 3.1, and 8.4 to 2.8 mg/l nitrate. ach ieve greater remova 1 s than pilot scale units performing under less than Previous nitrate removal results optimum conditions. were confirmed by Fox (1981) with removals ranging from 59 to 95 percent. Nitrates His results demonstrate that reverse osmosis is an effective treatment, as Sorg (1978) stated that nitrate the product water never exceeded the MeL excess 1S one of the most frequently of 10 mg/l of N03-N. Hollow fiber poly­ reported drinking water regulation amide membranes showed rejections of 80 violations and is certainly a major to 90 percent, independent of operating problem for small communities in agri­ pressures of 1.2 to 1.4 MFa (170 to 200 cultural areas utilizing groundwater psig) and feed pH (5.4 to 7.0). At an for drinking water purposes. Equipment assumed rejection rate of 85 percent, manufacturers list a wide removal range hollow fiber membrane system could meet (60 to 95 percent) for nitrate. Havens the MCL treating raw waters with less Industries (1965) reported 70 to 80 than 67 mg/l N03-N. Spiral wound percent reject ion for nitrate. Hindin cellulose acetate membranes were affect­ et al. (1968) examined aqueous solutions ed by pH as nitrate removals ranged from spiked with 25 to 250 mg/l nitrate­ 51 to 95 percent. When the feedwater nitrogen and recorded removals of 68 to N03-N concentration was maintained at 73 percent with a single stage reverse 13 mg/1 and the feed pH was increased osmosis system. from 5.2 to 7.0, the rejection decreased from 80 to 70 percent. Fox was unable Because the rejection of an ion or to account for this reduction in effi­ molecule by reverse osmosis is directly ciency. Varying the operating pressure related to its size and valence, mono­ from 1.4 to 1.6 MFa (200 to 230 psig) valent nitrate is not as effectively had no effect on removal. Based on a removed as divalent ions, such as rejection of 75 percent, the spiral sulfate. Other factors also affect wound system would meet the MeL treating nitrate removal eff.iciency, such as waters with N03-N concentrations less membrane type, numbe r of operat ing than 40 mg/l N03-N. stages, and operating pressure. Sorg (1978) pointed out that no reverse Guter (1981) conducted experiments osmosis system has been installed solely comparing the performance of five for nitrate removal and therefore, no different reverse osmosis membranes for specific removal data are available nitrate removal. The results showed a for full scale systems. wide range of removal depending upon the membrane type. DuPont B-9, a hollow Goo d ma n (1 9 7 5 ) rep 0 r ted t hat fiber polyamide membrane, achieved reverse osmOS1S could be used with the best removal and had the highest waters containing high nitrate concen­ water recovery. tration. In experiments using a bore hole feedwater source, nitrate con­ Huxstep (1981) presented results of centrations of 8 to 10 mg/l were reduced pilot plant studies conducted on the to 1.3 and 2.2 mg/l at recoveries of 33 removal of nitrates by low 1.4 MFa (200 to 60 percent, respectively. Total psig) and high 2.8 MPa (400 psig)

49 pressure reverse osmosis systems with feedwater. Selenium IV rejection raw water N03-N concentrations ranging was found to be independent of feedwater from 15 to 41 mg/l. Results of the pH from 7.3 and 6.3, and feedwater testing showed removals of 75 to 80 TDS concentration from 360 and 3000 percent for the high pressure system and mg/l. removals of 6 to 24 percent for the low pressure system. Product water concen­ Johnston and Lim (1978) reported trations were below the 10 mg/l MCL for selenium removals of 97.9 and 99.4 the high pressure system and above percent for two different cellulose the 10 mg/l MCL for the low pressure acetate membranes rated at 70 and 90 system. Assuming 75 percent rejection percent NaCl rejection, respectively. for the high pressure system and 25 In their tests, the influent selenium percent reject ion for the low pressure concentration was 10 mg/l, the pH value system, the 10 mg/l N03-N MCL could be was 6.8, and permeate flux for the ach ieved only for raw water nitrate NaCl70 and NaC190 membranes was 4.94 concentrations not exceeding 40 mg/l for and 2.53 ml/hr/cm2 , respectively. the high pressure system and not ex­ ceeding 13 mg/l for the low pressure Fox (1981) stated that unlike system. conventional coagulation treatment methods for selenium removal, selenium Selenium removal from drinking water by reverse osmosis was found to be independent of Sorg and Logsdon (1978) reported valence. Source water concentrations of that because of possible carcino­ selenium IV less than 0.12 mg/l were genicity, the U.S. Public Health Service reduced to below the MCL of 0.01 mg/l. lowered the acceptable selenium limit in A hollow fiber system produced a product drinking water from 0.05 to 0.01 mg/l in water that met the MCL for raw water the 1962 revised Public Health Service selenium IV concentrations less than 0.5 standards. EPA retained the 0.01 mg/l mg/l, while a spiral wound system met limit in their 1976 NIPDWR. Little the MCL for source water selenium informatiop is available to determine IV concentrations less than 0.6 mg/l. the extent of the selenium problem. Both systems produced a reduction in There is greater chance that it will be selenium concentration exceeding 98 present in groundwaters than in surface percent. Percent removal of selenium IV waters as it is an uncommon pollutant in was unaffected by either an operating industry. Selenium is associated with pressure range from 170 to 230 psig, an uranium mining and has been reported in increase in TDS to 1000 mg/l with groundwaters in m1n1ng areas in Colo­ calcium chloride, or a range of pH value rado, Arizona and New Mexico. Engsberg from 5.0 to 6.1. (1973) reported that 40 percent of 139 groundwater samples and 25 percent of Fox (1981) found selenium VI 39 surface water samples in Nebraska removals from both reverse osmOS1S exceeded the 0.01 mg/l selenium MCL. systems exceeded 98 percent. As with selenium IV, variations in feedwater pH . There is little data on selenium from 4.5 to 6.5, operating pressure from remova 1 by reverse osmos is. One manu­ 1.1 to 1.2 MPa (160 to 180 psig) and facturer estimates removals at 90 to 95 from 1.6 to 1.7 MPa (230 to 250 psig), percent (Polymetrics 1974). The Drink­ an increase in raw water TDS from 285 to ing Water Research Division of EPA 1000 mg/l, and raw water selenium VI performed two experiments using a small concentrations less than 0.5 mg/l had no port ab Ie reverse osmos is uni t with effect on selenium VI removal. cellulose acetate membranes (Sorg and Logsdon 1978), with Cincinnati tap water As sumi ng 98 percent se 1 en i um spiked with 0.1 mg/l selenium IV as the removal efficiency, a single stage

50 reverse osmosis system would meet the Kosarek (1979a) reported that MCL for raw water selenium concen­ reverse osmosis membranes have provided trations of less than 0.5 mg/l. product water with less than 5 pCi/l from feedwater levels of radium ranging Silver from 30 to 750 pCi/l. In addition to removal of radium, reverse osmosis Sorg (1978) stated that silver reduced alpha radiation 85 to 96 percent should not be a problem in either and beta radiation 95 to 99 percent. surface or groundwaters, except in a few is 01 a t ed cas e s • Mc Cab e eta 1 • Carnahan et al. (1979) conducted (970), in their 1969 Community Water studies on the removal of iodine 131, Supply Survey, did not find a sample of strontium 85, and cesium 134 by reverse finished water that had a silver concen­ osmosis. Reverse osmosis was capable of tration exceeding the MCL of 0.05 mg/l. removing the iBotopes but not to accept­ No data were found in the literature for able levels. Post treatment with carbon the removal of silver by reverse osmosis adsorption and ion exchange would be but equipment manufacturers claim required to produce a potable water. removal ranges of 93 to 95 percent (Polymetrics 1974) and 94 to 96 percent Sorg et al. (1980) studied radium (Osmonics 1974). 226 removal by eight reverse osmosis systems in Florida and found removals of Radiation 87 to 98 percent from waters containing radium concent rat ions ranging from 3.2 to 20.5 pCi/l. Sorg and Logsdon (1980) Sorg and Logsdon (l978) indicated stated reverse osmosis is a good treat­ that radium is a problem in northern ment method for most radionuclides and Illinois, central and western Florida, is most advantageous for the treatment and in uranium mining areas of the Rocky of small drinking water suppl ies con­ Mountain States. Schliekelman (1976) taining a mixture of radionuclides that reported that 151 of 241 towns monitored would require the combination of several in Iowa had water supplies with de­ treatment methods to be effective. tectable amounts of radium 226, 19 of which exceeded the MCL of 5 pCi/l. Subramanian and Sastri (1980) Gilkeson (1978) found more than 300 conducted laboratory tests on radium 226 wells in northern Illinois exceeding 3 removal using cellulose acetate mem­ pCi/l of gross alpha with some con­ branes. Feedwater was obtained from taining up to 15 pCi/l of radium 226. leach ing uranium mine tailings. Feed The Sarasota County Health Department in radium 226 concentrations were con­ Florida found that 40 out of 59 water siderably higher than those found in supplies they tested had radium 226 drinking water sources, 390 to 910 concentrations of 0.3 to 22 pCi/l with pCi/l; however, they concluded that 25 exceeding the MCL of 5 pCi/l (Sorg et reverse osmosl.S l.S one of the best al. 1980). methods available for alleviating' radium contamination from a water Brink et al. (1978) treated a source. brackish well water for Greenfield, Iowa, with a total solids content of Huxstep (1981) presented results of 2200 mg/l in a reverse osmosis unit pilot plant studies on radium 226 installed in 1971. Raw, product and removal by low 1.4 MFa (200 psig) and reject water samples were collected and high 2.8 MFa (400 psig) pressure reverse analyzed for radium 226. At 69 percent osmosis systems at the Charlotte Harbor recovery, the radium 226 concentration Water Association Treatment Plant. One was reduced from 14 pCi/l in the raw set of grab samples was analyzed water to 0.6 pCi/l in the product water. and results showed excellent radium

51 removal of 97.4 percent for tbe high osmosis has been shown to be effective pressure system and moderate radium for the removal of most of the con­ removal of 61.7 percent for the low taminants controlled by the NIPDWR. The pressure reverse osmosis system. significant characteristic of the reverse osmos is process is its abi I i ty Summary to remove contaminants from water suppl ies that would otherwise require While no treatment method is ideal a combination of treatment methods for for removing all contaminants, reverse their purification.

52 CHAPTER VI II

REMOVAL OF ORGANICS USING REVERSE OSMOSIS

While reverse osmosis has its invo lved capillary 1 iquid flow through primary application to inorganic solute the porous film. separation from a flow stream, it has a significant advantage over other de­ Sourirajan (1965) conducted addi­ mineralization systems 1.n that it also tional studies of the separation and effect ive ly rejects many organic con­ permeability characteristics of a taminants. cellulose acetate membrane for several organic solutes in aqueous solution. Single Component Systems The effects of the chemical nature of the solute, solute concentration, and Sourirajan (1963) presented data operating pressure and temperature on indicating the relative effective­ the performance of the membranes were ness of reverse osmosis membranes for investigated. Data indicated the the separation of selected organic following order of membrane rejection: substances from aqueous solutions. Results indicated the following order of n-PrOH > EtOH > n-BuOH organic solute rejection: Iso-PrOH > n-PrOH n-PrOH > EtOH Tert-BuOH > sec-BuOH > iso-BuOH > Iso-PrOH > PrOH n-BuOH

Iso-BuOH > n-BuOH Glycerol> ethylene glycol > n-PrOH

Tert-BuOH > sec-BuOH > n-BuOH Acetaldehyde > EtOH > acetic acid

Acetaldehyde> ethyl alcohol > ace­ Propionic acid > acetic acid tone > acetic acid NaCL > any of the above organ1.C Sourirajan (1964a) stated that for solutes any given membrane material, the degree of separation and rate of permeation The permeability of the cellulose varies with the porous structure varia­ acetate membrane was affected by its tion within the film. The chemical contact with aqueous organic solutions. nature of the membrane surface was found The extent of solute separation de­ to determine the direction of separation c rea sed, but 0 n 1 y slow 1 y, wit han for a given feed system. Operating increase in the feed concentration, pressure was shown to affect the separa­ while the corresponding product rate t ion and flow charac teri s tics of a decreased more rapidly. Percent solute cellulose acetate membrane for the removal increased with an increase in system n-heptane-EtOH. The variation of the operating pressure in the range from product flow rate and alcohol enrichment 3.4 to 10.3 MFa (500 to 1500 psig). The indicated that the separation process extent of solute separation decreased

53 and the product rate increased with an 1 00 c 0 u 1 d not be reI i e d up 0 n • Low lncrease in the operating temperature. permeation rates were observed for compounds of a molecular weight of 200 Sourirajan and Sirianni (1966) or above. Low molecular weight nitriles indicated the possible applicability and amines showed moderate retention of the membrane separation technique similar to oxygenated compounds of for studying the solution properties similar molecular weight. of surface act ive subs tances and i llus­ trated the use of high flow porous Lonsdale et al. (1969) conducted cellulose acetate membranes for the laboratory studies on two low molecular remova 1 of detergent s from aqueous weight organic solutes, urea and dex­ solutions by reverse osmosis. Several trose. Dextrose showed reject ions of polyoxyethylated nonionic surface active greater than 99 percent, whereas urea agents (Tritons) in aqueous solutions was rejected at a rate of less than 45 were examined. An increase in the feed percent. rate increased both the extent of solute separation and the product rate pre­ Hindin et a1. (1969) investigated sumably because of higher turbulence in the removal of organic compounds by the cell and less solute concentration reverse osmosis. Certain organic buildup at the film surface. species form colloidal particles, aggregates, milcelles, or macromolecules Kimura and Sourirajan (1968) in an aqueous medium. Examples of such analyzed the reverse osmosis separation species include detergents such as LAS data for the system sucrose-water using and ABS, soaps, motor oils, DDT, TOE, a number of Loeb-Sourirajan type porous proteins, starch, cellulose, humic acids cellulose acetate membranes. The and tannins. The authors observed solute transport parameter for sucrose solute rejections of 80 to 99 percent was shown to decrease with an increase for those species existing in the in its boundary concentration. A new colloidal, aggregate, micelle, or method of expressing membrane selectiv­ macromolecular form. Reductions of 50 ity on a relative scale was given. The to 80 percent were obtained for those predictability of membrane performance species existing as dispersed aggregates for the separation of sucrose in aqueous or discrete molecules in true solut ion solution and the effect of membrane wi th vapor pressures greater than that compaction on solute separation were of water. Reductions of 14 to 40 also illustrated and discussed. Only percent were obtained for those mole­ the initial specifications of the cules more volatile than water such film, given in terms of the pure water as p-chloro nitro-benzene and low permeability constant and the solute molecular weight esters. While reverse transport parameter for sodium chloride, osmosis was shown to be effective in were required. separating some organic materials from aqueous solutions, the authors noted Merten et a1. (1968) studied that compounds with significantly higher organic solute removal by reverse vapor pressures than water, such as osmosis systems and indicated that phenol, may appear in significant significant permeation rates were quantities in the product water. observed only for some small, usually oxygenated organics. The authors Kaup (1973) stated that small indicated that retention in a homologous hydrogen-bonding nonelectrolytes and series increases with increasing molec­ simple straight-chain organics of ular weight. At a constant molecular four carbons or less that possess weight, retention increases with in­ hydrogen-bonding abilities pass easily creasing branching. Retention of through reverse osmosis membranes. compounds with molecular weights below The rejection of organic substances was

54 observed to increase as the molecule for sodium chloride. On the basis of a became large, sterically complex and/or firm physicochemical criteria approach poly functional. Organic acids and to reverse osmosis, Matsuura et al. amines were shown to be permeable to the offered a practical technique for membrane in their free state, while predicting solute transport parameters they were relatively impermeable when for organic solutes used in conjunction neutralized to salts. Acetic acid with membranes of different surface passes through cellulose acetate as a porosities. free acid but is rejected at 98 to 99 percent as the sodium salt. Chian and Fang (1976) extended the use of physicochemical criteria for the Klein et al. (1975) invest igated analysis of organic solute separation by the separation of trace organics from reverse osmosis through the use of five aqueous systems. The retention of a membrane materials. The separation particular solute by a polymer membrane of organics was shown to depend both was found to be related to both physical upon the characteristics of the membrane interactions and ionic forces that material and the nature of the solute. determine the solubility of the solute Within a given solute group, separation in the membrane phase. Ionizable was shown to increase with the size, compounds, such as benzoic acid, benzene branch ing and degree of ionizat ion sulfonic acid, and amines were eas ily of the solute. The physicochemical rejected by both cellulose acetate and criteria and pressure effects on solute ethyl cellulose membranes. In the salt separation with cellulose acetate form, their rejection was even more membranes held for other membranes used pronounced. Rejection of weakly ionized in the study. This allowed the presen­ compounds was a function of pH, and the tation of generalized guidelines for the more highly charged the species, the choice of appropriate membrane materials greater was its rejection. Polyacids, for di fferent reverse osmos is appl ica­ phosphoric acids, and other high ly tions. For membranes with an appro­ ch arged species inc lud ing humic and priate surface structure, the more tannic acids showed the expected high nonpolar the membrane material is, the reject ions. The high reject ion of better the solute separation will be, glutaraldehyde when contrasted with especially for low molecular weight the low rejections of glycols, alcohols, polar organic solutes commonly found in and sugars indicated that solubility is water and wastewaters. For high molec­ indeed a good indicator of solute ular weight and/or less polar organics, rejection. In general, aldehydes, the choice of a favorable engineering ketones, and aromatics are less effec:­ system becomes more important than t ive ly rejected than ionized or high ly that of the membrane material. For hydrogen bonding compounds. separating dissociable compounds, improving the separation can be made by Matsuura et al. (1976a, 1976b) increasing the degree of ionization with i nve s t iga ted the use of free energy proper pH adjustment. parameters of various carboxylic acids and undissociated aliphatic organic Matsuura et al. (1977) stated that solutes for the prediction of their free energy parameters and the hydro­ s eparat ion from aqueous solution by phobic nature of a solute governed reverse osmosis membranes. The authors the separation of one to nine carbon showed that solute separation in reverse alcohols in dilute aqueous solutions osmosis systems can be predicted for using porous cellulose acetate mem­ many organic solutes from data on mem­ branes. The separation of many alcohol brane specifications given in terms of a solutes could be predicted based on pure water permeability constant and membrane specification of pure water a membrane solute transport parameter permeability and the solute transport

55 parameter for sodium chloride. The KPa (25 to 100 psig). Necessary physio­ authors concluded that the prediction chemical data were generated and practi­ technique could be extended to a wide cal techniques were developed for variety of organic solutes whose separa­ predicting membrane performance in terms tion by reverse osmosis was governed by of solute separation and product rates polar, steric, and/or nonpolar' effects. for the separation of PEG solutes in aqueous solutions from a single set of Johnston and Lim (1978) studied the experimental data for a reference feed effectiveness of reverse osmosis in system of PEG. removing specific toxic organic sub­ stances using cellulose acetate mem­ Multicomponent Systems branes rated at 70 and 90 percent NaCl reject ion. Complex cyanides and Ironside and Sourirajan (1967) nitrilotriacetic acid were almost reported on reverse osmos is separat ion completely removed by both membranes techniques for water pollution control with the NaCl70 membrane achieving us ing porous ce llu lose acetate mem­ twice the permeation flux of the NaC190 branes. Feedwater containing 370 and membrane. The reject ion of sodium 512 mg/l, respectively, of the anionic cyanide was s ig ni ficant ly les s than surface active agents sodium dioctyl for the complex potassium tetracyano­ sulphosuccinate and sodium alkyl-benzene nickelate II, with the NaC190 membrane sulphonate were reduced to less than 0.5 removing 15 percent more sodium cyanide mg/l and 0.6 mg/l, respectively, at than the NaC170 membrane at approxi­ product water rates of 0.98 m3/m2/day mately half the permeation flux. (24 gpd/ft2). Feedwater containing a 10.4 percent acidic brown lignin solu­ Johnston and Lim (1978) investi­ t ion had the lignin content reduced to gated the rejection efficiency of 0.035 percent at a product water rate of phenol and substituted phenols using 0.66 m3/m2/day (6.2 gpd/ft2 ), The cellulose acetate membranes and found operating pressure was 6.89 MFa (1000 essentially no separation for phenol and psig) for both tests. Ironside and p-chlorophenol. Sixty percent rejection Sourirajan showed that reverse osmos is was observed for napthol, while p-cresol could separate water polluting ingredi­ exhibited negative separation. ents from the feed solutions yielding product waters of acceptable quality at Kurokawa et al. (1979) applied significant production rates. solution theory to the prediction of reverse osmosis rejection of organic Hinden et al. (1969) investigated solutes from aqueous solution assuming the permeation of chemical species that the reject ion is primarily deter­ in a multiple component aqueous solution mined by the distribution of solute and found evidence that suggested that between the membrane and the aqueous organic solute transport through cellu­ solution. The authors concluded that lose acetate membranes was a function of solution theory could serve as a basis solute vapor pressure. The rejection of for predicting solute rejection by methyl formate was markedly greater in a reverse osmosis if membrane parameters solution of three other low molecular were reasonably estimated. weight esters than when it was in a solution by itself. Rejection of 2,4-D Hsieh et al. (1979) studied the isopropyl ester and chlorophenol was reverse osmos is separat ion of po ly­ found to be decreased in a mixture of ethylene glycol (PEG) solutes in aqueous phenol, p-chloro nitrobenzene and ethyl solutions in the concentration range of ace tate ind icat ing that synergi s tic 50 to 5000 mg/l of solute using porous effects assisted these nonvolatile cellulose acetate membranes in the species in permeating the membrane. operating pressure range from 172 to 690 Amino acids and monocarboxylates did not

; 56 , react as other organic molecules did through the membrane, namely a partition indicating that some mechanism, other coefficient and a diffusion coefficient. than that based upon solute vapor When the steric effect was absent, the pressure, also effects solute transport partition coefficient was a dominant through cellulose acetate membranes. factor in solute permeation. The partition coefficients were closely Kopecek and Sourirajan (1970) re­ related to the dipole moment of solutes ported that reverse osmos is is appl i­ and the authors concluded that their cable for the separation of binary results could provide a method of mixtures of alcohols and/or hydro­ prediction for the reverse osmosis carbons, including azeotropic and separation of organic compounds on isomeric mixtures. No simple generali­ the basis of liquid chromatographic zations were possible regarding the analysis. direction of separation, however, due to the complex nature of preferential Chlorinated Organics/Pesticides sorption in reverse osmosis. Hydro­ carbons tended to collapse the porous Lonsdale et ala (1969) conducted structure of the cellulose acetate laboratory studies on the rejection of membranes and Kopecek and Sourirajan chlorinated hydrocarbons representative stated that some other type of membranes of various pesticides and herbicides have to be utilized for feed mixtures us ing cellulose acetate membranes. The containing hydrocarbons. compound 2 ,4-d ich lorophenoxyacetic acid showed rejections of greater than 93 Sourirajan ,and Matsuura (1971) percent, while the rejection of 2,4- conducted reverse osmosis experiments dichlorophenol was negative as was for glucose-water, maltose-water, observed with phenol. The 34 percent lactose-water, ethylene glycol-water, negative rejection of the dichlorophenol propylene glycol-water, and ethylene exceeded that observed with phenol, glycol-propylene glycol-water systems. approximately 20 percent, and may Their results showed that the prediction indicate that flow coupl ing between technique developed for aqueous solution phenol and water is increased by the systems containing mixed inorganic presence of chlorine atoms. The authors solutes with a common ion was applicable stated that most phenolic compounds will for systems containing nonionic mixed not be highly rejected and they observed organic solutes. a 1 arge reduc t ion in produc t water flux with feed phenolic compound con­ Nomura et a1. (1978) investigated centrations as low as 5 x 10-4 M. reverse osmosis of some aromatic com­ Reject ion data of p-dichlorobenzene pounds in a I-propanol solution using indicated that chlorinated hydro­ porous cellulose acetate membranes along carbons in general would be expected to with some factors which influence be poorly rejected. Cellulose acetate organic solute permeability. Data for a membranes would therefore not remove number of benzene derivatives showed many chlorinated organic pesticides and that only phenol was rejected while h~rbicides from natural waters. others were enriched. Solute perme­ abilities for compounds with various Edwards and Schubert (1974) pre­ substituent groups had the following sented an excellent literature review of order: -OH < -CH3 < -H < -Cl < -NH2 < refractory organic removal by carbon -N02' For the benzene, naphthalene, and adsorpt ion and reverse osmos is and anthracene series, the permeability determined the selectivity of a number was related to the molar volume of of cellulose acetate membranes for solutes and varied as follows: benzene aqueous solutions of several 2,4- > napthalene and anthracene. Two dichlorophenoxyacetic acid salts. factors governed the permeation behavior Rejection of these salts was observed to

, 57 dec rease rapid ly wi th time and the ethanol and methoxychlor were determined authors concluded that reversible to be 35 and 99.5 percent, respec­ sorption of the solute by the membranes tively. Ethanol was significant 1n was occurring in their study. the adsorption-desorption kinetics for methoxychlor. A mechanism was proposed Chian et a1. (1975) evaluated which indicated that when a molecule of cellulose acetate and cross-linked methoxychlor adsorbs to the membrane, polyethylenimine membranes for the two ethanol molecules are released, one removal of a wide variety of pesti­ from the membrane and one from the cides including chlorinated hydro­ solvation sheath surrounding each carbons, organophosphates, and miscel­ methoxychlor molecule. Rate constants laneous pesticides. From a material for the methoxychlor adsorption and balance, it was determi ned that appre­ desorption were determined and the ciable amounts of these pesticides were equilibrium constant was calculated. adsorped onto the polymeric membrane An expression for the adsorption iso­ materials. The chlorinated hydrocarbons therm relating the quantity of adsorbed showed the highest adsorption potential methoxychlor to its concentration in with the exception of lindane, followed solution and to the concentration of by trifuluralin and captan in the ethanol in solution was obtained and the miscellaneous group along with all the membrane adsorption density at satura­ organophosphates. Randox and atraz ine tion was found. showed the poorest adsorption. It was found that the more nonpolar a membrane was, the greater was the removal of the Johnston and Lim (1978) investi­ pesticides analyzed. Removal of pesti­ gated the use of cellulose acetate cides in natural waters was expected to membranes in removing toxic organic be even greater than that observed in substances. Their study included the lab due to complexes formed between chlorinated hydrocarbon and organo­ the persistent pesticides and humic and phosphate pesticides. All pesticides fulvic acids. While greater than 99.5 analyzed were completely removed by percent remova Is were obt ained for the the membranes with the exception of nonpolar pesticides by the polyethyleni­ malathion which was rejected at 79.0 and m1ne membrane, such as the organo­ 93.5 percent by the NaC170 and NaC190 phosphates and the chlorinated hydro­ membranes, respec t ive ly. The high carbons, removal of more polar pesti­ removal efficiencies were presumably due cides was less satisfactory. The to adsorption as the solute concentra­ authors concluded that pesticide removal t ions in the concentrate were cons is­ from aqueous solutions can be explained tently lower than that of the feed while partially by the polar effect of the little or no solute was detected in the solute and part ially by the adsorption permeate. The reappearance of chemicals of the pesticide onto the membrane as contamination in later experiments materials. The extent of adsorption was' indicated that previously adsorbed shown to be governed by van der Waals­ molecules were dissolving and travelling London forces and by hydrophobic bonding! with the permeate through the membrane. between pest ic ide mo lecu les and the Adsorption appeared to take place on polymeric membrane materials. top of a membrane with the adsorbed molecules migrating through the membrane Seevers and Deinzer (1976) investi-, and being eluted in the permeate as the gated the characteristics of cross- i membrane became saturated with the linked po lyethyleneimine-toluene-2 ,4- chemical. The separation of the chemi­ di isocyanate membranes with regard to cals declined over time and it was adsorption, desorption and permeation of concluded that reverse osmosis was an the pesticide methoxychlor during impract ical process for removing these osmotic pumping using water and ethanol strongly sorbed substances from water. as cosolvents. The rejections for It was suggested that the polymeric 58 membrane material could be better toxicological sample preparation. employed as an adsorbent than as a Cellulose acetate, cellulose acetate physical membrane separation technique butyrate, ethyl cellulose, polyamide, for these chemicals. and polyurea NS-l membranes were evalu­ ated. The mechanism by which a membrane Malaiyandi and Blais (980) 1n­ rejected the passage of certain solutes vestigated the separation character­ while permitting water transport was not istics of cellulose acetate membranes resolved. However, the ability of a for trace leve ls of 1 indane in water. solute to form hydrogen bonds correlated Lindane was poorly separated by the with its apparent formation of bonds cellulose acetate membranes. It was with the membranes. found that once exposed to this con­ taminant, reverse osmosis membranes of Dissociated solutes, polyhydric the cellulose acetate type remained alcohols, and paraffins experienced contaminated and slowly released the greater rejections by cellulose acetate pollutant to the product water long membranes than did undissociated phenols aft e r the con t am ina ted fee d sou r c e and organics capable of ionizing. had been removed. Such an event 1n Rejection of organics generally in­ clinical or potable water treatment creased with the degree of branching and plants using reverse osmosis units with the number of carbon atoms for would, in effect, contaminate the compounds within the same functional quality of the product water for a group. However, there were exceptions prolonged period. Malaiyandi and Blais caused by other unknown factors being stated that this form of membrane involved in the permeability mechanism. impairment, wh ich is not usually tested for during routine maintenance of reverse osmOS1S plants, should be The NS-l polyurea membrane showed guarded against. much higher rejections for organics than did the cellulose acetate membrane. The Drinking Water Treatment ability of a solute to permeate this type of membrane structure was a reflec­ Deinzer et al. (1975) investigated tion of its ability to penetrate the the concent rat ion of organic compounds cross linked surface. The nature of in Cincinnati, Ohio, drinking water the functional group was less important using cellulose acetate membranes. The in rejection by the polyurea membrane reverse osmOS1S concentrates showed than by the cellulose acetate membrane. the presence of hyd roc arbons ~ alkyl Polyurea membrane rejection was shown to phthalates, a tetrachlorobiphenyl be related to a large extent to system isomer, 2,4,6-trichlorophenol, 1,1,3,3- operating pressure. Polyurea was found tetrachloro-acetone, phthalic anhydride, to be effective over a wide range of pH, and barbital. Certain classes of however, the sensitivity of the membrane compounds, such as the aromatics, were to chlorine was its major limitation. found to be adsorbed to cellulose acetate membranes rather than being rejected, yet the authors concluded that Polyamide membranes showed rejec­ reve rs e osmos is was use ful for the tions similar to the polyurea membrane concentration of trace organic con­ but were also sensitive to chlorine. A taminants in large volumes of drinking two unit series of cellulose acetate and water. polyamide membranes was proposed that would remove high molecular weight Cabasso et ale (1975) examined and products and salts in the first cellu­ te'sted the use of membrane materials for lose acetate stage and low molecular the separation of trace organic solutes weight solutes in the second polyamide from drinking water to facilitate stage.

59 Cabasso et al. (1975) concluded ineffect ive for the trace organics that reverse osmosis is feasible for evaluated. He concluded that reverse concentrating and recovering organic osmosis is effective when high molecular solutes from water with the degree of, weight or humic materials comprise recovery varying with the solute­ the major portion of the TOC or COD. membrane combination. While a mem­ Howe v e r , sin c ere v e r s e 0 s m0 sis i s brane's rejection of salts might indi­ expensive, other membrane systems cate mechanical integrity, the authors specifically designed for removal of found it did not indicate the membrane's high molecular weight materials were true potential for concentrating or­ thought to be more attractive. ganics. The applied pressure was found to influence solute recovery and might Coleman et al. (1980) concentrated be crucial in the concentration of low the organics in 1.5 m3 (400 gallons) molecular weight organics. The highly of Cincinnati, Ohio, drinking water by cross-linked surface structure of the reverse osmosis. Analysis of the polyurea limited molecular penetration concentrate identified polychlorinated by the solute, while for the cellulose biphenyls (PCBs), chlorinated aromatics, acetate membrane, chemical interaction and many polynuclear aromatics (PNA). was the dominant factor of retention Altogether, approximately 460 compounds behavior. Cellulose acetate membranes were identified, including 41 PNAs, 15 showed the least overall rejection of PCBs, and a number of amines, amides and organics but were chlorine resistant and other hilogenated species. showed excellent salt rejection and water permeability. They served as a satisfactory first separation membrane Wastewater Treatment for the polyurea and polyamide membranes which showed good rejection character­ istics toward a wide variety of solutes. Sourirajan (1965) investigated the applicability of cellulose acetate Carnahan et ala (1979) tested a 600 membranes for the concentration of a gph reverse osmosis unit designed to propionic acid/water mixture, a natural meet the United States Army's require­ maple sap, and two industrial lignin ments for producing water in a combat wastes. Solute separation ranged from environment. Three chemical contami­ 100 percent for the maple sap to 65 nants, agents GB, VX and BZ, were tested percent for the propionic acid/water in feed solutions to the reverse osmosis mixture. Sourirajan concluded that unit. The agents GB and VX are organo­ reverse osmosis was applicable for phosphate compounds similar to malathion the separation of a wide variety of and parathion. GB was the most diffi­ industrial solutes ~n aqueous or non­ cult agent to remove by reverse osmosis aqueous solutions. due to its low molecular weight. A polyamide membrane was shown to perform Merten et al. (1968) investigated better than a cellulose acetate mem­ organic solute separation from a number brane, however, neither membrane pro­ of food processing wastes. Citrus juice duced an acceptable product water. The residues, which are largely hydrocarbon authors indicated that reverse osmosis in nature, were much better retained could remove chemical contaminants from than were the aromatic components of water but post treatment with carbon apple juice which are largely esters, adsorption was required to produce a alcohols, and aldehydes. Protein potable water. retent ion of 98 to 99 percent in fish process~ng wastes, sugar retention of McCarty (1980) found the removal of 99.9 percent in maple sap residue, and trace organics at Water Factory 21 BOD and COD retent ions of 90 to 99 by reverse osmosis to be relatively percent were also recorded.

60 Hauck and Sourirajan (1969) pre­ COD reductions of 90, 92, and 96 percent sented performance data for CA-NRC-I8 for influent COD concentrations ranging type porous cellulose acetate membranes from 6 to 60 mg/l. used for the treatment of secondary effluent. Average BOD removals of 85.8 Reinhard et al. (1979) investigated and 80.8 percent at 6.9 and 3.45 MPa the removal of trace organics by ad­ 0000 and 500 psig), respectively, and vanced waste treatment. A pilot reverse 90 percent recovery were recorded for osmosis plant using spiral wound mem­ raw water feed BOD concentrat ions from brane elements was used to treat acti­ 21 to 46 mg/l. Average ABS removals of va ted-c arbon and mixed-medi a filter 93 percent were recorded for average effluent. No significant removal of product rates of 1.33 and 0.746 m3 /m2 / volatile compounds was observed through day (32.7 and 18.3 gpd/ft2 ) at 6.9 and the reverse osmosis process. The 3.45 MPa (1000 and 500 psig) for raw reverse osmosis unit was effective in water feed ABS concentrat ions from 0.4 overall COD removal indicating that to 2.0 mg/l. Hauck and Sourirajan while the more volatile and low molecu­ concluded that reverse osmosis had the lar weight substance permeated the potential of becoming an economic means membranes, many organics were rejected of wastewater renovation. by the reverse osmosis system.

The permeation of a number of organic compounds found in sewage Summary effluents was investigated by Hindin et al. (969) and a comparison of the percent reductions of specific species Wh He reverse osmos is possesses a ins ewa gee f f1 u en t , a que 0 u S mu 1 t i­ major advantage over many other membrane component systems, and singly in solu­ processes in its ability to reject tion was made. Percent reductions for organic contaminants, the nature and each species in the sewage effluent, extent of this organic solute rejection with the exception of ethyl acetate, was is, as with inorganic solute rejection, the same or greater than that obtained completely dependent upon the nature in either multi- or single component of the organic material being con­ systems. It was believed that if sidered. The application of reverse permeation data were known for a species osmosis to organic contaminant removal singly in solution, a close approxima­ was reviewed by Nusbaum and Riedinger t ion of the percent reduct ion of a (1980) and their comments are summarized specific species in sewage could be as follows: estimated. 1. Low molecular weight, nonpolar, Boen and Johannsen (1974) conducted water soluble organic species tend to a pilot study to determine the feasi­ pass through reverse osmOS1S membranes. bility of applying reverse osmosis to untreated and treated secondary efflu­ 2. Rejection of low molecular ents. While they acknowledged that weight organic acids and amines followev organics can be a significant factor in the same pattern as inorganic acids and membrane foul ing, the DuPont Polyamide, bases, i.e., undissociated species are Gulf Spiral cellulose acetate, and poorly rejected while the salts are Universal cellulose acetate reverse readily rejected. osmosis systems they used succeeded in produc ing average total COD reductions 3. Phenols, chlorinated hydro- of 90, 88, and 93 percent, respectively, carbons, pesticides and low molecul~r for feedwater total COD concentrations weight alcohols are poorly rejected or ranging from 6 to 60 mg/l. For soluble permeate slowly through reverse osmosis COD, the three systems yielded average membranes.

61 4. The highly rejected organic c. Lignins, humic acids, species include: fulvic acids, detergents, and many other organics occurring 1n wastewater a. Large complex organic discharges. molecules which cause color or' interfere with coagula­ The application of the reverse tion and filtration. osmos is proces s for organic remova 1 is extremely flow stream specific, b. Chlorination-interfering however, it can prove to be an effective nitrogen-containing mole­ water treatment or wastewater renovation cules. process under the proper circumstances.

62 CHAPTER IX

REMOVAL OF MICROORGANISMS

The removal of microorganisms from that bacteria with physical dimensions drinking water is essential in dis­ greater t han vi ruses penetr ated the rupting the cycle of waterborne diseases reverse osmosis membranes. This passage in a population. Chlorinat ion is the of bacteria was attributed to tiny primary control' measure in the United holes in the membrane surfaces due to States for microbial contamination of manufacturing defects and to other drinking water. Because of the costs imperfect ions in the cross 1 inkages of associated with disinfection and the the cellulose acetate. The authors also possible production of harmful halo­ pointed out that full scale plants with genated organic compounds, methods are large membrane areas would be expected being developed to reduce the raw water to produce treated water of a higher chlorine demand and the potential for microbial count than small pilot scale halogenated organ1c formation through units due to the greater probability of pretreatment. Reverse osmosis is one of membrane imperfections in the larger these pretreatment options. units. The presence of membrane defect holes was confirmed by Melzer and Myers Bacteria in 1971, when they showed pore diameters in some membranes 200 times greater than Originally, reverse osmosis was the average pore opening. hoped to be a potential disinfection process that could compete with chlori­ Deinzer et al. (1978) reported that nation. It was found early (Otten and it is possible to disinfect wastewater Brown 1973) however, that reverse by reverse osmos is if membranes with a osmosis could not be relied upon for the pore size smaller than viruses are used. complete retention of bacteria. Otten They pointed out, however, that capital and Brown concluded that either pre­ costs, membrane replacement costs, and treatment or post treatment would be pump ing cos ts make reverse osmos is necessary to prevent bacterial contami­ far more expensive than chlorination for nation of the distribution system from wastewater disinfection. Additionally, the reverse osmosis unit. for drinking water disinfection, reverse osmosis alone is not suitable because it Ford and Pressman (1974) evaluated produces no residual effect for distri­ a prototype reverse osmosis unit for bution system protection. coliform and virus removal. The proto­ type unit was preceded by cat ionic Cooper and Straube (979) investi­ polyelectrolyte addition and prefiltra­ gated microorganism removal from sewage t ion and was followed by hypochlorina­ by reverse osmosis. Both coliform and tion. The unit successfully reduced the seeded animal virus removal through the level of both coliforms and an f2 virus reverse osmosis unit was significant, to undetectable limits. greater than 99.99 percent; however, results of the investigation indicated Hinterberger et al. (974) investi­ that some form of disinfection would be gated the capability of reverse osmosis required if the product water was to remove bacteria from water and found to be used for domestic purposes.

63 Nusbaum and Riedinger (1980) stated of the cellulose acetate membranes used that complete rejection of bacteria, rejected high percentages of viruses and fungi, and viruses by reverse osmosis produced a product water of excellent depends on having a membrane free of all quality except in two experiments where imperfect ions and that the probability mechanical failure of the membranes was of having such a membrane is very low. observed. They indicated that while organisms may penetrate the membrane, colonize and The prototype reverse osmos is unit proliferate, continuous or inter­ utilized by Ford and Pressman (1974) mittent disinfection relieves this that incorporated cat ionic polyelectro­ problem. lyte addition and prefiltration followed by hypochlorination was shown to reduce Viruses f2 virus to undetectable limits. Dual media pressure filtration following Compared with other water and polyelectrolyte addition when used as a wastewater treatment processes, virus pretreatment step for the reverse removal by membranes processes has not osmosis unit yielded 99.99 percent f2 been extensively investigated. Most of virus removal from a natural feedwater. the early work with virus removal using When viruses were added to feed water reverse osmos is has dealt with concen­ without prefiltration, virus penetration trating and purifying viral stocks resulted in reverse osmosis removal of (Chian and Sellerdorf 1969 and Wang et 97.3 percent from a feedwater con­ al. 1969). Some membrane manufacturers taining 106 virus units. Virus removal claim that no viruses should appear in through prefiltration ranged from 91 to the product water, citing virus size and 99.99 percent uS1ng polymer addition, membrane transport theories as reasons while practically no virus removal was for viral rejection. attained without the polymer.

Hinden et al. (1968) collected a Summary small volume of product water from a reverse osmos is unit treating a feed­ Because of inherent imperfect ions water inoculated with coliphages T7 and in reverse osmosis membranes produced XI7S. Without concentrating the viruses during their manufacture, the complete in the product water, an attempt was rejection of microorganisms is not made to isolate them by directly plating considered feasible. Pretreatment samples of the product water onto EMB processes used in conjunction with auger previously inoculated with E. reverse osmos is have, however, been coli. This product water was found shown to be highly effective in removing to be free of viruses. microbial contaminants from both water and wastewater streams. Sorber (1971) inoculated various concentrations of coliphage T2 and Many of the organic and inorganic poliovirus in the feedwater of a bench compounds that interfere wi,th disinfec­ scale reverse osmosis unit and evaluated tion and increase the chlorine demand of the rejection of these viruses by a water are removed in the reverse commonly used commercial grade asymmet­ osmOS1S process. This reduces the rical cellulose acetate membranes. chlorine dosage required for effect ive Limited numbers of virus pentrated the disinfect ion and is of significant membranes. The virus penetration was economic importance, especially in water attributed to random areas of imperfect treatment applications in which a cross linkages of the cellulose acetate chlorine residual is required for in the dense layer of the membrane. All protect ion of the dis tribu tion system.

64 CHAPTER X

PERFORMANCE EVALUATION OF REVERSE

OSMOSIS INSTALLATIONS

To review and evaluate the design, deionized water for medical use were operation, and maintenance of commercial also specified for product water use. reverse osmosis installations and to identify problem areas in those in­ Pretreatment stallations, questionnaires were sent to 117 reverse osmosis installations in the Ninety-five percent of the plants United States and 11 other countries reporting the use of pretreatment (Appendix D). Replies were received employed some type of chemical addi­ from 28 of the installations contacted, t ion. To cont ro 1 cal c ium carbonate 24 percent, of which 5 were no longer in scale, sulfuric acid was used at 95 operation. Plant closings were the percent of the sites and hyd roch lorie result of a number of items ranging from acid was used at 5 percent. To prevent the utility's acquisition of improved calcium sulfate scaling, a threshold raw water to the inability of the scale inhibitor was used at 75 percent ut il i ty to af ford the high cos t of of the installations. This scale replacement membranes. While financial inh ibitor was sodium hexametaphos phate cons iderations were important in a at 93 percent and sodium zeoli te at 7 number of pI ant c los ings, operator percent of the plants. op1n1ons were received that suggested that better plant design and operation Particulate removal by coagulation, could have extended plant life and flocculation, and sedimentation was reduced product water costs. carried out by 25 percent of the in­ stallations prior to reverse osmosis Water Sources and Treatment Objectives treatment. Mechanical filtration, excluding cartridge filters, was used at By far the greatest source of 50 percent of the plants. Green sand feedwater for the reverse osmosis filters for iron and manganese removal installations replying to the survey was were used at 20 percent of the plants, groundwater, 88 percent. Since Utah has while dual media filters were used at not accepted reverse osmosis for surface the remaining facilities. Chlorination water treatment silt density index was difficult to tives. Groundwater injection for attain until a Culligan multi media seawater intrusion protection, and filter was installed. At one site,

65 the micron cartridge filters became Membrane cleaning was carried out plugged with sand and weekly filter at the plants surveyed using citric acid cleaning was necessary. When a silt for inorganics (53 percent) and using dens ity index test was run, the index BIZ for organic foul ants (27 percent). was high and the membranes no longer Membrane cleaning procedures were qualified for warranty. carried out on fixed schedules ranging from every 3 weeks to every 2 years, or System Operation on schedules based upon the occurrences of membrane fouling. Cellulose acetate membranes were used at 71 percent of the plants while Alarm and automatic shutdown 29 percent used polyamide membranes. procedu res for membrane fou 1 ing and Hollow fiber and spiral wound modules of membrane or system failure occurrences one to three sect ions per module were were utilized in 90 percent of the equally divided among the plants re­ plants surveyed. High-low pressure, pH, sponding to the survey. and electrical conductivity sensing devices were most commonly used by the The system operat ing time reported plants in their al arm systems. Other by the various plants was application sensing devices used in the alarms were specific with plants operating from 2 to for feed levels to ensure a water supply 24 hours per day, 2 to 7 days a week and to the reverse osmosis unit and for all but two plants operating 52 weeks storage levels to ensure unit shutdown per year. when storage capaci ty was reached.

The product recovery rate reported Only one plant responding to the from the plants ranged from 30 to 83 questionnaire, the Yuma test facility, percent and averaged 57 +8 percent. did not posttreat their product water. Solute rejection efficiency-averaged 86 Disinfection was practiced at 90 percent +17 percent, ranging from 17 to 99 of the facilities using chlorine (93 percent. percent). and iodi ne .(7 p.ercent). De­ gasification was practiced at all plants Because product recovery is not 100 for the removal of dissolved carbon percent efficient, a large quantity of dioxide and hydrogen sulfide and for pH concentrated brine may have to be adjustment. disposed. Methods of brine disposal were found to vary with geographical Operators location. Total containment ponds were use d mo s t f r e que n t I y, 4 2 per c e nt, Training and maintenance experience followed by tidal canals, 17 percent, of the operators at the reverse osmosis and ocean disposal, 13 percent. Dis­ installations responding to the survey posal into tidal canals entailed com­ are summarized in Tables 11 and 12. At bining the reject stream from the five sites, maintenance was performed by reverse osmosis system with surface outside personnel, either by service runoff and discharging this mixture into contract, by the government, or by a navigable waterway. In the United outside sections of the utility opera­ States, a permit issued by EPA is tion and maintenance department. required for this disposal method. Other brine disposal schemes included To improve operator and maintenance injection wells; its use in an energy training, a training program or school recovery turbine; disposal in a salt specifically for reverse osmosis opera­ barrens, a percolation pond, and a t ion was recomme nded by each pI ant sewage lagoon; mixing it with the report ing. Addi t ional recommendat ions outfall of a sewage treatment plant; and were that manufacturers should offer its discharge into a sewer system. short courses to teach reverse osmosis

66 Table 11. A summary of operator train­ identified as a desirable maximum ing and experience. allowable pretreatment product water quality parameter to ensure adequate operating cycles. Flushing with a Number formaldehyde solution was also recom­ mended to prevent bacterial growth on Prior experience membranes when a plant is to be down for in RO 3 (12 percent) over 24 hours.

Prior experience The inadequacy of operating person­ in water and/or nel was identified as a major potential wastewater 12 (48 percent) cause of operating problems and a number of suggestions were presented to correct On the job training 10 (40 percent) this problem. Periodic evaluations of operator instructions were suggested and the need for dai ly supervi s ion was stressed. While manufacturers adequate­ Table 12. A summary of operator main­ ly lecture on a system's automatic capa­ tenance training and experi­ bilities, the human operator oriented ence. instructions reportedly are severely lacking. Adequate training is required for successful system operation and it Number was suggested that plant start up by qualified, field-experienced individuals Prior experience 6 (40 percent) is essential if adequate plant per­ formance is to be expected. No prior training or experience 3 (20 percent) Recommendations For Future Reverse On the job training 6 (40 percent) Osmosis Installations

Because of the potent ially severe impact of raw water quality on membrane systems operation, instrumentation, fouling and process performance, the mechanics, cleaning and maintenance; importance of a complete and thorough that reverse osmosis should be included investigation of the raw water source in state certification and operator was stressed by a number of respondents. training; and that training should be An adequate pretreatment train was included in the overall cost of plant emphasized along with cleaning connec­ design and in the annual municipal t ions on all unit s even those that budget. were expected to require only infrequent cleaning. The proper development and Operating Problems and Recommendations construction of wells was also felt to be important as system failures due to Membrane fouling and subsequent well casing corrosion and subsequent product water flux declines were the membrane fouling were identified. most common operating problems identi­ fied. Long filter backwash cycles and Effective process monitoring was regular membrane flushing were recom­ felt to be limited by inadequate re­ mended for improving performance. verse osmosis plant design. It was Substantial pretreatment was suggested suggested that more sampling points, especially for surface feedwaters to meters, pressure gages, and alarms be prevent rapid membrane fouling. A installed in reverse osmosis systems silt density index of less than 3 was to allow individual membrane module

67 performance monitoring. This added modules, or insufficient pretreatment information would aid in the detection processes that result in progressive of faulty 0 r~ngs, faulty membrane membrane fouling.

68 CHAPTER XI

SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS

Summary and Conclusions at present. The choice of a part icular membrane module configuration for a Reverse osmosis membranes represent particular application will be a func­ a significant portion of the capital tion of raw water quality, pretreatment cost of reverse osmosis systems. Be­ requirements and costs, module costs, cause of this, a great deal of research and the economics of the overall system and system development has been devoted required. to membrane performance optimization. Cellulose acetate membranes were the Membrane fouling is a major cause first to be developed and although they of reverse osmosis system failure and an are stable to low pH conditions and effective pretreatment program is resistant to chlorine oxidation, the essential. Pretreatment may include cellulose acetate membranes are suscep­ filtration, coagulation, flocculation, t ib Ie to bacterial attack and high pH sedimentation, pH control, aeration, condi t ions. Polyamide membranes, ion exchange, softening, disinfect ion, synthetic organic nitrogen-linked dechlorination, or a combination of the aromatic condensation polymers, operate above to insure proper process per­ at higher temperatures than cellulose formance. Routine membrane cleaning and acetate membranes and are resistant to system maintenance is a good investment bacterial attack and high pH conditions as these practices will be effective in but are unstable in low pH waters and reducing the occurrence and extent of are extremely sensitive to chlorine membrane fouling. pxidation. Composite membranes, pro­ duced by forming a thin' surface layer The major purpose of reverse over a porous support substructure, osmosis systems is for the rejection have been developed in an effort to of inorganic solutes from aqueous optimize the formation of the separate solutions. Inorganic solute rejection layers to produce membranes with supe­ is a function of ionic charge and r ior overall performance. These com­ hydrated radius and decreases in the posite membranes remain highly suscep­ order of trivalent, divalent, and tible to chlorine oxidation, however. monova lent ions. Co-ions have been Nos ing Ie membrane is the bes t for all shown to affect the rejection of partic­ applications and research is ongoing ular ions due to ion pair formation to develop an ideal membrane with and undissociated or slightly dissoci­ chemical and biological s tabili ty and ated compounds are poorly rejected. improved process performance. Reverse osmos is membranes possess Four membrane module configurations the ability to reject a number of have been deve loped: the pI ate and organic solutes in addition to inorganic frame, the tubular, the spiral wound, solutes as described above. Large and the hollow fiber modules. All complex organic molecules, some nitrogen configurations except the pI ate and containing molecules, lignins, humic and frame design are being used in water fulvic acids, and detergents are among and/or wastewater treatment applications the organic species highly rejected by

69 reverse osmosis membranes. Low molecu­ thoroughly known prlor to the design of lar weight, nonpolar, water soluble a reverse osmosis system. compounds tend to pass through reverse osmosis membranes; however, as with in­ 3. Pretreatment should be designed organic solutes, while the undissociated for the worst possible case and should forms are poorly rejected, these species include colloidal removal processes such in the salt form are readily rejected. as coagulation and filtration to inhibit Phenols, ch 1 orinated hydrocarbons, membrane fouling. pesticides, and low molecular weight alcohols have been found to be poorly 4. Regular filter backwashing, rejected or to permeate slowly through routine membrane cleaning, and equipment reve rse osmos is membranes, and the maintenance is required to ensure possibility of adsorbed organics being adequate process performance. released into the product water should not be overlooked. 5. Disinfection following reverse osmosis treatment is required if product The production of reverse osmosis water is to be used for domestic pur­ membranes is not 100 percent error free, poses. subsequently, the complete retention of viruses, bacteria, and other larger 6. Dissolved gases will permeate microorganisms is not considered possi­ reverse osmosis membranes and posttreat­ ble. The major advantage of the reverse ment degasification systems will be osmosis process from the standeoint of required for carbon dioxide and hydrogen microbial contaminant removal is in its sulfide removal. ability to reject organic and inorganic compounds that interfere with dis­ 7. To prevent microbial membrane infect ion. enrichment and membrane foul ing and deterioration, reverse osmosis systems should be flushed with product water The survey of full scale reverse during emergency shutdowns and should be osmOS1S installations revealed that sterilized during extended shutdowns. inadequate raw water source investiga­ tion and subsequent inadequate pretreat­ 8. Operator t raining for reverse ment systems, along with inadequate osmosis system operation and maintenance personnel training led to the bulk of should be improved. process failures and occurrences of membrane fouling. Recommendations From an extensive literature review and analysis of the full scale reverse Future designs of reverse osmOS1S osmos is plant survey, the fo llowing systems should be made with the follow­ conclusions can be made: ing items being considered:

1. Reverse osmosis is most appli­ 1. Raw feedwater sources should be cable to water supplies with several comprehensively surveyed and the best contaminants that would otherwise water quality source should be developed requlre a combination of treatment to reduce the requirements and costs of methods for their removal. Reverse pretreatment and to limit membrane osmosis is particularly useful for water fouling. supplies containing high TDS and one or more other contaminants. 2. Hydrogeologic investigations should assess the potential intrusion of 2. Feedwater composition vari­ undesirable water into raw water well ability, temperature, and source must be fields.

70 3. PVC, ABS, f iberg lass or s tain­ s amp ling taps for the perme ate and less steel casing should be used in the concentrate should be standard equipment construction of wells to minimize the to allow effective membrane performance potential of membrane fouling from monitoring. corrosion products.

4. Feed and product water moni- 6. Alarms and automat ic shutdown toring along with pretreatment process provisions should be provided for performance monitoring should be in­ membrane protection uS1ng high/low cluded in normal operating procedures to pressure, pH, and EC sensing devices. detect and remedy membrane foul ing or deterioration that may occur. 7. Operators should be trained in proper reverse osmos is operat ing 5. Pressure gages, flow meters for procedures and defined maintenance the permeate and concentrate, and schedules should be established.

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Otten, G., and G. D. Brown. 1973. Reinhard, M., C. J. Dolce, P. L. Bacteria and pyrogens in water McCarty, and D. G. Argo. 1979. treatment. American Laboratory, p. Trace organic removal by advanced 54. waste treatment. J. Environ. Engr. Div., ASCE 8:675-693. OWRT. 1979. Reverse osmosis. Tech- nology Transfer, OWRT, U. S. Saltech. 1978. Reverse osmos is. El Dept. Interior, Washington, DC. Paso, TX. USGPO 0-287-792. 20 p. Sastri, V. S. 1977. Reverse osmosis Polymetrics. 1974. Pure drinking performance of cellulose acetate water. Polymetrics reverse osmosis membranes in the separation of zinc eq u i pme nt, Bull e t in 950-Re v • 1. from dilute solut ions. Separation Pol yme t ric s , Inc., San t a Cia r a, Sci. 12(3):257-269. CA. Sastri, V. S. 1978. Reverse osmosis Porter, M. C. 1978. What, why and when separation of nickel from di lute of membranes MF, UF, and RO. solutions. Separation Sci. 13(6): AlChE Symposium Series 171(3):83- 475-486. 103. Sastri, V. S. 1979. Reverse osmosis separation of metal ions in acid Rangarajan, R. R., T. Matsuura, E. C. mine-water. Separation Sci. Goodhue, and S. Sourirajan. 1976. 14(8):711-719. Free energy parameters for reverse osmosis separations of some in­ Sastri, V. S., and A. W. Ashbrook. organic ions and ion pairs in 1976. Performance of some reverse aqueous solutions. I & EC Process osmosis membranes and their appli­ Design & Development 15(4):529-534. cation in the separation of metals in acid mine-water. Separation Rangarajan, R. R., T. Matsuura, E. C. Sci. 11(2):133-146. Goodhue, and S. Sourirajan. 1978. Predictability of reverse osmosis Scanlon, L. 1980. Personal communica­ performance of porous ce llu lose tion. Utah Division of Environ. acetate membranes for mixed un1- Health, Salt Lake City, Utah. valent electrolytes in aqueous solutions. I & EC Process Design & Schl ickelman, R. J. 1976. Determina­ Development 17(1):46-55. tion of radium removal efficiencies in Iowa water supply treatment Rangarajan, R. R., T. Matsuura, E. C. processes. ORP/TAD-76-1. Office Goodhue, and S. Sourirajan. 1979. Rad. Progr., USEPA, Washington, DC. Pred ictabi 1 i ty 0 f membrane per­ formance for mixed solute reverse Seevers, R., and M. Deinzer. 1976. osmosis systems. 2. System cellu­ Absorption, desorption, and lose acetate membrane-1:l and permeation of methoxychlor on 2:1 electrolytes-water. I & EC semipermeable membranes under Process Design & Development osmotic pumping. J. Phy. Chern. 18(2):278-287. 800):761-766.

Reid, C. E., and E. J. Breton. 1959. Shields, C. P. 1979. Five years Water and ion flow across cellu- experience wi th rever se osmos is

78 systems uS1ng DuPont "Permasep" Sourirajan, S. 1964a. Separation of permeators. Desalination 28: some inorganic salts 1n aqueous 157-179. solution by flow under pressure, through porous cellulose acetate Sorber, C. A. 1971. Virus rejection by membranes. I & EC Fundamentals the reverse osmosis-ultrafiltration 3(3) :206-210. process. Ph.D. Dissertation, The University of Texas, Austin, TX. Souriraj an, S. 1964b. Characterist ics of porous cellulose acetate mem­ Sorg, T. J. 1978. Treatment technology branes for the separation of to meet the interim primary drink­ some inorganic salts in solution. king water regulations for in­ J. Appl. Chem. 14:506-513. organics: Part 1. JAWWA 70(2): 105-112. Souriraj an, S. 1965. Characterist ics of porous cellulose acetate mem­ branes for the separation of Sorg, T. J. 1979. Treatment tech- some organic substances in aqueous nology to meet the interim primary solutions. I & EC Product Research drinking water regulations for and Development 4(3):201-206. inorganics: Part 4. JAWWA 71(8): 454-466. Sourirajan, S., and T. Matsuura. 1971. Reverse osmosis separtion of Sorg, T. J., M. Csanady, and G. S. some organic solutes in aqueous Logsdon. 1978. Treatment tech­ solution using porous cellulose nology to meet the interim primary acetate membranes. I & EC Proces s drinking water regulations for Design and Development 10(1): inorganics: Part 3. JAWWA 70(12): 102-108. 680-691. Sourirajan, S., and A. F. Sirianni. 1966. Membrane separation studies Sorg, T. J., R. W. Forbes, and D. S. with some polyoxyethylated alkyl­ Chambers. 1980. Removal of phenols in aqueous solution. I & radium 226 from Sarasota County, EC Product Research and Development FL, drinking water by reverse 5 ( 1) : 30-34 • osmOS1S. JAWWA 72(4):230-237. Spatz, D. D., and R. H. Friedlander. Sorg, T. J., and G. S. Logsdon. 1978. 1978. Rating the chemical stabil­ Treatment technology to meet the ity of U.C. RO/UF membrane materi­ interim primary drinking water als. Water Sew. Works 125 (2) : 36- regulations for inorganics: Part 2. 40. JAWWA 70(7):370-393. Speight, L. W., and J. W. McCutchan. Sorg, T. J., and G. S. Logsdon. 1980. 1979. Reverse osmosis desalina­ Treatment technology to meet tion plant design and system the interim primary drinking water optimization based on the facility regulat ions for inorganics: Part at Firebaugh, CA. Water Resources 5. JAWWA 70(7):411-422. Center Desalination Report No. 70. UCLA School Applied Sci. Sourirajan, S. 1963. The mechanism of demineralization of aqueous Subramanian, K. S., and V. S. Sastri. sodium chloride solutions by flow, 1980. Reverse osmosis separa­ under pressure, through porous tion of radium from dilute aqueous membranes. I & EC Fundamentals solutions. Separation Technol. 2(1):51-55. 15(2):145-152.

79 Sudak, R. G., M. E. McKee, R. L. Fox, U.S. Environmental Protection Agency. and J. B. Bott. 1979. Develop­ 1977. State-of-the-art of small ment of a chlorine resistant water treatment systems. Office of reverse osmosis membrane and porous Water Supply, Washington D.C. membrane supports. NTIS, Spring­ field, VA. PB80-l02973. 91 p. Wang, D. I. C., A. J. Sinskey, and T. Takahashi, S., and K. Ebara. 1978. Sonoyama. 1969. Recovery of Scale prevention on a reverse biological materials through osmosis membrane for water treat­ ultrafiltration. Biotechnol. ment. Proceedings 6th Interna­ Bioengr. XI(5):987-ll03. t ional Sympos ium Fresh Water from the Sea 3:261-268. Williams, V. R., and H. B. Williams. Tan, M., and H. J. Davis. 1978. High 1967. Basic physical chemistry flux PBI reverse osmosis membranes for the life sciences. W. H. for desalinat ion and water reuse. Freeman and Company, San Francisco, NTIS, Springfield, VA. PB 297 285. CA.

80 SELECTED BIBLIOGRAPHY

Adam, J. W. H. 1980. Health aspects of McKee. 1980. Wastewater reuse in nitrate in drinking water and Saudia Arabia: The new oasis. possible means of denitrification. Water and Waste Engr. 17(6):28-40. Water SA 6(2):79-84. Kosarek, L. J. 1977. Improved water Al-Gholaikah, A., N. El-Rawly, 1. recovery through reverse osmosis - Jamjoom, and R. Seaton. 1979. The a technical breakthrough. Water world's largest seawater reverse Sew. Works 12:32-33. osmosis desalination plant at Jeddah, Kingdom of Saudia Arabia. Kosarek, L. J. 1979a. Purifying National Water Supply Improvement water by reverse osmosis. Plant Assn. J. January. Engineering 9:183-185.

Allard, J. J., J. M. Rovel, and R. Kosarek, L. J. 1979b. Significantly Treille. 1979. Before RO-pre- increased water recovery from treatment. Water Sew. Works cooling tower blowdown using R79: R102-R103. reverse osmOS1S. Water 1978. A1ChE Symposium Series 148-155. Argo, D. C. 1976. Wastewa'ter reclama­ tion plant helps manufacture Krauskopf, K. B. 19S6. Factors con­ fresh water. Water Sew. Works trolling the concentration of 13 R76:R153-R159. rare metals in sea water. ACTA 9: l. Beasley, J. K. 1977. The evaluation and selection of polymeric materi­ als for reverse osmosis membranes. Kropp, J. F., and R. C. Kroner. 1971. Desalination 22:181-189. Trace metals in the water of the U. S. Federal Water Quality B 1 u nk , R . 1964 • A study 0 f c r it e ria Admin., Cincinnati, OH. for the superpermeability of cellulose acetate membranes to Lloyd, D. R., J. P. Wightman, J. E. aqueous solutions. UCLA Dept. McGrath, M. Igbal, Y. Kang, L. E. of Engr. Report No. 64-28. Gerlowski, and C. D. Sunderland. 1981. Poly (aryl ether) membranes Channabasappa, K. C. 1976. Need for for reverse osmosis. Paper pre­ new and better membranes. Water sented at ACS Meeting in Las Vegas, Sew. Works R76:R153-R160. NV.

Criddle, C. S. 1980. Water quality McIntosh, A. L. 1977. Florida reverse study of the Cache Valley trout osmOS1S plant turns out potable farm. CEE 561 special project, water. Water Sew. Works 124(12): Fall Quarter, Utah State Univer­ 30-31. sity, Logan, UT. Mitsoyannis, E., and G. D. Saravacos. Kalinske, A. A., J. F. Willis, S. R. 1977. Precipitation of calcium Martin, and Camp Dresser and carbonate on reverse osmOS1S

81 membranes. Desalination 21:235- reverse osmosis units. Proceedings 240. of the 3rd Annual Conference of National Water Supply Improvement Moore, D. H. 1972. Greenfield, Iowa, Association. Key Largo, FL. reverse osmosis desalting plant. JAWWA 64(11):781-783. Sourirajan, S. 1964. Separation of hydrocarbon liquids by flow under Nusbaum, I., R. E. Cruver, and J. H. pressure through porous membranes. Sleigh, Jr. 1972. Reverse Nature 203:1348-1349. osmosis - new solutions and new problems. Chern. Engr. Prog. United States Public Health Service. 68(11): 69-70. 1962. Drinking water standards. Department Health Education Wel­ Osmonics. 1974a. Report ing of water fare, PHS Publ. No. 956. ana lys is resul t s. Engineering memo #4. Osmonics, Inc., Hopkins, Winfield, B. A. 1979. The treatment MN. of sewage effluents by reverse osmosis - pH based studies of the Osmonics. 1974b. Table of operating fouling layer and its removal. parameters for osmo 19 series Water Res. 13:S61-564. machines. Engineering memo #9. Osmonics, Inc., Hopkins, MN. Yasuda, H., and C. E. Lamaze. 1971. Salt rejection by polymer membranes Richard, M. E., and R. C. Cooper. 1975. in reverse osmosis - I~ J. Polymer Prevention of biodeterioration Sci., Part A-2, Polymer Physics and slime formation in tubular 9(9) : 1537-1551.

82 APPENDICES

83 J

Appendix A Chemical Cleaning Reagents for Reverse Osmosis Membranes Table AI. Chemical cleaning reagents (DuPont 1977b).

Foul ants Chemicals CaS04 BaS04 SrS04 Metal Inorganic Biological CaC03 CaF2 Si02 Oxides Colloids Matter Organics Hydrochloric Acida x x (HC1)(pH 4.0) 2.0 wt. % Citric Acid + NH40H (pH 4.0) x X X 5 wt. % Nutek NT-600 X 2 wt. % Citric Acid + NH40H (pH 8) X 1.5 wt.· % Na2EDTAc + NaOH (pH 7-8) co VI or 1.5 wt. % Na4EDTA + HCl (pH 7-8) X 1.0 wt. % Na Hydro­ sulfite (Na2S204) X X NaOH (pH 11. 0) b X X X 2.0 wt. % Citric Acid + 2.0 wt. % Na2EDTA + NH40H (pH 4.0) X X 0.5 wt. % "Biz"d + NaOH (pH 11.0) X X X 1 wt. % Drewsperse 738 X 1 wt. % NaHMP X X X 1/4 wt. % Formaldehyde followed by 0.25 wt. % "Biz" (with phosphate) x

aA lower pH may be more effective. Consult the RO system manufacturer for assistance. bA higher pH may be more effective. Consult the RO system manufactuer for assistance. CEDTA is ethylenediaminetetracetic acid. d"Biz" (with phosphate) is a product sold by Proctor & Gamble, USA. For alternative detergents consult the RO System manufacturer for assistance. Table A2. Chemicals cleaning reagents for reverse osmosis membranes (Burns and Roe 1979).

Chemical Cost, ~ Scale( s) Source Recommended Cleaning Procedure

I. Cleaning Solution A Citric Acid (2.0 percent) 0.50/lb Iron Hydrox­ FS Use at highest available temp. up Triton X-IOO (0.1 percent) 0.50/1b ides to 120°F for at least 45 min at Carboxy Methyl Cellulose maximum rate available up to 10 (0.001) percent) gpm/vessel. Adjust pH to 3 with N~OH

2. Citric acid (2.0 percent) 0.50/lb CaS04 and DuPont Circulate, followed by water adjusted to pH 8 with NH40H 'CaH04P rinse.

3. EDTA (1.5 percent), pH = 8 1.00/lb CaS04 and DuPont Circulate and flush temp. up to with NaOH CAH04P 120°C.

4. Cleaning Solution B Sodium Tripolyphosphate 0.29/lb Humic Acid FS Use at highest available temp. up (2.0 percent) Salts of Ca to 120°F for at least 45 min at ~ Triton X-100 (0.1 percent) 0.50/lb and Mg maximum rate available up to 10 Carboxy Methyl Cellulose! 0.76/lb gpm/vessel. (0.001 percent) Versene-IOO (39 percent solu­ 1.00/lb tion of EDTA) (2.0 percent) (100 percent basis) Adjust pH to 7.5 with H2S04

5. EDTA (2.0 percent Versene-IOO) 1.00/lb "Silt" and Dow Pressure less than 75 psi, flush Triton X-IOO (0.1 percent) 0.50/lb Organic for 2 hr, then run with permeate Trisodium phosphate (2.0 per­ 0.27/lb Fouling for 15 min, temp. less than 35°C. cent) pH 7.5 adjusted with H2S04 or HCL

6. Ammonium Bifluoride 0.41/1b Si02 ROGA Circulate and flush. (2.0 percent) W.R. Grace

7. HCl to pH 4.0 CaC03 DuPont

8. Citric Acid to pH 4.0 0.50.lb CaC03 DuPont

9. Nutek NT-600 or -500 (5.0 percent) CaC03 Dupont , J

Table A2. Continued.

Chemical Cost, scalers) Source Recommended Cleaning Procedure

10. H2S04 or HCl, Adjust feed­ Fe or CaC03 Dow Normal operating pressure. water to pH 2.0-3.5

11. Citric Acid (2.0 percent) Mn, Fe, Dow Recirculate 30 min, repeat if pH 2.5 CaC03 flush is not clear.

12. Citric Acid (2.0 percent), 0.50/lh Fe, Ni, Cu, DuPont NR40H to pH 4 Mn Hydroxides Silicates 13. Citric Acid (2.0 percent) Fe, Ni, Cu, DuPont Na2 EDTA (2.0 percent) Mn Hydroxides NR40H to pH 4 14. Sodium Hydrosulfite (4.0 Fe, Ni, Cu, DuPont percent) Mn Hydroxides co CaS04, CaH04P --...J 15. SHMP (1.0 percent) Silicates DuPont 16. Citric Acid (2.4 percent) Severe CaC03 Dow Circulate 30 to 60 min, manufac­ Ammonium bifluoride (2.4 percent) of silica turer's direction.

17. H2S04 or HCL to pH 2.0-3.5 CaC03 or Fe Dow Maximum 4 hr at operating Fouling pressure. 18. Citric Acid t(2.0 percent) o.50/lh Mn, Fe, or Dow Maximum 3 hr, circulate 1/2 to 1 pH 2.5 CaC03 hour. Flush with permeate and repeat if flush not clear. 19. Biz Detergent, pH 9.4 Organics DuPont, Dow (0.25 percent solution) Humic Acid W.R. Grace 20. C12 (1.0-5.0 ppm residual Organics Dow Maximum time 60 min circulate for (C1 2) from hypochlorite or 15 min, then flush, check for free gaseous C1 2 injection (not Cl2 in feed and effluent. If free for periodic cleaning, only C12 is not in effluent after 15 if other methods fail) min, reflush with fresh solution. pH 6.5-7.5 Table A2. Continued.

chemical Cost, $ cale(sJ Source Recommended Cleaning Procedure

21. Caustic, NaOH, pH 11 max. Organics DuPont Silicates only

22. Drewsperse 732 (1.0 percent) Organics DuPont

23. Cleaning Solution EBZ, pH 7.0 CaS04 W. R.Grace EDTA Na4 4H20 (20 percent) N~HC03 (7 percent) Zonyl FSA (0.005 to 0.01 percent)

24. Sodium Dithionite (2.0 percent Fe W.R.Grace Na2S204, pH 3.6

0:> 00 Appendix B Reverse Osmosis Membrane Cleaning Procedures

Table Bl. DOW iron or carbonate foulant cleaning procedure (Burns and Roe 1979).

Solution: H2S04 or HCl addition through acid feed system

Injection rate: As necessary to reduce feedwater pH to 2.0-3.5

Time: 4 hr maximum

Procedure: Inject acid to lower feedwater pH to 2.0 minimum and note changes in salt passage and pressure drop over hour. Discontinue if salt passage increases significantly after the first hour.

Table B2. DOW silt and organic foulant cleaning procedure (Burns and Roe 1979).

Solution: Two percent Versene 100; 0.1 percent Triton X-IOO; 2.0 percent Trisodium phosphate; mixed with permate water pH: Adjust solution pH to 7.5 with HCl or H2 S04

Flow Rate: 20-30 gpm per DOWEX 20K permeator

Pressure: Less than 75 psig

Quantity: 30 gal of formulation for each DOWEX 20K permeator

Procedure: Flush each stage of permator for approximately 2 hr and then r1nse with permeate for 15 minutes. The solution temperature must not exceed 30°C.

Table B3. DOW manganese, 1ron or carbonate foulant cleaning procedure (Burns and Roe 1979).

Solution: 2 percent citric acid in permeate (pH = 2.5)

Flow Rate: 20-30 gpm per DOWEX 20K permeator

Time: 3 hr maximum

Quantity: 30 gallons per 20K permeator

Procedure: Flush system thoroughly using permeate. Introduce citric acid flush. Recirculate 30 to 40 min. If solution turns to red-brown color, repeat the procedure. Flush with permeate. If permeate is not clear, repeat the procedure.

89 Table B4. DuPont "BIZ" detergent flushing procedure (Burns and Roe 1979).

solution: 0.5 percent BIZ in permeate (4 lb/lOO gal)

Flow Rate: 10-20 gpm per 8 in. unit

Pressure: 50-150 psig

Time: 1 hr minimum

Quantity: 7.5 gal for each permeator plus 10-20 gal for piping and hoses plus 100-150 gal in tank

Procedure: Flush once through 30 gal of product per permeator (discard permeate and reject). pH 6.0 minimum. Flush 20-25 percent of the cleaning solution to drain. Recirculate effluent and product to tank. Flush for 2 hr minimum.

Alternate: Flush 15 m1n. Soak 15 min. Cycle until effluent is no longer dis­ colored. Flush with feedwater less than 200 psi until no foaming occurs. (Shake sample in jar).

Table B5. ROGA solution B cleaning procedure (Burns and Roe 1979).

Solution: 2.0 percent sodium tripolyphosphate; 0.1 percent Triton X-lOO (Rohm & Haas); 0.001 percent percent carboxy methyl cellulose; 2.0 percent Versene 100 (39 percent solution); 1.0 percent formaldehyde (optional)

Flow Rate: 35 gpm per element

Pressure: Less than 60 psig

Temperdture: Highest available. Less than or equal to 120°F (40°C)

Time: 45 min recirculation

90 Appendix C Reverse Osmosis Membrane Rejuvenation Procedures

Table Cl. DOW membrane surface rejuvenation treatment (Burns and Roe 1979). solution: GELVA (Monsanto) C-5 V-16 10 wt. percent mixed with permeate pH: Not below 6.0

Flow Rate: Rated feed flow for system

Pressure: Rated system pressure

Quantity: 15 g of 10 percent solution for each gpm of feedwater

Procedure: Mix GELVA with the required amount of permate following recommenda­ tions for safe handling provided by the manufacturer.

Addition of ammonium hydroxide or household ammonia may be helpful Ln reducing the viscosity and getting the GELVA into solution.

The RO system should be thoroughly flushed after any cleaning attempt and any hypochlorite or acid addition pumps shut off for the duration of this procedure.

The system should then be started up and operated at its normal pressure, flow rate, and recovery.

By means of a chemical injection pump, the prepared solution should be pumped into the feedwater system at a rate to yield 20 ppm active GELVA in the feed. Continuous monitoring of the product water salinity during this period is critical.

Continue injection until salt passage declines to the desired level or for a maximum of 15 min. (If salt passage does not decline significantly, do not treat further.) Allow the system to operate another 15 min with no injection and note if salt passage remains stable.

Because rejection is restored by coating a portion of the available membrane surface area, a consequential decline in productivity is often seen with the increase in salt rejection.

If the permeate is used for potable water, the system should be flushed at rated conditions for at least 4 hr before the product water is once again collected for use.

91 Table C2. ROGA sizing rejuvenation treatment (Burns and Roe 1979).

Unit should be cleaned with the most thorough procedure available.

Unit should be restarted with normal operating parameters and performance checked.

Unit should be checked for flow and condition at each pressure vessel any any abnormally high vessels probed.

All bad "0" rings should be replaced and all leaking modules replaced (no amount of permaloid will overcome one or two fair-sized leaks).

Set the pH of the operating unit to 7.0 (or turn acid off).

Use a 3-4 percent (dilute 12 percent stock 3:1) solution of Colloid 189 for injec­ tion with acid pump.

The Colloid 189 solution should have a pH of 8-9. If not, adjust with N~OH.

Start injection to give 15-25 ppm polymer ln feed stream.

Continue injection until performance levels out.

Stop injection of polymer and flush out pump into system with product water ad­ justed with NH4 to pH 8.

Run unit for 15 min at pH 7.0 to flush out any residual polymer ln system •

. Start acid for standard unit operation (pH 5-6).

Mix up a 5 percent solution of ZnC12 in product water adjusted to pH 4.0 with HCl.

Begin injection at 10-20 ppm for one hour or so.

Performance should stabilize after ZnC12 injection has ceased.

92 , J

Appendix D Reverse Osmosis Installations Included in Operational Survey Table Dl. List of reverse osmosis installations to which questionries were sent, their response, and oper­ ational status as of April 1982.

State/Country Location Name ~ In Operation Alaska Fairbanks Univ. Alaska Power Plant Newtok Newtok School Sheldon Pt. Sheldon Pt. School Stebbins Stebbins School

Arizona Phoenix Bureau Land Mgmt. Tucson Hughes Aircraft Co. x Yes Yuma Bureau of Reclamation X Yes

Cali fornia Burbank City of Burbank Escondido City of Escondido Fountain Valley Orange County Water District X Yes Gaviota State of California at 1..0 State Beach W Pittsburgh Dow Chemical USA Romona San Diego Country Estates San Luis Obispo AT&T Relay Station

Colorado Englewood Consolidation Coal Co. Fort Lyons Verterans Administration Hospital Lamar AT&T Relay Station

Florida Boca Raton Pheasant Walk Estates Bonita Springs Imperial Harbor MH Estates Bradenton Christian Retreat Camp Bryn Maur Bryn Maur Camp Resort Cap'e Coral City of Cape Coral X Yes Christmas KOA Campground Englewood Fiveland Investment Utility X Yes Estero Estero Woods Village Flagler Beach Oceanside Acres Apts Ft. Myers Burnt Store Utilities Ft. Orange Riverwood Park Ft. Pierce Ft. Pierce Jai Alai Table Dl. Continued.

State/Country Location Name ~ In Operation Ft. Pierce Harbor Branch Foundation Ft. Pierce Ocean Village Harbor Hts. Charlotte Harbor Water Assn. Jensen Beach River Club Condos x Yes Kay Pase Rotonda West Utilities Key Largo Card Sound Golf Club Key Largo Florida Keys Aqueduct x No Authority Key Largo Ocean Reef Club Key West Florida Keys Aqueduct x Yes. Long Boat Key Westchester Condos Marineland Marineland Melbourne Cove South Beaches Melbourne Chuck's Steak Hosue Miami Reverage Canners \C -I:- Naples Pelican Bay Improvement District New Smyrna Beach Sugar Mill Country Club Estates Nokomis Bay Lakes Estates MHP Nokomis Fairwinds Condominium Village Nokomis Kingsgate TTP Nokomis Lake Village MHP Nokomis Lyons Cove Condominium Nokomis Nokomis Elementary School Nokomis Palm In Pines MHP Nokomis Sorrento Shores x Yes Ormond Beach 1414 MHP Corporation Ormond Beach Kingston Shores Osprey Sarasota Bay MHP Osprey Southbay Yacht and Racquet Club Palm Beach Harbor House Ponce Inlet City of Ponce Inlet Punta Gorda Punta Gorda Isles Inc. x Yes St. Augustine Marineland X Yes , J

Table Dl. Continued.

State/Country Location Name ~ In Operation Sanibel Island Island Water Assn. Sarasota Camelot Lakes MHP Sarasota Myakka Valley Campgrounds Sarasota Pelican Cove Subdivision Sarasota Peterson Manufacturing Sarasota Workmens Electronics Corp South Bay Gulf & Western Corp_ x Yes Stuart Indian River Plantation X Yes Stuart Joes Point Stuart Ocean Tower Venice City of Venice Vero Beach Bryn Mawr Beach Station Vero Beach Village Green West Palm Beach Palm Beach County Utilities X Yes West Palm Beach Riverside Memorial Chapel 1.0 \.Jl Illinois Homewood Surmas Restaurant

Indiana Hillsdale City of Hillsdale

Iowa Alta Municipality of Alta X Yes Greenfield Greenfield Municipal Water Works

Montana Decker Decker Coal Co. X Yes

Nevada Jean Town of Jean

New Mexico Albuquerque Mesa Rica Water Co. X Yes Conchas Dam Conchas Dam X Yes

North Carolina Ocracoke Town of Ocracoke

North Dakota Dickinson Jim Nelson Parshall City of Parshall Reeder Russell Earsley X Yes J

Table Dl. Continued.

State/Country Location Name ~ In Operation Ohio Medina Days Inn x No

Oklahoma Tulsa Lake County Mobile Homes

Pennsylvania Hastings City of Hastings

Texas Dallas Universoty of Texas x Yes Fabens Indian Cliffs Ranch Muleshoe U.S. National Park Service x No

Utah Hill AFB Hill AFB x Yes Moab Texas Gulf Corporation X Yes Salt Lake City Morton Salt Company X Yes Salt Lake City N. L. Industries

1.0 Wyoming Fontanelle AT&T Relay Station '" Muddy Gap AT&T Relay Station Sheridan Pieter Kiewit & Sons

Washington, D.C. Blue Plains Sanitary Treatment Plant

Bahamas Grand Bahamas lsI. Grand Bahama Hotel Paradise Islands Paradise Utilities Paradise Islands Resorts International

Bermuda Hamilton Bermuda Properties

Canada Brandoz Manitoba Manitoba Water Service Board X Yes

Dominican Republic Santo Domingo Inter Continental Hotel

Israel Eilat Mekeroth

Mexico Holvox Village of Holvox San Felipe City of San Felipe , J

Table Dl. Continued.

State/Country Location Name ~ In Operation Puerto Rico Maniti Schering Corporation Prasa Aqueduct & Sewer Authority

Saipan Mariana Islands Intercontinental Hotel x No

Saudia Arabia Riyadh Intercontinental Hotel

South Caicos lsI. Sharjah Admiral Arms Hotel x No

Virgin Islands St. Croix Schuster Water Service St. Thomas Frenchman's Reef St. Thomas Virgin Islands Housing Authority

1.0 "-I Appendix E Operational Survey

July 31, 1981

Ladi es and Gentl emen : The Utah Division of Environmental Health is currently evaluatinq the use of reverse osmosi~~in the treatment of drinking water. We would be most grateful if you could fill out the enclosed questionnaire as completely as possible. Annual reports or data sheets containing similar information will be of equal value. Your answers will help us evaluate reverse osmosis with respect to design, operation, and mainte­ nance criteria. Hopefully we can benefit from your experience and avoid any problem areas that you have encountered. We have tried to make the questionnaire as short and as simple to answer as possible. If there are any questions you cannot answer, do not worry about it. If insufficient space is provided for an answer, feel free to use the back of paqe. The answers from all the reverse osmosis plants respondinq to the questionnaire will be summarized. Unless you indicate otherwise, your plant and name wi-ll be listed as a contributor to our findings and your answers will remain confidential. Finally, you will be sent a copy of our findings. Thank you very much for your time and consideration in this matter. Cordially yours,

E. Joe Middlebrooks Dean, College of Engineering EJr"jjmj Enclosure

98 QJestionnai re

1. Prepared by Date = ------..N-am-e------~T~i~t~l-e------

Represent i ng ______--.,.;Phone : ______

Address -----=St~r-e-e~t------city State Zip

2. Objective of Treatment

Dri nk i ng ~/ater Wastewater Boiler Feedwater Cooling Water =Other '(Pleas~ Indicate) ______-- ____ 3. Source of Water Municipal Private --- Other (Please Indicate) -- Surface ------Well (Please Indicate Depth) =Other (Please Indicate) ------4. Water Requirements Expressed in Units ______

Maximum F1 ow Duration Minimum Flow-- Duration --

Average Flow Hours/Day Days/Heek -- \~eeks/Year __ Total Gallons Per Day ---- 5. Is Water Storage Available? No =Yes (Pl ease Indicate Storage Capacity) ______·6. Cucrent Cost of Raw or Treated Water in 4/1000 Gal (Please Inulcate)

7. Electricity 4/KWH (Please Indicate) Frequency of Power Outages _____ Reserve Power Source No -- Yes (Briefly Describe)

99 8. Labor Briefly Describe operator's training and experience.

Briefly describe maintenance's training and experience.

What would you recommend to improve operator and maintenance training? (Describe Briefly)

9. Pretreatment Chemical ftddition (Please Indicate Chemicals and Concentrations)

Coagulation Cl ari fi cati on Fl occu 1 at i on --- Disinfection (Please --- Indi cate Type) Sedimentation Ot her (P 1ea s e I""":"de-n-:-t-;""i -=-fy""""t)- === Filtration (Please Indicate Type)

Please provide a brief sketch of pretreatmento EXJIJ'1PLE : Raw Chemi ca 1 + + Flocc + Sediment. + Filter + Reservoir Water Pddltion + Chemicals Sludge

+ Buffer Tank + R.O.

Briefly describe any problems you have encountered in pretreatment and recommendations for avoidance.

10. Pumps

A. Type Multistage Process Centrifuga 1 --- Positive Displacement Vertical Turbine --- Other (Please Indicate) ----- B. Spare Pumps/Motors Indi cate Number ----- C. What System Feed Pressure is used for running your RO unit? Min Ave ---__ Max --

100 D. Briefly describe any significant problems you have encountered with pumps and recommendations for avoidance.

11. Reverse Osmosi s a) System designed by (Please Indicate) b) Operation ------

Hr/day Days/Week Weeks/Yr How long has unit been in operati on? --- c) Does unit have polishing membrane filter? No - Yes (Pl ease Indi cate) 5i ze d) Flow rate. Please indicate units --- Min Ave Max Feed Permeate Concentrate

e) Concentrations. Please indicate units if other than ~mhos/cm

Min Ave r4ax Feed Permeate Concentrate f) Membranes Manufacturer (Please Indicate) ------~------Type Ce 11 ul ose J!cetate Polyamide =Other (Pl ease Indi cate) ____ Confi gurati on Spiral Wound Ho 11 ow Fi ber Plate and Frame (Flat Membrane) Other (Please Indicate) _____ Diameter 4" -- 6" -8" Other (Please Indicate) ----- Flux Rate (Please indicate in units of flow per surface area per time.) Min ------Ave ------Max ---- 101 g) Brine or Concentrate Disposal

Recyc 1ed to Feed - Used to Run Punp - Tota 1 Contai nment Pond _ Other (Please Indicate), ------h) Cleaning. If applicable, please inoicate.

1. Cleanin~ Solution Used 2. How Often Used 3. Procedu re

i} Is RO provided with alarm or shutdown provisions? No Yes (Briefly Describe) j) Equipment Pressure gages up and downstream of polishing filter? Yes No Flowmeters for permeate and concentrate? Yes No Taps for samp 1 i ng permeate and concentrate? Yes No EC meters at sampling~oints? Yes No k) If possible, please provide sketch of membrane module arrangement.

1) Briefly describe any significant problems you have encountered in RO unit and recommendations for avoidance.

12. Post-treatment

pH adjustment ___ CO2 Removal (Please indicate type) - CaC03 addition or _ Disinfection{Please indicate type) -- - langlier Index - Adjustment "Other (Please indicate type) Ion Exchange =Other (Please indicate type) ----- Please provide brief sketch of post-treatment if possible.

102 Briefly describe any significant problems you have encountered in posttreatment and recommendations for avoidance.

13. Cost Operating cost 4/1000 Gal Capacity Capi ta 1 Cost Power Chemicals O&M Membranes Total GPO

14. Based on your experience, briefly describe any recommendations or suggestions you would give to future RO installations with respect to:

DES IGN =

OPERATION =

MAINTENANCE:

Once again, thank you for your time and consideration. Sincerely,

E. Joe Middlebrooks

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