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For my dad; he’ll always be O.K.

Acknowledgements

My enthusiasm for reverse osmosis (RO) began while working with my thesis advisor at UCLA, Professor Julius “Bud” Glater, a pioneer who worked at UCLA with Sidney Loeb in the early days of commercializing RO. Professor Glater was kind enough to extend a Research Assistantship to me, when my first choice was not available. That was fortunate for me, as membrane technology is a growing field with great future potential. Professor Glate’s guidance and support were invaluable to me as a graduate student and has continued to be throughout my career.

My knowledge grew at Bend Research, Inc. under Harry Lonsdale, another membrane pioneer who was involved in the theoretical and practical side of membranes since the early 1960’s at Gulf General Atomic (predecessor of Fluid Systems, now Koch Membrane Systems), Alza, and later Bend Research, which he co-founded with Richard Baker. At Bend Research, I had the opportunity to develop novel membranes and membrane-based separation processes, including leading several membrane-based projects for water recovery and reuse aboard the International Space Station.

My desire to write this book was fostered by Loraine Huchler, president of Mar-Tech Systems, which she founded in the mid 1990’s, and author of the book series, Operating Practices for Industrial Water Management. Loraine has provided both technical and moral support.

Thanks also go to Nalco Company, Naperville, IL, for supporting me in this endeavor. Individuals at Nalco who have provided technical and administrative support include: Ching Liang, Anne Arza, Anders Hallsby, Beth Meyers, Carl Rossow, Alice Korneffel, and Kevin O’Leary. Nalco-Crossbow LLC personnel who have provided support include Mark Sadus (contributor to Chapter 6), Scott Watkins, Mike Antenore, Jason Fues, and Dave Weygandt.

Valuable technical support has been provided by Julius Glater—Professor Emeritus UCLA; Mark Wilf of Tetratech; Rajindar Singh—Consultant; Madalyn Epple of Toray Membrane USA; Scott Beardsley, Craig Granlund, of Dow Water and Process Solutions; Jonathan Wood and John Yen of Siemens Water Technologies—Ionpure Products; Bruce Tait of Layne Christensen; Jean Gucciardi of MarTech Systems; Rick Ide of AdEdge Technologies; and Lisa Fitzgerald of ITT—Goulds Pumps.

I would like to thank my graphic artist, Diana Szustowski, for her excellent and tireless efforts.

Finally, I would like to thank Paul Szustowski and Irma Kucera for their support.

Preface

The use of reverse osmosis (RO) technology has grown rapidly through the 1990’s and early 2000’s. The ability of RO to replace or augment conventional ion exchange saves end users the need to store, handle, and dispose of large amounts of acid and caustic, making RO a “greener” technology. Additionally, costs for membranes have declined significantly since the introduction of interfacial composite membranes in the 1980’s, adding to the attractiveness of RO. Membrane productivity and salt rejection have both increased, reducing the size of RO systems and minimizing the amount of post treatment necessary to achieve desired product quality.

Unfortunately, knowledge about RO has not kept pace with the growth in technology and use. Operators and others familiar with ion exchange technology are often faced with an RO system with little or no training. This has resulted in poor performance of RO systems and perpetuation of misconceptions about RO.

Much of the current literature about RO includes lengthy discussions or focuses on a niche application that makes it difficult to find an answer to a practical question or problems associated with more.common applications. Hence, my objective in writing this book is to bring clear, concise, and practical information about RO to end users, applications engineers, and consultants. In essence, the book is a reference bringing together knowledge from other references as well as that gained through personal experience.

The book focuses on brackish water industrial RO, but many principles apply to sea water RO and process water as well.

1

FUNDAMENTALS

1

Introduction and History of Development

1.1 Introduction

Reverse Osmosis (RO) is a membrane-based demineralization technique used to separate dissolved solids, such as ions, from solution (most applications involve water-based solutions, which is the focus of this work). Membranes in general act as perm-selective barriers, barriers that allow some species (such as water) to selectively permeate through them while selectively retaining other dissolved species (such as ions). Figure 1.1 shows how RO perm-selectivity compares to many other membrane-based and conventional filtration techniques. As shown in the figure, RO offers the finest filtration currently available, rejecting most dissolved solids as well as suspended solids. (Note that although RO membranes will remove suspended solids, these solids, if present in RO feed water, will collect on the membrane surface and foul the membrane. See Chapters 3.7 and 7 for more discussion on membrane fouling).

1.1.1 Uses of Reverse Osmosis

Reverse osmosis can be used to either purify water or to concentrate and recover dissolved solids in the feed water (known as “dewatering”). The most common application of RO is to replace ion exchange, including sodium softening, to purify water for use as boiler makeup to low- to medium-pressure boilers, as the product quality from an RO can directly meet the boiler make-up requirements for these pressures. For higher-pressure boilers and steam generators, RO is used in conjunction with ion exchange, usually as a pretreatment to a two-bed or mixed-bed ion exchange system. The use of RO prior to ion exchange can significantly reduce the frequency of resin regenerations, and hence, drastically reduce the amount of acid, caustic, and regeneration waste that must be handled and stored. In some cases, a secondary RO unit can be used in place of ion exchange to further purify product water from an RO unit (see Chapter 5.3). Effluent from the second RO may be used directly or is sometimes polished with mixed-bed ion exchange or continuous electrodeionization to achieve even higher product water purity (see Chapter 16.3).

Figure 1.1 ‘‘Filtration Spectrum” comparing the rejection capabilities of reverse osmosis with other membrane technologies and with the separation afforded by conventional filtration.

Other common applications of RO include:

1. Desalination of sea water and brackish water for potable use. This is very common in coastal areas and the Middle East where supply of fresh water is scarce.

2. Generation of ultrapure water for the microelectronics industry.

3. Generation of high-purity water for pharmaceuticals.

4. Generation of process water for beverages (fruit juices, bottled water, beer).

5. Processing of dairy products.

6. Concentration of corn sweeteners.

7. Waste treatment for the recovery of process materials such as metals for the metal finishing industries, and dyes used in the manufacture of textiles.

8. Water reclamation of municipal and industrial wastewaters.

1.1.2 History of Reverse Osmosis Development

One of the earliest recorded documentation of semipermeable membranes was in 1748, when Abbe Nollet observed the phenomenon of osmosis.¹ Others, including Pfeffer and Traube studied osmotic phenomena using ceramic membranes in the 1850’s. However, current technology dates back to the 1940’s when Dr. Gerald Hassler at the Unitversity of California at Los Angeles (UCLA) began investigation of osmotic properties of cellophane in 1948.² He proposed an “air film” bounded by two cellophane membranes.³ Hassler assumed that osmosis takes place via evaporation at one membrane surface followed by passage through the air gap as a vapor, with condensation on the opposing membrane surface. Today, we know that osmosis does not involve evaporation, but most likely involves solution and diffusion of the solute in the membrane (see Chapter 4).

Figure 1.2 shows a time line with important events in the development of RO technology. Highlights are discussed below.

In 1959, C.E. Reid and E.J. Breton at University of Florida, demonstrated the desalination capabilities of cellulose acetate film.⁴ They evaluated candidate semipermeable membranes in a trial-and-error approach, focusing on polymer films containing hydrophilic groups. Materials tested included cellophane, rubber hydrochloride, polystyrene, and cellulose acetate. Many of these materials exhibited no permeate flow, under pressures as high at 800 psi, and had chloride rejections of less than 35%. Cellulose acetate (specifically the DuPont 88 CA-43), however, exhibited chloride rejections of greater than 96%, even at pressures as low as 400 psi. Fluxes ranged from about 2 gallons per square foot-day (gfd) for a 22-micron thick cellulose acetate film to greater than 14 gfd for a 3.7-micron thick film when tested at 600 psi on a 0.1M sodium chloride solution. Reid and Breton’s conclusions were that cellulose acetate showed requisite semipermeability properties for practical application, but that improvements in flux and durability were required for commercial viability.

A decade after Dr. Hassler’s efforts, Sidney Loeb and Srinivasa Sourirajan at UCLA attempted an approach to osmosis and reverse osmosis that differed from that of Dr. Hassler. Their approach consisted of pressurizing a solution directly against a flat, plastic film.³ Their work led to the development of the first asymmetric cellulose acetate membrane in 1960 (see Chapter 4.2.1).² This membrane made RO a commercial viability due to the significantly improved flux, which was 10 times that of other known membrane materials at the time (such as Reid and Breton’s membranes).⁵ These membranes were first cast by hand as flat sheets. Continued development in this area led to casting of tubular membranes. Figure 1.3 is a schematic of the tubular casting equipment used by Loeb and Sourirajan. Figure 1.4 shows the capped, in-floor immersion well that was used by Loeb and students and is still located in Boelter Hall at UCLA.

Figure 1.2 Historical time line in the development of reverse osmosis.

Following the lead of Loeb and Sourirajan, researchers in the 1960’s and early 1970’s made rapid progress in the development of commercially-viable RO membranes. Harry Lonsdale, U. Merten, and Robert Riley formulated the “solution-diffusion” model of mass transport through RO membranes (see Chapter 4.1).⁶ Although most membranes at the time were cellulose acetate, this model represented empirical data very well, even with respect to present-day polyamide membranes.⁷ Understanding transport mechanisms was important to the development of membranes that exhibit improved performance (flux and rejection).

Figure 1.3 Schematic on tubular casting equipment used by Loeb. Courtesy of Julius Glater, UCLA.

Figure 1.4 Capped, in-floor immersion tank located at Boelter Hall that was used by Loeb and Sourirajan to cast tubular cellulose acetate membranes at UCLA, as viewed in 2008.

In 1971, E. I. Du Pont De Nemours & Company, Inc. (DuPont) patented a linear aromatic polyamide with pendant sulfonic acid groups, which they commercialized as the Permasep™ B-9 and B-10 membranes (Permasep is a registered trademark of DuPont Company, Inc. Wilmington, DE). These membranes exhibited higher water flux at slightly lower operating pressures than cellulose acetate membranes. The membranes were cast as unique hollow fine fibers rather than in flat sheets or a tubes (see Chapter 4.3.4).

Cellulose acetate and linear aromatic polyamide membranes were the industry standard until 1972, when John Cadotte, then at North Star Research, prepared the first interfacial composite polyamide membrane.⁸ This new membrane exhibited both higher throughput and rejection of solutes at lower operating pressure than the here-to-date cellulose acetate and linear aromatic polyamide membranes. Later, Cadotte developed a fully aromatic interfacial composite membrane based on the reaction of phenylene diamine and trimesoyl chloride. This membrane became the new industry standard and is known today as FT30, and it is the basis for the majority of Dow Water and Process Solutions’ FilmTec™ membranes (e.g., BW30, which means “Brackish Water membrane,” FT30 chemistry”; TW30, which means “Tap Water membrane,” FT30 chemistry; and so on) as well as many commercially available membranes from other producers (FilmTec is a trademark of Dow Chemical Company, Midland, Michigan). See Chapter 4.2 for more information about interfacial composite membranes.

Other noteworthy developments in membrane technology include the following:

1963: First practical spiral wound module developed at Gulf General Atomics (later known as Fluid Systems®, now owned by Koch Membrane Systems, Wilmington, MA.) This increased the packing density of membrane in a module to reduce the size of the RO system (see Chapter 4.3)..

1965: The first commercial brackish water RO (BWRO) was on line at the Raintree facility in Coalinga, California. Tubular cellulose acetate membranes developed and prepared at UCLA were used in the facility. Additionally, the hardware for the system was fabricated at UCLA and transported piecemeal to the facility.⁹

1967: First commercial hollow-fiber membrane module developed by DuPont. This module configuration further increased the packing density of membrane modules.

1968: First multi-leaf spiral wound membrane module developed by Don Bray and others at Gulf General Atomic, under US Patent no. 3,417,870, “Reverse Osmosis Purification Apparatus,” December, 1968. A multi-leaf spiral configuration improves the flow characteristics of the RO module by minimizing the pressure drop encountered by permeate as it spirals into the central collection tube.

1978: FT-30 membrane patented and assigned to FilmTec (now owned by Dow Chemical Company, Midland, MI).

1.1.3 Recent Advances in RO Membrane Technology

Since the 1970’s, the membrane industry has focused on developing membranes that exhibit ever greater rejection of solutes while at the same time exhibiting higher throughput (flux) at lower operating pressure. Table 1.1 shows the growth in RO membrane development with respect to rejection, flux, and operating pressure.¹⁰ Along with advances in membrane performance, membrane costs have also improved. Table 1.2 lists costs of membranes relative to 1980.⁵

Table 1.1 Development of RO membranes for brackish water desalination.

In addition to the progress shown in Table 1.1, some membranes now exhibit up to 99.75% rejection (a drop of 17% in salt passage over membranes exhibiting 99.7% rejection). Other advancements in membrane technology include “low pressure” RO membranes that allow for operation at lower water temperatures (< 50°F (10°C)) with reasonably low operating pressure (see Chapter 4.4.2.1). And, “fouling resistant” membranes have been developed that purport to minimize fouling by suspended solids, organics, and microbes (see Chapter 4.4.2.3).

Table 1.2 Membrane cost decline relative to 1980.⁵

Year | Relative Cost
1980 | 1.00
1985 | 0.65
1990 | 0.34
1995 | 0.19
2000 | 0.14

Since the late 1970’s, researchers in the US, Japan, Korea, and other locations have been making an effort to develop chlorine-tolerant RO membranes that exhibit high flux and high rejection. Most work, such as that by Riley and Ridgway et.al., focuses on modifications in the preparation of polyamide composite membranes (see Chapter 4.2.2).¹¹ Other work by Freeman (University of Texas at Austin) and others involves the development of chlorine-tolerant membrane materials other than polyamide. To date, no chlorine-resistant polyamide composite membranes are commercially available for large-scale application.

Nanotechnology came to RO membranes on a research and development scale in the mid 2000’s, with the creation of thin-film nanocomposite membranes.2,12,13 The novel membranes created at UCLA in 2006 by Dr. Eric M.V. Hoek and team include a type of zeolite nanoparticle dispersed within the polyamide thin film. The nanoparticles have pores that are very hydrophilic such that water permeates through the nanoparticle pores with very little applied pressure as compared to the polyamide film, which requires relatively high pressure for water to permeate. Hence, the water permeability through the nanocomposite membranes at the highest nanoparticle loading investigated, is twice that of a conventional polyamide membrane.¹² The rejection exhibited by the nanocomposite membrane was equivalent to that of the conventional polyamide membrane.¹² The controlled structure of the nanocomposite membrane purports to improve key performance characteristics of reverse osmosis membranes by controlling membrane roughness, hydrophilicity, surface charge, and adhesion of bacteria cells.¹⁴ The thin-film nanocomposite membrane (TFN) technology was licensed from UCLA in 2007 by NanoH₂0, Inc. (Los Angeles, CA) for further research and development toward commercialization.¹⁵

Along similar lines, other researchers have been looking into nanocomposite membranes.¹⁶ Researchers at the University of Colorado at Boulder have been developing lyotropic liquid crystals (LLCs) to form what they call nanostructured polymer membranes.¹⁶ The LLCs can from liquid crystalline phases with regular geometries which act as conduits for water transport while rejection ions based on size exclusion. In bench-scale tests, nanostructuered polymer membranes exhibited a rejections of 95% and 99.3% of sodium chloride and calcium chloride, respectively.¹³ These membranes also exhibited greater resistance to chlorine degradation than commercially-available polyamide composite membranes. As is the case with the nanocomposite membranes, the nanostructured polymer membranes are not yet in commercial production.

1.1.4 Future Advancements

Improvements will be necessary as RO is used to treat the ever greater expanding candidate feed waters, including municipal and industrial wastewater effluents, and other source waters that are less than optimal for conventional RO membranes (e.g., wastewaters containing high concentrations of biological chemical demand (BOD), chemical oxygen demand (COD), TOC, silica, and suspended solids, such as food-processing condensates and cooling tower blowdown). Membranes will need to be developed that are tolerant of chlorine for microbial growth control, and resist to fouling with suspended solids and organics. Other membrane technologies, such as microfiltration and ultrafiltration, are finding fresh application in pre-treating RO systems operating on these challenging water sources.

There is also continuing research into higher-performance (high flux and high rejection) membranes to further reduce the size and cost of RO systems. Nanotechnology shows promise for having a role in the development of these high-performance membranes.

Improvements will be required in the chemistries used to treat RO. These chemistries include antiscalants, which will be needed to address higher concentrations of scale formers such as silica, and membrane cleaners, which will have to address microbes, biofilms, and organics.

References

1. Cheryan, Munir, Ultrafiltration and Microfiltration Handbook, 2nd ed., CRC Press, Boca Raton, FL, 1998.

2. Koenigsberg, Diana, “Water Warriors,” UCLA Magazine, www.magazine.ucla.edu/features/water warriors, July 1, 2006.

3. Glater, Julius, “The Early History of Reverse Osmosis Membrane Development,” Desalination, 117 (1998).

4. Reid, C.E. and E.J. Breton, “Water and Ion Flow Across Cellulosic Membranes,” Journal of Applied Polymer Science, vol 1, issue 2 (1959).

5. Baker, Richard, Membrane Technology and Applications, 2nd ed., John Wiley & Sons, Ltd, Chichester, West Sussex, England, 2004.

6. Lonsdale, H.K., U. Merten, and R.L. Riley, “Transport Properties of Cellulose Acetate Osmotic Membranes,” Journal of Applied Polymer Science, vol 9, 1965.

7. Sudak, Richard G., “Reverse Osmosis,” in Handbook of Industrial Membrane Technology, M.C. Porter, Ed., William Andrew Publishing, 1990.

8. Cadotte, John, R.S. King, R.J. Majerle, and R.J. Peterson, “Interfacial Synthesis in the Preparation of Reverse Osmosis Membranes,” Journal of Macromolecular Science and Chemistry, A15, 1981.

9. Glater, Julius, Professor Emeritus, UCLA, personal communications, February 24, 2009.

10. Advanced Membrane Technology and Applications, Li, Norman, Anthony Fane, W.S. Winston Ho, and Takeshi Matsuura, eds., John Wiley & Sons, Inc., Hoboken, NJ, 2008.

11. Riley, R.L., S.W. Lin, A. Murphy, I. Wiater-Protas, and H.F. Ridgway, “Development of a New Chlorine and Biofouling Resistant Polyamide Membrane,” technical report number A273214 under the SBIR contract number DAAD19-02-C-0031.

12. Jeong, Byeong-Heon, Eric M.V. Hoek, Yushan Yan, Arun Subramani, Xiaofei Huang, Gil Hurwitz, Asim K. Ghosh, and Anna Jawor, “Interfacial Polymerization of Thin Film Nanocomposites: A New Concept for Reverse Osmosis Membranes,” Journal of Membrane Science, 294, 2007.

13. Merkel, T.C., B.D. Freeman, R.J.Spontak, Z. He, I. Pinnau, P. Meakin, and A.J. Hill, “Ultrapermeable, Reverse-Selective Nanocomposite Membranes,” Science, Vol. 296, April 19, 2002.

14. NanoH20 Inc. web page, www.nanoh2o.com.

15. Flanigan, James, “California’s Glimmer of Hope: Nanotechnology,” The New York Times DealBook Blog, www.NYTimes.com, July 16, 2009.

16. Hatakeyama, Evan S., Meijuan Zhour, Brian R. Wiesenauer, Richard D. Noble, and Douglas L. Gin, “Novel Polymer Materials for Improving Water Filtration Membranes,” proceedings of the American Membrane Technology Association 2009 Conference and Exposition, July, 2009.

2

Reverse Osmosis Principles

Reverse osmosis is a demineralization process that relies on a semipermeable membrane to effect the separation of dissolved solids from a liquid. The semipermeable membrane allows liquid and some ions to pass, but retains the bulk of the dissolved solids. Although many liquids (solvents) may be used, the primary application of RO is water-based systems. Hence, all subsequent discussion and examples will be based on the use of water as the liquid solvent.

To understand how RO works, it is first necessary to understand the natural process of osmosis. This chapter covers the fundamentals of osmosis and reverse osmosis.

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