The nominal rating refers to an approximate particle size—the vast majority of which will not pass through the filter. In other words, a small amount of particles this size or larger may pass through.The absolute rating, however, indicates that all particles larger than that specified will be trapped within or on the filter and will not pass through. Absolute rating establishes a level of filter performance throughout its useful life, thereby guaranteeing consistent performance.

The pore size of media used in membrane systems can vary from reverse osmosis, which rejects everything but water, to microporous membranes with pores from 0.01 micron to 10 microns. (Particle filtration covers filtration in the range of 5 to 75 microns and is typically handled by cartridge filters.) Reverse osmosis removes undesirable materials from water by using pressure to force the water molecules through a semipermeable membrane. The process is called “reverse” osmosis because the pressure forces the water to flow in the reverse direction, from the concentrated solution to the dilute solution, than that occurring in natural osmosis. RO removes ion-sized material such as sodium, chloride, calcium, and sulfate as well as small organic molecules down to a molecular weight of 100 to 150.

Nanofiltration (NF) and ultrafiltration (UF) are other methods of cross-flow filtration that are similar to RO but use lower pressures. NF removes selected salts and most organics. The UF process falls between nanofiltration and microfiltration (MF) in terms of the size of particle removed, typically rejecting organics over 1,000 molecular weight while passing ions and smaller organics. UF is often used for removal of macromolecules, colloids, viruses, and proteins in the biomedical and pharmaceutical industry. UF is sometimes applied to surface or groundwater treatment for potable use when the source water is consistently low in turbidity. MF, another in the family of membranes, is best suited for removal of particulates, turbidity, suspended solids, and pathogens such as Cryptosporidium and Giardia. A typical Cryptosporidium oocyst is approximately 3 to 5 microns in size, which is 15 to 25 times larger than the pores in a typical 0.2 micron MF membrane.

While much of the focus for emerging membrane technologies has centered on residential and low-volume POU installations, the vast majority of benefits will accrue from growth in large-scale municipal applications and high-purity commercial water treatment systems. Although membrane processes have been used in water treatment for several decades, primarily for desalination, they are not yet part of standard treatment. Water suppliers have long been eager to apply membrane technologies to complex treatment situations, but cost has been a barrier. As the price comes down and durability increases, the potential of membrane filtration is becoming reality. The advantages include a smaller footprint than conventional treatment plants, the ability to capture pathogens and natural organic matter, and the potential to keep utilities ahead of tighter regulatory limits for surface water quality and disinfection by-products.

There is considerable interest in comparing the costs of emerging membrane technologies with costs for alternative potable water treatment processes. For example, based on pilot studies, the cost of particle removal by UF is estimated to be less than or comparable to that using conventional treatment for capacities of approximately 5 million gallons per day. That is to say that it can be a cost-effective option for small facilities. Further, many industries, from pharmaceuticals to electronics to beverages, rely on treated water to produce products. The development of new or refined high-technology and biotechnology products that require ultrapure water as part of manufacturing will also facilitate the rapid growth of membrane technology.

Membrane technologies are used increasingly where high-purity water is a necessity. Ultrapure water, which has been purified by a series of processes to the degree that remaining impurities are measured in parts per billion or trillion, is required by the semiconductor industry and other specialized industrial users. The demand for technologically advanced ultrapure water equipment and systems has increased as the industries that use ultrapure water have become more knowledgeable about their quality requirements. The semiconductor industry, in particular, has continued to demand higher-purity water as the circuits on silicon wafers have become more densely packed.

In addition, membrane technologies are rapidly emerging as a viable water treatment option for municipalities confronted with complex regulatory issues. Membranes can be used as the primary means to remove materials from water, but they can also be used in conjunction with other physical, chemical, or biological processes to separate phases or isolate organisms. Pressure-driven processes of barrier separation are also finding dramatic growth in the provision of high-purity water in an expanding number of industries. All told, yearly sales of membrane technology are predicted to top $5 billion by 2010. Judging by the fundamentals as well as the merger-and-acquisition activity in the membrane filtration business, this segment represents an area in the water industry with above-average growth and investment potential.

Treatment Chemicals

Chemicals have long been a basic component of water and wastewater treatment methods. Corresponding to the surge of technology-driven research in the water industry, however, chemicals are recognized as having a growing role in an increasingly complex technical and regulatory environment. Chemicals can be engineered to achieve a greater range of treatment applications or used in a multibarrier approach. Either way, the cost advantage of chemicals makes them an attractive alternative to many physical or mechanical treatment options. Few segments within the water industry have undergone the number of ownership changes that the chemicals segment has experienced. While there is a dwindling supply of pure-play public companies in water treatment chemicals, there are a number of companies that stand to gain from specialty market positions or the addition of chemicals to their business mix.

According to the American Chemical Society, the demand for water treatment chemicals in the United States is expected to rise at an annual rate of 5 to 6 percent. Much of the opportunity, however, results from worldwide demand. For example, China’s demand for water treatment chemicals is projected to grow at an annual rate of approximately 13 percent. By the end of the decade, the global business is estimated to be at over $7 billion. Driving the global growth is worldwide population growth, enforcement of regulatory mandates, innovation in industrial water treatment, and multibarrier approaches in drinking water treatment. The major applications of chemicals in water treatment include:

• Coagulants and flocculants

• Biocides and disinfecting chemicals

• Corrosion- and scale-inhibiting chemicals

• Filter media and adsorbent chemicals

• Softeners and pH adjusters

• Antifoaming agents

• Fluoridation agents

The most common types of treatment for surface water used for drinking supplies are clarification and disinfection. Clarification is usually accomplished by a combination of coagulation, flocculation, sedimentation, and filtration. Coagulation and flocculation are two liquid/solid separation processes that are heavily dependent on the use of chemical additives. Suspended particles cannot be completely removed from water by plain settling, even when they are given very long detention times and low overflow rates. One of the properties of very small turbidity-causing colloidal particles that keep them in suspension is the small electrostatic charge they each carry. Coagulation takes place when the energy barrier between suspended particles is lowered and effectively eliminated. Coagulant chemicals neutralize the effect of the colloidal charges.

Flocculation refers to the successful collisions that occur when the destabilized particles are driven toward each other. Agglomerates of a few very tiny colloidal particles then quickly bridge together to form larger and heavier particles or flocs. After the initial flash mix of the coagulant with the water, a gentle agitation caused by slow stirring further enhances the growth of flocs by increasing the number of particle collisions and enabling removal in a sedimentation tank.

Coagulation or flocculation is enhanced by the addition of chemicals to wastewater to aid gravity settling of suspended or colloidal materials.There are several different chemicals that can be used for coagulation. The most common coagulant is aluminum sulfate (alum); it has become the major coagulant for treating surface water.At the same time, aluminum compounds produce an aluminum hydroxide sludge that is difficult to dewater. The mounting regulation of biosolids (sludge) has led to the greater use of polymeric compounds. Polymeric flocculants (synthetic organic chemicals) are long-chain, high-molecular-weight compounds that help the formation of larger, heavier floc particles.

There are several reasons for the increased demand for water-soluble polymers, including regulations and various environmental concerns regarding volatile organic compounds in paints, adhesives, and cosmetics; the phosphate components in detergents and municipal and industrial water treatment; and the need for paper recycling. Other factors include the growth of the processed food market, changes in paper processing technology, and the highly versatile nature of these compounds in terms of end uses and applications. Worldwide trends toward water reuse, waste minimization, stricter discharge regulations, equipment life extension, and productivity improvement place a high demand on industrial water and process treatment chemicals. The current market breakdown for the United States shows manufacturing industries accounting for about 50 percent of shipments, followed by municipalities, electricity generators, and commercial and residential users.

In addition to the burgeoning industrial applications for wastewater treatment, chemicals used in clarifying drinking water have been found to be effective solutions for a growing list of contamination problems. In potable water treatment, slightly over two thirds of polymer consumption goes for clarification. Enhanced coagulation, proposed as a BAT in Stage 1 of the Disinfectants/Disinfection By-Products (D/DBP) Rule, is capable of controlling disinfection by-products by removing natural organic matter precursors. The D/DBP Rule regulates total trihalomethanes, a carcinogenic by-product of the disinfection process. The list of complex issues mitigated by water treatment chemicals in conventional unit processes continues to expand as research progresses: arsenic removal, reduction of hazardous sludge, enhanced filter performance, improved dewatering of sludges, and increased effluent quality.

It is for precisely these reasons that the specialty chemicals business of the water and wastewater treatment industry holds so much promise for investors. Chemical companies are following the lead set by the large water purification and wastewater treatment systems suppliers in providing integrated solutions that maximize performance and minimize costs.This integrated approach is an established trend in the water industry but for water chemical marketers it is just unfolding. Because of the specificity of this concept and the fact that extensive knowledge of the industry is required to implement the strategy, several large players dominate the market for engineered water treatment chemicals.

The water and wastewater chemical treatment business has undergone a tumultuous restructuring over the past decade. This is likely due to the consolidative nature of a commodity business in combination with one of the most traditional of water industry components that exhibits a fairly straightforward business model. General Electric acquired BetzDearborn from Hercules in 2002. About the same time, a consortium of private equity firms purchased Ondeo Nalco (renamed Nalco Company) from Suez. In 2004, Nalco returned to the public arena with an IPO at $15 per share and remains the preeminent publicly held water treatment chemical company in the world.

The water treatment chemicals business has historically been a fragmented, undercapitalized industry, vying to solve treatment problems with competing methodologies. That changed with the consolidation of key water treatment chemical technologies and the emergence of integrated service chemical providers. The common characteristics of the companies that signify substantial opportunity are a global reach, engineered chemical treatment, on-site innovation, and in-depth technical service and support.

Many water treatment chemical companies are minor parts of much larger companies or are private.Table 7.2 presents the prominent global water treatment stocks.

Disinfection:The Chlorine Controversy

Chlorine has been making our drinking water safe for almost 100 years. It is the most commonly used substance for disinfection in the United States. After chlorine’s introduction into the public water supply, U.S. typhoid deaths dropped from 25,000 in 1900 to less than 20 in 1960 to virtually none today, not to mention its role in preventing the spread of other waterborne diseases. Chlorine and chlorine-based compounds are used to disinfect 98 percent of the publicly supplied drinking water in the United States.At the same time, the use of elemental chlorine in water purification is the subject of a broader controversy that shows no sign of disappearing.

Table 7.2 Water Treatment Chemicals

In drinking water treatment, clarification (comprised of the unit processes of coagulation, sedimentation, and filtration) is followed by chlorination to remove pathogenic bacteria or viruses. In gaseous form, molecular chlorine (Cl₂) is very toxic. But when the chlorine is dissolved in low concentrations in clean water, it is not harmful. It reacts with the H⁺ ions and the OH^- radicals in the water to produce hypochlorous acid, HOCl, and the hypochlorite radical, OCl^-. These are the actual disinfecting agents. If microorganisms are present in the water, the HOCl and the OCl^- penetrate the microbe cells and react with certain enzymes. This reaction disrupts the organisms’ metabolism and kills them.

What is a growing concern, however, are the so-called “by-products” of the disinfection process (the growing list of so-called disinfection by-products or DBPs). Source waters often contain trace amounts of organic compounds, primarily from natural sources such as decaying vegetation. These substances can react with the chlorine to form trihalomethanes (THMs), which are suspected of causing cancer in humans. Chloroform is an example of a THM compound. It is for this reason that the Environmental Protection Agency (EPA) regulates disinfection by-products by setting maximum contaminant levels for total THMs and the sum of five haloacetic acids. The levels of these substances formed upon chlorination of natural waters depend on several operational conditions, such as chlorine dosage and free chlorine contact time, as well as water quality conditions, such as organic content, bromide, temperature, and pH.

As the debate over the health risks associated with chlorine disinfection by-products intensifies, the water industry continues to take a critical look at alternative disinfection processes. And while ozone and ultraviolet disinfection, among other methods, have benefited from the scrutiny of chlorine, it is unlikely that a change based solely on the chlorine controversy will occur overnight. First, other chlorine-based disinfectants such as chlorine dioxide, bromine chloride, and hypochlorites (solid and liquid chlorine compounds) do not lead to toxicity problems as often. For instance, chlorine dioxide does not produce chlorinated or brominated organics,THMs, dioxins, or other haloforms. Second, alternative disinfection methods also have potentially harmful by-products under certain conditions. And third, adjustments to the treatment process prior to chlorination, such as enhanced coagulation, can remove natural organic matter and reduce by-product formation.

Chlorine Dioxide

Chlorine dioxide (ClO₂) manufacturers may achieve some near-term gains in market share as a result of demand for chlorine-based disinfection methods other than the commonly used chlorine gas process. In addition, there are special situations that present an opportunity as the chlorine controversy heightens. For example, enhanced coagulation for the purpose of removing natural organic matter, which is the primary precursor of disinfection by-products, should help the coagulants business of water treatment chemical companies.

Ozone: Good Up High, Bad Nearby

While much is said about the potential for alternative disinfection methods to chlorine, little is written about the ways in which these technologies are actually being transferred to the marketplace. Ozone, however, is one segment that is relatively well established and developing in a rather deliberate manner. Major industrial gas producers are aligning themselves with leading ozone technology producers to create formidable alliances designed to take advantage of ozone’s potential in the water industry.

Ozone (O₃), which is an unstable gas comprised of three oxygen atoms, is an extremely powerful oxidant, second only to the hydroxyl free radical. It is capable of oxidizing many organic and inorganic compounds in water. Reactions with organic and inorganic compounds cause an ozone demand in the treated water that must be satisfied during ozonation prior to developing a measurable residual. Ozone gas readily degrades back to oxygen, and during this transition a free oxygen atom (free radical) is formed.

In the United States, ozone is gaining a foothold in the arsenal of water treatment technologies. Fueled by the ongoing regulation of disinfection by-products specifically and the efficacy of disinfection technologies generally, ozone treatment should be a segment of investor interest. Ozone treatment is utilized in a wide variety of applications in the water industry. It is used in treating landfill leachate and industrial wastewater, where it improves biodegradability, disinfects, and oxidizes nitrogen compounds. In drinking water, it replaces chlorine as the primary oxidant/disinfectant; eliminates pesticides and chlorinated hydrocarbons, removes iron and manganese; and improves odor, taste, and color. In combination with UV radiation or H₂O₂ (hydrogen peroxide), ozone is used to reduce chlorinated hydrocarbons and nitroaromatics in the remediation of contaminated groundwater. Ozonation is also growing in its use in the oxidation and disinfection of industrial process water for the food and beverage, semiconductor, and pharmaceutical industries. Most of the larger ozone equipment manufacturers make all components: ozone generators; ozone introduction equipment such as diffusers, injectors, or mixers; and destruction units.

The traditional way of producing ozone is by means of dielectric barrier discharge or silent electrical discharge. Because ozone is an unstable molecule, it is generated at the point of application. It is generally formed by combining an oxygen atom with an oxygen molecule in an endothermic reaction that requires a considerable input of energy. Dry feed gas (either oxygen or filtered ambient air) is pumped to ozone generators where it is passed over hundreds of glass tubes individually fused with an electrical filament. The gas is subjected to a corona (lightning-like) discharge at up to 15,000 volts causing an electron flow across the discharge gap. These electrons provide the energy to disassociate the oxygen molecules, leading to the formation of ozone.

Ozone generation does not form halogenated disinfection by- products (TTHMs and HAA5s) when used in oxidation/reduction reactions, but it does form a variety of organic and inorganic by-products. However, if bromide ions are present in the raw water, halogenated DBPs may be formed. These brominated DBPs pose a greater health risk than nonbrominated DBPs. Further, although ozone is an effective oxidant and disinfectant, it cannot be relied upon as a secondary disinfectant to maintain a residual in the distribution system. The advantages and disadvantages of ozone disinfection can be summarized as follows:

Advantages

• Ozone is more effective than chlorine, chloramines, and chlorine dioxide for inactivation of viruses, Crytosporidium, and Giardia.

• Ozone oxidizes iron, manganese, and sulfides.

• Ozone controls odor, taste, and color.

• Ozone can enhance the clarification process and turbidity removal.

• Ozone requires a very short contact time.

• In the absence of bromide, halogen-substitutes (DBPs) are not formed.

Disadvantages

• Ozone provides no residual.

• The initial cost of ozonation equipment is high.

• The generation of ozone requires high energy input.

• DBPs are formed in the presence of bromide.

• Ozone is highly corrosive and toxic.

Ozone technology is being transferred to the marketplace through a rapidly developing mechanism of alliances between global power-houses. Major joint ventures are seeking to take advantage of the explosive growth in ozone-based environmental technologies. Praxair, Inc. bought Henkel Corporation’s 50 percent share of its joint venture with Trailigaz Ozone, forming a global alliance bringing together its expertise in vacuum pressure swing adsorption (VPSA) oxygen generation systems with Trailigaz ozone production systems. Praxair is the largest industrial gas company in North and South America, and one of the largest worldwide. Trailigaz, the third-largest ozone water treatment technology company in the world, was a wholly owned subsidiary of Veoolia Environnement, until purchased by Wedeco AG, which itself was purchased by ITT Corporation. PCI-Wedeco has a strategic marketing and research-and-development alliance with British giant BOC Gases.

In another ozone consortium, Air Liquide S.A. (France) joined with Degremont S.A. (a subsidiary of Suez) to form a joint venture called Ozonia International, which took over the activities of Switzerland-based ABB AG (Asea Brown Boveri). The combination of Degremont’s water technology and the industrial application technology of Air Liquide make Ozonia a leading manufacturer of ozone generation equipment and ozone plants. The joint venture is also moving into UV applications. Suez has rebranded its water operations under the ONDEO brand. The ONDEO water business is the world’s second largest, behind the water unit of Veolia Environnement. Ozonia has grown into a group of five companies in Switzerland, the United States, Russia, South Korea, and Scotland, with the holding company, Ozonia International, in France. The worldwide ozone generation equipment market is segmented into municipal water treatment (70 percent) and industrial applications (30 percent).

Ultraviolet (UV) Disinfection

Ultraviolet energy is increasingly being used to disinfect wastewater, process water, sewage effluent, combined sewage runoff, and even drinking water. With UV’s efficiency in reducing Cryptosporidium established, ultraviolet light irradiation is positioned to become another option as best available technology for surface water treatment. With the added potential of UV light for inactivating C. parvum oocysts efficiently and cost-effectively, ultraviolet technologies promise to be a powerful tool for water suppliers as a viable disinfection alternative.

Ultraviolet irradiation is nature’s own disinfection method.The sun generates large quantities of ultraviolet energy that is naturally filtered by the ozone layer and does not occur in large quantities in the atmosphere. Ultraviolet energy is the photonic energy that lies just outside the visible violet end of the electromagnetic spectrum and is defined as light between the wavelengths of 100 and 400 nanometers (nm). This light has longer wavelengths than x-rays and shorter wavelengths than the light visible to the human eye.

Ultraviolet C (UVC) is part of the broad ultraviolet waveband. The portion of the UV spectrum that is important for the disinfection of water is the range absorbed by DNA (RNA in the case of some viruses). The “germicidal range” is approximately 200 to 300 nm, with a peak germicidal effectiveness at about 260 nm.This band of the UVC spectrum is highly destructive to microorganisms and is used for ultraviolet disinfection.The mechanism involves absorption of a UV photon by pyrimidine bases where two are positioned next to each other on the DNA chain. The photochemistry involves formation of a molecule that links the two bases together. This causes a disruption in the DNA chain, such that when the cell undergoes mitosis (cell division), the replication of DNA is inhibited. When water or wastewater is exposed to a special light source that produces this radiation, the cells of microorganisms are altered in a way that inhibits their ability to propagate.

The germicidal properties of UV lamps are a function of intensity, duration of exposure, and radiation wavelength. UV intensity dissipates with distance from a lamp so that a primary objective of UV disinfection system design is to maintain as close contact as possible between the UV lamps and the water being treated. In the past, the problem with this method of disinfecting wastewater, process water, or sewage streams has been the vast number of UV energy lamp sources needed at locations with poor effluent quality. However, recent versions of low-mercury, vapor pressure, ultraviolet-producing lamps have improved the electrical power to UV energy conversion efficiency without generating unwanted heat or other energy or light wavelengths. Lamps have been developed that continuously vary the UV energy output to match the effluent flow and clarity conditions. This has greatly extended the range of effluent streams that can be effectively treated while retaining the inherent benefits of UV irradiation.

The UVC germicidal waveband can treat liquid streams containing microbiological contaminants that cause infections, such as bacteria, viruses, and spores—and disinfect the streams without the use of chemicals and without producing changes in the fluid. This makes the technique extremely suitable for treating wastewater and effluent streams that empty into large bodies of water such as lakes, rivers, and oceans. Quality parameters such as biochemical oxygen demand (BOD) and chemical oxygen demand (COD) remain unaffected. In cases where discharge regulations severely limit the impact on receiving waters, UV technology can provide an effective solution.

Other advantages of UV disinfection include the elimination of the potential hazards of handling gaseous chlorine, alleviation of concerns about disinfection by-products, elimination of a dechlorination requirement, reduction in taste or odor problems and acceleration of treatment times. The disadvantages of UV disinfection include its sensitivity to water quality characteristics; dosage inflexibility; exposure risks; the lack of a residual; and the fouling of UV lamp tubes by oil, grease, mineral salts, and the like.

The disinfection process is used for different purposes in water and wastewater treatment plants. However, the types of devices used to inject disinfectant into the water or wastewater stream are similar. UV disinfection equipment is currently available in two configurations, enclosed systems and open-channel systems. Until the mid- to late 1980s, UV disinfection was accomplished in expensive, enclosed stainless steel tanks that were subject to fouling and troublesome to operate. Since that time, significant improvements to the equipment have been made. The advent of open-channel contactors with drop-in bulb assemblies has revolutionized the technology. The more recently developed open-channel systems are now the predominant UV system in wastewater treatment. Open-channel units are generally able to maximize use of the entire space around the lamps, since flow enters and leaves the lamp array without changing direction.

The application of UV radiation for primary disinfection is often limited by the turbidity (suspended particles) associated with many water supplies. This limits the transmittance, and hence the effectiveness, of the UV light. In addition, UV disinfection lacks a measurable residual as required in the distribution system. Although the use of UV radiation still lacks widespread application in the primary disinfection of drinking water, there is significant growth potential in large-scale installations and expanding specialized niche applications such as POU, wastewater reuse, industrial process water, and wastewater effluent disinfection.

Mixed Oxidants

The disinfection of drinking water is an area of continuous research to find more efficient disinfectants against presently known microorganisms for the protection of public health. The use of mixed oxidants, an emerging technology, while not new, is receiving a growing amount of interest. The general concept is that of an electrolytic cell and electrolyte used to generate amounts of anolyte and catholyte, believed to contain a variety of oxidants, the mixture of which is referred to as “mixed oxidants.” The oxidants are purported to include chlorine, chlorine dioxide, hydrogen peroxide, ozone, and hydroxyl radicals. This technology is thought to present a number of advantages over present disinfection methods. For one, the efficiency of the oxidants produced is, by mass, higher than that of chlorine. Second, a residual may be maintained in product water. Third, the oxidant concentration and composition may be adjusted according to specific needs. And, finally, the oxidant mixtures can be produced on-site using only electricity and sodium chloride.

In its application, mixed oxidant treatment is similar to chlorination. Rather than applying commercially available gaseous, solid, or liquid forms of chlorine, the process produces a strong disinfectant solution on-site. On-site oxidant generation (also known as anodic oxidation and salt brine electrolysis) is accomplished by an electrolytic process that generates a concentrated solution of oxidants, mainly free chlorine.This process involves passage of an electric current through a continuous-flow brine (salt) solution within a cell. The electrolyzed brine solution containing the concentrated disinfectant is injected into water for treatment. The concentrated solution is diluted approximately 100-fold in drinking water treatment. Although there is no record of the large-scale application of mixed oxidants in water disinfection, the technology can be a means of primary disinfection on small water treatment plants and to augment depleted disinfectant concentrations in distribution systems. In remote areas, mixed oxidants may be appealing because the application of chlorine can be problematic due to distance from the place of chlorine manufacture, the unreliability of delivery schedules, and the lack of sufficient expertise in chlorine dosing.

The chemistry of mixed oxidants is complex in the sense that while there are clearly constituents other than chlorine present in the reactions, the identity of these other components is not fully known. Although the chemistry is not completely understood, the other active oxidant components are limited to combinations of the oxygen and chlorine generated electrolytically in the saltwater brine used. Theoretically, due to the electrochemical processes within the cell, HOCl, ClO₂, O₃, and H₂O₂ could be formed.

Interestingly, the application of mixed oxidants in the disinfection of drinking water has been used for some time in eastern Europe. It is because of the chemical uncertainties that mixed oxidants have not yet been widely adopted in the United States. At the same time, the known benefits of mixed oxidants are enough to garner support by the EPA for certain applications and to continue promising research into lesser known, but theoretical, benefits. Mixed oxidants have been demonstrated through actual installations to have superior characteristics when compared to conventional chlorine, whether in the gas, liquid (sodium hypochlorite), or solid (calcium hypochlorite) form.

A number of scientific studies, some peer reviewed and some funded by manufacturers, have shown significant benefits of mixed oxidant disinfection. Mixed oxidants typically demonstrate lower THM production when compared to chlorine. Manufacturers report that THM formation can be reduced by 30 to 50 percent when compared to chlorine. Again, the chemistry is not completely understood, but the belief is that the oxidants in the mixed oxidant solution (apart from chlorine) react more rapidly with THM precursors. These oxidants are not prone to produce large amounts of THMs. Thus, most THM reduction observed in actual practice may be explained by the other oxidants of the mixed oxidant solution satisfying a major portion of the oxidant demand of the raw water, allowing satisfactory disinfection and residual maintenance at lower free available chlorine doses than would be required using chlorine alone. Reduced doses lead immediately to lower THM formation. There is also promise in the ability of mixed oxidants to inactivate Cryptosporidium parvum oocysts and other hard-to-kill microorganisms at free available chlorine doses that are normally used. Chlorine is unable to inactivate these microorganisms at practical doses.

Mixed oxidants enhance coagulation and flocculation processes in a manner similar or superior to ozone. The process creates a micro-flocculation effect following the same patterns generated by ozone pretreatment. The results are substantially lower alum and polymer requirements, reduced finished water turbidity, reduced sludge handling, and faster reaction times that allow for increased throughput and filter runs. Another key factor in the use of mixed oxidants as an alternative disinfection method is that the chlorine residual in the distribution system is much more stable and persistent in the distribution system. Mixed oxidants have been reported to have other beneficial characteristics. These include safety advantages over chlorine gas; biofilm removal and prevention of regrowth; improved taste and odor; oxidation of iron, manganese, and hydrogen sulfide; ammonia oxidation at subbreakpoint doses; and minimal increases in total dissolved solids (salt).

There are a number of regulations that support the benefits of mixed oxidants as an alternative disinfection method. The interim Enhanced Surface Water Treatment Rule (ESWTR) requires that large filtered surface water systems improve their reliability to remove at least 99% of Cryptosporidium through a dual-barrier approach. In the guidance document in support of the Surface Water Treatment Rule (SWTR), the EPA lists mixed oxidants as a small system compliance technology for disinfection. In addition, water systems serving more than 10,000 people must implement treatment strategies to achieve compliance with the Stage 1 D/DBP Rule, which lowers maximum levels for total THMs from 100 ppb to 80 ppb. Haloacetic acids, previously unregulated, will now be regulated at 60 ppb. Many systems will not be able to achieve compliance without making significant capital improvements. Nonetheless, the market for mixed oxidant technology is relatively small, and the investment potential is limited to the companies that sell on-site hypochlorite generators.

Carbon

Carbon is the sixth most abundant element in the universe, appearing in 94 percent of all known compounds. It is the only element on Earth capable of forming the complex and varied compounds essential for living organisms. Yet what is so ubiquitous in nature is also a material used extensively in the water industry. When treated at high temperature, carbon-based materials are transformed into products essential in purifying the water we drink.

Granular activated carbon (GAC), derived from naturally occurring materials like coal, wood, and coconut shell, has two unique properties that make it useful for water purification. First, it is a very porous material. In the activation process, high-temperature heat treatment creates an intricate network of microscopic pores and pathways within each carbon granule. GAC has an extremely high ratio of surface area to unit weight—up to 100 acres of area per pound. Second, the surface of activated carbon attracts and holds many of the impurities in water through the adsorption process. As a result, contaminants—which are highly concentrated in the liquid stream—move to the solid phase where the concentration is lower.

Adsorption on activated carbon is an effective method for removing dissolved organic substances that cause taste and odor problems in drinking water and has been sanctioned by the EPA as the BAT for organics removal. It is also effective in removing the organic precursors that react with chlorine to form harmful THM compounds after disinfection. In special applications, GAC can remove synthetic organic chemicals (SOCs) or volatile organic chemicals (VOCs) from contaminated water. As such, GAC is useful in complying with the D/DBP Rule established under the Safe Drinking Water Act amendments.

Carbon treatment can be used for both secondary and tertiary treatment directly in large, centralized physical/chemical treatment plants or to polish effluent from biological treatment systems. Powdered carbon is mixed with the water by a special dry-feeder device, at a point in the treatment plant that precedes the filtration process. It is then removed from the water by the filters. Granular carbon is sometimes used in the filter bed itself, combining both filtration and adsorption in one treatment unit. Similar treatment processes, on a miniaturized basis, are widely used in decentralized point-of-use filtration devices.

Environmental applications of activated carbon in wastewater and sewage treatment, groundwater remediation, and water purification offer enormous potential. In addition, substantial new opportunities are emerging within the process industries as environmental and process applications converge.Trends toward pretreatment and waste minimization as process improvement and cost reduction steps are also creating significant demand for GAC. Part of the reason is the physical nature of carbon. When the carbon surface becomes saturated with adsorbed impurities, it can be cleaned or reactivated by heating to a high temperature in a special thermal reactivation furnace or removed chemically in a regeneration process and then reused. On-site reactivation, rather than complete replacement with fresh carbon, is economical for large municipal water treatment plants. The ability to reuse granular carbon over and over makes it financially attractive as a treatment option but has also contributed to the past oversupply of carbon worldwide. In addition, activated carbon is used in manufacturing a variety of products from decaffeinated coffee to automobiles to magazines. In the food and beverage, oil and gas, chemical, pharmaceutical, and other industries, there are more than 700 different applications of activated carbon.This helps to explain why, with all the promise carbon holds for the water industry, manufacturers are sensitive to worldwide economic conditions.

The industry is dominated by several large manufacturers. Calgon Carbon Corporation is the world’s largest producer and marketer of GAC, related services, equipment, and systems for both environmental and industrial applications. Calgon’s share of the global market for GAC is estimated at approximately 30 percent, and its volume of sales is three times that of its closest competitor, Norit N.V. There are also many smaller manufacturers that comprise a fragmented component to the business and create competitive pressures. While the amount of Chinese carbon imported has slowed, it is still disrupting the industry’s pricing structure. In response, several major producers have diversified into other businesses.

Even though end-market improvement is still the key for an overall improvement in the carbon industry, the prospects for applications in the water industry are phenomenal. Product innovations such as extruded activated carbon blocks, catalytic carbons, and biological activated carbon offer opportunities in process applications and the growing POU market. As the industry works off excess capacity and pricing pressure subsides, there is tremendous potential for leverage and a return to the historically high growth rates to which the carbon industry is accustomed. With so many uses for activated carbon in the removal of contaminants, the overcapacity of the past is not likely to remerge. At the same time, carbon is a commodity and manufacturers face a great deal of competition; there is limited value added that can differentiate suppliers.

Resins: Ion Exchange

While physical treatment methods such as RO, adsorption, mechanical filtration and even ultraviolet light receive much of the attention in water treatment, the chemical treatment process of ion exchange is increasingly being utilized in a variety of treatment applications. After an extended period of overcapacity, the ion exchange segment has experienced substantial global growth, reflecting increased demand from Asian economies. While resin price increases have taken some competitive luster off the ion exchange process, the segment is developing into an effective option within the overall treatment scheme.

Ion exchange is a chemical treatment process in which undesired ions in water are replaced with less objectionable ones (the contaminant must therefore be present as an ion). An ion is an atom or molecule that has lost or gained one or more electrons, thereby acquiring a net electric charge. Ions are preferentially adsorbed from a solution by equivalently charged ions attached to small solid structures known as resins. Ion exchange is an equilibrium phenomenon. As untreated water passes through the device, the undesired ions are exchanged for ions on the exchange material and the process continues until equilibrium is reached.

The efficiency of the exchange depends on the concentration of ions in the water, the attraction between the ion exchange resin and the unwanted ions, and the contact time between untreated water and the resin. The exchange occurs in a fiberglass tank or plastic-lined steel tank filled with a special ion exchange material—either a commercial resin, which is a petrochemical compound shaped into beads, or a synthetic zeolite, which is a crystalline formulation of aluminates and silicates. The appropriate exchange material depends on the untreated water quality and the desired water quality. The two types of ion exchange units are cation and anion exchange devices. Water softeners remove cations (positively charged minerals such as calcium and magnesium) and replace them with sodium. Anion exchange devices remove anions (negatively charged ions such as arsenic and nitrate) and replace them with chloride.

The primary applications for ion exchange technology are water softening, industrial water treatment, dealkalization and demineralization. Water softeners (or water conditioners) are the most widely used point-of-entry (POE) home water treatment devices. Water softeners consist of a corrosion-resistant brine tank that is filled with resin beads saturated with sodium. The resin prefers calcium and magnesium (the principle components of hardness) over sodium so as water passes over the resin, sodium is released and calcium and magnesium are adsorbed. Softeners remove hardness minerals that form scale on water heaters and pipes. These devices can also remove barium, radium, small amounts of dissolved iron and manganese, and, in many cases, soluble iron (ferrous). Contrary to industry claims, water used for drinking generally does not need to be softened, nor should softened water be used for irrigation.

While there have been many improvements in home and commercial water softeners in recent years, the basic cation resin used has remained the same. The thrust for operating efficiencies and soft water quality has focused on obtaining higher salt efficiency and automatic regeneration. Other factors influencing design changes have been the effort to conserve water and minimize saltwater discharge to the wastewater system. These changes have spurred the demand for residential water softeners and have greatly contributed to the success of water softening equipment manufacturers. The end market is mature and overcrowded, limiting the value of the residential water softener segment as an investment play. This theme is discussed in greater detail in the context of decentralized treatment.

Where ion exchange is gaining momentum is in the industrial, municipal, and restoration markets. Variations of ion exchange technology such as deionization, demineralization, and complex mixed-bed ion exchange technologies are increasingly being used in specific applications. Ion exchange deionizers (DIs) use synthetic resins similar to those used in water softeners.Typically used on water that has already been prefiltered, DIs use a two-stage process to remove virtually all ionic material remaining in water. Two types of synthetic resins are used: cations to remove positively charged ions, and anions to remove negatively charged ions. Cation deionization resins exchange hydrogen (H⁺) ions with cations, such as calcium, magnesium, and sodium. Anion exchange operates on the same principle as cation exchange.The only difference is that anion exchange devices adsorb anions such as nitrate and sulfate instead of cations such as calcium and magnesium. Anion deionization resins exchange hydroxide (OH^-) ions for anions such as chloride, sulfate, and bicarbonate.The displaced H⁺ and OH^- combine to form H₂O.

Deionization can produce extremely high quality water in terms of dissolved ions or minerals. Deionization holds promise in the desalination of seawater, the extraction of harmful contaminants from wastewater, and the removal of inorganics associated with the application of agricultural fertilizers. Deionization is also used as a water purification method in bottling plants, electroplating operations, and pharmaceuticals, as well as in high-purity applications such as low-pressure boilers and power generators.

Much of the expansion in the use of ion exchange technology results from advances in the exchange materials. Resins give preferential treatment to certain ions and, by engineering special resins, consideration can be given to innovative applications. For example, resins typically prefer sulfate over nitrate (the order of adsorption depends on the characteristics and concentration of each ion in the water). Most resins are ineffective in removing nitrate if sulfate is also present in the water. Nitrate-selective resins have been designed to rearrange the preference order; nitrate is adsorbed first, then sulfate, then chloride, then bicarbonate. Nitrate-selective resins push sulfate off the exchange material if the two ions are competing but do not dump nitrate when the resin capacity is exhausted.

Table 7.3 Water Treatment Compains

The market for ion exchange technology is evolving from the more saturated water conditioning applications to complex industrial, remediation, high-purity, and even organic applications. At the same time, growth rates within the industrial segment are mixed. Generally, demineralization by ion exchange has been declining as the usage of reverse osmosis membranes has increased. Other contaminant-specific applications for ion exchange such as removal of radionuclides, nitrates and arsenic are showing significant growth.While much of the innovative technology still remains to be commercialized, breakthroughs in operating efficiencies and resin materials are creating exciting opportunities that investors should monitor.

Table 7.3 summarizes a diverse array of water treatment companies.

Centralized water and wastewater treatment evolved as the logical extension of increasing urbanization and the application of the economic model of economies of scale. At the same time, if we are to foretell the future of water, latitude must be given to the theorem that centralized treatment may not necessarily hold the answer to sustainability. Especially with respect to “bottom-of-pyramid” markets and the reverse flow of technological innovation, decentralized (distributed) treatment has a disruptive story to tell and a potentially compelling investment premise.