Exhibit 2.13: MF and UF Studies Documenting Cryptosporidium Removal Reference Process Membrane Pore Size Log Removal Scheider et al. ( 1999) MF 0.2 : m 4.2 Scheider et al. ( 1999) MF 0.1 : m > 4.2 Scheider et al. ( 1999) MF 0.1 : m > 4.2 Trussel et al. ( 1998) MF 0.2 : m > 4.7*

Jacangelo et al. ( 1997) MF 0.2 : m > 4.9*

Jacangelo et al. ( 1997) MF 0.2 : m > 6.4*

Trussel et al. ( 1998) UF 100,000 Daltons > 5.1*

Hagen ( 1998) UF 100,000 Daltons > 8*

Jacangelo et al. ( 1997) UF 100,000 Daltons > 4.9*

Jacangelo et al. ( 1997) UF 100,000 Daltons > 6.4*

Jacangelo et al. ( 1989a) UF 100,000 Daltons > 5*

Jacangelo et al. ( 1997) UF 100,000 Daltons > 6.4*

Jacangelo et al. ( 1997) UF 100,000 Daltons > 6.4*

Note: * Indicates removal to detection limit. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 26 Exhibit 2.14: MF and UF Studies Documenting Virus Removal Reference Process Membrane Pore Size Log Removal Scheider et al. ( 1999) MF 0.2 : m 0.5 Scheider et al. ( 1999) MF 0.1 : m 1.1 Scheider et al. ( 1999) MF 0.1 : m 2.3 Trussel et al. ( 1998) MF 0.2 : m 0.4 to 3.1 Jacangelo et al. ( 1997) MF 0.2 : m > 1 Jacangelo et al. ( 1997) MF 0.2 : m > 1.5 Kruithof et al. ( 1997) MF  0.7 to 2.3 Trussel et al. ( 1998) UF 100,000 Daltons > 6.9*

Jacangelo et al. ( 1997) UF 100,000 Daltons > 6 Kruithof et al. ( 1997) UF  > 5.4 Jacangelo et al. ( 1989a) UF 100,000 Daltons > 8*

Jacangelo et al. ( 1989a) UF  > 6 Note: * Indicates removal to detection limit.

 Data not available.

As shown in Exhibits 2.11 through 2.14, both MF and UF systems are capable of significant log removal of bacteria, Giardia cysts, and Cryptosporidium oocysts. The data presented indicate that MF/ UF are capable of bacteria removals of nearly 9 log and Giardia and Cryptosporidium removals in excess of 8 log. In fact, in nearly all cases, the log removal demonstrated is simply a function of the influent microbe concentration, since bacteria and cysts are typically removed to detection limits. As shown in Exhibit 2.14, however, MF and UF are differentiated by virus removal. The maximum virus removal reported for MF membranes is approximately 3 log, but the average reported removal is nearer to 1 log. UF membranes typically remove viruses to detection limits.

Note that the studies summarized in Exhibits 2.11 through 2.14 are conducted with intact membranes ( i. e., the membranes are not compromised). Had a fiber from one of these membranes been broken, either deliberately or accidentally, the results could be significantly different, since the potential would exist for microorganisms to pass into the treated water. For this reason, it is important to include membrane integrity testing when assessing the ability of a membrane to act as a barrier against microorganisms. Many types of membrane integrity tests exist. These tests fall into two categories: 1) direct methods and 2) indirect methods. Indirect methods include monitoring the treated water for parameters such as particle counts or turbidity. Direct methods include tests, such as air pressure decay and diffusive airflow, that directly assess the integrity of the membrane itself. Integrity testing represents an important aspect of a membrane system from a regulatory perspective, since it provides a measurement of the integrity of the filter. Commercial manufacturers have recognized this, and most systems are now provided with automatic integrity testing that can be conducted frequently ( e. g., hourly). Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 27 <IP_ADDRESS> DBP Formation Disinfection by MF/ UF is achieved through physical removal. Because of this, no DBPs are formed during disinfection by MF/ UF. Chlorine or chloramines must be added subsequent to MF/ UF to maintain a disinfectant residual. Chlorination and chloramination can produce DBPs as discussed in section 2.1.2.

MF and UF alone are generally not effective for DBP precursor removal. The pore sizes are typically large enough to allow most NOM to pass through these membranes, thus removing little NOM. Some tight UF membranes with MWCOs on the order of 10,000 Daltons may be capable of removing some NOM, but significant NOM removal cannot be achieved by MF or UF alone. MF/ UF systems may be combined with other processes to aid in removing DBP precursors. By associating the NOM with a filterable particulate matter ( e. g., powder activated carbon ( PAC) or coagulant floc), the membranes can, in effect, reject some NOM. Adsorption of organics onto PAC depends on the type and dose of PAC, the contact time available, and the type of NOM. Similarly, the efficiency of incorporating NOM into coagulant flocs depends on the type and dose of coagulant, the operating conditions, and the type of NOM.

<IP_ADDRESS> Factors Affecting Performance Membrane pore size greatly affects microorganism removal. To illustrate this, Exhibit 2.10 shows the size of several microbes of concern against different membrane filtration options. As shown in Exhibit 2.10, cysts ( including Giardia and Cryptosporidium) are larger than essentially all MF and UF pore sizes. Consequently, these processes are capable of large log removal of cysts. On the other hand, as shown in Exhibit 2.10, viruses are larger than most UF pore sizes, but smaller than most MF pore sizes. For this reason, UF is capable of large virus removal, but MF typically is not.

Membrane pores are typically a distribution of sizes ( Mallevialle et al. 1996), only as accurate as the manufacturing process allows. At the present time, no precise techniques for membrane pore size determination are available. For these reasons, a membrane of a given MWCO may have pores that are larger and smaller than the given MWCO. Imperfections in the membrane module or membrane system may result in passage of microorganisms into the treated water.

Imperfections can arise through manufacturing imprecision, allowing microbes to penetrate orings end seals, or spacers. Conversely, microbial contaminant removal may be increased by the cake layer, which forms on the membrane surface during a filtration cycle. This cake layer consists of contaminants rejected by the membrane, including particles, organic matter, and microorganisms. As this layer builds, it can aid filtration of suspended particulates, such as microorganisms, as water passes across the membrane. In this way, microorganisms that might normally pass through a membrane pore can be filtered from the feed water stream. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 28 One of the critical design parameters for a membrane process is flux, which is typically expressed in gallons of filtrate per day per square foot of membrane area ( gfd). The design flux determines the membrane area required for a specific plant capacity. Thus, flux has a significant impact on capital cost and results in a competitive motivation for design engineers to use a higher membrane flux, thereby reducing the area requirements. Although increasing the membrane flux can reduce the capital cost, it will increase operational costs due to higher operating pressure, more frequent chemical cleaning, and a potential increase in membrane replacement costs.

Another important design parameter is recovery, the ratio of feed water to product water. Recovery for MF and UF systems is typically 85 to 97 percent, and a function of the backwash method and frequency. Recovery can play a significant role in the design of membrane facilities, particularly in water scarce regions.

Feed water quality can also have a significant impact on membrane system design, operation, and performance. Suspended solids and other contaminants ( e. g., iron, calcium, barium, or silica) can result in more rapid fouling of the membrane, decreases in flux, and increases in transmembrane pressure ( TMP). TMP is the pressure applied to drive water through the membrane. As a result, most membrane systems include some level of pretreatment to reduce the concentration of these foulants, with the level of pretreatment dependent upon raw water quality.

2.2.6 Bag and Cartridge Filtration Like MF and UF, bag and cartridge filters act as selective barriers and are used to remove particles, including pathogens, in water treatment. As water passes through the bag or porous cartridge, particulate matter and organisms whose size exceeds the largest pore size are retained on the filter. The nature of the filter material and the direction of flow are two features that differentiate bag from cartridge filtration ( AWWA 1999).

Bag filters can be either woven or felt and made of materials such as polypropylene, polyester, nylon, or teflon. Typically, only felt filters will display nominal pore size ratings as low as 0.5 to 1 : m, which are values likely to be associated with high removal of pathogens. Bag filters can also comprise a sealing system on their open end in order to ensure flow integrity between the water inlet and the bag filter.

The bag is housed in a pressure vessel and supported by a mesh basket. The pressure vessel is made of carbon steel or stainless steel. The water flow is from inside the bag filter to outside. As filtered material ( i. e., suspended solids) accumulates on the filter surface, head loss increases, and a pressure differential develops between both sides of the filter. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 29 A number of bag filter configurations are commercially available. Pressure vessels exist in single, duplex or four plex, series or parallel modules, or as multi filter vessels. Manufacturers claim that a single vessel can filter flow rates from 10 to approximately 2,000 gallons per minute ( gpm), depending on its configuration. The standard pressure rating for vessels has been observed to be 150 psi.

Cartridge filters are typically composed either of fiberglass or ceramic membranes supported by a rigid core or are made from strings of polypropylene, acrylics, nylon, or cotton wrapped around a filter element. Nominal pore size ratings generally range from 0.3 to 200 microns. With regard to membranes, the number of pleats in a cartridge filter is typically larger relative to a bag filter, thus providing greater surface area. The cartridge is housed in a pressure vessel made of carbon steel or stainless steel, similar to the bag filter, but the direction of the flow is from the outside to the inside of the cartridge. Accumulation of particulate matter on the surface and in the depth of the cartridge element leads to increased pressure loss across the cartridge. Operation of the cartridge filter beyond the recommended maximum pressure drop would result in the structural failure of the cartridge and potential damage to the cartridge filter vessel.

Commercially available cartridge filter single vessels allow for housing of 1 to approximately 200 cartridges. It is possible to connect these vessels in series ( for multiple stage filtration) or parallel ( for treatment capacity increase and/ or continuous operation).

<IP_ADDRESS> Efficacy Against Pathogens Because their mode of operation is based on a size exclusion mechanism, bag and cartridge filters with the proper pore size rating can remove Cryptosporidium, Giardia, and other pathogens, depending on their size. Available studies assessing the efficacy of bag and cartridge filters against pathogens have frequently utilized polystyrene beads as surrogates for the Cryptosporidium oocysts and Giardia cysts ( Li et al. 1997, Goodrich et al. 1995, Long 1983). Cysts and oocysts are suspected to fold and deform, eventually passing through filtration pores that are smaller than their nominal diameter. In an effort to account for this flexibility, investigators have used polystyrene beads smaller than the pathogens they represent.

In a study by Li et al. ( 1997), log removals of Cryptosporidium oocysts and 4 6 µ m polystyrene microspheres by bag filters were determined and compared. The investigators concluded a linear correlation: 1 log removal of 4 6 µ m polystyrene microspheres is equivalent to 1.040 log removal of Cryptosporidium. This is attributed to similar size distributions.

The EPA Risk Reduction Engineering Laboratory assessed the ability of bag filtration to remove Cryptosporidium and surrogates under various flow ( 12.5 and 25 gpm) and pressure drop ( 0, 7, 15, and 25 psi) conditions ( Li et al. 1997). The study evaluated three polypropylene bag filters. The surrogates tested were turbidity, 1 25 : m particle counts, 4 6 : m particle counts, and 4 6 : m Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 30 polystyrene microspheres. The study found the polystyrene microspheres to be " accurate and precise" indicators of filter performance with respect to Cryptosporidium. The results of this study are summarized in Exhibit 2.15.

Exhibit 2.15: Summary of Bag Filter Performance Filter Type Nominal Pore Size Contaminant Log Removal ( Average)

Multi layer polypropylene 1 : m 4.5 : m microspheres 1.14  1.88 ( 1.39)

Cryptosporidium 1.35  1.48 ( 1.41)

Single layer polypropylene 1 : m 4.5 : m microspheres 0.14  0.72 ( 0.46)

Cryptosporidium 0.26  0.64 ( 0.42)

Multi layer polypropylene 99% removal of 2.5 : m particles, 95% removal of 1.5 : m particles 4.5 : m microspheres 0.93  3.42 ( 2.08)

Cryptosporidium 3.00  3.63 ( 3.29)

Source: Li et al. ( 1997).

The results presented in Exhibit 2.15 may indicate a benefit in removal efficiency associated with multi layering of the filter fabric. Based on this study, a multi layer fabric bag filter can achieve 1 to 2 log Cryptosporidium removal under proper operation conditions. One interesting result of these tests is that experimental controls performed with Cryptosporidium showed that 0.1 to 0.2 log removal can be attributed to the pressure vessels alone without bag filters. This is assumed to reflect the ability of Cryptosporidium oocysts to adhere to the surface walls of the vessel.

Another study by the Risk Reduction Engineering Laboratory ( Goodrich et al. 1995) evaluated cartridge filters for the removal of 4 6 : m polystyrene spheres. The results of this study indicate that a single cartridge filter, with a 2 : m rating, achieved an average microsphere removal of 3.6 log.

A study conducted by Long ( 1983) evaluated the log removal of 17 different cartridge filters for Giardia surrogates. These cartridge filters were tested using the same pressure vessel at a pressure of 45 psi and a flow rate of 0.5 gpm. The microspheres used as surrogates for Giardia cysts had an average diameter of 5.7 : m, with a standard deviation of 1.5 : m. The filters were made of a variety of materials ( cotton, cellulose, glass fiber, polypropylene, polyester) and configurations ( majority pleated or spirally wound). The pore ratings ranged from 0.2 to 10.0 : m.

According to a scanning electron microscopy analysis that allowed visual counting of the microspheres passing through the filter, ten cartridge filters out of seventeen had a microsphere removal of 99.99 percent ( 4 log reduction). The lower performances seemed to be associated with the absence of end seals on the cartridges and the use of cotton or polyester as the main filtering material ( Long Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 31 1983). Note that the tests were conducted at a flow rate of 0.5 gpm, which is significantly lower than the expected operation flow rate ( typically 20 gpm per unit). The impact of this reduced flow rate on removal performance is unclear.

<IP_ADDRESS> Factors Affecting Performance Feed water quality is the primary factor affecting the performance of both bag and cartridge filters. Although these filters can operate at turbidity levels from 0.1 to 10 NTU, it is recommended that turbidity be minimized to extend the filter lifetime. If turbidity of the feed water is above 1 NTU, bag filters may operate properly for only a few hours ( USEPA 1998). Thus, use as a secondary barrier following conventional treatment is a preferred mode of operation. Granular media filters can reduce feed water turbidity to less than 0.1 NTU and provide a feed water stream of appropriate quality for bag and cartridge filters.

Feed water should also contain very low levels of sand, silt, or algae to prevent clogging of the filters. If raw water quality is such that the concentrations of these parameters are high, pretreatment, such as sand, multimedia filters, or preliminary bag or cartridge filters with larger pore size ( e. g., 10 : m), is encouraged.

The appropriate choice of the pore size rating is an important issue. Giardia cysts and Cryptosporidium oocysts are suspected to deform and fold, enabling them to pass through pores that are nominally smaller than the pathogen. The selected pore size should be sufficient to achieve significant removal of microorganisms while maximizing the expected filter lifetime, based upon raw water quality and filter loading. Likewise, the quality of the system's seals will greatly impact the level of performance. The most critical seals appear to be between the filter and the pressure vessel and within the structure of the filter itself. A faulty seal is a way for pathogens to partially or completely bypass filtration.

Pilot testing ( i. e., challenge studies) is frequently recommended to assess the performance of bag and cartridge filters. However, the costs associated with pilot testing, particularly for small systems, can represent a significant portion of the installation costs. As a result, pilot testing may not be affordable for small systems and may limit the use of these technologies where pilot testing is necessary. Some States ( e. g., Oregon) accept manufacturer data regarding removal efficiency and permit systems to operate in a demonstration mode, with additional monitoring requirements.

The skill level required to operate bag or cartridge filters is typically described as basic ( AWWA 1999, Campbell et al. 1995a). Turbidity, head loss, and total number of gallons filtered should be monitored daily to evaluate the need to replace the bag or cartridge ( AWWA 1999). For example, cartridges are generally replaced when the pressure differential reaches 35 psi, after one to six months of operation ( Malcolm Pirnie 1993). The maximum allowable pressure differential is typically recommended by the manufacturer. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 32 Cartridges and bags are easily damaged at the time of installation. Bags should be replaced with caution to prevent tearing of the material. Likewise, the operator should carefully install new cartridges, as the filter seal can be damaged and induce leakage.

Because of their rigid structure and multi layer design, cartridge filters are generally more sturdy and offer more operational flexibility than bag filters. However, this higher performance is typically associated with higher cost. As mentioned previously, cysts and oocysts can adhere to and accumulate on the surface walls of the system. As a consequence, the inward flow of water in the cartridge filter requires that the housing be cleaned entirely when replacing the cartridge, which is not the case with bag filters.

2.2.7 Bank Filtration Bank filtration is a water treatment process that uses a river bed or the bank of a river or lake as a natural filter. Water from a river or stream flows through the bank and draws from one or more wells. Microorganisms and other particles are removed by contact with the aquifer materials as the water travels through the subsurface, either horizontally or vertically. High removal occurs when ground water velocity is slow and the aquifer consists of granular materials with open pore space, allowing water flow around the grains. In these granular porous aquifers, the flow path is very tortuous, thereby providing ample opportunity for the microorganism to contact and attach to a grain surface. Although detachment from the grains can occur, it typically occurs at a very slow rate. When ground water velocity is exceptionally slow, or when little or no detachment occurs, most microorganisms become inactivated before they can enter a well. Thus, bank filtration provides physical removal and, in some cases, inactivation to protect wells from pathogen contamination.

<IP_ADDRESS> Efficacy Against Pathogens Due to the low recovery rate of Cryptosporidium oocysts in influent and effluent samples, full scale treatment data are of limited utility for assessing removal of Cryptosporidium via bank filtration. However, measurement of other parameters indicate the potential for pathogen removal. Exhibit 2.16 summarizes bank filtration studies that measured coliform and spore removal. Cryptosporidium removal is site specific and highly dependent on the aquifer characteristics; therefore, these data are only an indication of contaminant removal that can be achieved by bank filtration. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 33 Exhibit 2.16: Bank Filtration Studies Measuring Coliform and Spore Removal Log Removal Reference Travel Distance ( m) Travel Time ( days) Total Coliform Thermotoleran t Coliform Spores1 Havelaar et al. ( 1995) 30 15 > 5.0 > 4.1 > 3.1 Havelaar et al. ( 1995) 25 63 > 5.0 > 4.1 > 3.6 Medema et al. ( 2000) 13 7 N/ A 4.1 3.3 25 18 N/ A 4.5 3.9 150 43 N/ A 6.2 5.0 Wang et al. ( 2000) 0.6 N/ A N/ A N/ A 2.0 1.6 2.0 3.0 2.0 16 3.0 1 Spore data are sulphite reducing clostridium for all references except Wang et al. ( 2000), where spore data are aerobic endospores.

<IP_ADDRESS> Factors Affecting Performance The main factor affecting the performance of bank filtration is the type of aquifer material through which the water is filtered. Granular media is the most effective, while fractured rock or gravel with large pore sizes may be the least effective and allow Cryptosporidium to pass through without contacting a grain surface. The flow rate is also an important factor in determining performance. Too high a flow rate can cause oocysts to detach from the aquifer material. Low flow rates, however, may make it difficult to meet volume demands.

2.2.8 Second Stage Filtration Second stage, or secondary, filtration requires the use of rapid sand, dual media, GAC, or other fine grain media in a separate stage following rapid sand or dual media filtration. A cap, such as GAC, on a single stage of filtration is not considered second stage filtration.

Filtration processes are standard in the water treatment process, and much design and operational information is available. However, the use of a second filtration stage is not as common, and little information is available. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 34 <IP_ADDRESS> Efficacy Against Pathogens There is relatively little published data on the removal of Cryptosporidium by second stage filtration. Results based on a number of single stage filtration studies demonstrate that rapid sand filtration, when preceded by coagulation, can achieve significant removal of Cryptosporidium. While these studies evaluated only a single stage of filtration, the same mechanisms of removal would occur with a second filtration stage. Studies have also shown that Cryptosporidium breakthrough occurs after the first stage of filtration; therefore, a second stage of filtration is likely to provide a barrier to these oocysts.

Many studies ( Dugan et al. 2001 and Emelko et al. 1999) have demonstrated that aerobic spores are a conservative indicator of Cryptosporidium removal by granular media filtration when preceded by coagulation. Consequently, EPA believes that data on spore removal by a second stage filtration process are indicative of the capacity of this process to remove Cryptosporidium.

Between 1999 and 2000, the Cincinnati Water Works collected spore and turbidity removal data from their GAC system. The specifics of their system are provided below.

° 11 foot deep GAC filter following dual media filter ° Loading Rate = 3.4  3.9 gpm/ ft2 ( average); 7.1 gpm/ ft2 ( design)

° 12* 40 mesh ° d10 = 0.5  0.75 millimeters ( mm); d10 is the diameter through which 10 percent of the media will pass ° Uniformity Coefficient ( UC) < 2; UC is the uniformity coefficient of the media ° Media age  new to 7 years old; carbon reactivation two times per year ° Empty Bed Contact Time ( EBCT) = 22 minutes at 120 million gallons per day ( mgd) ( average flow); 12 minutes at 220 mgd ( design flow)

A median incremental spore removal of 0.92 log was observed in their GAC filter. Additionally, the secondary GAC filters were observed to dampen or eliminate turbidity spikes from preceding dual media filters that occurred during ripening, breakthrough, etc. These data indicate that 0.5 log or greater removal of Cryptosporidium can be achieved by a secondary filtration process like GAC contractors. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 35 Based on information presented by Hall et al. ( 1994), up to a 50 percent improvement in turbidity removal was observed when using a second stage filter. However, no improvement in Cryptosporidium removal was observed due to the second stage filter. This information was collected after spiking 500 oocysts/ L into the raw water of a conventional filter followed by a secondary filter consisting of GAC.

<IP_ADDRESS> Factors Affecting Performance Filter Type There are several types of filters. Fine sand filters, dual media filters, and multimedia filters are the main types of filters used in conventional filtration plants. In order to encourage penetration of solids into the depth of the bed, the dual media filter, consisting of a layer of coarser anthracite coal on top of a layer of finer silica sand, was developed. Studies conducted by many researchers ( Conley and Pitman 1960a, Conley 1961, Tuepker and Buescher 1968) showed the benefits of dual media filters in reducing the rate of head loss development, which lengthened the filter run. Although dual media is presumed to improve the quality of the filtrate, this benefit has not been well demonstrated ( Water Quality and Treatment 1999). Research conducted by Robeck, Dostal, and Woodward ( 1964) demonstrated that the head losses in dual media filters were lower than the head losses in traditional fine sand filters. When a typical dual media filter and a fine sand filter are operated at the same filtration rate on the same influent water, the head loss development rate for the typical dual media filter should be about half the rate of the fine sand filter ( Water Quality and Treatment 1999). Multimedia filters add a layer of garnet to the media which allows for a finer layer of media at the bottom of the filter.

Filter Media As with all filters ( first or second stage), various properties of a filter medium, such as size, shape, density, and hardness, affect filtration performance. Filter media are defined by their uniformity coefficient ( UC) and effective size ( ES). The porosity of the filter bed formed by the grains is also important ( Water Quality and Treatment 1999). Filter media should be coarse enough to retain large quantities of floc, yet fine enough to prevent passage of suspended solids. The filter bed should also be deep enough to allow long filter runs and graded to permit backwash cleaning. In order to obtain high rates of filtration, coarse sands and dual media beds of anthracite overlying sand have been used in the recent past ( Water Supply and Pollution Control 1993).

The bed porosity and the ratio of the bed depth to media grain diameter affect the filter efficiency. The larger the depth of the filter bed ( L), the more opportunities exist for particle capture; the larger the average diameter of the media ( d), the more of the media is available to capture particles over the depth of the filter bed. The two most commonly used methods in selecting the optimal filter bed depth and media size are pilot plant studies and existing data from filtration facilities treating similar waters. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 36 Filter Hydraulics Hydraulic surges occur when the flow through a filter changes rapidly ( e. g., during either filter backwashing or servicing). Hydraulic shifts can lead to significant particle detachment. To ensure that the second stage filtration unit is unaffected by any hydraulic surges caused by the backwashing of the first stage filtration unit, the first stage filters should be hydraulically isolated during backwashing and servicing.

2.2.9 Pre Sedimentation Pre sedimentation is a preliminary treatment process used to remove particulate material from the source water before the water enters the main treatment plant. Because pre sedimentation reduces particle concentrations, it is also expected to reduce Cryptosporidium levels. In addition, by reducing variability in water quality of the source water, pre sedimentation may improve the performance of subsequent processes in the treatment plant. To remove pathogens through floculation and sedimentation, it is necessary to add coagulant.

Sedimentation processes are standard in the water treatment process, and much design and operational information is available. However, the use of a pre sedimentation basin is not as common, and little information is available.

<IP_ADDRESS> Efficacy Against Pathogens There is relatively little published data on the removal of Cryptosporidium by presedimentation Consequently, EPA analyzed studies that investigated Cryptosporidium removal by conventional sedimentation basins. The removal efficiency in conventional sedimentation basins may be greater than in pre sedimentation due to differences in surface loading rates, coagulant doses, and other factors. To supplement these studies, EPA reviewed data provided by utilities on removal of other types of particles, primarily aerobic spores, in the pre sedimentation processes of full scale plants. Studies have shown that, in the presence of a coagulant, spore removal is a conservative indicator of Cryptosporidium removal ( Dugan et al. 2001).

The literature studies reviewed by EPA show Cryptosporidium log removals of 0.6 to 3.8 ( Dugan et al. 2001, Payment and Franco 1993) and mean Bacillus subtilis and total aerobic spores log removals of 0.6 to 1.1 ( data collected independently by the Cincinnati, OH, and St. Louis, MO, water utilities) by sedimentation processes. The removal of aerobic spores through sedimentation basins in full scale plants demonstrate that pre sedimentation is likely to achieve mean reductions of greater than 0.5 log Cryptosporidium removal under routine operating conditions and over an extended time period. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 37 <IP_ADDRESS> Factors Affecting Performance Short Circuiting Short circuiting in the sedimentation tank occurs when a portion of the influent flow reaches the outlet of the sedimentation basin much faster than the designed detention time of the basin. Short circuiting increases the operational surface loading rate since the true settling area available for a portion of the flow is reduced. If short circuiting causes the basin to operate at an effective loading rate greater than 1.6 gpm/ ft2, the basin would not receive Cryptosporidium removal credit. High wind velocities and density and temperature differentials between the influent water and the water in the sedimentation basin cause short circuiting. Additionally, the design or configuration of both the inlet and outlet are important factors that can affect short circuiting and turbulence. Systems can minimize short circuiting by adding baffles or making other modifications to the flow pattern.

Coagulant Dose The principle goal of coagulation is to destabilize the particles so that they can be more easily aggregated into flocs. The commonly used coagulants are alum, ferric chloride, polyaluminum chloride ( PACl), activated charcoal, and activated silica. The coagulant dose required to treat an influent stream depends on the chemical composition of the influent, the characteristics of the colloids and suspended matter in the influent, the water temperature, and mixing conditions. The use of a coagulant improves the pathogen removal capabilities of the pre sedimentation process, although some pathogen removal is expected without coagulant addition. Optimizing a coagulation scheme for a two stage sedimentation process is site specific and not simple. It is therefore not possible to prescribe the type of coagulant and appropriate dose for an aggregate of source waters. To account for an additional sedimentation process, the standard jar test can be modified to a two stage process reflecting the two stages of sedimentation.

2.2.10 Watershed Control A well designed watershed control program can reduce overall microbial risk. The risk reduction would be associated with the implementation of practices that reduce Cryptosporidium, as well as other pathogens. Knowledge of the watershed and factors affecting microbial risk, including sources of pathogens, fate and transport of pathogens, and hydrology can also help a system reduce microbial risk.

<IP_ADDRESS> Efficacy Against Pathogens No data are available on the ability of watershed control programs to reduce Cryptosporidium loading to surface water. This is partly because, until recently, most watershed programs have focused Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 38 on improving water quality for recreational and ecological uses rather than for drinking water protection. Thus, studies of the success of such programs frequently monitor parameters such as phosphorus and sediment levels. Watershed programs that do have drinking water protection as a goal frequently track fecal coliform bacteria levels but do not regularly monitor Cryptosporidium. Fecal coliform concentrations do not always correlate with Cryptosporidium, but better indicator data are not usually available. E. coli may be a better indicator of fecal contamination than fecal coliform bacteria, but monitoring for E. coli is not common practice.

Most water systems that do monitor Cryptosporidium have been doing so for only a few years and would not have enough data to show a change in water quality resulting from watershed management. In addition, because Cryptosporidium occurs in such low concentrations and is often undetected, reductions in microbiological contamination are difficult to demonstrate.

Regardless of the constituents monitored, it is difficult to show that a watershed control program in its entirety has improved water quality. Often, reductions in contamination from one source can be overshadowed by increases from other sources, especially in urban areas. However, various components of a watershed control program have been shown to have a positive effect on microbiological water quality at a local level, at least for fecal coliform. Combined, these components should theoretically contribute to an overall decrease in microbiological contamination.

For instance, Thurston et al. ( 2001) showed that a constructed wetland could reduce fecal coliform levels in wastewater treatment plant effluent by 98 percent ( where effluent had previously received secondary treatment). Cryptosporidium reductions of 64 percent were also achieved through this study. A similar pilot scale study with untreated wastewater indicated an overall removal of microorganisms of 90 percent by constructed wetlands ( Quinonez Diaz et al. 2001). Preliminary results of a watershed restoration program in Vermont showed that streambank stabilization, fencing of riparian zones to prevent grazing, and protected stream crossings reduced bacterial levels ( Meals 2001). A fencing program in Virginia suggested some reduction in fecal coliform levels, and the proportion of fecal streptococci strains traced to livestock was reduced ( Hagedorn et al. 1999).

Another way to reduce microbiological contamination of an urban watershed is to upgrade wastewater collection systems. The Fairfax County, Virginia, Wastewater Collection Division decreased inflow and infiltration into its sewers and increased the sewers' capacity through a rehabilitation and maintenance program. Between 1995 and 2001, the utility reduced the number of sanitary sewer overflows throughout the county by 67 percent and reduced the peak flow to one of its wastewater treatment plants by 35 mgd ( USEPA 2001). Similar programs throughout the United States are contributing to reduced effluent volumes from sanitary sewer overflows and combined sewer overflows. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 39 <IP_ADDRESS> Factors Affecting Performance A combination of interventions such as those described above is expected to result in an overall decrease of Cryptosporidium in source water. However, many factors can negatively affect the success of a watershed control program. The interventions a system implements depend on the types of contamination sources in the watershed. Control of point source discharge ( e. g., waste water treatment plants and industrial discharges) can be straightforward. Agricultural and urban nonpoint sources are the most difficult to control. Reduction of Cryptosporidium from these sources generally depends on the voluntary cooperation of urban residents and farmers.

Urban watersheds are subject to increasing development, which increases surface imperviousness and the amount of runoff entering surface waters, along with the pollutant load. Acquisition of undeveloped land, particularly that closest to the source water and its tributaries, is one of the best ways to prevent degradation of the water quality, but it may not be feasible in some watersheds. Other restrictions on development, such as zoning requirements, can also control urban runoff to some extent, but, again, these may not be feasible or may not have the support of the public or other government agencies.

Another problem facing PWSs is that the watershed may extend beyond the municipal boundaries into other jurisdictions. A higher authority ( e. g., State or county government) may be needed to regulate activities outside a PWS's jurisdiction that could affect water quality.

2.2.11 Combined Filter Performance Combined filter performance reduces Cryptosporidium levels by enhancing filter performance to produce very low turbidity water. It is defined specifically as producing 0.15 NTU turbidity water in the combined filter effluent ( CFE) 95 percent of the time. Methods that systems may use to improve filter performance and lower turbidity include adding polymer, optimizing the filtration process by adding media or installing filter to waste capabilities, and improving staff ability to optimize the process by additional training, hiring new operators, and buying new laboratory equipment.

Systems likely to use this technology are those which operate conventional filtration or softening plants and which are already operating well below the current turbidity limits of 0.3 NTU. These systems more than likely target their effluent under 0.15 NTU already but are not currently hitting that target more than 95 percent of the time. These plants are assumed to be able to reach the target 95 percent of the time with relatively minor adjustments to their process. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 40 <IP_ADDRESS> Efficacy Against Pathogens There have been a number of studies examining the removal of pathogens by conventional filtration. Several of these studies have examined the relationship between finished water turbidity and protozoa removal. Studies by Dugan et al. ( 2001) and Patania et al. ( 1995) showed that turbidity is an adequate indicator of pathogen removal. Although the correlation between turbidity removal and pathogen removal is not one to one, removal of turbidity is a conservative indicator of pathogen removal.

Under the IESWTR and LT1ESWTR, conventional and direct filtration plants may claim 2.0 log Cryptosporidium removal credit if their CFE turbidity never exceeds 1 NTU and is less than or equal to 0.3 NTU in 95 percent of samples taken. Under the LT2ESWTR, systems using conventional filtration treatment or direct filtration treatment may claim an additional 0.5 log Cryptosporidium removal credit for any month that a plant demonstrates CFE turbidity levels less than or equal to 0.15 NTU in at least 95 percent of the measurements taken each month, based on sample measurements collected under § § 141.73,141.173( a) and 141.551.

EPA expects plants that rely on complying with a 0.15 NTU standard to consistently operate below 0.1 NTU. Results from studies conducted by Patania et al. ( 1995), Emelko et al. ( 1999), and Dugan et al. ( 2001) show that plants consistently operating below 0.1 NTU can achieve an additional 0.5 log or greater removal of Cryptosporidium than when operating between 0.1 and 0.2 NTU.

<IP_ADDRESS> Factors Affecting Performance Many factors can affect removal of pathogens through sedimentation and filtration and hinder a plant's ability to achieve 0.15 NTU in its CFE. In order to achieve 0.15 NTU 95 percent of the time, plants will need to have tight control of their process. The areas which require specific attention include: control of coagulant dosing and mixing, control of dosing of other chemical additions, filter hydraulics and media, and backwashing procedures.

Coagulant Dose Insufficient coagulant can lead to colloidal particles remaining in suspension, while too much coagulant can lead to inefficient settling. Therefore, coagulant must be optimized for the entire plant. It must also be adjusted as influent water quality varies or if there are other major changes in plant operation.

Filter Ripening During the period immediately after a backwash, the lack of particles on the filter media can make capture of the particles by the media more difficult and lead to breakthrough of particles and Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 41 turbidity. Hall and Croll ( 1996) studied removal in a pilot plant and saw peaks in both turbidity and oocysts in the filtered water for an hour after backwashing. West et al. ( 1994) found that removal increased from 2 log to of 3 log once the filters had ripened, and the turbidity had dropped from an initial value of 0.2 NTU to a value less than 0.1 NTU.

Filter Breakthrough During filter runs, particles can collect in the filter and, if not backwashed, will reach the point where an increased amount of particles pass through ( referred to as breakthrough). Emelko et al. ( 2000) studied the performance of filters throughout a typical run cycle. They found that removal was 5.5 log when the filters were operating at 0.04 NTU. When the turbidity began to climb, removal dropped to 2.1 log even while turbidities were still less than 0.1 NTU. By the time turbidity had reached 0.3 NTU, the removal had dropped to 1.4 log.

Filtration Rate If the filtration rate is too high, filtration effluent water quality can suffer. McTigue et al. ( 1998) found that removal dropped by 2 log when the filtration rate was doubled. West et al. ( 1994), however found no difference in removal between filtration rates of 6 and 14 gpm/ ft2.

Backwashing The flow rate used for backwashing is important in maintaining effluent quality. Too low a rate can leave the media dirty and lead to mudballs and eventual particle breakthrough. Too high a rate can cause loss of filter media and also lengthen filter ripening times. A surface wash can also help detach particles from the media and improve backwash performance.

2.3 DBP Precursor Removal Strategies 2.3.1 Granular Activated Carbon Adsorption Removal of undesired compounds from water supplies can be achieved through adsorption onto solids. GAC is used in water treatment to adsorb a variety of organic and inorganic compounds. Important properties of GAC that determine its effectiveness include particle size, specific surface area, pore size distribution, and chemical nature of the surface. GAC adsorption, as practiced in water treatment, is an non steady state process, with the effluent concentration of the contaminant increasing with time. Once the effluent concentration meets the maximum allowable concentration for a contaminant, the GAC column must be taken off line, and the GAC must be replaced with reactivated or fresh GAC. The operation time to this maximum effluent concentration is termed the reactivation interval. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 42 The EBCT is defined as the volume of media divided by the flow rate. GAC contactors should be used when longer EBCTs are required, while sand filters with a GAC cap, where the top portion of the sand is replaced by GAC, can be used when shorter EBCTs are feasible. These GAC capped filters are often called filter adsorbers. Filter adsorbers can also be filtration units which contain GAC alone. Because of their shorter EBCTs, filter adsorbers meet desired water quality goals for a much shorter period of time than GAC contactors. For the purposed of treating seasonal changes in water quality or contaminant shock loads, filter adsorbers may have an economic advantage over post filter GAC contactors. One disadvantage of filter adsorbers is that GAC losses are high during backwashing, and reactivation and equipment separating GAC from sand may be required before reactivation.

GAC contactors operate in either downflow or upflow configurations. Downflow fixed bed contactors offer the simplest and most common contactor configuration for drinking water treatment. Upflow beds are typically used in situations where very long contact times ( greater than 120 minutes) are required and/ or where the level of suspended solids is high. Flow through GAC contactors can be either gravity or pressure driven.

The hydraulic constraints of a given system govern the selection between pressure or gravity contactors. Pressure contactors may be more applicable for ground water systems, since these systems already are pumping their water. Gravity contactors are generally found in surface water systems, if sufficient head is available. Downflow contactors are typically placed downstream of the plant filters to minimize the solids loading to the contactor.

The GAC in a contactor is usually replaced when the effluent concentrations exceed the treatment objective. At this point, however, only a portion of the GAC is fully utilized, and replacement of the media will result in unnecessarily high carbon usage rates. Operating multiple GAC contactors in either series or parallel configurations are the two common methods to reduce GAC usage rates.

For contactors configured in series, the GAC in the first contactor is reactivated when the effluent from it no longer meets the treatment objective. The first contactor is taken offline while the second contactor continues operation. After the GAC in the first contactor is replaced, it is brought back online downstream from the operating contactor. That is, the position of the two contactors is reversed, with what was originally the second contactor becoming the first contactor and vice versa. For efficient operation, the mass transfer zone should be contained within the bed length of one contactor. This can be achieved using reasonable bed lengths for adsorption of micropollutants, but the mass transfer zone for TOC removal and, therefore, DBP precursor removal is usually too long. The use of two contactors in series does not result in significantly longer run times over single contactor operation ( USEPA 1999a).

For contactors configured in parallel, multiple GAC beds are operated with a staggered reactivation pattern. The effluent from individual contactors may contain contaminants at concentrations higher than the treatment objective, since they may be blended with effluent from other contactors with Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 43 little or no breakthrough. The combined effluent concentration, from all the GAC beds, can thus be maintained below the specified treatment objective, further reducing carbon usage rates. For DBP precursor removal, contactor effluents should be blended prior to disinfection.

The choice between a single contactor and contactors in series or parallel is site specific and depends on the type and concentration of the contaminant to be removed and its rate of adsorption. This choice also depends on the type, concentration, and adsorption rate of competing contaminants.

<IP_ADDRESS> DBP Precursor Removal In many circumstances, GAC is an effective process for the removal of NOM from drinking water sources. With an EBCT of 15 minutes and a reactivation interval of 180 days, GAC can remove 35 to 70 percent of the influent TOC on a running average basis. Running average TOC removals of 55 to 85 percent can be achieved with an EBCT of 30 minutes and a reactivation interval of 180 days.

<IP_ADDRESS> Factors Affecting Performance The removal of NOM by GAC adsorption depends on a large number of factors including the following:

° Molecular size, polarity, and concentration of NOM entering the GAC process ° Water quality characteristics such as pH and ionic strength ° GAC characteristics such as pore size distribution and surface chemistry ° Operational characteristics such as EBCT and GAC usage rate ° Treatment processes used prior to the GAC process ° Configuration of GAC contactors This section briefly describes the impacts of these factors as seen in several GAC studies.

Constituents of NOM are adsorbed within the GAC bed in a manner proportional to their adsorption potential. Weakly adsorbing components of NOM may irreversibly preload the GAC at the downstream end of the bed and may, therefore, reduce the capacity of the bed for stronger adsorbing components at the end of the bed. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 44 The impacts of pH on adsorption of NOM and humic extracts have been well documented in equilibrium studies using powdered activated carbon ( Weber et al. 1983, Randtke and Jepsen 1982, McCreary and Snoeyink 1980, Summers 1986). All of these studies showed increased removal of TOC with decreased pH levels. Unfortunately, some of the work has been done with different initial TOC concentrations, and the increased performance attributed to low pH may be because of the lower initial TOC. A relationship between the relative adsorption capacity for TOC at the same initial TOC and pH has been established for 13 different source waters and a bituminous coal based GAC ( Hooper et al. 1996b). Within the pH range of 5 to 10, a decrease in the pH of one unit yielded a six percent increase in adsorption capacity. However, the number of continuous flow evaluations of pH impacts is limited.

The relationship between GAC pore size distribution and NOM molecular size distribution has been shown to be important ( Summers and Roberts 1988, Lee et al. 1983, Semmens and Staples 1986, El Rehaili and Weber 1987, Chadik and Amy 1987). In general, investigators have found the GAC process to favor removal of NOM molecules of low to moderate size even though the adsorption process was expected to favor removal of large molecules. This phenomenon occurs because small GAC pores physically exclude large NOM molecules from adsorbing. Thus, GAC with a greater quantity of large pores can be expected to remove more NOM than GAC with a smaller quantity of large pores.

The impacts of EBCT on GAC usage rate for NOM removal have been studied in numerous continuous flow evaluations. The trend observed in all studies is that increasing EBCT can reduce the carbon usage rate. One study ( Miller and Hartman 1982) saw significant reduction in usage rates as the EBCT is increased from 2.8 to 15.2 minutes. Summers et al. ( 1997) evaluated EBCTs of 10 and 20 minutes for a number of water sources and concluded that EBCT had a definite effect in prolonging the bed life of a GAC contactor. However, the carbon usage rate is relatively unaffected by EBCTs at the ranges evaluated. They also noted that the balance between EBCT and the frequency of GAC replacement or reactivation is primarily a choice between larger capital investment ( i. e., longer EBCTs) and greater operational complexities ( i. e., more frequent reactivation). Another study indicated that GAC usage rate decreased with an increase in EBCT from 7.5 to 30 minutes. However, a further increase in EBCT from 30 to 60 minutes did not influence the GAC usage rate ( McGuire et al. 1989).

GAC systems may require some kind of pretreatment to prevent clogging of the GAC bed, to minimize the organic loading on the GAC, and to improve cost effectiveness. Clogging of the GAC bed could be caused by suspended solids in the raw water or by precipitation of calcium carbonate, iron, and manganese on the GAC. Suspended solids typically cause problems in surface water systems, while carbonate scaling, iron, and manganese precipitation may occur in both surface and ground waters. When the GAC bed life is long, clogging may also be caused by biological growths. Pretreatment methods include coagulation, filtration, or softening ahead of the GAC system. Conventional coagulation, clarification, and filtration processes may be optimized for the removal of organic material to reduce natural organic loading to the GAC bed. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 45 The impacts of coagulation on NOM adsorption have also been well documented in batch experiments studying adsorption equilibria ( Weber et al. 1983, Randtke and Jepsen 1981, Lee et al. 1981, El Rehaili and Weber 1987, Harrington and DiGiano 1989). Coagulation processes, as a pretreatment to GAC, can both reduce influent TOC concentration and decrease the influent pH to the adsorber, thus leading to improved GAC performance.

Several investigators have reported better GAC performance for TOC control after coagulation or after increasing the coagulant dose ( i. e., enhanced coagulation). Hooper et al. ( 1996a, 1996b, 1996c) have shown that the increase in GAC run time after enhanced coagulation can be attributed to the lower pH and lower initial TOC concentration associated with the enhanced coagulated water. This improvement is most often attributed to a decrease in solubility of NOM at lower pH ( Symons et al. 1998).

In most GAC applications of any significant size, multiple contactors are operated in a parallel configuration. Parallel GAC contactors are operated in a staggered mode wherein each contactor has been in operation for different lengths of time. In this mode of operation, one contactor at a time is taken off line when the blended effluent exceeds the target effluent concentration, and a column with fresh or reactivated GAC is then placed on line. The effluent from the contactor in operation the longest can be higher than the target breakthrough concentration, as it is blended with water from the contactors that have effluent concentrations much lower than the target concentrations. Consequently, the effluent of parallel contactors are blended prior to disinfection. Thus, parallel operation in a multiple contactor configuration will result in longer GAC bed life and the time between reactivation will be longer. Under ideal conditions, staged blending with multiple parallel contactors leads to near steadystate effluent concentration ( Roberts and Summers 1982).

Experimental and modeling methods for predicting the blended effluent concentration from GAC contactors were developed by Summers et al. ( 1997). The authors observed during this study that the time to GAC performance goals can be significantly extended by blending the effluent from multiple contactors. For the three waters examined, blending increased the run time by an average of 150 percent for both TOC and TTHM.

The research described above demonstrates how the performance of GAC systems can be influenced by many process variables. In general, the process can be modified to provide the same level of NOM removal at lower GAC usage rates by the following:

° Maintaining low pH conditions through the process ° Increasing NOM removal in processes that precede GAC adsorption ° Using an EBCT greater than or equal to 10 minutes Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 46 Ozonation prior to GAC does not guarantee improved NOM removals because it can either decrease or increase the ability to adsorb and increase the biodegradability of NOM. The overall impact of preozonation on NOM removal in GAC contactors depends on the efficiency of biotreatment to remove the weakly adsorbing hydrophilic fraction.

2.3.2 Nanofiltration Nanofiltration is a high pressure membrane process that has been traditionally used as a softening process to remove hardness ions. Generally, NF membranes reject divalent ions ( e. g., Mg2+, Ca2+), but pass monovalent ions ( e. g., Na+, Cl). Recently, NF has been used more extensively for removal of DBP precursors and color, particularly in brackish waters, as well as other surface waters. Although NF processes remove nearly all turbidity in feed water, they cannot be used for turbidity removal in the same manner as MF and UF due to smaller pore sizes ( Mallevialle et al. 1996). Smaller pore size makes NF membranes more prone to fouling. The application of NF for surface waters is generally not accomplished without extensive pretreatment for particle removal and possibly pretreatment for dissolved constituents.

The percentage of treated water that can be produced from the feed water is known as the recovery. Recovery is an important factor for cost of membrane processes and is one measure of the efficiency of a system. Recovery for NF systems is typically 75 to 90 percent and is impacted by feed water characteristics, membrane properties, and operating conditions, such as TMP. Since treatment and disposal of the reject stream ( i. e., waste stream) can be a significant portion of the overall cost of a system, recovery can greatly affect cost efficiency.

<IP_ADDRESS> Efficacy Against Pathogens As would be expected based on MF and UF microbial removal efficiencies, NF processes are capable of excellent disinfection by removing nearly all microbial contaminants in feed water, including Giardia, Cryptosporidium, and viruses. Historically, NF processes have not been used as a primary means of disinfection, since, in large part, they have been used to treat ground water or have been coupled with pretreatment processes such as MF or UF. When only disinfection is required, MF and UF processes are typically used instead of NF, since they are less costly and can achieve the required level of pathogenic rejection ( Mallevialle et al. 1996). Because of this, relatively few studies documenting microbial removal with NF membranes have been conducted in comparison to MF and UF processes. Because NF and RO processes represent systems that are very similar in terms of disinfection capabilities, available studies documenting microbial removal with RO as well as NF membranes are presented in Exhibit 2.17. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 47 Exhibit 2.17: NF Studies Documenting Microbial Removal Reference Process Membrane Giardia Log Removal Crypto Log Removal MS2 Virus Log Removal Gagliardo et al. ( 1999) RO HR   3.0 Gagliardo et al. ( 1999) RO DOW   5.4 Gagliardo et al. ( 1999) RO ESPA   4.7 Gagliardo et al. ( 1998) RO ULP   3.4 Seyde et al. ( 1999) NF ( Pilot) Acumem 4040 > 51 > 61 4.2 to 5.0 Colvin et al. ( 1999) RO ( bench) FilmTec BW30   > 42 Colvin et al. ( 1999) RO ( bench) FilmTec BW30   > 71 Trussel et al. ( 1998) RO ( MF pretreat) FilmTec BW30   4.1 to 5.9 Trussel et al. ( 1998) RO ( MF pretreat) Hydranautics 4040 UHA     3.7 to 5.7 Trussel et al. ( 1998) RO ( MF pretreat) Fluid Systems TFLC/ M48 20HR   2.1 to 3.3 Trussel et al. ( 1998) RO ( MF pretreat) Fluid Systems TFCL/ ULP     2.9 to 4.3 Gagliardo et al. ( 1997) RO ( pilot) TFC > 5.7 > 5.7 3.0 to 4.0 Gagliardo et al. ( 1997) RO ( pilot) CA > 5.7 > 5.7 3.3 to 5.1 Note: 1 Indicates removal to detection limit.

2 0.02 : m Fluospheres   Data not available As shown in Exhibit 2.17, NF and RO processes are capable of significant log removals of cysts and viruses, which is to be expected since these microbes are much larger than the pore size of the membranes. However, the data in Exhibit 2.17 show that NF and RO systems are not an absolute barrier; they can allow microorganisms to pass through the membrane into the treated water. For this reason, it is important to consider membrane integrity testing when assessing the ability of a membrane to act as a barrier to microorganisms. Although no standard NF integrity testing method exists, some tests that have been proposed include vacuum testing and monitoring effluent water quality parameters such as chloride, UV 254 absorbance, microorganisms, and particle counts ( Spangenberg et al. 1999). Vacuum testing entails taking the membrane off line. This has the disadvantage of being unable to provide on line integrity monitoring. Should a system become compromised, it would not be realized until the module is taken off line and tested. Effluent water quality monitoring does provide real time results. However, the parameters being monitored must be sensitive enough to provide an alert if the Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 48 system is compromised. Sensitivity of various parameters will depend on the influent level of that particular parameter along with the amount of removal accomplished by the membrane. The parameter acting as a surrogate for membrane integrity must be removed to a significant degree such that a noticeable increase in effluent concentration would be seen if the membrane system were compromised.

NF processes are also capable of reducing biodegradable organic carbon ( BDOC) ( Escobar and Randall 1999). Since BDOC serves as substrate for microorganisms in the distribution system, reducing BDOC can reduce the potential for regrowth in a distribution system, disinfectant doses, and DBPs. A recent full scale study was performed to document the microbiological and disinfection benefits derived from implementing NF where conventional treatment had previously been practiced ( Laurent et al. 1999). The results of this study showed significant decreases in chlorine residual fluctuations, microbiological counts, DOC, and BDOC in treated water and in the distribution system. In effect, this created greater water quality stability in all areas of the distribution system, particularly in areas with high residence times. In addition, the finished water chlorine dose required was lowered from about 1 mg/ L to 0.2 mg/ L by the use of NF.

<IP_ADDRESS> DBP Precursor Removal Membrane processes can remove DBP precursors through filtration and adsorption of organics. Membranes remove NOM through filtration ( i. e., sieving) when NOM molecules are larger than a given membrane pore size, causing them to be rejected. Size, however, is only one factor that influences NOM rejection. Shape of the NOM molecules and membrane pores, along with chemical characteristics of the NOM molecules and membrane also play important roles in the permeation of NOM across a membrane ( Mallevialle et al. 1996). Membranes may also remove NOM through adsorption of organics directly on the membrane surface. The level of adsorption to the membrane surface depends on the chemical characteristics, particularly charge and hydrophobicity, of both the membrane material and the NOM. Unfortunately, organic adsorption is generally undesirable since it has proven to be a primary cause of irreversible fouling of membranes, thereby shortening membrane life.

Without pretreatment, NF processes remove NOM to varying degrees. NOM removals for NF and RO processes are typically on the order of 50 to 99 percent. NOM removal depends on many factors, including membrane MWCO and hydrophobicity, characteristics of the NOM, and membrane system operating parameters such as recovery and operating pressure. Results from several studies on NOM removal by NF processes are provided in Exhibit 2.18. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 49 Exhibit 2.18: NOM Removal Through NF Processes Reference Design Criteria Conclusions of Study Taylor et al. ( 1987 and 1989) Operating pressure: 98 141 psi Flux: 8.9 16.4 gpd/ sf Recovery: 50 79% ° MWCO of 100 to 500 are needed for DOC removal up to 90%. ° MWCOs of 1000 to 3000 may achieve 50% DOC removal. ° Trihalomethane formation potential ( THMFP) and total organic halide formation potential ( TOXFP) reductions up to 95% could be achieved with 300 MWCO. ° Operating pressure had a negligible impact on NOM removal. ° TDS1 and hardness rejection are increased by increased operating pressure.

Conlon and McClellan ( 1989) Operating pressure: 90 100 psi Recovery: 75% ° NOM removal greater than 90% for 200 MWCO.

Allgeier and Summers ( 1995) Operating pressure: 95 psi Flux: 15 24 gpd/ sf Recovery: 30 87% ° 66 94% TOC removal for 200 MWCO. ° TOC removal decreased by up to 15% as recovery approached 90%.

Lozier et al. ( 1997) Operating pressure: 70 psi Flux: 10 gpd/ sf Recovery: 85% ° 69 98% TOC removal using MF pre treated water.

Chellam et al. ( 1997) Operating pressure: 70 psi Flux: 10 gpd/ sf Recovery: 85% ° 90 95% TOC removal with 200 MWCO on MF and UF pretreated water. ° 95 99% SDS THM precursor removal. ° 96 99% SDS HAA6 precursor removal.

Mulford et al. ( 1999) Operating pressure: 100 psi Flux: 15 gpd/ sf Recovery: 82% ° 96% DOC removal with 200 MWCO.

Fu et al. ( 1995) Operating pressure: 80 psi Flux: 15 20 gpd/ sf Recovery: 75 90% ° 85 97% TOC removal with 100 to 500 MWCO.

Yoon et al. ( 1999) Not reported ° 60 90% TOC removal with 200 to 8,000 MWCO. ° Slightly higher NOM removal is achieved at pilotscale than at bench scale.

Legube et al. ( 1995) Not reported ° 79 91% DOC removal. ° 91 95% TOXFP reduction. ° 93 94% THMFP reduction.

1TDS = total dissolved solids Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 50 In addition to NOM removal, NF processes are capable of some DBP removal, although little work has been performed in the area. Bromide removal is also important for the reduction of brominated DBPs. NF membranes are capable of significant bromide removal. Several studies documenting the use of NF processes for bromide removal are summarized in Exhibit 2.19.

Exhibit 2.19: Bromide Removal Through NF Processes Reference Conclusions of Study Amy and Siddiqui ( 1999) 38 41% bromide removal with 150 to 300 MWCO.

Mulford et al. ( 1999) 50 63% bromide removal with 200 MWCO.

Allgeier and Summers ( 1995) 40 61% bromide removal with 200 MWCO.

Fu et al. ( 1995) 24 38% bromide removal with 100 to 500 MWCO.

Prados Ramirez et al. ( 1993) 63% bromide removal.

Conlon and McClellan; Taylor et al. ( 1989) 60 70% chloride removal, with bromide removal expected to be nearly identical.

As shown by the data in Exhibit 2.19, NF is capable of high percentage bromide removal. Overall, however, bromide removal using NF would probably not be cost effective if used only for that purpose. If the process were incorporated into a treatment train and used for other contaminant removal, membrane removal of bromide may become cost effective ( Amy and Siddiqui 1999). It is important to note that, if bromide is not removed sufficiently but TOC levels are reduced, the bromideto TOC ratio will increase considerably and will cause a net shift in speciation of DBPs to the more brominated compounds. In the worst case, such a scenario could cause a net increase in the absolute level of brominated DBPs ( i. e., bromoform) after chlorination ( Amy and Siddiqui 1999).

<IP_ADDRESS> Factors Affecting Performance NF is gaining popularity as a DBP precursor removal process, since production costs are comparable with competing processes ( Mallevialle et al. 1996). Due to the small pore size associated with NF, other feed water constituents will also be removed. For example, divalent salts, some metals, and some soluble organic carbon ( SOCs) may be rejected by these membranes and, therefore, be concentrated in the waste stream. This may increase the cost associated with disposing of the waste stream compared to disposal costs associated with MF, UF, and conventional treatment processes. If regulatory limits prohibit sending the waste stream to a receiving body, costs for waste handling and disposal can be a substantial portion of the overall treatment cost. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 2 51 MWCO is a key characteristic affecting membrane performance. Membranes with MWCOs in the 100 to 500 range appear to be very effective as a means of DBP precursor removal. TOC, THMFP, and TOXFP reductions of 70 to 95 percent are commonly achieved in systems using such membranes. These processes can effectively remove bromide as well, with reductions up to 95 percent. Larger MWCO membranes ( i. e., MWCO near and above 10,000), however, will not be as effective for NOM reduction.

Commercial NF ( as well as MF and UF) membranes are available in many types of material ( e. g., cellulose acetate and polysulphone) and in various configurations ( e. g., spiral wound and hollow fiber). The chemistry of the membrane material, particularly surface charge and hydrophobicity, can play an important role in rejection properties, since membranes can remove contaminants through adsorption on the membrane surface as well as through sieving across the membrane pores. These factors must be taken into consideration to accommodate source water characteristics and removal requirements.

Source water quality can also dictate pretreatment requirements. The small pore size of NF and RO membranes makes them more prone to fouling than UF or MF membranes, necessitating higher quality feed water. The application of NF and RO for surface water treatment is generally not accomplished without extensive pretreatment for particle removal and possibly pretreatment for dissolved constituents. For example, the rejection of scale forming ions, such as calcium and silica, can lead to precipitation on the membrane surface since these ions are concentrated on the feed side of NF and RO membranes. Organic constituents and metal compounds, such as iron and manganese, can promote fouling through precipitation and adsorption as well. Precipitation and adsorption can result in irreversible fouling and must be avoided through appropriate pretreatment, including anti scaling chemical and/ or acid pretreatment and possibly pretreatment for organics removal.

In terms of contaminant removal, membrane performance can also be influenced by the operating pressure and percent recovery, depending on the mechanism of rejection. ( This is true for NF and RO systems, but generally not true for MF and UF systems.) Contaminant rejection by NF and RO systems generally increases with decreasing operating pressure and with decreasing recovery. Thus, rejection can be enhanced by changing operating parameters, but not without corresponding increases in operating costs. To increase recovery, membranes are often staged ( i. e., the concentrate of one stage of membranes is treated by another stage of membranes). Two to three stages are common for NF and RO systems. ( Staging, however, is generally not used for MF and UF.) Staging is also used to keep the fluid velocity across the membranes at a specified rate. The maximum attainable percent recovery is usually governed by the degree to which the water can be concentrated without the occurrence of precipitation for NF and RO. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 1 3. Technology Design and Criteria 3.1 Introduction This Chapter provides assumptions related to the overall design for each technology addressed in this document. Types of information provided in this Chapter include:

° Assumed water quality conditions ( e. g., median filter water quality assumptions for UV design)

° Chemical doses ( e. g., ozone dose for Cryptosporidium inactivation)

° Equipment type ( e. g., types of UV lamps for various system sizes)

Chapter 4 builds on this Chapter by providing more detailed design assumptions for technology components and presents the costs for each technology.

Section 3.2 describes the assumed based treatment plant used for all technology modifications. Sections 3.3 and 3.4 describe the design approach for alternative disinfectant and DBP precursor removal technologies, respectively.

3.2 Base Treatment Plant The base treatment plant is assumed to represent the existing treatment configuration. All modifications with alternative disinfection strategies and removal of DBP precursors are assumed to be retrofitted from this base treatment plant. The base plant is represented by a conventional treatment plant, employing the basic processes of coagulant addition and mixing, flocculation, clarification, granular media filtration, and chlorination for both primary disinfection and maintenance of a distribution system residual. A schematic of the base plant is shown in Exhibit 3.1. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 2 Cl Cl 2 Coagulant Coagulant Rapid Mix Flocculation/ Sedimentation Filtration Storage Caustic Caustic Cl Cl 2 Exhibit 3.1: Base Plant 3.3 Alternative Disinfection Strategies Pertinent to compliance with the Stage 2 DBPR and the LT2ESWTR, alternative disinfection strategies may be selected to provide additional treatment for Cryptosporidium and/ or to limit the formation of DBPs. This section describes the overall design approach used for costing a number of alternative disinfection strategies capable of achieving these goals.

3.3.1 Chloramination Chloramines can be used for secondary disinfection to limit DBP formation in the distribution system. Chloramines are less effective for microbial inactivation than chlorine and are typically ineffective as a primary disinfectant; however, they may be used in combination with other technologies discussed in this section ( e. g., ozone for primary disinfection) to reduce DBP formation in the distribution system. Typically, ammonia is added after filtration ( or possibly after storage) to quench the chlorine residual and form chloramines. A schematic of a chloramine system is shown in Exhibit 3.2 Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 3 Cl Cl 22 Rapid Mix Flocculation/ Sedimentation Filtration Storage Caustic Caustic NH NH 3 Description of Process: Pre chlorination for primary disinfection; add ammonia after filtration at a residual chlorine to ammonia ratio of 4: 1. Coagulant Coagulant Exhibit 3.2: Chloramines for Secondary Disinfection A range of finished water chlorine residuals were derived using the ICR database. The 10th and 90th percentile finished water chlorine residuals from the ICR database are approximately 0.6 and 2.2 mg/ L, respectively. From these residuals, the ammonia dosages of 0.15 and 0.55 mg/ L were derived assuming a 4: 1 chlorine to ammonia ratio ( typical chlorine to ammonia ratios are between 3: 1 and 5: 1 to ensure monochloramine formation). Upgrade costs were generated only for ammonia storage and feed systems ( the base plant is assumed to provide the necessary chlorine). It is assumed that all chloramination can be accomplished at the plant and that no distribution system booster stations are required.

Aqueous ammonia is assumed for small systems (< 1 mgd), and anhydrous ammonia is assumed for large systems (> 1 mgd). Anhydrous ammonia is generally more cost effective for larger utilities; however, safety and handling issues with anhydrous ammonia also need to be considered. The aqueous ammonia system consists of a chemical storage container, metering pumps, an on line process analyzer, piping, and valves. The anhydrous ammonia system consists of bulk storage pressure vessels, a vacuum feed system, an on line process analyzer, piping, and valves: The larger systems may also include a vaporizer and an emergency scrubber system.

3.3.2 Chlorine Dioxide Chlorine dioxide is an effective oxidant/ disinfectant that is frequently used to control THM formation. It has also been shown to inactivate Cryptosporidium, as described in Chapter 2. Thus, chlorine dioxide can replace chlorine ( or other oxidants) as the primary disinfectant and potentially achieve a greater level of pathogen inactivation while decreasing THM and HAA formation. However, controlling the formation of chlorite ions can be a considerable challenge in chlorine dioxide treatment implementation. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 4 ClO ClO 2 Rapid Mix Flocculation/ Sedimentation Filtration Storage Caustic Caustic Description of Process: Replace chlorination with chlorine dioxide addition. Point of addition may be 1) prior to rapid mix, or 2) prior to flocculation, or 3) prior to filtration, or 4) post filtration Coagulant Coagulant Because of the significant operator attention required to monitor and control chlorite formation as well as to address safety concerns, it is assumed that systems serving fewer than 500 people will not have the expertise necessary to use this technology. Therefore, costs are only developed for systems with a design flow of 0.091 mgd or greater.

Many plants add chlorine dioxide as a pre oxidant, but it can also be added after filtration. For the analysis presented here, it is assumed that chlorine dioxide can be added at any point in the process train. ( A schematic of the chlorine dioxide system is shown in Exhibit 3.3.) Chlorine dioxide costs do not include construction of a basin for additional chlorine dioxide contact time. It is assumed that plants can achieve adequate contact time with their existing configuration.

Exhibit 3.3: Disinfection with Chlorine Dioxide All chlorine dioxide cost analyses presented in this document are based on an applied dose of 1.25 mg/ L. This is close to the maximum dosage of chlorine dioxide that can be added while remaining in compliance with a 1.0 mg/ L MCL for chlorite, conservatively assuming a 70 percent conversion of chlorine dioxide to chlorite and a safety factor to account for impurities, such as unreacted chlorine, in the chlorine dioxide feed. This analysis evaluated chlorine dioxide costs at the maximum dosage because chlorine dioxide is being considered here for inactivation of Giardia and Cryptosporidium. Protozoa inactivation by chlorine dioxide typically requires high CT values as described in Chapter 2. Additionally, evaluating the maximum chlorine dioxide dose provides a degree of conservatism to these cost estimates. The level of Cryptosporidium inactivation that would be achieved by this dose depends on water quality and contact time and is not assessed in this cost analysis. Higher doses that would necessitate the removal of chlorite are not evaluated at this time due to uncertainty about the applicability and efficacy of chlorite removal processes. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 5 For all systems, the use of an automatic generator is assumed. Key design assumptions for large systems are presented below.

° Chlorine dioxide generation is accomplished through addition of sodium chlorite to a chlorine solution created by dissolution of chlorine gas in water.

° A sodium chlorite metering and mixing system is provided.

° A chlorine dioxide generator ( detention time = 0.2 minutes) is provided.

° A polyethylene day tank and mixer are provided to store chlorine dioxide prior to its addition to the process.

° A dual head metering pump is provided to add chlorine dioxide to the process.

° A 1: 1 mass ratio of chlorine gas to sodium chlorite is assumed to ensure that the sodium chlorite is completely utilized. ( The additional chlorine serves to lower the pH for reaction through creation of hypochlorous acid.)

It is assumed that small systems (< 2 mgd) will rent the ClO2 generation equipment and only incur capital costs for instrumentation and piping and valves.

3.3.3 Ultraviolet Light UV light is an effective disinfectant for bacteria, viruses, Giardia, and Cryptosporidium and does not form THMs or HAAs ( see Chapter 2). For cost estimates in this document, a conceptual design for retrofitting the base plant with a UV disinfection system was developed based on plant flow ( i. e., system size category) and water quality. Because particulate matter may affect the performance of UV systems, the cost estimates assume that the UV system is installed downstream from the filter. Exhibit 3.4 presents a schematic of a conventional water treatment plant ( WTP) with UV disinfection. As shown in the schematic, interstage pumping is assumed because many utilities will not have sufficient hydraulic head to support the addition of UV disinfection facilities without significantly affecting plant operation. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 6 Rapid Mix Flocculation/ Sedimentation Filtration Caustic Caustic Storage UV Light Description of Process: Replace chlorination with UV light for disinfection. Coagulant Coagulant Interstage Pumping Exhibit 3.4: UV Disinfection The filtered water quality conditions assumed for all UV costs are based on median values reported in the ICR, as indicated in Exhibit 3.5.

Exhibit 3.5: Water Quality Assumptions for UV Disinfection Parameter Value UV 254 absorbance1 ( cm 1) 0.051 UVT (%) 1 89 Turbidity ( 0.1 Alkalinity ( mg/ L as CaCO3) 2 60 Hardness ( mg/ L as CaCO3) 2 100 1 Median of maximum filtered water UVT ( minimum UV absorbance) from the ICR data 2 Median of all ICR filtered water data Source: ICR Data Cost estimates for UV are provided for two UV doses: 40 and 200 mJ/ cm2. As discussed in Chapter 2, a UV dose of 40 mJ/ cm2 has been shown to be sufficient for 3 log inactivation of Cryptosporidium and Giardia and 1 to 2 log inactivation of viruses. Studies have shown that a UV dose of 200 mJ/ cm2 is adequate for 4 log inactivation of viruses.

Low pressure UV lamp based systems have been used for small treatment plants but are not typically installed at larger facilities due to the high number of lamps that would be required. Medium pressure lamp systems are not typically used for smaller utilities due to higher capital costs in comparison to LP systems at low flow rates. Therefore, UV reactors utilizing LP lamps are assumed for the small system (< 1 mgd) designs. Depending upon the manufacturer, LPHO and/ or MP reactors are provided in the large system (> 1 mgd) cost estimates. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 7 All UV systems are designed with an equipment redundancy of one extra UV reactor ( n+ 1) or 15 percent capacity above design flow, whichever is greater. The number of reactors costed for each system size is shown in Exhibit 3.6 below. The number of reactors for each design flow is based on currently available UV reactor sizes and flows.

Exhibit 3.6 Number of Assumed UV Reactors Design Flow ( mgd) Duty UV Reactors Standby UV Reactors Total Number of UV Reactors 0.022  3.5 1 1 2 17 3 1 4 76 5 1 6 210 11 2 13 430 22 4 26 UV disinfection systems are sensitive to power interruptions and fluctuations. When a UV reactor goes down, it can take from four to ten minutes for the UV lamps to regain full power. A utility with poor power quality might have problems with their UV systems going down too frequently. One way to prevent this problem is to install a uninterruptible power supply ( UPS), which is essentially a battery that smooths out the power interruptions and fluctuations. Because some systems may need UPS systems, cost estimates in Chapter 4 are completed at UV doses of 40 and 200 mJ/ cm2, with and without UPS systems.

3.3.4 Ozone Ozone can be used to replace chlorine for primary disinfection and can provide a higher level of inactivation of certain pathogens, such as Cryptosporidium, while reducing formation of THMs and HAAs. Ozone is one of the most powerful oxidants available for water treatment ( second only to the hydroxyl free radical). Disinfection with ozone is influenced by water quality characteristics such as pH, temperature, alkalinity, TOC, and certain inorganic compounds like iron and manganese. The use of ozone can be limited by raw water bromide levels and consequent bromate formation. These factors, in conjunction with the CT necessary for the desired level of pathogen inactivation, impact the design and operation of the ozone system.

A schematic of the ozone configuration is shown in Exhibit 3.7. The costing process allows for ozone application to either raw or settled water ( settled water application is depicted in Exhibit 3.7). To control bromate formation during ozonation, it may be necessary to lower the pH in certain waters. Separate costs are estimated for pH adjustment so that this cost may be added to the costs of ozonation, where appropriate. The pH adjustment costs include addition of a chemical feed system. To reduce the pH, sulfuric acid is used and caustic ( after ozonation) is used to raise pH. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 8 Rapid Mix Flocculation/ Sedimentation Filtration Caustic Caustic Storage Ozone Generator & Contact Basin Description of Process: Replace chlorination with ozonation. Coagulant Coagulant Exhibit 3.7: Ozone Disinfection Costs for ozone treatment systems are directly related to the dose applied. For the purposes of the LT2ESWTR and the Stage 2 DBPR, three ozone doses are costed based on the three levels of Cryptosporidium inactivation: 0.5, 1.0, and 2.0 log. The Surface Water Analytical Tool ( SWAT) model is used to calculate the ozone dose required for each inactivation level, based on CT tables in Chapter 2 ( Exhibit 2.13) and assuming an ozone CT of 12 minutes. For each plant in the ICR survey, and for each month with data, the SWAT model was used for raw water characteristics and existing plant configurations to determine the dose required to achieve the desired Cryptosporidium inactivation. Mean and maximum doses were then determined for each ICR plant.

For costing purposes, two doses were established for each of the three Cryptosporidium inactivation levels ( 0.5, 1.0, and 2.0 logs). The median of all plant mean ozone doses ( 1.78, 2.75, and 3.91 mg/ L, respectively) were used to calculate operation and maintenance costs. This is the dose which will be the most common for all plants achieving the given inactivation and the dose most representative of daily plant flows. To determine capital costs, the median of the plant maximum doses ( 3.19, 5.0, and 7.0 mg/ L, respectively) are used, as systems will be designed to meet the maximum dose that could be required under typical conditions.

The primary components of the ozone process include in plant pumping, ozone generation system, ozone contactor, off gas destruction facilities, effluent ozone quench, stainless steel piping ( including valves and ductwork), electrical and instrumentation ( E& I), and chemical storage facilities. Components not related directly to the process ( e. g., for which indirect costs are calculated) include piloting, permitting, land, operator training, and housing. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 9 Rapid Mix Flocculation/ Sedimentation Filtration Caustic Caustic Storage Micro/ Ultrafiltration Description of Process: Addition of microfiltration or ultrafiltration following granular media filtration. It may be necessary to move the point of chlorination to after MF/ UF, as some membranes can be damaged by chlorine. Coagulant Coagulant Interstage Pumping Cl Cl 2 3.3.5 Microfiltration and Ultrafiltration Microfiltration or ultrafiltration can be added to the base plant process train to enhance particle and microbial removal, including removal of Cryptosporidium. MF/ UF may also allow treatment plants to reduce DBP formation by decreasing the disinfectant dose required to meet plant CT requirements. MF/ UF can be added to the treatment process following conventional media filtration, or, in some cases, may be added as a replacement for media filtration. In certain applications ( e. g., low total suspended solids ( TSS) surface waters or groundwaters), MF/ UF can replace the entire conventional treatment process. However, the design assumptions and costs presented in this document assume addition of MF/ UF to an existing conventional treatment plant for enhanced removal of Cryptosporidium and/ or DBP control. Consequently, the costs presented in Chapter 4 do not include all of the components that would be required to replace a conventional treatment train. A schematic of the MF/ UF treatment process is shown in Exhibit 3.8 As discussed in section 2.2.5, flux is a critical design parameter for membrane applications and is often used in membrane procurements as a specification. However, the configuration of one membrane is often very dissimilar to that of another. Membrane fiber diameter, pore size, flow configuration ( i. e., cross flow vs. dead end, pressure vessels vs. submersible membranes), and other membrane specific factors can impact flux and other design and operating parameters. As a result, membrane feed water quality is used as the basis of design for the membrane portion of the costs presented.

Exhibit 3.8: Microfiltration and Ultrafiltration Cost estimates are based upon a design feed water temperature of 10 ° C. As previously discussed, temperature can have a significant impact on membrane system design. As the water temperature decreases, water viscosity increases. This, coupled with temperature effects on the membranes themselves, can result in the need for increased membrane area and/ or increased operating Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 10 pressures to maintain the desired level of production. It is important to note that this effect can vary from membrane to membrane, and many manufacturers have developed membrane specific correction factors.

Membrane system costs were approximated using estimates provided by four manufacturers ( all pressure vessel systems). The only criteria given to the manufacturers was the feed water temperature of 10 ° C. Since the design assumes a post filtration retrofit, the effect of solids loading on the membrane is considered minimal and was not specified for manufacturer estimates. Each manufacturer then used its own flux specifications and temperature correction factor to provide cost estimates for design flows ranging from 0.01 to 430 mgd. Estimates for design flows of 0.007 and 520 mgd were extrapolated from these estimates.

The membrane costs from the manufacturers include skid mounted membrane modules with associated piping, feed pumps, backwash and recirculation pumps ( where appropriate), chemical cleaning feed tanks and pumps, and instrumentation and control for proper operation. Additional instrumentation and control and pipes and valves were included in process costs for interconnection with existing plant control systems and processes. Interstage pumping was also added based on the assumption that the existing plant may not have sufficient hydraulic head to accommodate the membrane process. O& M costs include replacement membranes ( membrane life is 5 years), process power, chemicals for cleaning, and labor.

For the purposes of design, it was assumed backwash and reject water could be discharged to a sanitary sewer for treatment at a publicly owned treatment works ( POTW). This assumes the sanitary sewer has sufficient capacity to accommodate the increase in flow, and the POTW is able to handle the increase in daily flow. However, in many cases, the reject and backwash water can be recycled to the head of the treatment plant. In some instances, recycle may be a lower cost option than discharge to a POTW. In other cases, recycle may require additional pumping and site piping, modification or addition of chemical feed systems, installation of equalization basins, or expansion of other process components. Therefore, the costs associated with POTW discharge represent a conservative estimate in some cases ( i. e., where recycle requires few process improvements) and may underestimate costs in others ( i. e., where extensive improvements are necessary). However, for the purposes of approximating treatment costs, POTW discharge represents an approximate average cost per utility.

3.3.6 Bag and Cartridge Filtration Bag and cartridge filters may be an attractive, low cost option for small systems to improve microbial removal. Filter bags and cartridges are available in a number of different materials and a wide range of pore sizes. The removal efficiency can be affected by the filter material, pore size distribution, and filter durability. Filter durability affects how a filter stands up to routine cleaning and affects replacement frequency. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 11 Description of Process: Addition of bag filters OR cartridge filters following granular media filtration. Rapid Mix Flocculation/ Sedimentation Filtration Caustic Storage Bag or Cartridge Filters Coagulant Interstage Pumping It is assumed, for the purposes of this document, that bag or cartridge filters are installed downstream of existing granular media filters. Exhibit 3.9 presents a schematic of bag and cartridge filtration.

Exhibit 3.9: Bag and Cartridge Filtration Costs for different bag and cartridge filter construction materials were used to develop a range of costs. The frequency of replacement depends upon the durability of construction and water quality and can vary from a few weeks to as long as a year. This can have a significant impact on O& M costs. Filter housings are available in carbon steel for approximately half the cost of a stainless steel unit. However, for drinking water application, stainless steel is more likely to be the material of choice. As a result, only stainless steel housing was considered in development of costs.

3.3.7 Bank Filtration Bank filtration may be advantageous for systems that currently have surface intake from a stream which is underlain by a granular media. Such a system would essentially drill a well below the water table created by the surface water source. The well would replace the existing surface water intake. Particles and other contaminants would be trapped in the pores of the river bed material or adsorb onto the river bed material. The river bed material thus acts as a pre filtration step for the treatment process.

3.3.8 Second Stage Filtration Second stage filtration may be a desirable option for systems with frequent fluctuations in hydraulics and turbidity. Second stage filtration, like single stage filtration, operates by depth removal. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 12 Depth filtration is when the solids are removed within the granular media. The surface area of the media provides attachment sites for the particles suspended in the influent water.

To meet EPA's proposed 0.5 log credit for Cryptosporidium removal, second stage filtration must have the following characteristics:

° First stage of filtration must be preceded by a coagulation step.

° Both filtration stages must treat 100 percent of plant flow.

3.3.9 Pre Sedimentation Pre sedimentation basins will be useful for systems with high influent turbidities and high particle counts. EPA is proposing to give pre sedimentation basins with coagulant addition 0.5 log credit if the following criteria are met:

° All flow must pass through basin.

° Continuous flow through basin and coagulant addition near the influent of the presedimentation basin while plant is in operation.

° Maximum day settling surface loading rate of 1.6 gpm/ ft2.

° Annual mean influent turbidity > 10 NTU or maximum daily influent turbidity > 100 NTU.

Systems with existing pre sedimentation basins may monitor after the pre sedimentation basin and prior to the main treatment plant for the purpose of determining LT2ESWTR bin assignment. Costs in Chapter 4 were determined assuming that the basin met all the above specifications.

3.3.10 Watershed Control Each PWS's watershed control program plan is expected to be site specific and will depend on the hydrology and land use in the watershed, the location and type of Cryptosporidium sources in the watershed, the population served, size of the watershed, funding, and other issues. Watershed programs may include the following:

° Monitoring for Cryptosporidium or indicator organisms throughout the watershed ° Fencing or otherwise restricting access to the source water Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 13 ° Land acquisition ° Managing land owned by the PWS ° Working with sewer or stormwater utilities to develop plans to upgrade treatment or otherwise reduce pollutant loads ° Working with municipal governments to regulate land use and development,

° Conducting outreach to other stakeholders To receive credit for removal of Cryptosporidium, a watershed control program must have the following elements:

° It must be reviewed and approved by the primacy agency.

° It must include an analysis of the system's source water vulnerability to the different sources of Cryptosporidium identified in the watershed. The vulnerability assessment must include a characterization of the watershed hydrology and identification of an " area of influence on source water quality" ( i. e., the area to be considered in future watershed surveys). The assessment must also address sources of Cryptosporidium, seasonal variability, and the relative impact of the sources of Cryptosporidium on the system's source water quality. It is likely that water systems will obtain much of the information to be provided in the vulnerability assessment from the source water assessment performed as part of the State source water assessment program.

° It must present an analysis of sustainable interventions and an evaluation of their relative effectiveness in reducing Cryptosporidium in source water. Interventions may include anything from outreach to point source elimination.

° It must address goals and define and prioritize specific actions to reduce source water Cryptosporidium levels. The plan must 1) explain how actions are expected to contribute to specified goals, 2) identify partners and their roles, resource requirements and commitments, and 3) include a schedule for plan implementation.

° It must include submission of an annual report performance of a watershed survey, and submission of a request for review and reapproval.

A watershed control program could include interventions such as 1) the elimination, reduction, or treatment of discharges of contaminated wastewater or storm water, 2) treatment of Cryptosporidium contamination at the site of generation or storage, and 3) prevention of Cryptosporidium migration from the source ( e. g., farms or wastewater treatment plants). The Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 14 feasibility and sustainability of various interventions may depend on the cooperation of other stakeholders in the watershed. Stakeholders that have some level of control over activities that could contribute to Cryptosporidium contamination include municipal government, private operators of wastewater treatment plants, livestock farmers, and other government and commercial organizations.

The LT2ESWTR does not specifically mandate any interventions that must be included in a watershed control program plan. The only required elements are those submitted with an application for approval of the watershed control program plan. These are the delineation of an " area of influence on water quality" and a vulnerability assessment. Watershed delineation and susceptibility analyses are already required under the Source Water Assessment Program; data gathered under this program can, in many cases, be used in preparing information required for the application.

3.3.11 Combined Filter Performance Combined filter performance is not a single technology but many different activities that can improve existing filtration processes to enhance performance. Plants, which can operate their filters in such a way to produce 0.15 NTU or lower turbidity water 95 percent of the time, will receive a 0.5 log Cryptosporidium reduction credit under the LT2ESWTR.

The Regulatory Impact Analyses ( RIAs) for the IESWTR and LT1SWTR identified 35 actions that facilities could take to lower the finished water turbidity from the SWTR standard of 0.5 NTU to the IESWTR standard of 0.3 NTU. These tasks were examined and professional judgement was applied to determine which of these actions would be helpful in further lowering turbidity from 0.3 to 0.15 NTU.

In determining processes that could further reduce filtered water turbidity, systems that would select this Cryptosporidium removal option were assumed to be conventional filtration or softening plants which were already operating well within the 0.3 NTU standard currently. These plants would likely have to make only minor modifications to the treatment process to meet the 0.15 NTU standard. These plants were also assumed to be operating under 0.15 NTU less than 95 percent of the time or to be capable of achieving 0.15 NTU.

Based on these assumptions, the filter improvements listed in the IESWTR were reviewed for applicability to this treatment option. The following were considered as possible actions that systems may take to implement this option:

° Installing backwash polymer feed capability ° Installing coagulant feed points ° Adding filter media Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 15 ° Adding filter to waste capabilities ° Replacing the filter rate of flow controller ° Increasing plant staffing ° Increasing staff qualifications ° Purchasing or replacing bench top turbidimeters ° Purchasing or replacing jar test apparatus ° Purchasing or replacing a particle counter or streaming potential meter ° Staff training It is not assumed that each system using this technology will use all eleven tasks. Instead, it is assumed that each system would have to use at least one of these tasks and, most likely, two or more to meet the turbidity targets ( successfully). To develop costs for this technology, the percentage of the plants choosing each action was determined. The percentage of systems choosing a particular task was then multiplied by the unit cost for that task to arrive at an average unit cost for all plants. Further details of the percentages and costs are given in Chapter 4 of this document.

The assumptions for each filter improvement action is discussed below.

Installing Backwash Water Polymer/ Coagulant Feed Capability Adding coagulant to backwash water aids in filter ripening and helps to reduce post backwash turbidity spikes. Systems choosing backwash polymer to lower turbidity were assumed to not have this capability currently. Costs were for a dry polymer feed system that can be loaded with a seven day polymer supply.

Installing Additional Coagulant Feed Points Installing additional coagulant feed points can help to improve coagulation of particles and their removal by settling. Capital costs were based on feeding an additional 5 parts per million ( ppm) dose of primary coagulant. The primary coagulant is assumed to be ferric chloride, ferric sulfate, or alum. Thirty days of bulk storage are assumed for ferric chloride or ferric sulfate ( equivalent to approximately fifteen days of storage for alum).

Adding Filter Media Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 16 Often during routine operation of filters, media is lost either through attrition and passage out the underdrains or through the backwash. If too much media is lost, filter performance will suffer. Therefore, adding additional media can often improve turbidity in the effluent.

Adding Filter to Waste Capabilities Filter turbidity often spikes immediately after backwashing. Installing filter to waste capabilities allows water to be wasted after a backwash instead of sending the high turbidity water to the CFE. Costs included piping, valves, and fittings.

Installing or Replacing Filter Rate of Flow Controllers Flow surges can cause spikes in filter turbidity. Installing a rate of flow controller or replacing a faulty one can improve performance. Costs were for replacing a unit and were based on assumed 24 hour operation.

Increasing Plant Staffing Systems which only have part time staff or are understaffed may have trouble controlling filter conditions closely enough to meet the 0.15 NTU turbidity target. Hiring additional staff or extending current staff's hours may help systems to more finely control filter operations.

Increasing Staff Qualifications Better trained staff may be able to recognize conditions which lead to filter turbidity breakthrough and to prevent it. Costs for this option were based on the cost of sending an operator to a training class. Costs include class registration fees to attend an operator certification class.

Purchasing or Replacing Bench Top Turbidimeters Typically, every plant has at least one bench top or on line turbidimeter. However, some of these units may be obsolete to meet the monitoring requirements of the LT2ESWTR for combined and individual filter effluents. Bench top turbidimeters do not appear to be suited to fulfill these monitoring tasks. Therefore the purchase of up to date on line turbidimeters with electronic data acquisition interface was costed.

Purchasing or Replacing Jar Testing Apparatus A jar testing apparatus is necessary for optimizing coagulant and polymer dosing. Old units will need to be replaced, and new units purchased if a facility does not have one. Systems serving greater than 100,000 people were assumed to buy two units, and those serving more than 1,000,000 people were assumed to purchase three units. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 17 Rapid Mix Flocculation/ Sedimentation Filtration Caustic Caustic Storage Coagulant Coagulant GAC Filter Description of Process: Install GAC filter following granular media filter. Interstage Pumping Purchasing or Replacing a Particle Counter Instruments such as particle counters, zetameters, and streaming current monitors can be used to optimize filter processes. The cost for this option assumes the purchase of one of these instruments. The cost of a particle monitor was used as a surrogate for any one of these three instruments.

Staff Training Better trained staff will be better able to spot and fix problems in filter performance. The costs for this option were based on hiring a consultant to provide on the job training for 10 to 140 hours.

3.4 DBP Precursor Removal Technologies A strategy for reducing DBP formation is removal of DBP precursors ( e. g., natural organic matter). The technologies discussed in this section may not be applicable for all systems. Each technology section presents the approach and assumptions used to develop the costs presented in Chapter 4.

3.4.1 Granular Activated Carbon Adsorption GAC filters reduce DBP formation by removing organic carbon. For the purposes of this document, installation was assumed after the existing filters. A schematic of the GAC process is shown in Exhibit 3.10.

Exhibit 3.10: GAC Filtration The application of GAC adsorption involves the following process design considerations:

° Empty bed contact time, volume of empty contactor divided by flow rate Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 18 ° Reactivation interval or frequency, which affects the GAC usage rate ( pounds of GAC used per gallon of water treated) ° Pre treatment ° Contactor configuration ( e. g., downflow versus upflow, pressure versus gravity, singlestage versus multi stage or parallel, filter adsorber versus post filter GAC contactor)

° Method of GAC reactivation ( e. g., on site versus off site)

° Interstage pumping ° Performance monitoring ( for TOC)

EBCTs of ten and twenty minutes were chosen for the cost evaluation based upon an analysis of EBCTs and NOM removal. This analysis indicated that EBCTs lower than 10 minutes do not remove sufficient NOM to warrant installation as a control for DBP precursors. Similarly, EBCTs in excess of 20 minutes do not provide significant improvements in NOM removal. Accordingly, 10 minutes and 20 minutes were selected to represent the upper and lower bounds of appropriate EBCTs for NOM removal.

Reactivation/ replacement frequencies vary based on water quality and the number of contactors in parallel. For the purposes of this document frequencies of 90, 240, and 360 days were evaluated. Ninety days was selected as a minimum value based upon best professional judgement that reactivating at intervals lower than 90 days is impractical from an operational standpoint. Three hundred and sixty days was selected as the maximum reactivation frequency since the cost of GAC technology increases insignificantly for reactivation frequencies of greater than 1 year. High operating costs were captured by considering 90 day regeneration frequency for the GAC facility with EBCT of 20 minutes. Low operating costs were captured by considering 360 day regeneration frequency for the GAC facility with EBCT of 10 minutes. An intermediate operating cost was also captured by considering 240 day regeneration frequency for the GAC facility with EBCT of 20 minutes.

Based upon best professional judgement, it was decided that small systems are unlikely to regenerate on site, since it requires more substantial capital investment and operator attention. As a result, small systems ( less than 1 mgd) were assumed to operate on a replacement basis ( i. e., when the carbon is spent, it is discarded and replaced with new carbon). Large systems ( greater than 1 mgd) were assumed to regenerate on site using multiple hearth furnaces.

Very small system GAC installations (< 0.1 mgd) include: pressure GAC contactors, virgin GAC, pressure booster pumps, pipes and valves, and instrumentation and controls. O& M is a function of regeneration frequency. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 19 Description of Process: Addition of nanofiltration following granular media filtration, OR replacement of granular media filters with nanofiltration Rapid Mix Flocculation/ Sedimentation Filtration Caustic Caustic Storage Nanofiltration Coagulant Coagulant Interstage Pumping Small system GAC installations (> 0.1 mgd and < 1 mgd) include: pressure vessels designed for working pressure of 50 psi; factory assembled units mounted on steel skid 12 feet high and varying diameter depending on the EBCT; access for filling and removing carbon; pressure booster pump, valves, piping and pressure gauges, initial charge of activated carbon, supply and backwash pump, and electrical control panels.

Large system GAC installations (> 10 mgd) include: concrete gravity contactors 8.3 feet high; loading rate 5 gpm/ ft2; troughs and pipes for carbon removal as a slurry; other pipe gallery; pressure booster pump; flow measurement and instrumentation; master operations control panel; building; initial virgin carbon; single multiple hearth furnace for carbon regeneration loading rate of 50 pounds per square foot per day; and two TOC analyzers.

3.4.2 Nanofiltration Nanofilters remove NOM, thereby reducing DBP formation. NF is an advanced treatment process which typically requires higher levels of pre and post treatment than traditional water treatment processes. For this cost analysis, nanofilters were assumed to be located downstream of existing filters. A schematic of the NF technology is shown in Exhibit 3.12.

Exhibit 3.11: Nanofiltration Typically, NF requires both physical and chemical pre treatment. Pre treatment is usually required for NF treatment of all surface waters and some ground waters. Physical pre treatment often includes a component to remove particles, typically multi media filtration, microfiltration, or cartridge filtration. Chemical pre treatment often includes acid or anti scalant addition to reduce the fouling potential of the feed water. Particle removal and softening with chemical addition are also used as pretreatments Attention should be paid to the compatibility of coagulant and the membrane for such situations. Technologies and Costs for Control of Microbial Contaminants and Disinfection Byproducts June 2003 3 20 Post treatment may also be required, depending on the characteristics of the product water. NF product waters usually have low pH and total dissolved solids levels. This creates the potential for an unstable and corrosive finished water. Chemical post treatment may be required to create a more stable and non corrosive water. Commonly used post treatments include addition of caustic ( to raise the pH), soda ash ( to raise pH and alkalinity), and poly/ ortho phosphates for stabilizing the water. Blending a portion of raw water with finished water can also be used to stabilize the finished water.

The design criteria in this document assume that the NF system is an " add on" process to an existing treatment plant which is generating a water that can be fed directly to the NF process without further pre treatment. It is assumed that 100 percent of the design flow is passing through the NF membranes. Recoveries of 85 percent and operating pressures of 90 110 psi were assumed. Costs were developed assuming a design feed water temperature of 10 degrees Celsius. Like MF, the cost of a NF system can vary significantly with temperature because the membrane productivity, or flux ( gallons/ ft2 day), is strongly dependent on feed water temperature. Empirical relations are available to estimate the flux at a design temperature using the flux at a reference temperature ( i. e., 10 degrees Celsius). These relations are available both in published literature and with membrane manufacturers.

NF system cost quotations were obtained from manufacturers for all NF equipment items, including membrane elements, online instruments, booster pumps, clean in place systems and acid/ antiscalant addition systems. Unlike other treatment processes, membrane systems are typically supplied by the equipment vendor as package, skid mounted units; therefore, smaller multipliers are assumed. Capital cost multipliers of 1.67 and 2.0 were used respectively for small and large systems to estimate total capital cost. It was assumed that a unit NF skid can produce up to 2 mgd of product water. NF systems smaller than 2 mgd were assumed to have fewer membrane modules and membranes.

The O& M costs include chemical usage, membrane replacement ( assumed membrane life of five years), process/ building power, additional labor hours, and process monitoring. Efforts were made to capture the drop in prices of the membranes, modules, and associated equipment over the past few years due to increasing use of the NF systems. Where necessary, the costs for retrofitting and operating an NF plant were verified with data from various surveys, including Florida's softening plants ( Bergman 1996) and the Bureau of Reclamations ( BOR 1997) surveys. The cost curves presented in Chapter 4 were verified with real plant data for different flow levels.

NF design criteria developed here include handling of the brine stream generated by the NF process. This handling assumes direct discharge of the brine to a receiving body, ocean outfall, sanitary sewer, storm drain, or a salinity interceptor. The costs presented in Chapter 4 pertain only to plants located in areas where brine can readily be discharged to either a receiving water body, a sewer/ storm drain, or a salinity interceptor. Plants located in areas where this is not an option will have significantly higher waste stream treatment and handling costs.