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TREATMENT TECHNOLOGIES



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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop TREATMENT TECHNOLOGIES

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop Large Scale Systems Stephen M. Lacy ABSTRACT The arid Southwest of the United States has a very similar climate to portions of Iran. With little rainfall, communities must share freshwater sources from rivers and aquifer systems with agriculture. The scarcity of freshwater sources is driving decisions to look at wastewater effluent as a resource. Recent technological advances borrowed from the water industry are opening up more opportunities for the safe reuse of effluent. This paper will look at the treatment standards commonly set for several categories of reuse and the treatment technologies that are being employed to obtain differing levels of effluent quality to meet the needs of the reuse opportunities. It will also look at new emerging technologies in the area of microfiltration and how it is being applied in reuse. Finally it will look at the treatment technologies being incorporated for indirect potable reuse applications. INTRODUCTION In the past, reuse of wastewater effluent was typically limited to irrigation of agricultural pasture lands and turf areas with limited public access. As freshwater sources become more limited, other applications for reuse are being employed that result in greater contact between the effluent and the public and food crops. This has invited ever-increasing regulation and restriction, thus requiring more sophisticated treatment processes to be incorporated into the typical treatment train of a wastewater facility.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop Wastewater reuse provides a drought-proof resource for a community that automatically increases as population growth occurs. Reuse also provides for some immediate reductions in water diversions by replacing existing demands (such as turf irrigation at parks) with nonpotable irrigation water. This water resource offers strategic benefits to the community in terms of increased sustainability. However, because most nonpotable uses (such as irrigation) are limited and the demand diminishes in the winter months, many communities look at other options for use of the resource rather than simple discharge. Figure 1 shows wastewater production levels and a typical variation in annual demand for nonpotable irrigation uses. During periods of low irrigation demand, wastewater reuse can also be accomplished by indirect potable reuse. Indirect potable reuse occurs where highly treated reclaimed water is introduced to a surface water or groundwater system that is ultimately used as a potable water supply. In an indirect system, the reclaimed water is blended with the natural system, with a significant delay (12 months or more) between the point of reclaimed water discharge and the withdrawal into the potable water system. Dilution of the reclaimed water with natural waters results in only a portion of the water being withdrawn for potable use originating from the reclaimed water. There is a very significant direct benefit to the water resource by reducing groundwater depletions and pumping effects through aquifer recharge. In order to maximize beneficial reuse, a range of water reuse alternatives and wastewater treatment technologies is needed. FIGURE 1 Typical annual irrigation demand pattern.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop COMPARISON OF WATER QUALITY STANDARDS FOR NONPOTABLE REUSE Water quality standards for nonpotable uses have been established by many states within the United States and continue to be revised as a result of developing technologies in wastewater treatment and a better understanding of the health effects. The focus of these standards is to provide policy direction and regulation of reuse applications that are protective of public health. California’s Title 22 Standards have been in use since 1978, and the latest revisions were adopted in December 2000. The level of public exposure and contact typically categorizes the allowed effluent irrigation uses. Prescriptive treatment standards and water quality limits are listed for the various categories of use and are widely accepted to be protective of public health. There are many examples throughout the western United States where reclaimed water has been safely used for many years to irrigate turf (golf courses, parks, and recreational sport fields). As communities look to expand beneficial use of reclaimed water, it is expected that many more nonpotable reuse applications will be implemented to preserve and extend potable supplies. The following discussion summarizes the typical reuse categories identified in regulations: agricultural reuse, urban reuse, and industrial reuse. Restricted Reuse for Commercially Processed Food Crops and for Non-Food Crops This category describes how effluent may be used to irrigate commercially grown food crops that must undergo commercial pathogen-destroying processing before being consumed. It also includes irrigation of non-food crops, such as hay and seed crops, or for food crops where the reclaimed water does not come into contact with the edible portion of the crop (orchards or vineyards). California standards require secondary treatment (≤30 mg/1 biochemical oxygen demand [BOD] and total suspended solids [TSS]). Newer regulations additionally require disinfection to ≤200 fecal coliforms/100 milliliters (ml) (median for prior seven samples) with no single sample exceeding 800 fecal coliforms/100 ml. Common activated sludge treatment with simple disinfection can meet these criteria. If the disinfection limit is higher, such as 1,000 MPN/100 ml, a lagoon system consisting of facultative lagoons followed by maturation ponds can meet secondary standards with long detention times. This category does not include pasture for animals producing milk for human consumption. If the reclaimed water is to be used for irrigation of pastures for milking animals, the disinfection must be increased to medium-level. This would require additional disinfection facilities to consistently disinfect the reclaimed water to a fecal coliform bacteria concentration of less than 23 fecal coliforms/ 100 ml (median for the prior seven samples), with no single sample exceeding 92 fecal coliforms/100 ml.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop Restricted Reuse for Non-Commercial Food Crops This category describes how reclaimed water may be used for surface or spray irrigation of food crops that can be consumed raw or that are not commercially processed. California requires that reclaimed water receive secondary and tertiary treatment followed by high-level disinfection. This standard is identical to the standard for urban irrigation use with unrestricted access described in the following section. The organic content must be reduced to less than 10 mg/l of BOD, and the solids to less than 2 nephelometric turbidity units (NTU) (5 mg/l TSS). Fecal coliform bacteria must be reduced to less than 2.2 MPN/100 mg/l. Common activated sludge treatment followed by sand filtration will comply with the organic and solids limits. Extensive disinfection facilities are required to consistently meet the coliform levels. Urban Irrigation Use—Restricted Access This application typically involves minimal public exposure to the irrigation water and is used where public access is prohibited, restricted or infrequent. Examples include freeway landscapes, cemeteries, sod farms, silviculture sites, and potentially golf courses where public access is restricted. California standards allow use of disinfected secondary treated (≤30 mg/l BOD and TSS) effluent. The California standard has set a medium level of disinfection for this use category, ≤23 total coliform/100 milliliters (ml) based on the last seven samples. It is expected that most nonpotable uses identified in a community will not qualify as restricted access. Common activated sludge treatment with simple disinfection can meet these criteria. Urban Irrigation Use—Unrestricted Access This category describes how reclaimed water may be used to irrigate landscaping where people walk, play, or otherwise spend time. Examples of these uses are playgrounds, schoolyards, sports fields, public golf courses, and parks. The reclaimed water must meet the highest standards for reuse to protect the public from exposure to pathogens found in domestic wastewater. California standards require secondary treatment with filtration (tertiary treatment) and a high level of disinfection. The standards additionally require coagulation prior to filtration and that the filter effluent turbidity does not exceed 2 NTU and the filter influent turbidity does not exceed 5 NTU for more than 15 minutes and never exceeds 10 NTU. The disinfection standard requires that the effluent achieve ≤ 2.2 total coliforms/100 ml (median for the prior seven samples), with no single sample exceeding 23 total coliforms/100 ml. It is expected that most nonpotable uses in a community will be required to meet this treatment and disinfection standard.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop The organic content must be reduced to less than 10 mg/l of BOD and the solids to less than 2 NTU (5 mg/l TSS). Fecal coliform bacteria must be reduced to less than 2.2 MPN/100 mg/l. Common activated sludge treatment followed by sand filtration will comply with the organic and solids limits. Extensive disinfection facilities are required to consistently meet the coliform levels. Coagulation will be required as part of the filtration treatment to achieve consistently low filter turbidities. Flocculation may be required as well. Industrial Reuse The use of reclaimed water in industrial applications must comply with the quality levels set above for the level of contact by the public in urban irrigation applications. Additional treatment may be required to meet water quality for the industrial process for direct use or to meet a prescribed pretreatment level. In most cases, the unrestricted access irrigation use category is of adequate quality to meet larger industrial uses such as cooling water and may be of adequate quality for industrial process water applications. TREATMENT TECHNOLOGIES TO MEET NONPOTABLE WATER REUSE STANDARDS Different levels of treatment are required to implement different reuse strategies. They range from simple upgrades to the existing treatment facilities for irrigation of agricultural and urban areas, to multiple barrier treatment for indirect potable reuse. Treatment technologies for indirect potable reuse are discussed later in the paper. Common to each strategy is the need for preliminary and secondary treatment prior to any advanced treatment. Preliminary treatment would include screening and grit removal. Secondary treatment would consist of a biological treatment process such as activated sludge or trickling filters. A lagoon system could be utilized in a restricted use agricultural application; however, the low quality effluent and high algae content in a lagoon effluent makes the water unacceptable for further high level treatment. Primary clarification could be included as a unit process prior to secondary treatment in larger plants. Figure 2 shows a typical configuration of a large treatment plant providing high quality reuse water. Also common to the treatment plants would be sludge treatment. Stabilization of the sludge could result in biosolids acceptable for beneficial use on agricultural land or distribution to the public. The two main additions to the treatment train at a treatment plant to attain the high levels of effluent quality required for the different nonpotable reuse strategies are the addition of tertiary treatment and increased levels of disinfection. These two processes are discussed below.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop FIGURE 2 Typical large water reclamation plant configuration. Tertiary Treatment With the advancements in membrane technology into the wastewater area, there are now two viable media that can be used effectively to filter secondary effluent: traditional sand (or similar media) and the newer membrane materials. Filtration has been used for many years in water and wastewater applications. Some improvements have simplified the operation and reduced the head required to pass through the process. Membrane technology improvements have made their application in wastewater treatment feasible. Common activated sludge treatment followed by filtration and extensive disinfection facilities have been shown to comply with all current standards for agricultural and urban reuse categories. Both filters and membranes will also remove helminths. A third medium is disk filtration. This process utilizes large disks of cloth media attached to rotating drums for filtration. This process is fairly new and lacks experience in large applications. Coagulation and Flocculation Prior to sand filtration, it may be necessary to chemically treat the wastewater to enhance the effectiveness of the filtration process. Coagulation and flocculation constitute a two-step process utilized to chemically pre-treat the wastewater prior to filtration. In reuse systems, chemical coagulation of the wastewater is typically required if the secondary effluent has turbidity greater than 5 NTU. This step is not required prior to membrane treatment. Alum can be injected at a static mixer to coagulate the solids. The wastewater then can be treated in flocculation basins, where larger, stronger solid particles are formed. Vertical mechanical mixers slowly mix the floc and create the larger solid particles. Detention time in a flocculation basin is about 10 to 20 minutes. Wastewater with these larger solid particles then can be subjected to the filtration process.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop Filtration Filters come in many forms, but the basic concept by which they work is the same. It is a physical straining process where the solid particles pass through a bed of sand or other media. As the wastewater solids accumulate in the filter, the flow is reversed through the bed, expanding it, and allowing the solids to be backwashed out of the media. The waste backwash water is returned to the treatment plant for retreatment. The traditional sand or multimedia filter was brought to wastewater applications from the water field. The traditional high head, high rate, deep bed filter has excellent performance characteristics, producing effluent turbidity less than 1 NTU. Though the performance is compatible with the intent of eliminating all solids that could be harboring bacteria and viruses, its large size and complexity makes it mainly applicable at very large treatment facilities. Following is a discussion of other types of filtration processes. High Rate-Low Head. A filter configuration similar to that of the traditional filter is a low head, high rate, shallow bed design that has many of the same features as the traditional filter. The most significant difference in the two types of filters is that the shallow bed filter utilizes a 300 mm deep bed of sand, versus a 1,200 mm or deeper bed. This type of filter is backwashed when the head in the filter results in excessive headloss. This filter has outstanding performance but has much of the same complicated operation as the traditional filter. Also, like the traditional filter, a large quantity of waste backwash water is produced in a short period of time, requiring the capture and equalization of the return flow to the plant to prevent upsetting the main plant treatment processes. Traveling Bridge (Segmented Bed). This filter utilizes a shallow bed (300mm to 600mm) of sand or other media installed in a segmented bed arrangement. The backwash system is suspended from the bridge that moves across the bed. A pump takes filtered water from the effluent channel and directs it back into a segment of the filter bed, forcing the water back up through the filter bed, dislodging the particles removed from the wastewater. A second pump, attached to a hood that covers the segment being backwashed, draws the waste backwash water into the hood and discharges it into a trough for return to the head of the treatment plant. By continuously moving across a filter bed, this filter produces a continuous low volume of waste backwash water, eliminating the need for a separate backwash water storage basin and a basin to equalize the flow of waste backwash water returning to the main treatment plant. Significantly less operating head is needed to pass through a traveling bridge filter, allowing it to fit within many treatment plant hydraulic profiles without additional intermediate pumping into the filters.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop Continuous Backwash. This type of filter also requires a low operating head (450mm to 600mm). It also produces a continuous low rate of waste backwash flow to eliminate the need for flow equalization of the waste backwash return to the main treatment plant. An air lift pump continuously moves the sand media from the bottom of the filter bed to the top where the solids are separated from the sand particles and the freshly cleaned sand is returned to the filter bed. The influent is introduced at the bottom of the filter and moves countercurrent up through the downward moving sand to overflow the filter bay. The only mechanical component of this type of filter is an air compressor to produce the air needed for the airlift pumps. Membranes Membrane filtration also comes in many varieties. Depending on the pore opening size, the membranes remove various size particles and can produce reclaimed water of the quality required for aquifer injection or nonpotable reuse. The type most commonly applied to wastewater treatment for urban reuse has been microfiltration. Membranes have been shown to be very effective in the removal of pathogens and viruses, to the point of approaching compliance with the disinfection standards for urban reclaimed water, but have not been shown to consistently meet the stringent coliform standards. In any case, it is common practice in reuse systems to provide a minimum of two processes to limit the potential of pass-through of viruses (known as multiple barrier treatment). Microfiltration has a slightly slower filtration rate than filters but requires considerably greater pressure to pass through the process. Microfiltration membranes treating secondary effluent are designed to handle a loading (flux) of about 70 l/h/m2. The normal operating pressure is about 1 bar, with a maximum operating pressure of 2 bars. The waste backwash water volume is comparable to that of a filter, amounting to about 5 percent of the average flow rate. Flow equalization of the waste backwash water is not required. Chemical pretreatment is also not required. The operation of a membrane system is significantly more complicated than any of the filter systems. Auxiliary equipment required as part of the microfiltration process includes pumps, strainers, high-pressure air compressors, feed/break tanks, and a master control system. The master controller operates the system to maintain pressures, to perform intermittent air pulse cleanings, and approximately every 3 days, to perform an in-situ cleaning. DISINFECTION With the advances in ultraviolet light technology in wastewater disinfection, there are two viable methods that can be used effectively to disinfect tertiary efflu-

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop ent to the high level required for unrestricted reuse of reclaimed water. Chlorine has been used for many years in water and wastewater applications. Ultraviolet light (UV) has gained acceptance over the past few years due to its effectiveness in the reduction of coliform and viruses without creating toxic by-products. Chlorination Chlorine is a very effective disinfectant. When combined with the ammonia that is present in wastewater, it creates chloramines that continue to protect the quality of the reclaimed water within the distribution system. To reach the low levels of coliform required to meet the disinfection standards, the wastewater must be in contact with the chlorine for an extended period of time. The contact time (CT) is expressed as the concentration multiplied by the detention time. To meet the disinfection standard, a CT in excess of 1,000 is recommended. For instance, for an average chlorine concentration of 10 mg/l, a chlorine contact tank must be constructed to provide 100 minutes of detention at average flow. A chemical building with equipment sized to feed and store adequate chlorine would be required. This building would have to be specially designed to control the flow of air out of the storage room in the event of a leak. A chemical scrubber system must be installed on the exhaust air to remove any chlorine before it can be released to the atmosphere. Ultraviolet Light There are several different configurations of ultraviolet light (UV) systems available. They are available as low pressure-low intensity, low pressure-high intensity, and medium pressure-high intensity. The systems cover a wide range of efficient uses of the UV light produced at the most effective disinfection point of a wavelength of 254nm. The amount of maintenance required also varies with the type of system. Of the various combinations of low or medium pressure and intensity mentioned above, the low pressure-high intensity systems provide the best utilization of the input power at the disinfecting wavelength and the lowest maintenance requirements. These systems operate at a relatively low temperature, with most light produced at the disinfecting wavelength of 254nm. This allows the system to operate efficiently, maximizing the use of the input power, thus reducing operating costs. These factors also result in lower maintenance requirements due to extended life of the lamps and other system components. Redundant UV system capacity must be installed to allow for maintenance and reduced effectiveness with age. Spare lamps are stored on site to allow for quick replacement as lamps burn out. A small amount of chlorine must be added to the disinfected effluent to create a residual in the distribution system.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop USE OF MICROFILTRATION IN THE MEMBRANE BIOREACTOR PROCESS The increased need for reclaimed water in arid environments has resulted in the emergence of new wastewater reclamation technologies. One of the most promising and innovative technologies in water reclamation today is the membrane bioreactor (MBR) process. The membrane bioreactor combines activated sludge treatment with a membrane separation process. The reactor is operated in a similar way to conventional activated sludge (CAS), but a clarifier is not needed. Instead, a low-pressure microfilter (MF) membrane is used to perform the sludge separation. The combination of an activated sludge and membrane process produces water that has undergone secondary, tertiary and low-pressure membrane treatment using only one unit operation. The MBR process has been shown to provide high quality effluent with high BOD removal and complete TSS reduction. Depending on the design, configuration, and need for nutrient removal, the activated sludge portion of the process can provide significant denitrification and phosphorus reduction. The MBR effluent has the added advantage of being low in turbidity, making it possible for use as feed water to reverse osmosis (RO) in industrial or indirect potable reuse systems. Because a membrane instead of a clarifier is performing the sludge separation, the MBR can be operated at higher mixed liquor suspended solids (MLSS) concentrations and longer solids retention times (SRT). The removal of the clarifier from the treatment train eliminates such problems as sludge bulking, pin floc, and various other settling problems associated with clarifier operation. The overall footprint of an MBR system is much smaller than a CAS facility. The membrane operation can be performed in one of two ways. An in-line MBR configuration pumps sludge from an activated sludge reactor to a pressure-driven membrane where the solids are retained and the water passes through the membrane. The membranes are systematically backwashed in order to remove solids build-up and are chemically cleaned when operating pressures become too high. Only one company currently markets the in-line configuration MBR, mainly for industrial applications. A submerged MBR configuration has low-pressure membranes submerged in the reactor and operates under vacuum pressure. The membrane is agitated by coarse air which assists in preventing solids build up on the membrane surface. When operating pressures become high, the submerged membranes are also systematically backwashed and are chemically cleaned. There are several companies marketing the submerged MBR configuration, which makes it the most common configuration in municipal applications. Figure 3 shows a comparison of the unit processes of a conventional treatment plant and a submerged membrane MBR plant.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop FIGURE 3 Treatment plant process comparison. INDIRECT POTABLE REUSE DEFINITIONS, WATER QUALITY REQUIREMENTS, AND TREATMENT TECHNOLOGIES Due to the seasonal nature of demands for nonpotable water reuse, it is likely that the supply of reuse water in a community can exceed the demand for turf irrigation and other nonpotable applications. Therefore, indirect potable reuse by aquifer recharge is a consideration for use of the excess supply of reuse water. Site-specific hydrogeologic evaluations and chemical modeling are needed to identify potential aquifer recharge processes and evaluate their suitability to the hydrogeology and the regulatory and stakeholder interests. The following discussions are focused on outlining those process options that could become part of a potable reuse strategy. Potable Reuse Potable reuse is subcategorized into direct potable reuse and indirect potable reuse. Direct potable reuse refers to a configuration where wastewater, treated by advanced treatment processes, is introduced directly into the potable water source for direct potable supply. Indirect potable reuse refers to a configuration where the advanced treatment waters pass through two additional stages before reaching the potable system. First, the treated waters are introduced into an environmental buffer such as a groundwater aquifer, engineered recharge gallery, surface

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop water body, or wetland. This provides additional time and treatment by naturally occurring processes. Second, the potable water pulled from the environmental buffer also receives conventional water treatment prior to introduction back into the potable water system. Indirect potable reuse offers two benefits not found in direct potable reuse: 1) additional treatment in the environmental buffer and water supply treatment system, and 2) time to react while the advanced treatment waters pass through the environmental buffer. Today, all active potable reuse projects in the United States employ indirect potable reuse. Direct potable reuse is currently being considered overseas and is typically an option of last resort, where pressures on available land and water resources do not allow for the additional safeguards offered by the environmental buffer. The following discussions focus on evaluating surface infiltration and indirect recharge processes in the context of the physical, regulatory, and stakeholder environment. Aquifer Recharge Aquifer recharge is a desirable component in the indirect potable water reuse strategy because it offers the potential for year-round storage. Further, aquifer recharge helps to maximize sustainability of a community’s groundwater resource. To the degree that a community can locally replenish the aquifer, it will limit future infrastructure costs related to a declining water table and offer reliability of water supply to its residents over the long term. Aquifer recharge benefits the groundwater supply and also helps reduce depletion of rivers and other surface water resources. It is important to recognize the public health concerns related to indirect potable reuse. The National Research Council (NRC) recently issued a report on potable reuse, entitled Issues in Potable Reuse (NRC, 1998). The report was largely supportive of indirect potable reuse, citing, as its general conclusion, “…that planned, indirect potable reuse is a viable application of reclaimed water.” This report, however, does present conflicting messages on the public health risks of potable reuse, but nevertheless, contains a technical review and provides contemporary thoughts on potable reuse by the scientific community. Water Quality Requirements of Aquifer Recharge Water quality standards for indirect potable uses have not been formally adopted by many states. Guidelines for aquifer recharge are generally expected to maintain, at a minimum, a drinking water quality standard with additional treatment burdens for multiple barriers with stringent disinfection for pathogen removal. It is also expected that the water treated for aquifer recharge will not degrade the quality of a potable aquifer. As an example of water quality requirements, guidelines recommended by the state of California for aquifer recharge using reclaimed water are summa-

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop rized in Table 1. It should be noted that very stringent treatment and monitoring requirements are expected in the permitting process and that as more indirect reuse applications are proposed, the policies, water quality standards, and regulations are likely to change. Indirect potable reuse applications are often permitted on a case-by-case basis dependent on the treatment technologies and monitoring requirements that are demonstrated to be protective of the public health. It is likely that water quality considerations will be the most stringent for direct injection, as this alternative places treated water directly into the aquifer and has the potential for the shortest residence times in the environmental buffer. As indicated in Table 1, reclaimed wastewater is also allowed to make up only a fraction of water actually recharged to the aquifer. Facility setback distances and residence time requirements are also likely considerations in the implementation of aquifer recharge, as these requirements provide reassurances that the environmental buffers provide additional treatment and mixing opportunities. Treatment Technologies for Indirect Potable Reuse Advanced water treatment beyond conventional secondary and tertiary treatment is required to remove or further reduce constituents in reclaimed water. The following constituents are targets for reductions and removal for indirect potable water uses: virus and pathogen removal nutrient (nitrogen and phosphorus) removal trace metals removal organics removal total dissolved solids removal. To consider the disposal of reclaimed water into the groundwater with the possibility of that water being withdrawn in the future for domestic use, the reclaimed water must essentially meet drinking water standards. To determine the level of treatment required, pilot testing must be performed. In addition to conventional wastewater treatment processes, units to remove organics, pesticides, dissolved metals, and ultra-high level disinfection may be required. Treatment facilities in the United States are using, or considering installing, granular activated carbon (GAC), membranes providing micro- and ultra-filtration, reverse osmosis, ozonation, and ultraviolet disinfection. Treatment trains consisting of several of the above processes are required to provide multiple barriers prior to disposal of the effluent. Figure 4 summarizes the effectiveness of advanced treatment processes and the contaminants that are removed. Figure 5 summarizes the limits and effectiveness of membrane systems to remove contaminants of concern.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop TABLE 1 Sample Criteria for Aquifer Recharge with Treated Effluent     Depth to Groundwater     Project Category/Level of Treatment Maximum Percent Reclaimed Water Perc. Rate ≤ 0.20 in/min Perc. Rate ≤ 0.33 in/min Retention Time Underground (months) Horizontal Distance (feet)a Surface Spreading   Organics removalb, oxidizedc, filteredd, & disinfectede 50d 10 20 6 500 Oxidized, filtered, & disinfected 20 10 20 6 500 Oxidized and disinfected 20 20 50 12 1,000 Direct injection Organics removal, oxidized, filtered, & disinfected 50d NAf NA 12 2,000 aHorizontal Distance measured from the injection well or closest edge of the recharge basin to the nearest point of extraction. bReclaimed water used for project categories I and IV are subject to organics removal, to achieve the following product water TOC concentrations:   Maximum TOC (mg/L) Reclaimed Water Contribution (%) Category I Category IV 0-20 20 5 21-25 16 4 26-30 12 3 31-35 10 3 36-45 8 2 46-50 6 2 cOxidized wastewater is not to exceed 20 mg/L total organic carbon, 30 mg/L total suspended solids, and 30 mg/L biochemical oxygen demand. dFiltered wastewater is not to exceed an average turbidity of 2 units and shall not exceed 5 turbidity units more than 5 percent of the time. eFor Category I, II, and IV projects, the median number of total coliform organisms in the disinfected wastewater is not to exceed 2.2 per 100 milliliters. The number of total coliform organisms is not to exceed 23 per 100 mL in more than one sample within any 30-day period. fNot applicable

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop FIGURE 4 Summary of effectiveness of advance treatment process. FIGURE 5 Summary of effectiveness and limitations of membrane process.

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop Table 2 compares conventional treatment removal mechanisms with removal mechanisms found in soil-aquifer treatment. An advanced water treatment facility (AWTF) system is also available for treating reclaimed water for aquifer injection. Reclaimed water that has been treated with microfiltration will be delivered to the treatment site via the nonpotable reclaimed water system. The primary elements of the AWTF are two-stage reverse osmosis (RO) and ozone oxidation. The RO process pressurizes the water through semipermeable membranes that reject 90 percent to 95 percent of the total dissolved solids (TDS) in the feed water. The RO membranes also provide a barrier to all microorganisms, including protozoa such as Giardia and Cryptosporidium, bacteria, and viruses. The RO membranes will also reject most of the natural organic matter (NOM) and any synthetic organic chemicals (SOCs) present in the feed water. As indicated, acid and/or a threshold inhibitor are added ahead of the RO process to lower the pH and reduce the likelihood of calcium and other ions precipitating on the membrane surfaces. Sets of cartridge filters are also included to catch any suspended material that could potentially clog the RO membrane units. The RO permeate will receive further treatment using ozone oxidation. Ozone will provide another barrier to microorganisms. Also, ozone oxidation will provide for oxidation treatment of SOCs that could potentially pass through the RO membranes. An advanced oxidation process (AOP) can be provided by adding hydrogen peroxide or through the application of ultraviolet light following ozone addition. Sodium hypochlorite added to the water ahead of the treated water storage tank will provide a small residual in the water prior to aquifer injection. Treated water is stored for approximately eight hours in the treated water tank. The system is designed to allow the treated water to be returned to TABLE 2 Comparisons for Soil-Aquifer Treatment Pollutant Conventional Treatment Removal Mechanisms Soil-Aquifer Treatment Removal Mechanism Virus/Pathogens Coagulation Flocculation Filtration Disinfection Precipitation Adsorption Filtration Nitrogen Biological nitrification/denitrification Aerobic and anaerobic biological degradation Inorganics/Metals Coagulation Filtration Tertiary sedimentation Precipitation Adsorption Filtration

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Water Conservation, Reuse, and Recycling: Proceedings of an Iranian-American Workshop the reclaimed water storage tank at the head of the AWTF if the treated water is determined not to meet the water quality requirements for aquifer injection. A pilot study is necessary to develop design criteria prior to finalizing the AWTF process design. Additional treatment processes that may be incorporated into the AWTF include softening ahead of the RO process to remove calcium and other ions that could potentially precipitate on the membranes at higher water recovery rates. Operating the RO system at a higher recovery rate will reduce the amount of brine reject produced as well as increase the amount of water available for aquifer injection. An ion exchange could potentially be incorporated if the RO process did not adequately remove specific ions. REFERENCE National Research Council, Committee to Evaluate the Viability of Augmenting Potable Water Supplies with Reclaimed Water. Issues in Potable Reuse. National Academy Press, Washington, DC: 1998.