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# Identification a nd Characterization of

Typical Drinking Water Treatment Residuals

Peer Involvement for the Drinking Water Treatment Effluent Guidelines EPA D ocket Number EPA- HQ - OW -2004 - 0035 (www.regulations.gov) September 2007

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O VERVIEW OF T HIS D OCUMENT This document is the first of three EPA documents that summarize the major technical and engineering issues related to the management of drinking water treatment residuals. EPA developed th e s e thre e documents to support the Drinking Water Treatment effluent guidelines rulemaking. 1 EPA invited a broad range of stakeholders to review these three documents to allow for early stakeholder involvement into the rulemaking process and to improve EPA’s record and analyses. The other two EPA documents included in this peer involvement process are: (1) Iden tification of Technology Options ; and (2) Evaluat ion of Potential Subcategorization Options for the Category
. This document and its p eer involvement will be placed in the Drinking Water Treatment effluent guidelines rulemaking record ( http://www.regulations.gov , Docket Number: EPA- HQ - OW - 2004 - 0035). This document identifies and discusses the characteri stics of typical waste products, known as residuals, generated at drinking water treatment plants . Section 1 describes the general classifications of water treatment plants
. Section 2 describes the general types of residuals generated at each type of water treatment pla nt
. Section 3 lists the questions EPA posed to reviewers. Section 4 lists the references used in developing this document
. EPA will use this document and other information in its record to develop regulatory options for the proposed rulemaking. Standard D isclaimer Neither the United States government nor any of its employees, contractors, subcontractors, or other employees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party’s use of, or the result s of such use of, any information, apparatus, product, or process discussed in this report, or represents that its use by such a third party would not infringe on privately owned rights. References to proprietary technologies are not intended to be an endo rsement by the Agency.

1 EPA published the 2004 Effluent Guidelines Program Plan (2 September 2004; 69 FR 53705) and identified the “drinking water treatment point source category” as a candidate for effluent guideline rulemaking. See http://www.epa.gov/guide/dw.

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1 . 0 WATER T REATMENT P LANT C LASSIFICATION Potable water systems use one or more water treatment processes to provide and maintain reliable, high - quality water to their customers. The type of water treatment process used at a given treatment plant is influenced by a number of factors , including source water quality, the contaminant ( s) to be remove d , reliability of the treatment process , flexibility to varying conditions , utility capabilities, costs, environmental compatibility, and d istribution system water quality. Water treatment plant types can generally be classified into one of the following f ive categories based on the primary treatment process used at the plant (ASCE , 1996) :

 Coagulation and Filtration ;  Precipitative Softening ;  Membrane Separation ;  Ion Exchange ; and  Adsorption. Drinking water processes may be used individually or together in a “treatment train” design. The term “treatment train” refers to treatment units in series. The basic unit processes of each primary treatment process are only described once. For example, oxidation can apply to any of the above categories but is only described under the first category, coagulatio n and f iltration. Drinking water treatment plants also contain other processes such as fluorid ation or disinfection (without filtration)
. These other processes are not discussed because they typically do not generate residuals requiring management or disposal. 1.1 Coagulation and Fi ltration Coagulation/filtration processes are traditionally refe rred to as conventional water treatment. Conventional treatment is the most widely used technology for removing turbidity and microbial contaminants from surface water supplies . These processes may also be used to remove color and taste - and odor- causing compounds. The basic unit processes may include screening, chemical pretreatment, presedimentation, aeration, oxidation, coagulation/flocculation, sedimentation/flotation, filtration, and disinfection. Other nonchemical variations include direct filtration and diatomaceous earth filtration. 2 Depending on the raw water quality and the constituents to be removed, the unit processes are combined to design a water treatment pant. The typical unit processes that may be included in a coagulation/filtration plant are di scussed below. Additionally, drinking water treatment utilities may periodically use adsorption technologies such as activated carbon to remove pesticides (e.g., atrazine) or other organic materials in the surface waters. Activated carbon is an adsor bent material that possesses vast amounts

2 Slow sand filtration , which primarily relies on biological mechanisms to achieve the required turbidity and microbial removal rates , is not being included in th e analysis of water treatment plant residuals. These types of filters are not backwashed, but rather are cleaned by periodic removal of the surface media. The spent media is generally stored on site or disposed of in a landfill. As a result, slow sand filt ration does not typically generate solid or liquid waste streams that require discharge to a surface water or wastewater treatment plant.

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of surface area on which contaminants can be extracted and reside. Intermolecular attractive forces within the small pores of the carbon are the mechanism by which the removal and retention of the contaminants are achieved. Activated carbon is available in two common forms: powdered (PAC) and granular (GAC). The adsorptive properties of PAC and GAC are fundamentally the same because they both depend on pore size and surface area to effect separation and retention of the pollutants. Although the two forms of activated carbon are similar in function, they differ in application
. PAC is usually applied early in the treatment process to reduce problems associated with taste and odors. GAC is usually applied later in the treatment process to remove dissolved organic chemicals and disinfection byproducts or their precursor materials. When PAC is applied early in the treatment process, it is mixed with the influent water before coagulation chemicals are added and travels t hrough the treatment process with removal in the sedimentation/filtration unit operations. 1.1.1 Screening and Presedimentation Screening captures large debris such as leaves, logs, plastic bottles, sticks, and fish at the intake where water is drawn in to the treatment plant. Presedimentation allows removal of settleable solids in the water by gravity prior to additional treatment. These are physical separation processes that occur at or near the drinking water intake. Drinking water utilities will typ ically use presedimentation on surface waters with high suspended solids as a means to remove a large portion of the largest suspended solids and to control organic material that can cause taste and odor problems. A typical presedimentation train includes a rapid mixing chamber, a flocculation basin, and a sedimentation basin equipped with sludge collection equipment. Treatment chemicals used in presedimentation include powdered activated carbon, alum, potassium permanganate, coagulant polymer, and chlorine
. 1.1.2 Oxidation Oxidants are used in water treatment to disinfect, control nuisance aquatic growths, mitigat e objectionable tastes and odors, remove color, remove iron and manganese, and/or oxidate organic chemicals. I n some cases, oxidants may also i mprove the performance of, or reduce the required amount of , coagulants. (AWWA, 1998 ; AWWA, 1999) Common oxidation processes include addin g chlorine, potassium permanganate, ozone, or chlorine dioxide. Ozone is sometimes used with hydrogen peroxide or ult raviolet irradiation to produce radicals that have powerful oxidative properties. These oxidants are often added at the head of the treatment plant, prior to or at the rapid mix basin, but they can also be added after clarification and/or prior to filtrati on. (AWWA, 1999) Chlorine is the most widely used oxidant in water treatment practice
. Chlorine is typically applied in one of three forms: chlorine gas, sodium hypochlorite, or calcium hypochlorite. These compounds produce hypochlorite ions that inactive pathogens. Chlorine dioxide exists as a gas a nd is highly soluble in water. Since it is explosive under pressure , it must also be generated on site. Most commercial generators use sodium chlorite as the common precursor feedstock to generate chlorine diox ide for drinking water application.

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While these disinfectants are effective in controlling many microorganisms, they react with natural organic and inorganic matter in source water and distribution systems to form DBPs. Results from toxicology studies have shown several DBPs (e.g., bromodichloromethane, bromoform, chloroform, dichloroacetic acid, and bromate) to be carcinogenic in laboratory animals. Other DBPs (e.g., chlorite, bromodichloromethane, and certain haloacetic acids) have also been shown to ca use adverse reproductive or developmental effects in laboratory animals. As a result of E PA’s Stage 1 Disinfection Byproduct Rule requires water producers to further limit DBPs in their distribution system s ( see 16 December 1998 ; 63 FR 69389 )
. In order t o control the production of DBPs operators are increasingly switching from chlorination to chloramin ation as chloramin ation exhibits less tendency to convert organic materials to DPBs. Additionally, u nlike chlorine, chloramine has a longer half life in the distribution system and still maintains effective protection against pathogens. The reason chloramines persist in the distribution is due to the relatively lower redox potential in comparison to free chlorine. Chloramine is formed by the addition of ammon ia into drinking water to form mono - , di - , and trichloramines
. Ozone exists as a gas at room temperature. Because ozone is an unstable molecule, it is generated on site at the point of application by passing a stream of air or oxygen through a high voltage electrical discharge
. Potassium permanganate is used primarily to control objectionable taste and odors, remove color, control biological growth in treatment plants, and remove iron and manganese. Although potassium permanganate has many potential use s as an oxidant, it is a poor disinfectant. In water treatment, potassium permanganate is usually added as a solution prepared from the granular solids. The solids are added to a hopper and metered into the makeup water with a screw feeder. The resulting s olution is then injected into the raw water by a metering pump
. (USEPA, 1999) 1 .1. 3 Coagulation and Flocculation Coagulation in water treatment refers to the process of destabilizing a particle suspension using a chemical coagulant and gentle agitation t o promote the formation of sett le able and/or filterable floc particles. Coagulation is performed in three separate and sequential steps: coagulant formation, particle destabilization, and inter - partic le collisions. The coagulation and flocculation process has traditionally been used to remove solids from drinking water supplies. However, the process is not restricted to the removal of particles. Coagulants render some dissolved species ( e.g., natural organic matter, inorganics, and hydrophobic synthetic org anic compounds ) insoluble , and the metal hydroxide particles produced when metal salt coagulants (typically aluminum sulfate, aluminum chloride, ferric chloride, or ferric sulfate, and polymers) are added can adsorb other dissolved species. Major component s of a basic coagulation and flocculation facility include chemical feed systems, mixing equipment, basins for rapid mix, and flocculation basins. In conventional treatment, the coagulant is dispersed evenly throughout the water. This treatment step can o ccur in flash mix basins equipped with mechanical mixers, in an influent pipe with static mixers , or in an open channel with a hydraulic jump. After the rapid mixing, a longer period of slow mixing is needed to reduce surface charges,

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promote particle coll isions , and enhance the growth of the floc. Flocculation basins are typically equipped with slow moving mechanical mixers. 1 .1. 4 Sedimentation/Flotation Sedimentation and flotation are solid - liquid separation processes used in water treatment mostly to l ower the solids concentration, or load, on filters and membranes . As a result, filters and membranes can be operated more easily and cost effectively to produce acceptable filtered water quality. In most conventional treatment plants, once the floc is for med, the water enters a quiescent basin where it is allowed to settle out. The accumulated sludge resting on the floor of the sedimentation basin is then removed for eventual disposal. Sludge can be removed continuously or intermittently through floor drai ns and scrapers or using suction equipment. In conventional water treatment, flotation has become accepted as an alternative to sedimentation. Facilities use f lotation mainly to treat nutrient - rich reservoir waters that may contain heavy algal blooms and low- turbidity, low- alkalinity, colored waters. These types of water are difficult to treat by sedimentation, because floc produced by chemical treatment has a low settling velocity. Flotation is a separation process in which gas bubbles attach to solid particles to cause the apparent density of the bubble - solid agglomerates to be less than that of the water, thereby allowing the agglomerate to float to the surface. Flotation is used to remove low- density solids from source water. Dissolved air flotation (D AF) is the most commonly used flotation method for drinking water. In DAF, bubbles are produced by the reduction in pressure of a water stream saturated with air. In this process, the whole influent flows either through the flocculation tank or directly to the flotation tank if separate flocculation is not required. Part of the clarified effluent is recycled, pressurized , and saturated with air. The pressurized recycle d water is introduced to the flotation tank through a pressure - release device. As the pres sure is reduced to atmospheric pressure, air is released in the form of fine bubbles. The air bubbles attach themselves to the flocs, and the aggregates float to the surface. The float ing material is removed from the surface, and the clarified water is taken from the bottom of the tanks. Float or sludge can be removed either continuously or intermittently by flooding or mechanical scraping. 1 .1. 5 Filtration Any particles remaining after sedimentation or flotation are removed from the water through the fi ltration process. Filters for suspended particle removal can be made of graded sand, granular synthetic material, diatomaceous earth, mixed media (layers of various sizes of gravel, high - density garnet, sand , and anthracite coal), screens of various materi als, and fabrics. The most widely used filters are gravity filters consisting of two or three different granular media in rectangular tanks. When the water passes through the filter, solid particles are removed by adhering to the media. At a point in the operation, the pores in the filter media become clogged with particles causing increased headloss and deteriorated effluent quality. To restore filter performance, the media has to be backwashed. Backwashing entails reversing the flow through the filter at a rate sufficiently high to fluidize the bed until the backwash effluent

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has become reasonably clear (turbidity < 10 NTU) (AWWA, 1999)
. The filter backwash residual will contain any solids collected by the filters. Additionally, finished water is used for the filter backwash process so this residual will contain chlorinated compounds. Pressure filters operate in the same manner as gravity filters. However, instead of an open tank, the media is contained in a cylindrical steel vessel that can be pressurize d. Pressure filters are widely used in small conventional plants or in membrane applications. 1.1.6 Filter- to -Waste This residual is also generated at the filters and is generated immediately after the filter backwash process. Operators will typically ‘r ipen’ their filters immediately after backwashing and will waste the filtered water for 15 minutes to one hour (ASCE, 1996). Typically this is residual is clear but will often contain chlorine compounds as chlorinate will almost always precede filtration. This residual is most often equalized and recycled to the head of the plant (ASCE, 1996). 1.2 Precipitative Softening The p recipitative s oftening treatment process uses some of the same processes as coagulation and f iltration process such as s creening an d p resedimentation , activated carbon, oxidation, sedimentation, filtration , and filter- to - waste . The key difference between the two treatment processes is that in addition to providing safe drinking water the p recipitative s oftening treatment reduces the n atural hardness in the surface waters. This section describes the p recipitative softening process. Precipitative softening u se s chemical precipitation with slaked lime (calcium hydroxide) and other chemicals to reduce the water’s hardness and, in some cas es, to enhance clarification before filtration. Lime is the most commonly used chemical in precipitative softening and is sometimes used with soda ash. To a lesser extent, sodium hydroxide is used in place of lime. (AWWA, 19 99 ) Hardness is usually caused by calcium and magnesium compounds in water. Lime softening removes this hardness by creating a shift in the carbonate equilibrium. Adding lime to water raises the pH. As the pH increases, b icarbonate is converted to carbonate and calcium is precipitated a s calcium carbonate. Soda ash (sodium carbonate) is added if insufficient bicarbonate is present in the water. Softening for calcium removal typically takes place at a pH range of 9 to 9.5. To remove magnesium, excess lime is added beyond the point of calc ium carbonate precipitation. Magnesium hydroxide precipitates at pH levels greater than 10.5. The recarbonation with carbon dioxide is generally used to neutralize the pH if it exceeds 9.5. The lime softening process generally consists of pretreatment (w here required); single stage, two - stage , or split - treatment softening; and filtration, supplemented by disinfection. Softening can be combined with iron and manganese removal, coagulation for turbidity removal, or both. The conventional softening basins ar e similar to conventional basins used for coagulation and clarification , in which rapid mixing, flocculation, and sedimentation occur . Lime, soda ash, coagulant, and a polymer coagulant aid (if required) are added at the rapid mix basin and mixed using mec hanical mixers, with a detention time of approximately 30 seconds. Flocculation and

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sedimentation follow as unit processes that are similar to the conventional coagulation/filtration process. Alternatively, upflow solids blanket clarifiers may be used in p lace of conventional sedimentation basins. Depending on the source water type an d concentration of contaminants, facilities use both precipitation and coprecipitation with calcium carbonates and magnesium hydroxides to remove both hardness and nonhardness contaminants. The four types of coprecipitation are:

 Inclusion
. A portion of the solution surrounding the growing particle is mechanically trapped
.
 Adsorption
. A n impurity in attached onto the surface of a particle of precipitate.

 Occlusion
. A contamin ant is trapped i n the interior of a particle of precipitate.

 Solid -solution formation . A particle of precipitate becomes contaminated with a different type of particle that precipitates under similar conditions. 1.3 Membrane Separation Membrane processe s can be classified according to driving force, membrane type, configuration, and removal capabilities. Membrane processes in the drinking water industry are classified as desalting membranes or low- pressure membranes. Desalting membranes are used to remove dissolved contaminants, both inorganic and organic. Low- pressure membranes are designed for particle removal. Desalting includes the high - pressure - driven processes of reverse osmosis (RO ) and nanofiltration (NF) and the electrically- driven processes of e lectrodialysis (ED) and electrodialysis reversal (EDR). The low- pressure membranes include ultrafiltration (UF) and microfiltration (MF)
. High pressure and low- pressure membranes use semipermeable membranes to remove contaminants from feed water. Pressure is the driving force for these membranes. Increased pressure on the feed side of the membrane transports some of the water from the feed side, through the membrane, to the permeate side. The membrane may reject other constituents depend ing on the propertie s of the particular membrane used and the operating conditions. Water and other constituents not permeating the membrane flow out of the membrane system as the concentrate stream. ED and EDR use an electrical potential to force dissolved ions through ion - exchange membranes. Membrane fouling and scaling are the biggest problem s in the membrane industry and cause an increased permeate rejection rate and increased operating costs. To minimize fouling and scaling , low- pressure membrane system s are designed to include an online backwash system and isolated chemical cleaning
. Desalting membrane processes require the feed water to be pretreated to minimize scaling and fouling as feed water flows across the membrane surface
. The desalting membranes produce concentrate on a continuous basis and chemicals are added to inhibit scale formation. These membranes are typically chemically cleaned every 3 to 12 months
. 1 .3. 1 Low- Pressure Membrane s

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Microfiltration (MF) and ultrafiltration (UF) are low- pressure membrane filt ration processes that have gained considerable acceptance in the drinking water industry over the past 10 years. MF and UF are primarily used for particle removal as a stand - alone treatment, or as a retrofit of existing conventional treatment plants (as a replacement for conventional particle removal processes). MF and UF have been demonstrated to remove protozoa cysts to below detection levels and meet the turbidity requirements of current and future surface water treatment regulations. For low- pressure membranes , residuals include backwash, concentrate (for cross -flow and immersed systems), and chemical cleaning wastes ( clean in place ( CIP ) and chemically- enhanced backwash ( CEBW) )
. Membrane backwashing uses air, water, or a combination of both. A typica l range of backwash frequencies for MF/UF systems is between 15 and 60 minutes, and the backwash duration ranges from 30 seconds to 3 minutes. Most systems experience a gradual increase in post - backwash transmembrane pressure (TMP) that must be addressed by chemical cleaning. Chemical cleaning is used to restore the post - backwash TMP to its initial level ( i.e., the TMP of a new, clean membrane ) . In the chemical cleaning process, acid, caustic, chlorine and/or surfactants are circulated through the membran e system to dissolve or dislodge contaminants that have not been removed by backwashing. Most systems are chemically cleaned once every 1 to 6 months, depending on system design and operation . Irreversible fouling is known to occur in all membrane systems, requir ing the membranes to be replaced. 1 .3. 2 Desalting Membrane s Desalting membrane processes include two classes, pressure driven and electrical driven. The former includes NF and RO, which utilize semi - permeable membranes designed to separate dissolved substances from water using a pressure differential. The electrically- driven processes include ED and its variant, EDR. ED/EDR membranes are ion exchange membranes using an electrical potential to separate impurities from water. For desalting membranes , residuals include concentrate ( produced on a continuous basis during normal operation ) and spent cleaning solutions ( produced periodically from off - line chemical cleaning of the membrane train through a CIP process )
. (AWWA, 2004) 1.3. 2 .1 Nanofiltration a nd Reverse Osmosis NF and RO are desalting membranes used in applications that require remov ing dissolved contaminants, as in the case of softening or desalination. NF/RO membranes are designed to remove dissolved solids through reverse osmosis. RO memb ranes are typically used for seawater or brackish water applications. Most ions are completely rejected (rejections greater than 99 percent). The NF process softens water by removing calcium and magnesium ions. This process has removed monovalent ions by 5 0 to 70 percent and multivalent ions (hardness) by 90 percent. It is also effective in removing other dissolved organics, biological contaminants, and suspended solids that are not removed in pretreatment steps ; however, pretreatment is used to remove biol ogical material and particulates.

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A high quality of feed water with reduced turbidity and total suspended solids (TSS) is required to prevent plugging of the flow spacers in the membrane elements. Generally, turbidity levels higher than 0. 3 NTU or silt de nsity index levels higher than 3 units can cause physical damage to the membrane elements by plugging the flow path. In addition, membrane fouling and scaling will increase the required pressure to maintain a constant water production. Chemical scaling occ urs when the concentration of scale forming compounds reaches the solubility limit and begins to precipitate. 1.3.2.2 Electrically- Driven Processes The ED/EDR process is designed for desalting brackish water supplies and is not applicable to the removal of non - charged solutes, such as silica, or particles and pathogens. It is inefficient at removing dissolved organics, which are weakly charged. (AWWA 2004) ED and EDR use an electrical potential to force dissolved ions through ion - exchange membranes that are virtually impermeable to water. The water is purified by the movement of contaminants, not water, across the membrane. The ED process places alternating pairs of cation (+) and anion ( - ) membranes between positively and negatively charged electrodes. W hen a voltage is applied, a current causes cations to move in the direction of the negatively charged electrode (cathode). The cations move through the cation membrane but are restrained by the anion membrane. The anions move in the direction of the positi vely charged electrode (anode) through the anion membrane, but are restrained by the cation membrane. Water flows in all channels; flow from channels where contaminants are removed becomes the desalted product stream. Flow from channels to which salts are transferred becomes the concentrate. Feed pressures for ED/EDR are typically between 50 and 70 psi to overcome head losses in the ED/EDR membrane modules or “stacks.” (AWWA 2004) With ED, the direction of electrical charge is always the same. With EDR, the direction of charge is reversed several times hourly by reversing the electrical polarity, which changes the direction of ion movement through the membranes and "electrically flushes" fouling ions from the membrane surfaces to control the buildup of scale , improve recovery, and reduce the need for scale - inhibiting chemicals. (AWWA 2004) 1.3. 2 .3 Forward Osmosis Forward osmosis (FO) is a method of desalination in development for drinking water applications
. Osmosis is the natural tendency for water to flow from areas of lower concentration to higher concentration. FO uses this tendency to desalinate seawater. A FO unit uses a “draw solution” with dissolved molecules at higher concentration than sea water. The draw solution is separated from the feed water b y a semi - permeable membrane. The greater concentration of the draw solution to the feed water will caus e water to cross the membrane into the draw solution. The dissolved molecules in the draw solution are removed, typically though evaporation. Forward o smosis is hypothesized to be less energy intensive than reverse osmosis. RO requires high pressure on the feed side of the membrane, which can be energy intensive. FO does not require pressure to force water through the membrane, but does require heat to evaporate the dissolved molecules from the draw solutio n. This treatment

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may also be applicable to further concentrating the brine generated from other membrane technologies and the ion exchange technology. 1.4 Ion Exchange Ion exchange (IX) is a physical - chemica l process by which objectionable ionic contaminants are removed from the water. In this process, an ion on the solid phase is exchanged for an ion in the feed water. This solid phase is typically a synthetic resin that has been chosen to preferenti ally adsorb the particular contaminant of concern. To accomplish this exchange of ions, feed water is continuously passed through a bed of ion exchange resin beads in a down -flow or up -flow mode until the resin is exhausted (i.e., when all sites on the res in be ads have been filled by contaminant ions ) . At this point, the bed is regenerated by rinsing the IX column with regenerant brine - a concentrated solution of ions initially exchanged from the resin. Most useful IX reactions are reversible. The number of bed volumes that can be treated before exhaustion varies with resin type and influent water quality. Typically 300 to 60,000 bed volumes can be treated before regeneration is required. (USEPA, 2000) IX can remove a number of contaminant cations (e.g., ha rdness, barium, strontium, and radium ) and anions (e.g., fluoride, nitrate, DOC, fulvates, humates, arsenate, selenate, chromate, perchlorate, and anionic complexes of uranium ) from water. Residuals include backwash and regeneration waste. 1.5 Adsorptio n Technologies There are numerous solid adsorptive media that are increasingly used for radionuclide removal. Some media are capable of being regenerated, which would make a regenerate waste stream in the same fashion as ion exchange. However, these media are often regenerated offsite , or disposed as solid waste
. Carbon has been used as an adsorbent for centuries. Activated carbon removes contaminants from water by adsorption . Adsorption is a natu ral process by which molecules of a dissolved compound adhe re to the surface of an adsorbent solid. Adsorption occurs when the attracti ve forces at the car bon surface overcome the attractive forces of the liquid. There are two different forms of activated carbon used in the water industry: powdered activated carbo n (PAC) and granular activated carbon (GAC). PAC is widely used in conventional treatment of surface waters to adsorb taste - and odor- causing substances. On a limited basis, PAC is also used to remove seasonally occurring pesticides such as atrazine. In m ost designs, PAC is fed from a silo into a screw feeder to prepare a slurry that is metered into the raw water. Therefore, use of PAC would not typically be considered as a stand - alone process. GAC is a particularly good adsorbent medium due to its high s urface - area- to -volume ratio. One gram of a typical commercial activated carbon has a surface area equivalent to 1,000 square meters. This high surface area permits a large number of contaminant molecules to accumulate . It is generally used in beds or tanks through which the water passes for treatment. As a contaminated water stream passes through the activated carbon bed and exits , the effluent begins to slow contamination . This condition is classified as “breakthrough” and the amount of material adsorbed i s considered the

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breakthrough capacity. If the GAC is used in a polishing application to remove undesirable organic chemicals, the carbon would not have a waste discharge stream, but would require periodic replacement or rejuvenation as breakthrough of the carbon occurred. If the GAC application is used in conjunction with particulate removal, a backwash stream will result and have similar TSS properties to the conventional treatment multimedia filters discussed earlier. 1. 6 Miscellaneous Drinking Water Pl ant Wastewasters In a previous discussion with the National Association of Clean Water Agencies (NACWA) , it was noted that other miscellaneous wastes that could be discharged are discharged from some drinking water treatment facilities. These discharges i nclude:

 Copper Sulfate, Cu(SO 4), residual discharges. This chemical is used by DWT facilities for control of algae in drinking water reservoirs and pre sedimentation lagoons at the DWT facility.  Laboratory wastewaters.  Re - generation wastewaters for boiler make - up waters  Boiler blow- down wastewaters.  Chlorine analyzer and flow- through sampler wastewaters  Equipment washdown wastewaters which can be as much as 10,000 gallons per day.  Contact and non - contact cooling wastewaters. EPA is gathering additional in formation about the characterization, management, treatment, and disposal options for these residuals. 2. 0 WATER T REATMENT R ESIDUAL C HARACTERISTICS As the water passes through different treatment processes, it is subjected to mixing, chemical interaction , aggregation, and phase transformation to remove the contaminants of concern. The contaminants removed f rom the water are called resid ual wastes and vary in type, size, and characteristics. They range from large suspended particulates such as leaves, debr is, and other material that can be removed by screens in the intake to dissolved gases such as volatile organic compounds and sulfides that can be removed by aeration processes. Regardless of the raw water source and quality and the processes used, water t reatment plants can produce three types of residuals:

 Solids, including spen t media, spent membranes, and dewatered residuals ;

 Liquids, i ncluding brines, concentrates, backwash water, rinse water, and filter to - waste water; and

 Sludges, including coagu lant/polymetric, chemical softening, and oxidized i ron/manganese sludges
. As indicated in Section 1 , the quality and characteristics of the waste streams generated by a water treatment plant are related to the treatment processes in use
.

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Screening and p resedimentation, coagulation, filter backwashing , filter-to -waste, l ime softening, iron and manganese removal, spent materials (spent IX resins, GAC, and filter media), and slow sand and diatomaceous earth filtration all generate residuals. This paper foc use s on liquid and sludge residuals that may be discharged to surface waters or POTWs. Some limited studies have been conducted to analyze water treatment residuals , and the results , though helpful in identifying possible pollutants of concern , confirm t hat the concentrations of the pollutants in the residuals vary significantly from plant to plant. For example, EPA’s study of eight water treatment plants published in 1992, Inorganic Chemical Characterization of Water Treatment Plant Residuals , detected m any inorganic contaminants (e.g., aluminum, arsenic, barium, chromium, copper, iron, magnesium, nickel) at concentrations that varied up to an order of magnitude from one plant to another . (US EPA, 1992) [XXX - ERG to reference section the more recent AWWA report.] The remainder of this section discusses the typical characteristics and generation rates of sludges and liquid residuals generated by the five treatment processes described in Section 1 with only limited information on pollutant concentrations
. 2 .1 Solid and Sludge Residuals The three most common types of sludges are coagulant/polymeric, chemical softening, and oxidized ion/manganese 

##   A SS Fe Al CO MgNCH CaNCH MgCH CaCH Q S          9 . 2 44 . 0 2 6 . 1 6 . 2 0 . 2 34 . 8 Where: S = sludge production (lb/day) Ca = calcium hardness removed as CaCO 3 (mg/L) M g = magnesium hardness removed as CaCO 3 (mg/L) Fe = iron dose as Fe (mg/L) Al = dry alum dose (mg/L) (as 17.1 percent Al 2 O 3) Q = plant flow (mgd) SS = raw water suspended solids (mg/L) A = other additives (mg/L) Ca NCH = calcium hardness removal as CaCO 3 ( mg/L) Mg NCH = noncarbonated magnesium hardness removed as CaCO 2 (mg/L) CO 2 = carbon dioxide removed by lime addition, as CaCO 3 Note s :  PACl (polyaluminum chloride dose (mg/L)) can be used in the equation as 0.27 PACl, varying by manufacturer
.  EPA may ne ed to correlate turbidity measurements to suspended solids
. The above equation presents the mass of residuals produced. The percentage (mass) of these residuals that are due to the addition of treatment chemicals are estimated as XXX (insert table or rang e). Additionally, the following table provides and estimate of the trace

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impurities in the treatment chemicals (use AWWA report to provide table or range
– this should be mostly be done from the PR BPJ report ). The volume and solids concentration of the s ludge leaving a presedimentation, sedimentation basin , or clarifier is also a function of the sludge removal method. S ludge can be removed using either a periodic cleaning method or a continuous removal method. Periodical sludge removal systems accumulate a compact and thicken ed stratification of solids. The volume of sludge produced depends on the amount of water used to remove the solids. In a continuous sludge collection system, the solid concentration s are generally as shown below:

 Circular or chain a nd flight - 1.5 to 2.5 percent  Suction type
– 1.5 to 2.0 percent  Blanket type clarifiers
– 0.5 to 1.0 percent  Sand Ballasted type
– 0.1 to 0.5 percent  DAF (mechanical)
– 3 to 4 percent  DAF (hydraulic)
– 0.1 to 0.5 percent Specific characteristics of sludg es and solids generated by coagulation/filtration, precipitative softening, membrane separation, and ion exchange unit processes are presented below. 2.1.1 Coagulation and Filtration Solid and Sludge Residuals The type s and amount s of coagulant used in a water treatment facility have a significant effect on the type and amount of residual waste produced by the plant. An example is enhanced coagulation where the use of higher coagulant dosages may produce a residual that is much more difficult to dewater ( Cornwell D.A., 1999). The amount of residual (weight and volume) impacts the cost of treatment and the overall environmental significance of the plant. In most conventional water treatment facilities, coagulation generates the bulk of residual waste materi al. The sludge produced by the coagulation processes predominately contain the coagulant metal hydroxides along with raw water natural organic matter, suspended solids, microorganisms, radion u c l ides , and other raw water organic and inorganic constituents
. The metals found in coagulant sludges include aluminum, arsenic, and occasionally cadmium, chromium, copper, iron, lead, manganese, nickel, and zinc (Cornwell D.A., 1999). If the source water has a high concentration of total suspended solids (TSS), the alum/iron coagulant sludges will contain a high percentage of gelatinous, hydroxide precipitates (e.g., Al(OH) 3 , Fe(OH) 3) and will likely exhibit the characteristics in Table 2 - 1. (ASCE , 1996)

Table 2 - 1. Typical Alum/Iron Coagulant Sludge Characteristics Sludge Characteristics Percent Solids Content

Liquid 0
– 5 Spongy, semi - solid 8
– 12 Soft clay 18
– 25

### 15 Stiff clay 4 0
– 50 It has been observed that alum and iron coagulants tend to produce 0.1 to 1.0 percent solids from conventional sedimentation ba sins when treating waters of low to moderate raw water turbidity. S ludge blanket clarifiers can produce over 2 percent solids from the same water. Flotation can produce 2 to 5 percent solid s at the top of a unit. Generally, alum sludge generation quantiti es range from 0.001 to 0.37 percent of the treated water flow rate with an average of 0.11 percent
. Table 2 - 2 presents typical chemical coagulant sludge volumes by water treatment plant flow . Backwash uses approximately 0.5 to 5 percent of the plant intake
. (US EPA, 1993) Additionally, filter- to waste typically uses an equal amount of the plant intake.

### 16 Table 2 -2 . Typical Chemical Coagulation Sludge Volumes Water Treatment Plant Flow

(mgd) Typical Sludge Volume Range (gal/day) Average Sludge Volume (gal/ day) 0.7 7 – 2,600 770 1.8 18
– 6,700 2,000 4.8 48
– 17,800 5,300 11 110
– 40,900 12,100 18 180
– 66,800 19,800 26 260
– 96,600 28,600 51 510
– 189,400 56,200 210 2,100
– 779,900 231,300 430 4,300
– 1,596,900 473,500 2.1.2 Precipitative Softenin g Wastes T he sludge produced by softening processes contains predominately calcium carbonate and magnesium hydroxide, other divalent ions , raw water natural organic matter, inorganics, suspended solids, microorganisms, and radionuclides . Metals found in t he precipitate sludges include calcium, magnesium, arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver. Calcium carbonate sludges are generally dense, stable, and inert materials that dewater easily to a solid content up to 50 to 60 per cent. The sludge pH is normally greater than 10.5. However, if the hardness is due to magnesium, the hydroxide sludge is more difficult to handle and dewater (Cornwell D.A., 1999). If the water softening is performed by pellet reactor, a sludge pelletizati on occurs. This precipitated hardness is withdrawn as a sand - like granular material. (AWWA, 1998). In precipitative softening the sludge concentration is a function of the calcium carbonate (CaCO 3) to magnesium hydroxide (Mg(OH) 2 ) ratio and the type of cl arifier. Conventional sedimentation basins may only produce solid concentrations of 2 to 4 percent , w hereas, sludge blanket clarifiers can p roduce solids concentrations up to 30 percent. Table 2 - 3 lists the solids content of typical chemical softening slud ge. (ASCE , 1996)

Table 2 -3 . Typical Chemical Softening Sludge Characteristics Sludge Characteristics Percent Solids Content

Liquid 0
– 10 Viscous Liquid 25
– 35 Semi - Solid 40
– 50 Crumbly Cake 60
– 70 Generally, the volume of sludge generated from lime softening plants ranges from 2,800 to 6,600,000 gallons per day depending on the water treatment plant capacity. The typical lime sludge volumes by treated water design flow are summarized in Table 2 - 4

### 17 Table 2 -4 . Typical Lime Softening Sludge Volume s Water Treatment Plant Flow

(mgd) Typical Sludge Volume Range (gal/day) Average Sludge Volume (gal/day) 0.7 2,800
– 10,700 8,500 1.8 7,200
– 27,400 21,900 4.8 19,300
– 73,100 58,300 11 44,200
– 167,500 133,600 18 72,300
– 274,100 218,600 26 104,400
– 395,900 315,800 51 204,800
– 776,600 619,400 210 843,400
– 3,198,000 2,550,600 430 1,726,900
– 6,548,200 5,222,700 2.1.3 Low- Pressure Membrane Separation Wastes The solids generated by low- pressure ( MF/UF ) membranes is from the concentrate (for cross -flow and immerse systems) , backwashing, and spent chemical cleaning. Normally, residuals in the concentrate and backwash system s contain raw water suspended solids , metal hydroxides , and PAC if coagulation/precipitation and PAC are used as part of the pretreatment process or if coagulant and PAC are used with the membrane process. The solids from low- pressure membranes are similar to solids in spent backwash water from conventional filters 2.1.4 Desalting Membrane Separation Wastes The concentration of solids from high - pressure membranes (NF/RO) is typically low, less than 10 mg/L of TSS in the concentrate
. For ED/EDR , ionized contaminants in the feed water are removed and exit the system through the concentrate stream, similar to NF/RO. 2.1. 5 Ion E xchange and Adsorption Wastes The residuals formed in IX and adsorption system s include backwash water and spent regenerant chemical and media . The challenge with IX and adsorption treatments is the handling and disposal of spent regenerants and media
. Th e spent media residual s are mainly solid waste media and the contaminant s absorbed to it. GAC treatment is mainly for the removal of taste - and odor- causing organic compounds along with organic compounds like disinfection by - product precursor material. As a polishing step, activated carbon can be used to remove disinfection by - products generated in the production of drinking water. As a result , the spent carbon is mainly exhausted with organic compounds; however, some inorganics are strongly adsorbed on t he carbon surface like antimony, arsenic, bismuth, chromium, tin, silver, mercury, cobalt, zirconium, chlorine bromine iodine, and fluoride. 2 .2 L iquid Phase Waste Liquid waste is generated from filter backwashing, filter-to - waste, ion exchange regeneration, membrane reject water, chemical cleaning, and GAC transport water. The waste characteristics are highly depend ent on the nature of the source water and the

### 18

treatment processes incorporated. If the liquid waste contains a high total dissolved solid (T DS) content, it is often referred to as brine waste. This would apply to ion exchange proces ses and membrane processes used to remove salt from seawater or brackish groundwater. Low-TDS wastes are referred to as concentrate. 2.2.1 Filter Wastes Waste gen erated from filters includes filter backwash water and filter- to - waste from rapid filters and pre - coat filters, and dirty sand from scraping of slow sand filters. The filter backwash and filter- to - waste are liquid residual waste stream s that contain partic ulates including clay and silt particles, microorganisms (bacteria, viruses, and protozoan cysts), colloidal and precipitated humic substances , and other natural organic particulates from the decay of vegetation; and precipitates of aluminum or iron used i n coagulation (Cornwell D.A., 1999). Additionally, these liquid filter wastes will contain chlorinated compounds as they are g enerated from chlorinated water, which typically contains a chlorine concentration of XXX mg/L in the water treatment plant. When precoat filters and slow sand filtration are used the spent filter media becomes a solid waste. The filter backwash and filter- to - waste operations generate large volumes of water with relatively low concentration s of solids. Filter backwash and filter-to - waste operations each use approximately 1 to 5 percent of the drinking water intake. Normally, filter backwash contains 50 to 400 mg/L of suspended solids. In some cases 15 to 20 percent of the backwash water solids are spent filter media. In general, larg e treatment plants generate a lower percentage of filter backwash than small treatment plants because they tend to operate more efficiently (US EPA, 1993). 2.2. 2 Low- Pressure Membrane Liquid Wastes The primary residuals of MF/UF systems result from the wastes generated during backwashing and chemical cleaning (either CIP or CEBW). Cross -flow filtration systems additionally generate concentrate wastes, which can be considered similar in nature to the backwash wastes. All MF/UF systems produce residuals on an intermittent basis, with two exceptions: one type of submerged system that operates in a feed - and - bleed mode, where backwash water is discharged into the membrane tank (containing feed water) and waste (concentrate) is continuously drawn from the tank; and cross -flow systems that use a continuous discharge of concentrate. However, it should be recognized that when multiple MF/UF trains are assembled to produce larger permeate flowrates (>10 mgd or 38 ML/day), backwash flowrates from the plant essentiall y become continuous. (AWWA, 2003) Backwash and Concentrate Wastes MF and UF essentially remove a large size range of particles from water, including turbidity, inorganic and organic colloids, and pathogens (protozoan cysts and bacteria). UF, because of its smaller pore size, also removes virus es and some organic fractions. S olids accumulate on the surface of the membrane or in the cross -flow concentrate circulating through the membrane units. The solids are removed by frequent backwashing or flushing, wi th or without air scour, or by bleeding - off a portion of the concentrate flow to maintain an acceptable solids level on the feed side of the membrane (as in cross -flow and certain immersed membrane systems). (AWWA, 2003)

### 19

Residuals produced from backwashin g of low- pressure membranes will consist of filtrate together with naturally occurring feedwater solids retained by the membrane. As such, backwash residuals in general are not expected to have a significant environmental impact. Where chemicals , such as a coagulant, oxidant, or adsorbent , are dosed to the source water prior to membrane treatment for the purposes of removing dissolved contaminants, membrane backwash water will be enriched in both the pretreatment chemical and dissolved matter, both of which can make disposal of the backwash more challenging. Likewise, when chemicals are dosed to filtrate during backwashing ( known as chemically enhanced backwash) to improve foulant removal, increased care must be given to backwash disposal. (AWWA, 2003) Spec ific characteristics of low- pressure backwash and concentrate residuals depend upon the quality of the water being treated, and the recovery of the membrane system. Net recoveries typically range from 85 to 98 percent, which results in concentrating the fe edwater solids by a factor ranging from 7 to 50 times the feedwater concentration. Logically, as contaminant concentrations and recovery increase, the contaminant concentrations in the residuals increase. With high recoveries and high feedwater contaminant levels, MF/UF residuals can have very high concentrations of suspended solids and turbidity. If chemicals are used during backwash (CEBW), backwash wastes will resemble CIP wastes. Table 2 - 5 summarizes the characteristics of some typical backwash waste so lutions. (AWWA, 2003)

Table 2 -5 . Typical Characteristics of Low - Pressure Membrane Backwash Residuals* (AWWA, 2003) Frequency of application Every 10- 60 minutes Volume of waste produced 2- 15% of plant feed flowrate for recoveries of 85- 98% (Daily CEBW wastes might be 0.2 to 0.4% of plant feed flowrate) Algae, precipitated solids, possible chemical residues if using CEBW TOC of 1 to 2 times the feedwater concentration (if no coagulant or absorbent is used) If coag ulant is used, the TOC could be 5 times the feed concentration For recoveries of 85 to 98%, wastes will have a concentration factor of 7 to 50 times the feedwater: TSS of 7 to 1,250 mg/L for feedwater of 1 to 25 mg/L, and Giardia and Cryptosporidium of 7 to 1,250 count per 100 liters for feedwater of 1 to 25 count per 100 liters Characteristics of backwash residuals

If using CEBW (with chlorine, acid or base): pH may be <6 or >9, and Chlorine residual may be up to 1,000 mg/L as Cl 2 *Backwash characteristics will vary with feed flowrate (fl ux) and recovery / backwash frequency. The volume of backwash flowrates is typically 2 to 15 percent of the plant flowrate for systems operating at 85 to 98 percent recovery. Typically, these flows will represent 95 to 99 percent of the total volume of re sidual wastes from MF/UF treatment processes. The remaining 1 to 5 percent of membrane residual wastes comes from chemical cleaning procedures. If coagulants, PAC , or other pretreatment chemicals (e.g., potassium permanganate) are applied, the characteristics of the MF/UF residuals become more similar to the residuals from a conventional water treatment plant (WTP). (AWWA, 2003)

### 20

Chemical Cleaning Wastes The second type of membrane residual is generated from the chemical cleaning processes used to contro l fouling (CEBW and CIP). Cleaning solution residuals reflect the chemicals used in the cleaning process. Only a portion of the active chemical ingredient is consumed during the cleaning process, so the resulting chemical cleaning waste includes some remai ning active chemical ingredient, as well as salts from chemical reactions between the chemicals and foulants, “dissolved” organic materials, and suspended solids. While some plants refresh the active ingredient in spent cleaning solutions and reuse it to m inimize waste quantities, this practice can result in more concentrated CIP waste solutions. Table 2 - 6 summarizes the characteristics of some typical chemical cleaning waste solutions. (AWWA, 2003)

Table 2 - 6 . Typical Characteristics of Low - Pressure Membra ne Chemical Cleaning Solutions and Wastes (AWWA, 2003) Frequency of application Daily to once every 3 or 4 months Volume of waste produced Monthly CIP wastes normally < 0.05% of plant feed flowrate (Daily CEBW wastes might be 0.2- 0.4% of plant feed flowrate) Sodium hypochlorite
– 500 to 1,000 mg/L as Cl 2 Citric or hydrochloric acid
– pH 1 to 2 Caustic soda
– pH 12 to 13 Chemicals commonly used Surfactant
– 0.1% by weight pH from 2 to 14 Chlorine residu al up to 1,000 mg/L as Cl 2 Low concentrations of surfactants TSS up to 500 mg/L (neutralization may precipitate additional solids) TOC 10 to 30 times the feedwater concentration Characteristics of spent cleaning solution BOD5 up to 5,000 or 10,000 mg/L (if citric acid is used) Chlorine re siduals in CEBW and CIP wastes may range from 1 to 1,000 mg/L as Cl 2 , and pH may be acidic (pH<6) or basic (pH>9) depending on the chemicals used. Surfactants may also be used at low concentrations, and may cause foaming when the spent cleaning solution is discharged, depending upon the type of surfactant. While mixing the acid and caustic waste solutions will minimize the need for additional neutralization chemicals, it may also precipitate additional solids, such as calcium carbonate and iron compounds, w hich increases the suspended solids concentration of the waste solution. If citric acid is used in the CIP, the biochemical oxygen demand ( BOD 5) of the spent cleaning solution is likely to be very high as well. (AWWA, 2003) Chemical cleaning residuals have a different composition and typically a smaller volume compared to the concentrate and backwash residuals generated during water production. Since chemical cleaning is performed less frequently than backwashing (from once a day to once every 3 or 4 month s), the yearly residual volume is much smaller than the volume generated as concentrate or backwash. The volume of cleaning solution used and the amount of waste solution generated as residuals are functions of the following factors: (AWWA, 2003)

 Source water characteristics (type and level of foulants present);  M embrane process and module/system characteristics ;  Size/capacity of membrane train ;

### 21

 Cleaning system design (piping diameter and lengths) ; and  Frequency of cleaning (CIP)
. The volume of chemical c leaning waste generated from CEBW is typically very low, especially if CEBW is performed intermittently and at low chemical concentrations that do not require segregation of CEBW wastes from regular backwash wastes. In other instances where stronger chemical concentrations are used, a daily CEBW typically will be less than 0.2 to 0.4 percent of the plant flowrate, and may be reduced further if the solutions are reused. Recently, there has been a trend among low - pressure membrane suppliers to move away from using low concentrations of chlorine in the regular backwash (<5 ppm) to control biofilm formation. Instead, many manufacturers are switching to less frequent use of higher concentrations of chlorine (100 to 500 ppm) and acid (pH of 1 to 2) for more effect ive organic and precipitated metals removal. With this trend comes the generation of wastes more similar to CIP wastes in chemical strength, making their reuse more difficult and the need for neutralization prior to discharge more likely. Specific CEBW sol ution volumes are relatively small for pressurized systems but can be significant for immersed systems because of the need to fill up the entire tank in which the membranes are housed. (AWWA, 2003) Monthly CIP wastes normally will be less than 0.05 percen t of plant flow. While specific cleaning solution volumes will vary depending upon the system geometry and the type of solution, typically they will be two to three times the volume normally present in the membranes and piping for each cleaning solution (o ne volume for the actual cleaning solution and one or two additional volumes to rinse the solution from the system) or for immersed systems equal to the working volume of the membrane process tank. Rinse waters have low levels of contamination and may be h andled differently than the cleaning solution, such as by recycling to the feedwater, combining with the backwash wastes for recycling or disposal, or using the rinse water for making up the next batch of cleaning solution. Annual volumes of spent CIP solu tions can be calculated by multiplying the volume for each cleaning by the number of annual cleanings. This small volume of wastewater reduces the subsequent handling and disposal impacts, as it represents a volume that is easier to collect, store, neutral ize, and transport (if necessary). (AWWA, 2003) 2.2. 3 Desalting Membrane Liquid Wastes Desalting membrane processes generate a residual waste stream from the concentrate and chemical cleaning. Desalting membrane processes generate a concentrate that cont ains mostly dissolved contaminants removed from the feedwater. In general, the percentage of wastewater produced decreases as the size of the water systems increase due to increased efficiencies (US EPA, 1993). Concentrate is produced continuously while sp ent cleaning solutions are generated intermittently (typically every 3 to 12 months). Also , the volume of concentrate is much greater than the volume of spent chemical solution. Concentrate The concentrate from NF, RO , and ED/EDR systems are considered s imilar. ED/EDR systems also produce a specialized waste stream of limited flow called “electrode waste,” which contains significant levels of hydrogen and chlorine gases that are

### 22

typically stripped from the electrode waste stream using a degasifier (which is part of the EDR system). (AWWA, 2004) Since desalting membrane processes produce a high - purity stream by rejecting high percentages of contaminants in the feed stream, the concentrate stream is primarily a more concentrated version of the feed water. As such, the characteristics of concentrate are directly related to the feed water quality. Typical contaminants removed during desalting are presented (by source water) in Table 2 - 7 . For NF and RO, these contaminants and other constituents in the feed wate r will be rejected by the membrane and will become part of the concentrate stream. Contaminant concentrations are typically 4 to 10 times the feed water concentration and depend upon the rejection characteristics of the membrane and the water recovery. If pre - treatment is used, the feed water to the desalting membranes will have lower levels of certain constituents and particles. However, the pre - treatment may increase inorganic ions, such as sulfate, iron , and aluminum, if coagulants are used , and possibly residual organics from polymer or sulfuric acid use. (AWWA, 2004) Table 2 -7 . Typical Target Contaminants by Source Water (AWWA, 2004)

Source W

ater Typical T arget Contaminants Total Organic Carbon (TOC) DBP Precursors Pathogens Pesti cides / Synthetic Organic Compounds (SOCs) Surface water
Taste & Odor Compounds Hardness Color TOC Groundwater Inorganic and organic compounds / chemicals TDS Hardness Brackish surface water and groundwater Chloride and sodium TDS Chloride and Sodium Bromide Seawater Boron Concentrate quantity is a function of the amount of feed water purified (or converted to permeate), as defined by the product water recovery. Table 2 - 8 presents typical recoveries for the various types of water sources treated by desalting membrane processes and associated concentrate quantity as percent of feed. NF and brackish water RO systems operate at recoveries of 80
–90 percent and 65 - 85 percent, respectively; seawater RO system recoveries are lower, typically 40
–60 percent. NF and brackish RO residuals differ somewhat because NF salt rejection is lower. Therefore, for a given feed and recovery, NF concentrate is less saline than RO concentrate. Further, NF provides low rejection of monovalent ions (e.g., sodium and chloride) compared to multivalent ions (e.g., calcium and sulfate). Consequently, NF concentrate has a higher ratio of multivalent to monovalent ions than feed water. Lastly, since RO typically treats higher salinity waters, the TDS levels in the RO concentrate are much higher, especially for seawater. (AWWA, 2004)

### 23

Table 2 - 8. Typical Desalting Membrane System Design Parameters (AWWA, 2004) Parameter Surface Water Fresh

Groundwater Brackish

Groundwater Seawater Feed TDS (mg/L) 200-400 400-500 500- 10,000 30,000-40 ,000 Water recovery (% of feed) 80- 90 80- 90 65- 85 40- 60 Concentrate quantity (% of feed) 10-20 10-20 15-35 40- 60 Concentrate TDS (mg/L) (at example recovery) 1,330-2,660 (85%) 2,660-3,330

(85%) 2,000-40,000

(75%) 60,000- 80,000

(50%) Concentration factor* 5- 10 5- 10 2.9-6.7 1.7-2.5 *Ratio of total dissolved solids in concentrate to total dissolved solids in feed, assuming 100 percent salt rejection As previously mentioned, the concentration of contaminants is proportional to water recovery and membrane rejection, with concentration increasing as water recovery increases. Typical source water quality, water recovery, and residuals concentrations are included in Table 2 - 8 , where the values represent the maximum concentrations for residuals streams based o n a simplifying assumption that all of the salts are rejected (100% salt rejection). The amount of particles or TSS in desalting membrane concentrates is low, typically <10 mg/L, because of the extensive pretreatment required to control fouling. The acid a nd scale inhibitor added to the membrane feed water to control mineral precipitation will be concentrated in the desalting membrane concentrate. Scale inhibitor levels in the concentrate are typically <20
–30 mg/L and consist of phosphates or organic polyme rs (such as polyacrylates or dendrimers). (AWWA, 2004) For simplicity, the residuals stream concentration can be estimated based on the feed water quality and a concentration factor related to the water recovery, as shown in the equation below:

r w r 

### Q C C  Where: C r = Concentration in the rejected water C w = Concentration in the raw water Q r = Fraction of water rejected Chemical C leaning (CIP) Residuals Cleaning solutions were developed to address specific contaminants that cause fouli ng and loss of performance, and CIP residuals reflect the chemical characteristics of both the spent cleaning solution and material removed from the membrane system during CIP. Reactions with foulants will tend to raise the pH of acid solutions and lower t hat of basic ones. (AWWA, 2004) Typically, the "cleaning solution volumes" generated during a CIP of NF and RO are about 3 gal/100 sq. ft. (1.2 liter/m 2 ). This volume does not include rinse water volumes. Typical cleaning solution volume is estimated by a dding the total empty vessel volume and pipe volume. Spent cleaning solutions, which may be diluted with rinse water (feed

### 24

or permeate), can contain detergents, surfactants, acid, caustic, or other chemicals used to remove foulants from the membrane system . Typically, the spent cleaning solution volume is an extremely small perce ntage of the treated flow (<0.1 %). (AWWA, 2004) 2 .2. 4 I on Exchange Brine Wastes Ion exchange is used extensively in water treatment for the removal of hardness or cations , such as magnesium and calcium and anions such as chloride. Anion exchange resins have been employed to treat drinking water sources with high nitrate levels as well as high concentrations of disinfection by- products precursor material. IX has been observe d to effectively re move barium, radium, arsenate, selenate, fluoride, lead , and chromate (C ornwell D. A., 1999). Brines are produced from rinsing, regenerating, and backwashing the ion exchange unit. Of these three streams, the regeneration stream contains the h ighest levels of TDS, ranging from 10 to 300 times the levels found in the feed water. This high TDS content is due to the salts removed from the exchange resin during regeneration and excess regeneration salts. The regeneration stream is often mixed with the ri nse and backwash streams, diluting the regenerant by as much as an order of magnitude. (US EPA, 1993). T he predominant ion in the spent regenerate streams is often the coion in the regenerant ( e.g., chloride, sulfate, carbonate, or sodium ). (ASCE , 1996) The other ions present are those removed by the resin and reclaimed by the regenerant. With chlorides present, brine is corrosive to materials it contacts. The pH of the spent regenerant could be low or high depending on the type of resin used . For example, a cationic exchange re s i n may be regenerated using concentrated sulfuric or hydrochloric acid , while an anionic exchange resin may be regenerate d using a strong base
. (AWWA, 1998) In addition to the spent regenerant waste, IX generates backwash wat er used before and after regeneration. Table 2 - 9 presents typical ranges of ion concentrations in the ion exchange wastewater. (ASCE, 1996) Table 2 -9 . Typical Chemical Constituents of Ion Exchange Wastewater

Constituents Range of Averages (mg/L) TDS 1 5,000
– 35,000 Ca ++ 3,000
– 6,000 Mg ++ 1,000
– 2,000 Hardness (as CaCO 3) 11,600
– 23,000

Na + 2,000
– 5,000 Cl 9,000
– 22,000 The volume of brine generated from ion exchange units range from 1.5 to 10 percent of the treated water depending on the ha rdness of the feed water and the type of ion exchange unit used. In general, for every kilogram of hardness removed, approximately 3 to 15 gallons of brine are produced. Table 2 - 10 presents typical brine generation rates by water treatment plant flow. (US EPA, 1993)

### 25 Table 2 - 10 . Typical Ion Exchange Brine Volumes Water Treatment Plant Flow

(mgd) Typical Flow Range (gal/day) Typical Volume (gal/day) 0.7 12,300
– 63,200 12,300 1.8 31,500
– 162,500 31,500 4.8 84,000
– 433,300 84,000 11 192,500
– 993,000 192,500 18 315,000
– 1,624,900 315,000 26 455,000
– 2,347,100 455,000 51 892,600
– 4,604,000 892,600 210 3,675,200
– 18,957,700 3,675,200 430 7,525,400
– 38,818,100 7,525,400 2.2. 5 Adsorption Wastes Adsorption processes often generate a backwash effluent (backwashing disengages solids that have been entrapped in the bed ) . Backwashing of GAC filter- adsorbers is essential to remove solids and to maintain the desired hydraulic properties of the bed. The residual of the backwash wastewater is generally suspended solids, biological films, and some filter media
.

### 26

2.3 Summary of Residuals Generated by Drinking Water Treatment Process Table 2 - 11 summarizes the typical residuals generated from drinking water treatment processes and p otential pollutants in e ach waste stream
. (ASCE, 1996; AWWARF 1987) Table 2 - 11 . Drinking Water Treatment Processes and Waste Streams Major Water Treatment Plant

Type Typical Residual Waste Streams Typical Waste Stream Constituents
Presedimentation, sedimentation , and coagulation basin residuals Aluminum hydroxide Ferric hydroxide Suspended solids Metals Organics Radionuclides Biological Silica Polymers Coagulation and Filtration

Filter backwash and filter-towaste Similar to sludge, but more dilute

Presedimentation, sedimentation , and precipiitive softening settling basin residuals Calcium carbonate Magnesium hydroxide Unreacted lime Suspended solids Metals Organics Radionuclides Biological Polymers Aluminum hydroxide Ferric hydroxide Precipitative Softening

Filter backwash and filter-towaste Similar to sludge, but more dilute Concentrate stream Suspended solids Organics Viruses Metals Radionuclides Backwash See Table 2-5 Low- Pressure Membrane Separation Chemical cleaning See Table 2- 6

### 27

Table 2 - 11 . Drinking Water Treatment Processes and Waste Streams (Cont.) Major Water Treatment Plant

Type Typical Residual Waste Streams Typical Waste Stream Constituents Concentrate stream See Table 2-7 for a breakdown by source water Desalting Membrane Separation Chemical clea ning Reflects the spent cleaning solution and material removed from the membrane system during CIP

Brine stream (regenerate waste) TDS Metals Hardness Calcium Magnesium Sodium Sulfate Chloride Nitrates Radionuclides Ion Exchange

Rinse water and/or backwash Dilutes regenerate waste Adsorption Technologies Backwash Suspended solids Metals Organics Radionuclides 3.0 STAKEHOLDER I NPUT EPA solicited input from the EPA Drinking Water Treatment Costing Reviewers on the following aspects of the identificati on and characterization of drinking water treatment residuals. 1. I s it appropriate to focus on the five types of water treatment processes described in Section 1? 2. EPA is gathering additional information about the characterization, management, treat ment, a nd disposal options for the miscellaneous wastes listed in Section 1.6. Are there any other miscellaneous wastes discharged from drinking water treatment plants? 3. I s it appropriate to focus on the seven typical residual waste streams presented in Table 2 - 1 1 ? 4. Is the listing of possible pollutants by waste stream presented in Table 2 - 11 reasonable and inclusive of all major pollutants types that are likely to be present in the residual? 5. Should the volume of generated sludge be calculated using the equation presented in Section 2.1? Or, should EPA develop a curve of typical sludge generation volumes using data obtained from industry questionnaires ?

### 28

6. Is it appropriate to use percent solid ranges presented in Tables 2 - 1 and 2 - 3 for coagulation/filtration and precipitative softening sludges, respectively? Or, should EPA develop ranges using data obtained from industry questionnaires? 7. Is it appropriate to use the membrane concentrate generation rates presented in Table 2 - 8 to estimate the volume of concentrate/br ine produced by membrane separation processes? Or, should EPA develop generation rates using data obtained from industry questionnaires? 8. EPA is planning on collecting discharge monitoring reports (DMR) for most if not all of the large drinking water treat ment plants (those serving greater than 50,000 people). Is it reasonable to use the DMR data to estimate pollutant concentrations in the discharged residuals? EPA documented its responses to these comments in a document titled, “ Summary of Peer Input: Ide ntification and Characterization of Typical Drinking Water Treatment Residuals ,” which is located in the public record for the Drinking Water Treatment effluent guidelines rulemaking ( EPA- HQ - OW - 2004 - 0035 ).

### 29

4.0 R EFERENCES American Society of Civil Engine ers, American Water Work Association, U.S. Environmental Protection Agency. 1996. Management of Water Treatment Plant Residuals: Technical Transfer Handbook. ASCE & AWWA. American Water Work Association, American Society of Civil Engineers. 1998
. Water Tr eatment Plant Design . 3 rd ed. McGraw- Hill, New York. American Water Works Association. 1999. Water Quality and Treatment: A Handbook of Community Water Supplies . 5 th ed. McGraw- Hill, New York. American Water Works Association Research Foundation. 1987. W ater Treatment Plant Waste Management. AWWA & AWWARF. American Water Works Association Research Foundation. 2005. Water Treatment Residuals Engineer

ing
. AWWA Residual Management Research Committee Subcommittee on Membrane Residual Management, 2003 Committee Report: Residuals Management for LowPressure Membranes. Jour. AWWA, 95:6:68. AWWA Residual Management Research Committee Subcommittee on Membrane Residual Management, 2004 Committee Report: Residuals Management for Desalting Membranes. Jour. AWWA, 96 :12:73. Cornwell, D.A. 1999. Water Treatment Plant Residual Management . In Water Quality and Treatment: A Handbook of Community Water Supplies . 5 th ed. McGraw- Hill, New York. U.S. Bureau of Reclamation. 1993. The Desalting and Wate r Treatment Membrane Manual: A Guide to Membranes for Municipal Water Treatment. R-96- 15 U.S. Environmental Protection Agency. 1992. Project Summary: Inorganic Chemical Characterization of Water Treatment Plant Residuals . EPA 600/SR - 92/117. U.S. Environm ental Protection Agency. 1993. Large Water System Byproducts Treatment and Disposal Cost Document. EPA 811 - D - 93 - 002. U.S. Environmental Protection Agency. 1999. Alternative Disinfectants and Oxidants Guidance Manual. EPA 815 - R - 99 - 014. U.S. Environmental Protection Agency. 2000. Technologies and Cost for Removal of Arsenic from Drinking Water
. EPA 81 5 - R - 00 - 028.