Technologies and Costs for Removal of Arsenic From Drinking Water

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ackwash streams to a sanitary sewer is generally only an option for treatment plants with an averageflow of less than 10 mgd.Selection of Handling and Disposal OptionsAs previously discussed, C/F blowdown and filter backwash are high volume waste streamscharacterized by low solids content. Gravity thickening may be used to increase the solids content ofC/F sludges and backwash prior to handling by other mechanical or non-mechanical dewateringprocesses. Filter presses are capable of attaining final solids contents in the range of 35 to 50 percent,while scroll centrifuges may achieve final solids contents of 15 to 30 percent. Evaporation ponds andstorage lagoons may be suitable for smaller treatment plants, but because they are a land-intensivedisposal option, they may not be applicable for large water systems.Disposal of C/F residuals containing arsenic is largely dependent on influent arsenicconcentration, coagulant dose and suspended solids content. Disposal by direct discharge to a surfacewater is not typically appropriate.Depending on the arsenic concentration of C/F sludges, land application may be a suitabledisposal method. As discussed in section 4.3.2, total arsenic cannot exceed 41 mg/kg if sludges areto be applied with no restrictions. Sludges with arsenic concentrations between 41 and 75 mg/kg maybe land applied provided that the total loading does not exceed 41 kg per hectare.All C/F sludges must be dewatered prior to landfill disposal. If the residuals pass the TCLPtest, they may be disposed of in a sanitary landfill. Otherwise, residuals must be disposed of in ahazardous waste landfill. A 1992 study (Bartley et al., 1992) found that the waste sludges from C/Fplants would pass the TCLP test. In this study, samples were taken from the waste sludges generatedby four different water treatment plants and subjected to the TCLP test. One of these systems reliedon C/F, and another used both C/F and lime softening processes. These two systems treated rawwaters characterized by arsenic concentrations averaging 1.1 mg/L and less than 0.001 mg/L,respectively. The results of the TCLP tests conducted on the waste residuals from both systems werebelow 0.040 mg/L (range: 0.007 to 0.039 mg/L)–well below the current criterion for treatment ashazardous waste (5.0 mg/L).A recent study (EPA, June 2000), examined the characteristics of the waste sludges generatedby two C/F plants (Plant A and Plant B). The sludge from Plant A was generated from backwashinganthracite coal/pea gravel filters, while that from Plant B was generated as a result of sedimentationin primary and secondary clarifiers and from filter backwashing. Both sludges passed the TCLP test4-12
for arsenic toxicity by a substantial margin (ranges: less than 0.050 to 0.106 mg/L and 0.058 to 0.160mg/L, respectively) and would not have exceeded the strict TCLP limits established by California fornonhazardous waste. However, the sludge from Plant A would violate the soluble threshold limitconcentrations (SLTCs) established by California for arsenic and copper. As a result, the sludgegenerated by this treatment plant would be considered a hazardous waste, requiring appropriatehandling and disposal.Tests conducted by the University of Colorado confirm the results found in these two studies,indicating that most C/F sludges will pass the TCLP test (AWWARF, 1998). Hazardous wastelandfill disposal should only be used as a last resort if waste fails the TCLP test or exceeds anotherregulatory limit established for water treatment sludges by individual States.4.4.2 Enhanced CoagulationEnhanced coagulation is a modified C/F process that includes increased coagulant dosage,reduction in process pH, or both. As a result, enhanced coagulation process residuals are nearlyidentical to typical C/F residuals. The exception is increased solids production as a result of theincreased coagulant dosage.Sludges removed from enhanced coagulation sedimentation basins are high in water contentand typically have a solids content of only about 1.0 percent (AWWARF, 1998). As a result, suchsludges are usually discharged to a sanitary sewer or dewatered by one of the methods discussedearlier in this chapter. Discharge to sanitary sewers is generally only an option for treatment plantswith an average flow of less than 10 mgd.Filter backwash is a high volume liquid waste stream with a solids content generally less than1.0 percent. Typical volumes range from 1.0 to 2.0 percent of the treated flow. Backwash streamsare typically discharged to a sanitary sewer or processed using one of the mechanical methodsdiscussed in section 4.2.2. As for sedimentation sludges, discharge of filter backwash streams to asanitary sewer is generally only an option for treatment plants with an average flow of less than 10mgd.Selection of Handling and Disposal OptionsAs previously discussed, enhanced coagulation blowdown is characterized by high volumeand low solids content. Typical solids contents range from 0.5 to 2.0 percent, depending on coagulanttype. Gravity thickening may be used to increase the solids content of enhanced C/F sludges prior to4-13
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United StatesEnvironmental Protecti
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ACKNOWLEDGMENTSThis document was pr
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2.5.7 Reverse Osmosis .............
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5.0 POINT-OF-ENTRY/POINT-OF-USE TRE
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LIST OF FIGURES2-1 Pressure Driven
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LIST OF ACRONYMSAAAWWAAWWARFBLSBVC/
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POUpoint-of-useppbparts per billion
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# Alternative treatment processes s
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ends up as ferric hydroxide. In alu
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Optimization Hierarchy for Coagulat
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Substantial arsenic removal has bee
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Vickers et al. (1997) reported that
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was reduced to 0.05 mg/L when the i
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Field StudiesSurveys of lime soften
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Effect of pHpH may have significant
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RegenerationRegeneration of AA beds
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een developed provide important inf
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applicability of IX at a particular
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TABLE 2-1Typical IX Resins for Arse
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solution strength. Arsenic elutes r
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2.4.12 Typical Design ParametersThr
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2.5.2 Important Factors for Membran
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arsenic size distribution to correl
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AWWARF (1998) also performed UF pil
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presumably due to changes in electr
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RO performance is adversely affecte
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TABLE 2-10Arsenic Removal with RO a
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eversal is the decreased potential
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2.6 ALTERNATIVE TECHNOLOGIES2.6.1 I
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20 mg As per gram of iron was remov
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The most significant weakness of th
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3.0 TECHNOLOGY COSTS3.1 INTRODUCTIO
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included in the estimates presented
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Table 3-3Water Model Capital Cost B
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3.2.3 Implementing TDP Recommended
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sources. The September 1998 index v
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Amortization, or capital recovery,
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3.3 ADDITIONAL CAPITAL COSTSThe cos
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PilotingThe Technology Design Panel
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The 1993 Technology and Cost Docume
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cause disinfection by-product (DBP)
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Figure 3-1Pre-oxidation - 1.5 mg/L
Page 91 and 92: 3.6 PRECIPITATIVE PROCESSES3.6.1 Co
Page 93 and 94: enhanced coagulation treatment plan
Page 95 and 96: Figure 3-4Enhanced Coagulation/Filt
Page 97 and 98: Small Systems (Less than 1 mgd)The
Page 99 and 100: Figure 3-6Coagulation Assisted Micr
Page 101 and 102: 3.6.6 Enhanced Lime SofteningEnhanc
Page 103 and 104: Figure 3-8Enhanced Lime SofteningO&
Page 105 and 106: 3. Empty Bed Contact Time (EBCT) is
Page 107 and 108: For design flows greater than 1 mgd
Page 109 and 110: Figure 3-9Activated AluminaCapital
Page 111 and 112: Figure 3-11Activated Alumina (pH 8
Page 113 and 114: Figure 3-13Activated Alumina (pH Ad
Page 115 and 116: 3.7.2 Granular Ferric HydroxideGran
Page 117 and 118: 6. The capital costs include a redu
Page 119 and 120: Figure 3-15Bed Volumes to Arsenic B
Page 121 and 122: Figure 3-17Anion Exchange (< 20 mg/
Page 123 and 124: Figure 3-19Anion Exchange (20-50 mg
Page 125 and 126: quality feed stream and often requi
Page 127 and 128: Figure 3-20Greensand FiltrationCapi
Page 129 and 130: 3.11 COMPARISON OF COSTSThe April 1
Page 131 and 132: 4.0 RESIDUALS HANDLING AND DISPOSAL
Page 133 and 134: mechanical dewatering processes. Wh
Page 135 and 136: Storage lagoons are best suited for
Page 137 and 138: the current Industrial Pretreatment
Page 139 and 140: 4.3.3 Dewatered Sludge Land Applica
Page 141: usually determined by the Paint Fil
Page 145 and 146: The solids content of the backwash
Page 147 and 148: carbonate hardness removal produces
Page 149 and 150: Domestic sewage means untreated san
Page 151 and 152: 4.4.10 Reverse OsmosisReverse osmos
Page 153 and 154: Figure 4-1Anion Exchange (< 20 mg/L
Page 155 and 156: Figure 4-3Anion Exchange (20-50 mg/
Page 161 and 162: Figure 4-9Activated Alumina (pH 7 -
Page 163 and 164: Figure 4-11Activated Alumina (pH Ad
Page 165 and 166: Figure 4-13Greensand FiltrationWast
Page 167 and 168: 5.0 POINT-OF-ENTRY/POINT-OF-USE TRE
Page 169 and 170: chromatographic peaking, which occu
Page 171 and 172: 5.3.1 Case Study 1: Fairbanks, Alas
Page 173 and 174: Manufacturer and laboratory data su
Page 175 and 176: Figure 5-2POU Reverse OsmosisO&M Co
Page 177 and 178: # Installation time - 1 hour unskil
Page 179 and 180: Figure 5-3POU Activated AluminaTota
Page 181 and 182: 6.0 REFERENCESAmy, G.L. and P. Bran
Page 183 and 184: Cooperative Research Centres for Wa
Page 185 and 186: Fuller, C.C., J.A. Davis, G.W. Zell
Page 187 and 188: Le, X.C., and M. Ma (1998). “Dete
Page 189 and 190: Scott, K., J. Green, H.D. Do and S.
Page 191: Appendix AVery Small Systems Capita
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Table A4 - VSS Document Capital Cos
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Table B1.1 - Base Costs Obtained fr
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Table B11.1 - Base Costs Obtained f
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Table B13.1 - Base Costs Obtained f
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Appendix CW/W Cost Model Capital Co
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Table C2.1 - Base Costs Obtained fr
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Table C10.1 - Base Costs Obtained f
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APPENDIX D: BASIS FOR REVISED ACTIV
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Company case study is 18 minutes (2
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egressed against their respective v
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costs for small systems is as follo
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were based on $40/sq ft). The proce
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Basis. Capital cost components incl
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The source water at Plant D has the
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equation y = (2*10 -8 )x 2 + 0.0002
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The maximum run length is 18,500 be
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Since the available arsenic capacit
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If the first column can be operated
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which includes lighting, ventilatio
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disposal costs, if needed, are cove
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Appendix EBasis for Revised Anion E
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2. The estimated cost of the anion
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9. The capital costs have been esti
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Thus, the cost of a road and fence
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length when sulfate is at or below
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the labor rates for both large and
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2. US EPA. Technologies and Costs f
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Technologies and Costs for Removal of Arsenic From Drinking Water

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