Technologies and Costs for Removal of Arsenic From Drinking Water

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handling by other mechanical or non-mechanical dewatering processes. Filter presses are capableof attaining final sludge solids contents in the range of 35 to 50 percent, while scroll centrifuges mayachieve final solids contents of 15 to 30 percent. Evaporation ponds and storage lagoons may besuitable for smaller treatment plants, but may not be applicable for large water systems since they areland intensive.Disposal of enhanced coagulation arsenic residuals 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 suitablemethod of disposal. Total arsenic should not exceed 41 mg/kg if sludges are to be land-appliedwithout restrictions. Sludges with arsenic concentrations between 41 and 75 mg/kg may be landapplied provided that the total loading does not exceed 41 kg per hectare.All enhanced coagulation sludges must be dewatered prior to landfill disposal. If the residualspass the TCLP test, they may be disposed of in a sanitary landfill. Otherwise, residuals must bedisposed of in a hazardous waste landfill. Note that hazardous waste disposal is unlikely since testsconducted by the University of Colorado indicate that enhanced coagulation sludges will pass theTCLP test (AWWARF, 1998). Due to its high cost disposal to a hazardous waste landfill should onlybe relied on as a last resort if waste fails the TCLP test.4.4.3 Direct FiltrationDirect filtration is a modified C/F process that lacks the sedimentation unit process.Accordingly, direct filtration residuals are the result of filter backwash, and typically have lower TDSconcentrations than a typical C/F process. This is due to the reduced coagulant dose used in thisprocess. Sludge production is also affected by the suspended solids content of the raw water.Systems are unlikely to install direct filtration solely for arsenic removal. If this technology wereinstalled, the disposal alternative discussed for coagulation/filtration would be appropriate for thistechnology.4.4.4 Coagulation Assisted MicrofiltrationCoagulation assisted microfiltration is a modified C/F process wherein theflocculation/sedimentation and filtration unit processes are replaced by microfiltration. Residualsgenerated by this process consist of a filter backwash stream containing a dilute Fe(CH) 3 precipitate.4-14
The solids content of the backwash from coagulation assisted microfiltration processes were foundto be less than 0.5 percent in one study (Clifford et al, 1997).Selection of Handling and Disposal OptionsThe wastes from coagulation assisted microfiltration processes will consist of a very diluteslurry. Gravity thickening may be used as to increase the solids content of the sludge prior to the useof other mechanical or non-mechanical dewatering options. Filter presses and centrifuges areappropriate methods of residuals handling. However, these methods are capital intensive and maynot be appropriate for extremely large systems. Evaporation ponds and storage lagoons are alsoappropriate means of handling the residuals generated by coagulation assisted microfiltration. Bothrequire little oversight and maintenance, but are land intensive. As such, they may not be appropriatefor large systems. A thorough comparison of handling options should be conducted to select the mostcost effective method.Land application may be a suitable disposal method for sludges from coagulation assistedmicrofiltration processes. As discussed in section 4.3.2, total arsenic cannot exceed 41 mg/kg ifsludges are to be applied with no restrictions. Sludges with arsenic concentrations between 41 and75 mg/kg may be land applied provided that the total loading does not exceed 41 kg per hectare.All coagulation assisted microfiltration sludges must be dewatered prior to landfill disposal.If the residuals pass the TCLP test they may be disposed in a sanitary landfill. Otherwise, residualsmust be disposed in a hazardous waste landfill. However, tests conducted by Clifford (Clifford,1997) and the University of Colorado (AWWARF, 1998) indicate that the sludges from this treatmentprocess will pass the TCLP test for arsenic toxicity by a considerable margin, making it unlikely thathazardous waste disposal will be necessary. Hazardous waste landfill disposal should only be usedas a last resort if waste fails the TCLP test.4.4.5 Lime SofteningThe quantity of residuals produced at LS facilities is typically much greater than the quantityproduced by C/F plants (AWWARF, 1998). The quantity of sludges produced is a function of waterhardness. LS for carbonate hardness removal produces approximately twice the amount of solids perpound of hardness removed than the use of LS for the removal of non-carbonate hardness.LS plants typically produce 1,000 to 8,000 pounds of solids per million gallons of watertreated depending on the hardness of the influent water (AWWARF, 1998). Arsenic concentrations4-15
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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
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3.6 PRECIPITATIVE PROCESSES3.6.1 Co
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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 and 142: usually determined by the Paint Fil
Page 143: for arsenic toxicity by a substanti
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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