Technologies and Costs for Removal of Arsenic From Drinking Water

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The use of evaporation ponds and drying beds involve the discharge of brine waste to a pondfor storage and dewatering via the natural process of evaporation. Typically, such ponds are designedto have large surface areas to maximize evaporation of residual water by the sun and wind. Pond sizeis determined by waste flow and storage capacity requirements.As previously mentioned, evaporation ponds and drying beds are used primarily for brinewastes generated by RO and IX. Such processes produce large volumes of liquid wastescharacterized by high levels of total dissolved solids (TDS), for which mechanical dewateringprocesses, such as filter presses, are impractical. Depending on the solids concentration of the brinewaste stream, intermittent removal of solids may be required. For brines with a TDS content rangingfrom 15,000 to 35,000 mg/L, solids will accumulate in an evaporation pond at a rate of ½ to 1½inches per year (DPRA, 1993a). When the depth of the solids in the pond reaches a predeterminedlevel, discharge to the pond is halted and evaporation is allowed to continue until the solidsconcentration of the waste is suitable for disposal.The use of evaporation ponds is extremely land intensive, requiring shallow basins with largesurface areas. This can be an important consideration in densely populated regions. Reverse osmosisprocesses produce very large volumes of liquid wastes which increases land requirements andultimately construction costs. As a result, evaporation ponds may not be suitable for large watersystems utilizing RO. Evaporation ponds and drying beds have few O&M requirements, but are onlyfeasible in regions with favorable climatic conditions, i.e., high temperatures, low humidity, and lowprecipitation (DPRA, 1993a). Waste streams with low TDS concentrations can be discharged to thesame pond for several years (assuming adequate total capacity) before solids accumulation warrantsremoval.4.2.4 Storage LagoonsLagoons are the most common, and often least expensive, method to thicken or dewatertreatment sludges. However, lagoons, like evaporation ponds, are land intensive (DPRA, 1993a).Storage lagoons are lined ponds designed to collect, retain, and dewater sludge for a predeterminedperiod of time. Dewatering occurs through the evaporation and decanting of the supernatant. Lagoonsize is determined based on the volume of sludge that must be handled and the desired storage time.As with evaporation ponds, when a lagoon reaches its design capacity, solids can be removed bymeans of heavy equipment and shipped for disposal.4-4
Storage lagoons are best suited for dewatering lime softening (LS) process sludges, thoughthey have been applied with some success to coagulation/filtration (C/F) process sludges. Storagelagoons can operate under a variety of sludge flows and solids concentrations, and chemicalconditioning of alum sludges is not required (DPRA, 1993a). Typically, lime sludges are dischargedto a lagoon with 3 percent solids, and are dewatered to 50 to 60 percent solids, whereas alum sludgesare typically characterized by 1 percent solids when first discharged to a storage lagoon and can bedewatered to 7 to 15 percent solids (DPRA, 1993a). As evident from this data, alum sludges do nottypically dewater well in storage lagoons. When the top layer of an alum sludge is allowed to dry,it hardens, sealing moisture in the layers below. Even after several years, alum sludges may requireadditional dewatering to achieve the 20 percent solids content required for acceptance at mostlandfills (DPRA, 1993a). Further, thickened alum sludges can be difficult to remove from lagoons,often requiring dredging or vacuum pumping by knowledgeable operators.As previously stated, lagooning is a land intensive process with limited applicability indensely populated areas, or areas with limited land availability. Such areas need to compare the costof regular lagoon cleaning and disposal with land acquisition costs. Lagoons are best suited for areaswith favorable climatic conditions, i.e., high temperatures, low humidity, and low precipitation. Innorthern climates, winter freezing can assist in the dehydration of alum sludges.4.3 DISPOSAL ALTERNATIVES4.3.1 Direct DischargeDirect discharge to a surface water is a method of disposal for some water treatmentbyproducts. No pretreatment or concentration of the byproduct stream is necessary prior to discharge,and the receiving water will naturally dilute the waste concentration and gradually incorporate thesludge or brine (DPRA, 1993a).However, the discharge of liquid residuals to surface waters is subject to compliance with andpermitting under the National Pollution Discharge Elimination System (NPDES). NPDES establisheslimits for specific contaminants (including total solids and arsenic) based on a variety of factors,including ambient contaminant levels, low flow condition of the receiving water, and anticipatedvolume of the proposed discharge. Most NPDES limits for solids discharge are around 30 mg/L(AWWARF, 1998).4-5
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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
Page 83 and 84: PilotingThe Technology Design Panel
Page 85 and 86: The 1993 Technology and Cost Docume
Page 87 and 88: cause disinfection by-product (DBP)
Page 89 and 90: Figure 3-1Pre-oxidation - 1.5 mg/L
Page 91 and 92: 3.6 PRECIPITATIVE PROCESSES3.6.1 Co
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Page 95 and 96: Figure 3-4Enhanced Coagulation/Filt
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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: mechanical dewatering processes. Wh
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Page 139 and 140: 4.3.3 Dewatered Sludge Land Applica
Page 141 and 142: usually determined by the Paint Fil
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Page 145 and 146: The solids content of the backwash
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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
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Fuller, C.C., J.A. Davis, G.W. Zell
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Le, X.C., and M. Ma (1998). “Dete
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Scott, K., J. Green, H.D. Do and S.
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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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