Technologies and Costs for Removal of Arsenic From Drinking Water

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to reduce arsenic levels below 5 Fg/L. Moreover, if optimal operating practices are adopted, it isanticipated that effluent levels of less than 3 Fg/L will be obtainable.Arsenic in the pentavalant arsenate form is more readily removed than the trivalent arseniteform. At pH 7.6 or lower iron and aluminum coagulants are of equal effectiveness in removing As(V).However, iron coagulants are advantageous if pH is above 7.6, if soluble coagulant metal residualsare problematic, or if As(III) is present in the raw water. In general, higher arsenic removalefficiencies are achieved with increased coagulant dosages. The effectiveness of iron coagulants inremoving As(III) diminishes at pH 6.0. Recent studies have shown that arsenic removal isindependent of initial concentration. This contradicts initial findings which indicate that arsenicremovals decrease with increasing initial concentrations. The presence of sulfates significantlydecreases As(III) removal, but only slightly affects As(V) removal. At pH higher than 7.0, removalof As(V) increases in the presence of calcium.2.2.2 Iron/Manganese OxidationIron/Manganese (Fe/Mn) oxidation is commonly used by facilities treating groundwater. Theoxidation process used to remove iron and manganese leads to the formation of hydroxides thatremove soluble arsenic by precipitation or adsorption reactions.Arsenic removal during iron precipitation is fairly efficient (Edwards, 1994). Removal of 2mg/L of iron achieved a 92.5 percent removal of As(V) from a 10 µg/L As(V) initial concentrationby adsorption alone. Even removal of 1 mg/L of iron resulted in the removal of 83 percent of influentAs(V) arsenic from a source with 22 µg/L As(V). Indeed, field studies of iron removal plants haveindicated that this treatment can feasibly reach 3 Fg/L (see discussion below). However, the removalefficiencies achieved by iron removal are not as high or as consistent as those realized by activatedalumina (see section 2.3.1) or ion exchange (see section 2.4).Note, however, that arsenic removal during manganese precipitation is relatively ineffectivewhen compared to iron even when removal by both adsorption and coprecipitation are considered.For instance, precipitation of 3 mg/L manganese removed only 69 percent of As(V) of a 12.5 µg/LAs(V) influent concentration.Oxidation filtration technologies may be effective arsenic removal technologies. Research ofoxidation filtration technologies has primarily focused on greensand filtration. As a result, thefollowing discussion focuses on the effectiveness of greensand filtration as an arsenic removaltechnology.2-6
Substantial arsenic removal has been seen using greensand filtration (Subramanian, et al.,1997). The active material in "greensand" is glauconite, a green, iron-rich, clay-like mineral that hasion exchange properties. Glauconite often occurs in nature as small pellets mixed with other sandparticles, giving a green color to the sand. The glauconite sand is treated with KMnO 4 until the sandgrains are coated with a layer of manganese oxides, particularly manganese dioxide. The principlebehind this arsenic removal treatment is multi-faceted and includes oxidation, ion exchange, andadsorption. Arsenic compounds displace species from the manganese oxide (presumably OH - andH 2 O), becoming bound to the greensand surface - in effect an exchange of ions. The oxidative natureof the manganese surface converts As(III) to As(V) and As(V) is adsorbed to the surface. As a resultof the transfer of electrons and adsorption of As(V), reduced manganese (MnII) is released from thesurface.The effectiveness of greensand filtration for arsenic removal is dependent on the influent waterquality. Subramanian et al. (1997) showed a strong correlation between influent Fe(II) concentrationand arsenic percent removal. Removal increased from 41 percent to more than 80 percent as theFe/As ratio increased from 0 to 20 when treating a tap water with a spiked As(III) concentration of200 mg/L. The tap water contained 366 mg/L sulfate and 321 mg/L TDS; neither constituent seemedto affect arsenic removal. The authors also point out that the influent Mn(IV) concentration may playan important role. Divalent ions, such as calcium, can also compete with arsenic for adsorption sites.Water quality would need to be carefully evaluated for applicability for treatment using greensand.Other researchers have also reported substantial arsenic removal using this technology, includingarsenic removals of greater than 90 percent for treatment of groundwater (Subramanian, et al., 1997).As with other treatment media, greensand must be regenerated when its oxidative andadsorptive capacity has been exhausted. Greensand filters are regenerated using a solution of excesspotassium permanganate (KMnO 4 ). Like other treatment media, the regeneration frequency willdepend on the influent water quality in terms of constituents which will degrade the filter capacity.Regenerant disposal for greensand filtration has not been addressed in previous research.Effect of Co-occurring Inorganic SolutesMcNeill and Edwards (1995) demonstrated that a Fe/Mn facility with 400 mg/L sulfate and5.2 µg/L arsenic in the raw water attained 83 percent removal of arsenic. Results from two otherFe/Mn facilities with 10 mg/L sulfate in the raw water showed 87 and 93 percent arsenic removals.2-7
Page 1: United StatesEnvironmental Protecti
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Page 12 and 13: LIST OF FIGURES2-1 Pressure Driven
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Page 23 and 24: ends up as ferric hydroxide. In alu
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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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enhanced coagulation treatment plan
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Figure 3-4Enhanced Coagulation/Filt
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Small Systems (Less than 1 mgd)The
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Figure 3-6Coagulation Assisted Micr
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3.6.6 Enhanced Lime SofteningEnhanc
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Figure 3-8Enhanced Lime SofteningO&
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3. Empty Bed Contact Time (EBCT) is
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For design flows greater than 1 mgd
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Figure 3-9Activated AluminaCapital
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Figure 3-11Activated Alumina (pH 8
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Figure 3-13Activated Alumina (pH Ad
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3.7.2 Granular Ferric HydroxideGran
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6. The capital costs include a redu
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Figure 3-15Bed Volumes to Arsenic B
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Figure 3-17Anion Exchange (< 20 mg/
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Figure 3-19Anion Exchange (20-50 mg
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quality feed stream and often requi
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Figure 3-20Greensand FiltrationCapi
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3.11 COMPARISON OF COSTSThe April 1
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4.0 RESIDUALS HANDLING AND DISPOSAL
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mechanical dewatering processes. Wh
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Storage lagoons are best suited for
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the current Industrial Pretreatment
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4.3.3 Dewatered Sludge Land Applica
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usually determined by the Paint Fil
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for arsenic toxicity by a substanti
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The solids content of the backwash
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carbonate hardness removal produces
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Domestic sewage means untreated san
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4.4.10 Reverse OsmosisReverse osmos
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Figure 4-1Anion Exchange (< 20 mg/L
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Figure 4-3Anion Exchange (20-50 mg/
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Figure 4-9Activated Alumina (pH 7 -
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Figure 4-11Activated Alumina (pH Ad
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Figure 4-13Greensand FiltrationWast
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5.0 POINT-OF-ENTRY/POINT-OF-USE TRE
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chromatographic peaking, which occu
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5.3.1 Case Study 1: Fairbanks, Alas
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Manufacturer and laboratory data su
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Figure 5-2POU Reverse OsmosisO&M Co
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# Installation time - 1 hour unskil
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Figure 5-3POU Activated AluminaTota
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6.0 REFERENCESAmy, G.L. and P. Bran
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Cooperative Research Centres for Wa
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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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