IX1 Arsenic Removal by Ion Exchange Joe Chwirka - Camp Dresser & McKee Bruce Thomson - University of New Mexico with contributions from Jerry Lowry and Steve Reiber

IX2 Introduction Arsenic removal by Ion Exchange (IX) is effective for many applications Presentation will discuss: Chemistry of the process Variables affecting process performance Especially competing ions and resin selectivity Salt use & brine production and disposal Design considerations Two example systems

IX3 Arsenic Treatment Technologies Likely Technologies Coagulation/ Microfiltration Fixed Bed Adsorption Technologies Coagulation/ Filtration POU or POE Unlikely Technologies Ion Exchange Activated Alumina or Regenerable Media NF or RO or EDR Enhanced Softening

IX4 Ion Exchange Reactions Cation Exchange (water softening) 2 (R-Na) + Ca 2+ = R 2 -Ca + 2 Na + Anion Exchange (arsenic removal) R-Cl + H 2 AsO 4 - = R-H 2 AsO 4 + Cl - Will only remove ionic species Regenerate resin with concentrated NaCl brine R = Resin site

IX5 BACKWASH TO WASTE RAW WATER RINSE TO WASTE TREATED WATER RAW WATER FOR BACKWASH BRINE TANK (NaCI) Softening Processes Ion Exchange System

IX6 Point of Entry Softening

IX7 Cation and Anion Exchange System

IX8 Acid-Base Chemistry of As(V)

IX9 Acid-Base Chemistry of As(III)

IX10 Resin Selectivity Sequence Strong Base Type II Anion Resin selectivity sequence UO 2 (CO 3 ) 3 4- > SO 4 2- > HAsO 4 2- > NO 3 - > H 2 AsO 4 - > Cl - > HCO 3 - All SO 4 2- must be removed before As is removed Other anions may also have higher selectivity than As (i.e. VO 4 3- )

IX11 Concentration Profiles in IX Column All SO 4 2- is removed before HAsO 4 2- is removed Can result in chromatographic peaking: SO 4 2- elutes HAsO 4 2- from resin Effluent As concentrations are much higher than influent concentrations

IX12 Chromatographic Peaking

IX13 Chromatographic Peaking

IX14 Chromatographic Peaking

IX15 SEPARATION & BREAKTHROUGH Kinetics & EBCT Bed Capacity & SO 4 2- Leakage As & N0 3 - Peaking Alkalinity, pH/Corrosivity

IX16 Kinetics & Empty Bed Contact Time Exchange kinetics are rapid and internal mass transport limitations are small Empty Bed Contact Time (EBCT) EBCT min = 1.5 min Breakthrough is sharp & leakage is low

IX17 Bed Capacity & SO 4 2- Sulfate Removal Technology!

IX18 IX System - Unity, ME 11 Years Old As(III) at ≈100 µg/L Trace of Sulfide & Fe 65 gpm Design Flow Filox Oxidizing Filter SB II Anion Resin

IX19 FJ School IX System Filox + IX 1200 gpd As ≈ µg/L (sol) SO 4 2- ≈ 25 mg/L pH = 7.6 Capable of < 1.0 µg/L treated water

IX20 EPA Study at Medical Facility - Arsenic

IX21 EPA Study at Medical Facility - pH & Alkalinity

IX22 Design EBCT = 1.5 min operated to regen. BEFORE SO 4 2- causes breakthrough down flow service & regeneration single or multiple beds single or multiple brine use

IX23 Process Design Small Systems single or double vessels EBCT > 1.5 min and long service cycle intermittent flow single use of brine may not be feasible w/o POTW for brine disposal Large Systems multiple parallel vessels staged regeneration possible reuse of brine may not be cost effective w/o POTW for brine disposal

IX24 Regeneration Small Systems use a standard softener control & small brine tank 8-15 lb salt used/cf of resin backwash, brine, slow rinse, & fast rinse Large Systems parallel vessels and staged regeneration with salt storage & brine maker 5.4 lb salt used/cf of resin backwash, brine, & rinse steps

IX25 Brine Disposal Options Municipal sewer Likely only for very small systems Systems near coast where salinity isn’t problem Evaporation ponds Deep well injection

IX26 IX Brine Recycling Brine Tank Precip. Tank IX BaSO4 IX Regeneration Brine Reuse BaCl2 After 3 Cycles

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IX29 Fruitland, Idaho Water Chemistry As – 34 micrograms/L Nitrate mg/L Sulfate-51 mg/L pH-7.3 1,500 X sulfate 429 X nitrate 1,929

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IX31 10 gpm water loss

IX32 Floor Drain To POTW 10 gpm Water loss

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IX36 Plan Ah e a d

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IX38 Floor Drain To POTW Sequentially regenerated pH Alkalinity 6 – 8,000 lb $0.10/lb 50% production loss for 5 hours (~85 gpm) Regenerate 1/30 hours

IX39 Rimrock, Arizona Basin Water IX

IX40 $ per acre-foot

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IX48 Ten in parallel Seven in production pH Alkalinity Chromatographic peaking

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IX51 Truck fill

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