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Arsenic Removal by Ion Exchange

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Title: Arsenic Removal by Ion Exchange


1
Arsenic Removal by Ion Exchange
  • Joe Chwirka - Camp Dresser McKee
    (chwirkajd_at_cdm.com)
  • Bruce Thomson - University of New Mexico
    (bthomson_at_unm.edu)
  • with contributions from Jerry Lowry and Steve
    Reiber

2
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

3
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

4
Ion Exchange Reactions
  • Cation Exchange (water softening)
  • 2 (R-Na) Ca2 R2-Ca 2 Na
  • Anion Exchange (arsenic removal)
  • R-Cl H2AsO4- R-H2AsO4 Cl-
  • Will only remove ionic species
  • Regenerate resin with concentrated NaCl brine

R Resin site
5
Softening Processes
  • BACKWASH
  • TO WASTE

RAW WATER
Ion Exchange System
RINSE TO WASTE
BRINE TANK (NaCI)
TREATED WATER
RAW WATER FOR BACKWASH
6
Point of Entry Softening
7
Cation and Anion Exchange System
8
Acid-Base Chemistry of As(V)
9
Acid-Base Chemistry of As(III)
10
Resin Selectivity Sequence
  • Strong Base Type II Anion Resin selectivity
    sequence
  • UO2(CO3)34- gt SO42- gt HAsO42- gt NO3- gt
    H2AsO4- gt Cl- gt HCO3-
  • All SO42- must be removed before As is removed
  • Other anions may also have higher selectivity
    than As (i.e. VO43-)

11
Concentration Profiles in IX Column
  • All SO42- is removed before HAsO42- is removed
  • Can result in chromatographic peaking
  • SO42- elutes HAsO42- from resin
  • Effluent As concentrations are much higher than
    influent concentrations

12
Chromatographic Peaking
13
Chromatographic Peaking
14
Chromatographic Peaking
15
SEPARATION BREAKTHROUGH
  • Kinetics EBCT
  • Bed Capacity SO42-
  • Leakage
  • As N03- Peaking
  • Alkalinity, pH/Corrosivity

16
Kinetics Empty Bed Contact Time
  • Exchange kinetics are rapid and internal mass
    transport limitations are small
  • Empty Bed Contact Time (EBCT)
  • EBCTmin 1.5 min
  • Breakthrough is sharp leakage is low

17
Bed Capacity SO42-
Sulfate Removal Technology!
18
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

19
FJ School IX System
  • Filox IX
  • 1200 gpd
  • As 25-60 µg/L (sol)
  • SO42- 25 mg/L
  • pH 7.6
  • Capable of lt 1.0 µg/L
  • treated water

20
EPA Study at Medical Facility - Arsenic
21
EPA Study at Medical Facility - pH Alkalinity
22
Design
  • EBCT 1.5 min
  • operated to regen. BEFORE SO42- causes
    breakthrough
  • down flow service regeneration
  • single or multiple beds
  • single or multiple brine use

23
Process Design
  • Small Systems
  • single or double vessels
  • EBCT gt 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

24
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

25
Brine Disposal Options
  • Municipal sewer
  • Likely only for very small systems
  • Systems near coast where salinity isnt problem
  • Evaporation ponds
  • Deep well injection

26
IX Brine Recycling
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29
Fruitland, Idaho
  • Water Chemistry
  • As 34 micrograms/L
  • Nitrate - 14.6 mg/L
  • Sulfate - 51 mg/L
  • pH - 7.3

1,500 X sulfate 429 X nitrate 1,929
30
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31
10 gpm water loss
32
Floor Drain To POTW
10 gpm Water loss
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Plan Ah e a d
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  • Sequentially regenerated
  • pH
  • Alkalinity
  • 6 8,000 lb salt/week _at_ 0.10/lb
  • 50 production loss for 5 hours (85 gpm)
  • Regenerate 1/30 hours

Floor Drain To POTW
39
Rimrock, Arizona
  • Basin Water IX

40
per acre-foot
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  • Ten in parallel
  • Seven in production
  • pH
  • Alkalinity
  • Chromatographic peaking

49
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51
Truck fill
52
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