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Can redox manipulations remove dissolved arsenic from groundwater

Background. Arsenic most soluble with Eh<100 mVRelease of arsenic to anoxic groundwaters frequently reported:Bangladesh, West Bengal India, Taiwan. After Masscheleyn et al., Environmental Science and Technology, 1991.Activities of As, Mn, Fe ~10-4. Winthrop, Maine, USA. Closed, unlined landfill sited in glacial till and outwashLeachate has shifted groundwater chemistry more reducing (ORP -105 mV)Sediments contain ~7 mg/kg AsSediment reducing GW = ~300 mg/L AsGroundwater extraction and33001

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Can redox manipulations remove dissolved arsenic from groundwater

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    1. Can redox manipulations remove dissolved arsenic from groundwater? Alison R. Keimowitz1,2, Pamela Cole2,3, Brian J. Mailloux2, Martin Stute2,3, H. James Simpson1,2, Steven N. Chillrud2, Yan Zheng2,4

    2. Background Arsenic most soluble with Eh<100 mV Release of arsenic to anoxic groundwaters frequently reported: Bangladesh, West Bengal India, Taiwan

    3. Winthrop, Maine, USA Closed, unlined landfill sited in glacial till and outwash Leachate has shifted groundwater chemistry more reducing (ORP -105 mV) Sediments contain ~7 mg/kg As Sediment + reducing GW = ~300 mg/L As Groundwater extraction and treatment system ineffective Other landfills show similar processes

    4. If redox is the problem, can redox be the solution?

    5. ORC® Pilot Experiment ORC– Oxygen Release Compound Contains magnesium peroxide, phosphate and minor components Designed to release O2 over ~6 months 1400 kg ORC injected through aquifer thickness

    6. ORC® Pilot Experiment

    7. ORC® Pilot Experiment– Results

    8. ORC® Pilot Experiment– Results

    9. ORC® Pilot Experiment 1400 kg ORC released ~330 kg O2 But what is the subsurface oxygen demand?

    10. Arsenic Removal via Sulfide Precipitation?

    11. Proof of Principle Previous studies have demonstrated removal of arsenic by SRB Sulfate is high at Winthrop due to GWETS Preliminary studies indicate that native microbial communities at Winthrop are carbon-limited

    12. Experimental Setup Incubate sediment + acetate + artificial GW for ~7 weeks in reaction vessel and microcosms Microcosms permit sediment sampling, replicate samples Reaction vessel permits electrode monitoring, sampling from 1 reservoir Monitor changes in water and sediment

    13. Results– Acetate Respiration, Sulfate Reduction

    14. Results– Metals

    15. Results– pH, ORP

    16. Explanation of Data?

    17. Ongoing Research Characterization of sediment Sequential extractions XANES/EXAFS XRD? Characterization of microbial processes Phospholipid fatty acids DNA

    18. Conclusions Remediation by oxidation Opposes natural redox buffering of sediment Remediation by further reduction Requires C addition pH changes reduce effectiveness (?) Both difficult due to complex hydrogeological flowpaths More research is warranted– in situ remediation may prove very difficult

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