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Perchlorate Treatment Technologies
Treatment of perchlorate contamination in water is complicated because the perchlorate anion does not respond to typical water treatment techniques due to its fundamental physical and chemical nature. The perchlorate tetrahedron itself is structured such that the four oxygen atoms surround the central chlorine atom, effectively blocking reductants from directly attacking the chlorine. The perchlorate anion is soluble and very mobile in aqueous systems. It can persist in the environment for many decades under typical groundwater and surface water conditions because of its resistance to react with other available constituents. While perchlorate is thermodynamically a strong oxidizing agent, with chlorine in the +7 oxidation state, it is a kinetically sluggish species, such that its reduction is generally very slow, rendering common reductants ineffective.
Perchlorate treatment technologies may be generally classified into categories of destruction or removal technologies:
- Destructive processes:
- biological reduction
- chemical reduction
- electrochemical reduction
- Physical removal processes*:
- anion exchange
- membrane filtration (including reverse osmosis and nanofiltration)
- electrodialysis
The optimum treatment technology for a given perchlorate occurrence may depend on several factors, including perchlorate concentration, the presence and concentration of co-contaminants, other water quality parameters (pH, alkalinity, natural organic matter (NOM), total dissolved solids (TDS), metals, etc.), and geochemical parameters (nitrate, sulfate, chloride, dissolved oxygen, redox potential, etc.). The presence of indigenous perchlorate-reducing microbes (PRM), and substances inhibitory to PRM activity will also influence perchlorate treatment technology effectiveness. For in situ treatment of perchlorate contamination, variables related to the site hydrogeological setting, such as depth to and distribution of contaminants, soil permeability, groundwater flow velocity, etc. are also additionally important. As stated previously, this document does not evaluate the effectiveness of different treatment technologies, but rather seeks to provide basic information on the compiled case studies involving perchlorate treatment, pertinent data on some of the above factors that create complexity, and where available, resultsoriented data.
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