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Selenium Treatment Technologies
BUTLER, B. Selenium Treatment Technologies. Presented at 2010 NPDES States Mining Meeting, Pittsburgh, PA, June 23 - 24, 2010.
To present a discussion of Se geochemistry, synopses of technologies with pros and cons of each, and case study results.
Selenium (Se) is a metalloid that is a dietary requirement in small quantities, but toxic at higher quantities. It also is known to bioaccumulate. In oxic environments, it exists as selenate (+6) and selenite (+4), both of which are soluble. Selenite will sorb more strongly to metal oxide solids. Elemental selenium (0) and selenide (-2) will exist in reducing environments. The elemental form is an insoluble solid and selenide is soluble and toxic as hydrogen selenide (HSe-1); this can be precipitated in the presence of metals as metal selenide, similar to hydrogen sulfide precipitation of metal sulfides. Se is present in both natural and anthropogenically impacted regions of western states, but primarily associated with coal mining in the eastern states. The TMDL for Se is 4.6 µg/l. Current treatment technologies include reverse osmosis, iron reduction/precipitation (e.g., zero valent iron), active biological treatment (e.g., ABMet process), aerobic wetlands, and biochemical reactors or anaerobic wetlands. Most of these treatments show promise in mining-impacted water, but efficiency or a given technology to attain the water quality limit is dependent upon site-specific water chemistry. To be presented is a discussion of Se geochemistry, synopses of technologies with pros and cons of each, and case study results.