Evaluation of nano-scale zero-valent iron for removal of organo-selenium species from industrial wastewater

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Selenium is a contaminant of concern that is present in industrial wastewaters from many Canadian industries, including coal mining, oilsands mining, petroleum refining, and coal-fired powerplants. In wastewater, selenium is typically present in inorganic form which include selenate (SeO4)2- and selenite (SeO3)2- oxyanion species. Biological treatment processes applied to treat industrial wastewaters have shown to reduce inorganic selenium oxyanions to elemental selenium. However, formation of organic selenium compounds such as selenomethionine with higher toxicity and tendency to bioaccumulate have been noted during biological treatment. Recent regulations target magnitude of bioaccumulation of selenium in fish tissues rather than selenium concentrations in end-of-pipe effluents. The environmental effects, toxicity and stringent regulations demand removal of organoselenium species from industrial wastewater. Stantec is keen in developing a technology that will effectively remove organoselenium from industrial wastewaters as there are no technologies that has been demonstrated for these compounds. ****This research work proposes to evaluate removal of organoselenium species from industrial wastewaters by adsorption using nano zerovalent iron (nZVI) composites. Use of nZVI composites is promising as the material has demonstrated high potential for removal of wide range of inorganic metals and metalloids from wastewaters. The ability of nZVI to adsorb organoselenium species will be evaluated through laboratory batch and continuous experiments. Experiments will be conducted with selenomethionine, selenocyanate, and S-(methyl)selenocystine as references for organoselenium compounds. Adsorption isotherms and the effect of various process parameters such as wastewater pH, ionic strength, temperature and other competing anions will be evaluated for these reference compounds. These new understanding developed under this project will be employed for the removal of organoselenium compounds from industrial wastewaters.****************