Resume/ Abstract
Selenium (Se) is a constituent of concern in mine influenced water (MIW) from many metal and coal mines. Soluble forms of Se must be removed down to µg/L levels before treated MIW can be safely discharged into the receiving environment. This is due to high trophic transfer factors for Se as it bioaccumulates up the food chain and its toxicity to birds and fish. Biological treatment using microorganisms that metabolize the chemical forms of Se, selenate and selenite, present in the MIW into insoluble forms is considered one best available treatment technology. The chemistry of the MIW and the nature of the carbon source used greatly influence biological treatment extent and the chemistry of the Se products. Laboratory bioreactor experiments were performed to measure the impact of total dissolved Se, nitrate, and carbon source concentrations on the extent and rate of soluble Se removal using native mine-site microorganisms. The rate of dissolved Se removal appeared to be independent of Se concentration in the MIW. Nitrate can impact Se removal positively and negatively. The nature and concentration of the carbon source had a large impact on the extent and kinetics of Se removal and the nature of the organo-selenium products formed. These results highlight the importance of MIW chemistry and bioreactor operation for effective treatment of MIW containing Se. Also, controlling bioreactor chemistry might be useful for influencing Se speciation.