| Description |
This research was conducted to investigate the capabilities of different facultative anaerobic microorganisms to remove selenium present as selenate at high concentrations in mining water. In initial observations, a combination of different bacterial strains was more effective in selenate reduction than any single microbial species examined. The same result was obtained when water from mines containing heavy selenium load, Yukon mine water, was used to cultivate these bacteria. Research presented here address four areas (1) Growth curves generated for these microbes using common sugar and protein based nutrients, including trypticase soy broth (TSB), molasses, yeast extract and phosphate showed a 2-fold growth increase in less than 2.5 hours with TSB as a nutrient. The experiments were performed at room temperature and for a duration of 48 hours. Significant growth increase was not observed with yeast extract and molasses in combination or with yeast extract, molasses and phosphate in combination as nutrients. (2) Alginate bead immobilized enzyme extracts from microbial consortia Mix-1 and Mix-2 and microbial live cells consortia, Mix-1 and Mix-2 were tested for selenium reduction capabilities in synthetic water spiked with selenate over a period of 48 hours at room temperature. Mix-2 live cells exhibited highest selenium reduction capability with 99.5% reduction of selenate to elemental selenium. A small-scale reactor, 50ml, designed to serve as a model for immobilized live cells treatment method, obtained the highest level of selenium depletion from Yukon mine water- 99.1% reduction in selenate concentration after 12 hours. However, loss of stability was observed after 48 hours of operation. (3) A design and application of a bioreactor is also presented in this study. Two fixed bed reactors in series packed with pumice, a volcanic rock material, containing Mix-2 consortium microbes tested for selenium reduction in Yukon mine water with pH adjusted between 6.8 and 7.2 exhibited an average reduction of 88.2% with a total retention time of 44 hours for the reactors. Further reduction of selenium by fine-tuning the system and using more controlled conditions of temperature, feeding the reactors could be possible. (4) An electro-bioreactor designed by applying voltage to stimulate selenate transformation to elemental selenium by the Mix-2 microbes demonstrated approximately 91.5% average reduction with a retention time of 22 hours using pH 6.8 to 7.2 waters. |
