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UBC Theses and Dissertations

Removal of soluble selenium in the presence of nitrate from coal mining-influenced water Nkansah-Boadu, Frank


Biological treatment to remove dissolved selenium from mining-influenced water (MIW) is inhibited by co-contaminants, especially nitrate. It was hypothesized that selenium reducing microorganisms can be obtained from native mine bacteria at sites affected by MIW due to the selection pressure from elevated selenium concentrations at those sites. Enrichment of these microorganisms and testing of their capacity to remove dissolved selenium from actual coal MIW was the objective of this dissertation. Fifteen sediments were collected from eleven different vegetated or non-vegetated seepage collection ponds and one non-impacted natural wetland. Nine sediments achieved greater than 90% dissolved selenium removal within 72 hours when inoculated into selenate-reducing bacteria growth medium. To find microorganisms capable of removing dissolved selenium in the presence of nitrate, six of the sediments were inoculated into two different types of growth media; one with selenate as the sole electron acceptor and the other with both nitrate and selenate as electron acceptors. Both media were otherwise identical and contained lactate as the electron donor. Decrease in dissolved selenium concentration was observed in all enrichments, but the effect of nitrate on the rate and extent of removal was variable. Nitrate inhibited dissolved selenium removal rates in four of the enrichments. However, in one instance, microorganisms enriched from a natural vegetated marsh receiving coal MIW (Goddard Marsh) were not inhibited by nitrate and the dissolved selenium removal rates were similar in both media. In another instance, the presence of nitrate enhanced dissolved selenium removal by enrichments from a pond receiving coal mine waste seepage (Lagoon A). When enrichments from Lagoon A and Goddard Marsh, respectively, were tested for dissolved selenium removal from actual coal MIW, the former achieved greater (40%) than the latter (10%). Through 16S and whole genome sequencing studies, species capable of removing selenate in the enrichments were classified as Bacteroides, Serratia, Clostridium and Methanosarcina. However, most of these species did not survive in the MIW. The dominant species in the MIW were classified as Sulfurospirillium, Veillonella, Pseudomonas and Bacteroides, which were shown to be capable of reducing selenium, based on putative metagenome assembled genomes (MAGs) obtained for these species.

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