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UBC Theses and Dissertations

Kinetics of total dissolved selenium removal in a chemostat Mohammadi, Elnaz


Biological treatment of selenium is a preferred method for total dissolved Se removal from mining-influenced water. The rate of total dissolved Se removal in bioreactors depends on the influent water chemistry and microorganisms in the bioreactor. It was hypothesized that at otherwise optimal conditions of temperature, pH, and salinity, the variables that affect the rate of total dissolved Se removal in bioreactors are total dissolved Se concentration, carbon source concentration and, the type of carbon source. The overall objective of this research was to investigate the effect of these variables on total dissolved Se removal kinetics in a chemostat. To estimate the kinetic parameters, the steady-state data were collected over time from the chemostat experiments. The effects of these variables were also studied on the microbial community composition. The effect of total dissolved Se concentration on the rate of its removal was investigated at two different feed Se-selenate concentrations. The estimated kinetic constants were equal for both concentrations; meaning that the kinetics of total dissolved Se removal was not dependent on total dissolved Se concentration in the chemostat. The effect of carbon source concentration on total dissolved Se removal was investigated over a wide range of concentrations. The results showed the dependency of the rate of carbon utilization and total dissolved Se removal on carbon source concentration. Methanol was studied as an alternative carbon source. Methanol-grown enrichments did not remove Se but inoculum that was previously grown on acetate showed Se removal activities in the presence of methanol. However, the maximum extent of total dissolved Se removal was lower compared to when acetate was present. Acetate was determined as a better alternative carbon source compared to methanol for Se removal bioreactors. The morphology of produced elemental selenium and the structure of biofilm was studied as a function of carbon source concentration. At non-limiting carbon concentrations, the microbial community was more diverse and extensive amounts of extracellular polymeric substances (EPS) were formed compared to limiting carbon conditions. When the carbon source was in excess, nanoparticles were formed as opposed to nanowires that were formed when the carbon source was limiting.

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