Hapuarachchi, Suminda, Mass balance and trapping of headspace samples of bioremediation in selenium-amended samples, Master of Science (Chemistry), August 2002, Sam Houston State University, Huntsville, Texas, 67 pp. (pdf version of this thesis)

One of the purposes of these experiments was to determine the mass balance in the bioremediation of selenium amended samples and to try to improve the efficiency of the bioremediation of selenium. The other purpose was to study the interference of glass containers in selenium determination by atomic absorption spectrometry with hydride generation.

In this research, the first step was to develop a gas phase trapping method and to prove the success of that method using known concentrations of known organo-selenium compounds. Fifty percent nitric solution was a good trapping solution to collect volatile organoselenium compounds purged from live, liquid bacterial cultures. Then, bioreactor experiments were carried out to determine the mass balance of selenium as it was biologically processed by a selenium-resistant bacterium. First, bioreactor experiments were undertaken anaerobically with different amended selenium concentrations and the mass balance of each process measured. After that, bioreactor experiments were carried out under sequential anaerobic/aerobic culture growth conditions and the distribution of selenium among three different physical states was determined.

As a percentage of amended selenium, selenite was more effectively reduced to Se0 by Pseudomonas fluorescens than selenate. When low amounts of selenite were present in the solution, reducing efficiency as a percentage of added Se was higher as measured by the production of Se0. Sequential anaerobic/aerobic growth conditions did not have a big effect in this detoxification process as carried out. We saw no real difference in elemental Se production between culture grown completely anaerobic as compared to mixed anaerobic and aerobic periods. To remove the interference of glass containers in selenium determination by HGAAS, glass test tubes were treated with different chemical solutions to minimize interferences and the most successful reagent for this process determined. Rinsing borosilicate test tubes with concentrated nitric acid was most successful at reducing the poor recovery rates of Se in HGAAS. The poor recovery rates of selenium in glass test tubes may be due to adsorption of Se to the glass instead of dissolution and the contribution of interfering ions to sample solution during the analysis.

Thomas G. Chasteen
Thesis Director

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