Purpose
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.
Methods
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.
Results
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.