Abstract:
With the drastic increase in selenium-releasing anthropogenic activities, the bioaccumulation of toxic selenium
oxyanion in the environment has increased significantly, posing deleterious effects to living organisms. The
bio-removal of selenite by Enterococcus spp. under both aerobic and anaerobic batch conditions was
examined using batch reactors containing Tryptone Soy Broth (TSB) laced with sodium selenite. The optimal
conditions for bacterial growth and selenite reduction were determined under anoxic conditions.
Enterococcus spp. reduced selenite more effectively under anaerobic conditions, with 77 % selenite reduction
after 20 h. The bacteria also reduced selenite under aerobic conditions, but the process was much slower,
with approximately 68 % reduction after 72 h. This correlated with the more rapid bacterial growth seen in the
anaerobic batch reactor. Optimal growth conditions for Enterococcus spp. were obtained at a temperature of
25°C, pH of 6 and initial selenite concentration of 30 mg/L. Optimal selenite removal was at temperature of
35°C, pH of 7, and initial selenite concentrations of 30 mg/L. A red precipitate was formed during the selenite
removal experiments, a probable sign that the selenite was being reduced to form elemental selenium. The
results of this study demonstrated the capability of Enterococcus spp. to bio-transform toxic selenite oxyanions
under both oxic and anoxic conditions.
