Effect of Heavy Metal Co-Contaminants on Selenite Bioreduction by Anaerobic Granular Sludge

This study investigated bioreduction of selenite by anaerobic granular sludge in the presence of heavy metals and analyzed the fate of the bioreduced selenium and the heavy metals. Selenite bioreduction was not significantly inhibited in the presence of Pb(II) and Zn(II). More than 92% of 79 mg. L⁻¹ selenite was removed by bioreduction even in the presence of 150 mg. L⁻¹ of Pb(II) or 400 mg. L⁻¹ of Zn(II). In contrast, only 65-48% selenite was bioreduced in the presence of 150 to 400 mg. L⁻¹ Cd(II). Formation of elemental selenium or selenide varied with heavy metal type and concentration. Notably, the majority of the bioreduced selenium (70-90% in the presence of Pb and Zn, 50-70% in the presence of Cd) and heavy metals (80-90% of Pb and Zn, 60-80% of Cd) was associated with the granular sludge. The results have implications in the treatment of selenium wastewaters and biogenesis of metal selenides.