Removal of selenite from artificial wastewater with high salinity by activated sludge in aerobic sequencing batch...

Selenite (Se(IV)) in artificial wastewater under high-salinity conditions of 70 g/L was treated by using sequencing batch reactors (SBRs). Activated sludge derived from a municipal wastewater treatment plant was acclimated to high salinity and was subsequently subjected to Se(IV) treatment. Two SBRs with different operating conditions, SBR-A and -B, were tested; the former was fed with influent containing a higher concentration of Se(IV) at 100 mg Se/L, whereas the Se(IV) concentration of influent for the latter was increased stepwise at 20-100 mg Se/L. Both SBRs showed high removal efficiency of up to 98% from the beginning. The removal efficiency gradually worsened in the middle stage, from the 11th and 16th batches in SBR-A and -B, respectively. After the 18th batch, a batch cycle with twice the duration was employed, and the removal efficiency was recovered from the 20th batch onward in both SBR-A and -B. This indicated that the hydraulic retention time is an important factor in maintaining efficient and stable performance of Se removal. The mass balance analysis revealed that Se was removed mainly through biovolatilization, which was attributed to a carbon source containing proteins or peptides. This study was the first to investigate the possibility of using biotreatment for Se-containing saline wastewater.