ABSTRACT
102Selenium (Se) discharged into natural waterbodies can accumulate over time and have negative impacts on the environment. Se-laden wastewater streams can be treated using biological processes. However, the presence of other electron acceptors in wastewater, such as nitrate (NO3 −) and sulfate (SO4 2-), can influence selenate (SeO4 2-) reduction and impact the efficiency of biological treatment systems. SeO4 2- removal by biofilms formed from an anaerobic sludge inoculum was investigated in the presence of NO3 − and SO4 2- using drip flow reactors operated continuously for 10 days at pH 7.0 and 30°C. The highest total Se (~60%) and SeO4 2- (~80%) removal efficiencies were observed when the artificial wastewater contained SO4 2-. A maximum amount of 68 μmol Se/cm2 was recovered from the biofilm matrix in SO4 2- +SeO4 2- exposed biofilms and biofilm mass was 2.7 fold increased for biofilms grown in the presence of SO4 2-. When SeO4 2- was the only electron acceptor, biofilms were thin and compact. In the simultaneous presence of NO3 − or SO4 2-, biofilms were thicker (> 0.6 mm), less compact and exhibited gas pockets. The presence of SO4 2- had a beneficial effect on biofilm growth and the SeO4 2- removal efficiency, while the presence of NO3 − did not have a significant effect on SeO4 2- removal by the biofilms.
