ABSTRACT
74Simultaneous removal of selenate (SeO4 2-), nitrate (NO3 −) and sulfate (SO4 2-), typically present in Se-contaminated wastewaters, by Eerbeek anaerobic granular sludge, was investigated in batch and continuous bioreactor experiments. Batch experiments showed SeO4 2- removal was enhanced to 91% in simulated wastewater with SeO4 2- + NO3 − + SO4 2- (1:40:100 SeO4 2-:NO3 −:SO4 2- molar ratios) compared to simulated wastewater with SeO4 2- alone (67%). SeO4 2- removal was severely impacted by high concentrations of SO4 2- (SeO4 2-:SO4 2- > 1:300). Removal of SeO4 2-, NO3 − and SO4 2- at a 1:40:100 ratios was studied in a 2 L lab-scale upflow anaerobic sludge blanket (UASB) reactor operated at 20°C, 24 h hydraulic retention time and 2 g COD/L·d organic loading rate using lactate as electron donor. The removal efficiencies were stabilized at 100, 30 and 80% for NO3 −, SO4 2- and total Se, respectively, during 92 days of UASB operation. The total Se removal efficiencies dropped to 47% or even to a negative value when, respectively, SO4 2- and NO3 − were sequentially excluded from the influent. Speciation of Se, particularly the microbial production of colloidal Se0 levels, was influenced by both SO4 2- and NO3 −. The results presented here demonstrate that UASB reactors are capable of removing SeO4 2- in the presence of millimolar concentrations of NO3 − and SO4 2- typically found in Se- wastewaters.
