Effect of selenate on treatment of glycerol containing wastewater in UASB reactors

Abstract

The effect of selenate on the removal of glycerol in up-flow anaerobic sludge blanket (UASB) reactors was investigated. Two UASB reactors, RControl and RSelenium, were operated at a hydraulic retention time of 48 h and an upflow velocity of 2 m/h at 37 °C. A GAL (glucose, acetate and lactate) and glycerol mixture were used as the only feedstock throughout the experiment for RControl. After acclimation to GAL and glycerol in the start-up period, RSelenium was additionally exposed to selenate (SeO42−) concentrations from 1.43 to 71.49 mg/L (10–500 μM) in a stepwise manner. An average daily methane yield of about 150 mL/g COD, which was comparable with RControl, and 90% Se removal were achieved until 400 μM SeO42−. Simultaneously, SeO42− was reduced to elemental Se or metal selenide, supported by X-ray diffraction, as well as scanning and transmission electron microscopy. However, the methane production rapidly deteriorated when the influent SeO42− concentration was increased to 500 μM. The Se toxicity was evident from the reduction in the activity of Methanosaeta. This study showed that the SeO42− concentration, but not the COD/SeO42− ratio, governs the AD of selenate rich wastewaters.