Effect of selenate on treatment of glycerol containing wastewater in UASB reactors
Mohanakrishnan Logan, Lea Chua Tan, Corine Nzeteu, Piet N.L. Lens
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.