Effect of selenate and thiosulfate on anaerobic methanol degradation using activated sludge.

Anaerobic bioconversion of methanol was tested in the presence of selenate (SeO42−), thiosulfate (S2O32−), and sulfate (SO42−) as electron acceptors. Complete SeO42− reduction occurred at COD:SeO42− ratios of 12 and 30, whereas ~ 83% reduction occurred when the COD:SeO42− ratio was 6. Methane production did not occur at the three COD:SeO42− ratios investigated. Up to 10.1 and 30.9% of S2O32− disproportionated to SO42− at COD:S2O32− ratios of 1.2 and 2.25, respectively, and > 99% reduction was observed at both ratios. The presence of S2O32− lowered the methane production by 73.1% at a COD:S2O32− ratio of 1.2 compared to the control (no S2O32−). This study showed that biogas production was not preferable for SeO42− and S2O32−-rich effluents and volatile fatty acid production could be a potential resource recovery option.