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.