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

Anaerobic bioconversion of methanol was tested in the presence of selenate (SeO₄^2-), thiosulfate (S₂O₃^2-), and sulfate (SO₄^2-) as electron acceptors. Complete SeO₄^2- reduction occurred at COD:SeO₄^2- ratios of 12 and 30, whereas ~ 83% reduction occurred when the COD:SeO₄^2- ratio was 6. Methane production did not occur at the three COD:SeO₄^2- ratios investigated. Up to 10.1 and 30.9% of S₂O₃^2- disproportionated to SO₄^2- at COD:S₂O₃^2- ratios of 1.2 and 2.25, respectively, and > 99% reduction was observed at both ratios. The presence of S₂O₃^2- lowered the methane production by 73.1% at a COD:S₂O₃^2- ratio of 1.2 compared to the control (no S₂O₃^2-). This study showed that biogas production was not preferable for SeO₄^2- and S₂O₃^2--rich effluents and volatile fatty acid production could be a potential resource recovery option.