Anaerobic treatment of high-sulfate wastes

Six parallel upflow anaerobic sludge bed reactors were operated at chemical oxygen demand (COD) loads from 3 to 10 kg COD/(m3∙d). Four reactors (R1–R4) were fed sodium sulfate at loads of 1–3 kg S-SO4/(m3∙d). Reactors R1 and R2 were fed spent cheese whey with R1 being operated in an unstripped and R2 in a stripped mode. At COD loads below 5 kg/(m3∙d), the removal in R1 was 60–80% COD and generally trailed R2 by a margin of 0–15%. At higher COD loads and at higher SO4/COD ratios, the performance of R1 deteriorated significantly. A similar situation was found in the pair R3 (unstripped) and R4 (stripped), which was fed a mixture of spent whey and sulfite cooking liquor. Reactors R5 and R6 were subjected to the same feed as R3 and R4, but no sulfate was added. A comparison of R4 with R6 indicated slightly lower COD removal in R4 with similar amounts of volatile fatty acids accumulating in both reactors in cases of overloading. Key words: anaerobic treatment, sulfides, methanogenesis, inhibition, sludge bed r...