Effect of influent COD/SO42− ratios on biodegradation behaviors of starch wastewater in an upflow anaerobic sludge blanket (UASB) reactor

• Sulfidogenesis was essential to the UASB operation and process stability.
• Reactor showed the high stability at COD/SO42− ratios ⩾2 with efficient removal of COD and sulfate.
• Sulfidogenesis promoted propionate degradation and acetoclastic methanogenesis.
• Excessive sulfidogenesis suppressed methanogenesis, deteriorating bioenergy conversion.

A lab-scale upflow anaerobic sludge blanket (UASB) has been run for 250 days to investigate the influence of influent COD/SO42− ratios on the biodegradation behavior of starch wastewater and process performance. Stepwise decreasing COD/SO42− ratio enhanced sulfidogenesis, complicating starch degradation routes and improving process stability. The reactor exhibited satisfactory performance at a wide COD/SO42− range ⩾2, attaining stable biogas production of 1.15–1.17 L L−1 d−1 with efficient simultaneous removal of total COD (73.5–80.3%) and sulfate (82.6 ± 6.4%). Adding sulfate favored sulfidogenesis process and diversified microbial community, invoking hydrolysis–acidification of starch and propionate degradation and subsequent acetoclastic methanogenesis; whereas excessively enhanced sulfidogenesis (COD/SO42− ratios <2) would suppress methanogenesis through electrons competition and sulfide inhibition, deteriorating methane conversion. This research in-depth elucidated the role of sulfidogenesis in bioenergy recovery and sulfate removal, advancing the applications of UASB technology in water industry from basic science.

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