Effect of influent COD/SO₄^2- ratios on biodegradation behaviors of starch wastewater in an upflow anaerobic sludge blanket (UASB) reactor

A lab-scale upflow anaerobic sludge blanket (UASB) has been run for 250 days to investigate the influence of influent COD/SO₄^2- ratios on the biodegradation behavior of starch wastewater and process performance. Stepwise decreasing COD/SO₄^2- ratio enhanced sulfidogenesis, complicating starch degradation routes and improving process stability. The reactor exhibited satisfactory performance at a wide COD/SO₄^2- 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/SO₄^2- 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.