Spatial separation and bio-chain cooperation between sulfidogenesis and methanogenesis in an anaerobic baffled reactor with sucrose as the carbon source

Abstract We investigated the sulfidogenesis and methanogenesis processes in a five-compartment anaerobic baffled reactor fed with sucrose at an organic loading rate of 4 g COD L d −1 . We decreased the influent COD/SO 4 2− ratio from 12.5 to 2.0 stepwise; the variation in the spatial pattern of sulfidogenesis and methanogenesis was observed by then the variation in concentrations of sulfide and volatile fatty acids (VFAs) in the supernatant liquors. Biogas production was stable at a COD/SO 4 2− ratio ≥6.9, and a peak biogas value of 7.18 L d −1 was obtained, which decreased to 0.75 L d −1  at a COD/SO 4 2− ratio of 2.0. High-throughput sequencing analysis identified sulfate-reducing bacteria and acetoclastic methanogens as dominant bacteria in the compartments (#1 and #2) and compartments (#3 and #4) at a COD/SO 4 2− ratio of 6.9, respectively. However, the above dominant bacteria were shifted to later compartments at a COD/SO 4 2− ratio of 2.0. The VFA composition indicated an acetic-acid-type microbial metabolism pathway was present in the early compartments at high COD/SO 4 2− ratios. Formation of this acetic-acid-type microbial metabolism pathway in sulfidogenesis produced acetate as a substrate for methanogenesis. The COD/SO 4 2− ratio is the key factor in the control of bio-chain cooperation between sulfidogenesis and methanogenesis, which determines the efficiency and stability of the sulfate wastewater treatment system.