Wanting Du, Ke Shi, Bo Wang, Hongwei Tang, Qing Jiang, Xiaoyu Zhou, Guomeng Sun, Jianliang Xue
The challenge of treatability arising from its low organic carbon content makes the increasing discharge of high-sulfate wastewater a serious environmental threat to natural water bodies. Anaerobic biological treatment is commonly applied to treat low-carbon and high-sulfate wastewater. However, the mechanism by which a low COD/SO 4 2− ratio (< 1) limits microbial sulfate reduction in anaerobic reaction systems remains unclear. In this study, a laboratory-scale upflow anaerobic sludge bed (UASB) reactor was operated continuously. The experiment was operated in four phases to investigate the effect of decreasing COD/SO 4 2− from 1 to 0.2 on the sulfate reduction properties, microbial communities, and metabolic pathways. Results indicated that peak sulfate-reducing bacteria (SRB) metabolic activity and sulfate reduction efficiency (80%) occurred at a COD/SO 4 2− of 0.4. High concentrations of sulfate inhibited the growth of most SRB, weakened the metabolic ability of the microorganisms, and concurrently changed the microbial community structure. In detail, Desulfobulbus and Desulfomicrobium were the dominant genera of the primary issue. Conversely, Desulfomonile gradually became the predominant SRB under a low COD/SO 4 2− ratio (0. 2) and sustained approximately 50% sulfate reduction efficiency because of its competitive metabolic adaptability and high substrate affinity under nutrient stress. Additionally, decreasing the COD/SO 4 2− ratio reduced the abundance of functional genes in both the assimilatory and dissimilatory sulfate reduction pathways, especially the former. This study will help to reveal the microbial mechanisms for controlling sulfate reduction under carbon emission-limited conditions and provide theoretical support for the efficient and low-cost treatment of organic wastewater containing sulfate. • Sulfate reduction's microbial mechanisms under carbon limitation was studied. • Lower COD/SO 4 2- suppressed assimilatory and dissimilatory sulfate reduction genes. • Peak SRB activity and sulfate reduction occurred at a 0.4 COD/SO 4 2- ratio. • Sulfate removal dropped obviously due to insufficient carbon for SRB. • Desulfomonile dominated S removal under C limitation due to its competitive strategy.