Biochar-mediated enhancement of dark fermentative H₂ production from xylose wastewater: Insight into the microbial community structure succession to metabolic performance

To resolve low hydrogen (H₂) yield of xylose wastewater through dark fermentation, it seems vital to develop and understand effective functional fermentative microbe and reinforcement measures. This study presented the microbial succession characteristics through xylose selective culture medium continuous stimulation and evaluated the H₂ production process by biochar-driven in batch assays. Results showed that Thermoanaerobacterium-dominated (>99.94 %) bacterial consortium was obtained using xylose involving 5 times repeated transfers. Compared with the control group, H₂ yield increased from 0.71 mol-H₂/mol-xylose to 2.08 mol H₂/mol xylose at 7 g/L biochar addition with increases of 2.53 times. Moreover, the presence of biochar made the lag phase time decrease from 9.0 to 7.3 h and led to over 90 % of xylose being removed. The enhanced biohydrogen production performance served to factors such as stabilizing the culture's pH, maintaining intracellular NADH/NAD⁺ ratio, and enhancing the redox power and conductivity. Additionally, scanning electron microscopy revealed that the addition of biochar acted as attachment points for bacteria and enhanced cell immobilization, thus improving H₂ production efficiency. This study suggested inoculation dominated by Thermoanaerobacterium is a superior option for Bio-H₂ production from xylose wastewater in thermophilic, and a supplement of biochar could be a technically viable approach.