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Summary Anaerobic digestion is one of the most efficient methods for pig manure management. In this study, methane measurement of a liquid fraction obtained from 0.1 mm sieve mesh filtration and raw pig manure was conducted, and the corresponding dynamic evolution of metabolites and microbial community structure was investigated. The results showed that the liquid fraction filtered through a 0.1 mm sieve mesh gave a maximum methane production yield of 468.13 mL‐CH4/g‐VSadded, 4.50‐times higher than raw pig slurry after 60 days. This result indicates that the 0.1 mm sieve filtration effectively provided an appropriate concentration of biodegradable compounds for high methane production in the slurry. Interestingly, the filtrates from 0.1 mm sieve mesh initially produced a high amount of volatile fatty acid, which later considerably decreased the concentrations of acetic and butyric acids on the day when the methane concentration increased. The metabolite results were consistent with the microbial community analysis, which revealed an increase in the populations of acid‐producing bacteria and archaea in the filtrates from 0.1 mm sieve mesh samples as compared to the non‐filtered samples. These findings indicate that the filtrates from a 0.1 mm sieve mesh sample contained a greater proportion of cooperative producers of acid and methane than the non‐filtered samples. In addition, the techno‐economic analysis demonstrated that this method would be economically viable when applied to a large‐scale system (100 tons of pig slurry) since it can yield a substantial profit margin of 1,847,723 $/year and a return on investment of 25%.

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Microbial production of hydrogen (future ideal fuel and important gas for industries) under anoxic conditions has limited ATP availability and low efficiency. We engineered E. coli K12 to acquire a flavin-based electron bifurcation (FBEB) system, a bioenergetic route typically found in strict anaerobes, which uses NADH to generate low potential reduced ferredoxin and high potential butyryl-CoA. The oxygen-tolerant FBEB-E. coli showed higher H2 and succinate production (2-4 folds), lower cellular reduction potentials, greater accumulation of cellular reductants and various metabolites, including ATP (up to a 7-fold increase). It could better tolerate prolonged and recycled usage of the engineered cell for H2 and succinate production than the native strain. FBEB-E. coli could also use various substrates such as formate, D-glucose and food waste for H2 and succinate production. This is a promising pathway to sustainable H2 and succinate production. This work also demonstrates that E. coli with an extra electron bifurcation system is a robust synthetic biology host.

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