Waste resources efficient and clean production of solid-state anaerobic fermentation using cow dung and weathered coal

BACKGROUND: With the rapid development of society and demand for meat and dairy products, China generates a large amount of livestock manure each year. However, the low utilization rate of cattle manure has led to environmental problems such as soil imbalance, water eutrophication and ammonia emissions. Weathered coal, owing to its low calorific value, low ignition point and poor caking property, is often abandoned. Both weathered coal and cattle manure present dual environmental challenges of pollution and resource wastage. Their combined utilization through solid-state anaerobic fermentation provides a promising strategy for sustainable clean energy production and waste valorization. Nevertheless, the underlying mechanisms driving such synergistic enhancement remain poorly understood. RESULT: Co-fermentation of weathered coal and cow manure resulted in a 4.5-fold increase in biomethane production compared to cow manure mono-fermentation. Gas chromatography, humus/ammonia quantification and metagenomic analyses revealed that Bacillota, Bacteroidales, Methanocalculus and Methanosarcina were the dominant microbial consortia supporting enhanced methane yield. Metagenomic functional annotation indicated a significant upregulation of cofactor and vitamin biosynthesis, methane metabolism, and nitrogen cycling pathways. Additionally, enhanced phenylalanine metabolism – characterized by increased phenylalanine ammonia-lyase activity – was positively correlated with elevated humus content during co-fermentation. CONCLUSION: This study demonstrates that the synergistic solid-state anaerobic co-fermentation of weathered coal and cow manure substantially enhances biomethane production while promoting humus formation. The findings provide insights into microbially mediated pathways underpinning this enhancement and highlight new opportunities for waste-to-energy conversion and environmental remediation.