Enhanced biogasification of bituminous coal via modified waste activated sludge-derived biochar

• Modified waste activated sludge-derived biochar boosts methane production of coal. • Non-nutrient modification yields a synergistic physical–chemical-biological boost. • Modified biochars shift microbial composition, enriching methanogen-related consortia. • H 2 SO 4 -Treat biochar addition increases coal pore complexity, enhancing methanogenesis rate. Biomethane production from coal was constrained by the limited bioavailability and low methane production efficiency of bituminous coal, which required catalytic enhancement to facilitate sustainable energy development. This study examined how modified biochar derived from waste activated sludge (via acid/alkali/oxidation treatments) enhanced bituminous coal biogasification by influencing methane production, microbial communities, and metabolic pathways. Physicochemical characterization revealed that different treatment approaches had substantially modified the microstructural morphology and surface functional groups of biochar. Spectroscopic analyses (FTIR and XPS) identified distinct variations in functional group distribution: H 2 SO 4 - and Na 2 CO 3 -treated biochars exhibited increases in –OH and –CO groups, while NaOH-treated biochar demonstrated pronounced increases in –OH and –COOH groups. The modified biochars significantly boosted methane production rates, with H 2 SO 4 -treated biochar addition achieving a maximum production rate of 0.258 ± 0.046 ml·g −1 ·d −1 , corresponding to a 226.25 % improvement in production efficiency relative to the control. Comparatively, Na 2 CO 3 -, K 2 Cr 2 O 7 -, and NaOH-treated biochars addition enhanced production by 135.60 %, 50.37 %, and 60.23 %, respectively. Microbial community analysis revealed that modified biochars had substantially altered microbial diversity, with H 2 SO 4 - and K 2 Cr 2 O 7 -treated biochars addition markedly increasing the abundance of Pseudomonadota , while NaOH-treated biochar addition promoted Acidobacteriota populations. Metabolomic profiling demonstrated that H 2 SO 4 - and K 2 Cr 2 O 7 -treated biochars had significantly influenced glycerophospholipid metabolism, linoleic acid metabolism, alpha-linolenic acid metabolism, and terpenoid backbone biosynthesis. Pore structure analysis following H 2 SO 4 -treated biochar addition revealed increased structural complexity, with a 134 % increase in adsorption capacity, which promoted microbial colonization and stabilized interfacial processes. These findings collectively established the multifunctional role of biochar in enhancing coal bioconversion through integrated physicochemical and biological mechanisms, offering practical solutions for renewable energy advancement.