Coupling alternating current field with biostimulants enhances lignite biomethanation, with evidence consistent with...

Anaerobic conversion of lignite to methane is hindered by its aromatic structure and phenolic toxicity. Applying an alternating-current (AC) electric field (1.0 V_rms/cm, 500 kHz) with biostimulants markedly enhanced methane production by stimulating microbial redox pathways. Food waste yielded 294.7 mL CH₄/g COD_r (123.3 mL CH₄/g lignite), 3.2 times higher than control (94.2 mL CH₄/g COD_r), while maintaining stable pH and alkalinity. Pig manure achieved 228.3 mL CH₄/g COD_r, underscoring the importance of complex substrates. Electrochemical analyses revealed stronger redox currents and ∼ 28 % lower charge-transfer resistance, indicating more efficient electron transfer. Spectroscopic analyses showed depletion of humic-like compounds and emergence of aliphatic and quinone groups. Microbial profiling demonstrated enrichment of Clostridium, Bellilinea, and Methanothrix, while functional inference suggested genes associated with extracellular electron transfer, electron bifurcation, and cometabolism. Overall, AC field stimulation with complex biostimulants represents a promising strategy for methane production from lignite and supports scalable bioelectrochemical energy recovery.