Overcoming Methanogenesis Barrier to Acid Inhibition and Enhancing PAHs Removal by Granular Biochar During Anaerobic Digestion

•Biochar addition promoted PAHs removal during continuous anaerobic digestion (AD).•VFAs accumulation inhibited PAHs biodegradation and related genes expression.•Distribution and biodegradation mechanisms of PAHs during AD were revealed.•Biochar enhanced functional pathways of hydrolytic acidification and acetogenesis.•Direct interspecies electron transfer was key to efficient and stable methanogenesis.