Effects of citrus peel biochar on anaerobic co-digestion of food waste and sewage sludge and its direct interspecies electron transfer pathway study

• Citrus peel biochar application improved the performance of anaerobic digestion . • Citrus peel biochar addition promoted the utilization and conversion of fatty acids. • Methanosaeta and Geobacter were enriched in the digester by citrus peel biochar. • Citrus peel biochar enhanced the direct interspecific electron transfer pathway.