Enhancing anaerobic digestion performance of food waste through direct interspecies electron transfer via conductive materials

To enhance the anaerobic digestion efficiency of food waste, this study investigated the effects of four conductive materials, including granular activated carbon (GAC), powdered activated carbon (PAC), magnetite (Fe₃O₄), and hematite (Fe₂O₃), on direct interspecies electron transfer (DIET). Results indicated that all four conductive materials enhanced the digestion performance. PAC at 10 g/L exhibited the best performance, achieving a methane yield of 308 mL/g volatile solids (VS), 12.41% higher than the control group without conductive material addition. At the end of the reaction, the system pH was 6.76, volatile fatty acids concentration decreased to 486 mg/L, soluble chemical oxygen demand removal reached 81%, and ammonia nitrogen accumulation was 713 mg/L. Microbial community analysis showed that adding PAC selectively increased the relative abundance of acidifying bacteria (<i>Firmicutes</i> and <i>Bacteroidota</i>) by 8.16% and methanogenic bacteria (<i>Euryarchaeota</i>) by 4.36%. The relative abundance of <i>Methanosaeta</i> increased from 39.23% to 49.15%. Response surface methodology optimisation further identified ideal conditions: total solids content of 9.49%, inoculum ratio of 2.77/1, and PAC dosage of 10.87 g/L, resulting in a maximum methane yield of 347.60 mL/g VS. These findings demonstrate PAC's potential as an effective additive for improving anaerobic digestion performance by enhancing DIET, methane production and overall efficiency in food waste resource utilisation.