Electron transfer performance and mechanism in twin microbial fuel cell powered electro-Fenton system with waste activated sludge as substrate

The twin microbial fuel cell powered electro-Fenton system (twin-MFCⓅEFs), combining active oxygen component and microbial metabolism, was constructed to improve the treatment process of waste activated sludge (WAS). Nevertheless, the performance and mechanism of electron transfer underlying this enhancement remain poorly understood. This study investigated the performance and mechanism of electron generation and utilization in twin-MFCⓅEFs with WAS as substrate. The higher electron generation and recovery efficiency (8.25 % of coulombic efficiency) was attributed to the higher content of amino acids (such as tryptophan), humic substances and their aromatic groups and unsaturated conjugated double bonds in the soluble organic matter, which facilitated biodegradation and electron transfer. The higher electron utilization performance (52.76 % of faraday efficiency) relied on the superior electron supply system that exhibited greater free radical oxidation. Metagenomic analysis indicated that an increased secretory capacity of glycosyltransferases (including glucosyltransferases and β-glucosidases) and a reduced activity of acetate kinase and methyl-coenzyme M reductase alpha subunit in cellular metabolic processes favored signaling and electricity production. The study focused on electron flow in twin-MFCⓅEFs and offered a promising strategy for improving the sludge treatment process.