Biochar-enhanced alternating current-microbial remediation of petroleum-contaminated soil: Extracellular polymeric...

Bio-electrochemical remediation systems have emerged as a promising approach for petroleum hydrocarbons (PH)-contaminated soils, while the treatment efficiency is often limited by inefficient interfacial electron transfer and insufficient microbial habitats. Here, activated-sludge-derived biochars (BC) engineered by pyrolysis temperature (400/600/800 °C) and post-treatments (HNO₃, KBH₄, liquid nitrogen) were integrated into an alternating current-assisted microbial system (BEM) to improve PH removal performance. BC800 had a more developed pore network, higher electrical conductivity, and stronger electron-accepting capacity (EAC = 2.6 mmol e^- g^-1), leading to the highest PH removal (83.4%) after 27 d. BC800 also increased extracellular polymeric substances production and promoted a protein-rich matrix in BEM, consistent with enhanced biofilm formation and extracellular electron transfer, while HNO₃-treated BC800 attenuated these effects. Microbial community, network analysis, and functional genes prediction indicated BC800 shifted the consortium in BEM toward a more cooperative, degradation-oriented configuration. Overall, this work proposes a link between the electrochemical and structural properties of BC and BEM performance, and supports the valorization of waste sludge into conductive BC for efficient remediation of PH-contaminated soils.