Enhanced anaerobic treatment of coal chemical wastewater using iron- and carbon-based materials: Efficiency optimization, response strategy, and enhancement mechanism.

Coal chemical wastewater contains complex and highly biotoxic compounds that inhibit anaerobic microbial activity, leading to unstable system performance. This study evaluated the effects of magnetic biochar, biochar, magnetite, iron, and biochar-magnetite composites on enhancing system resilience and pollutant removal. The magnetic biochar-amended system achieved the highest treatment performance, with average effluent chemical oxygen demand and total organic carbon concentrations of 409.1 and 104.4 mg/L, respectively, methane production increased by 87.8% in the treated system compared with the control, and effluent biodegradability was significantly improved. All reactors exhibited low concentrations of aromatic and heterocyclic compounds, particularly in intracellular fractions. Iron- and carbon-based materials promoted the secretion of microbial extracellular polymeric substances. In the optimal system, protein contents in loosely bound and tightly bound extracellular polymeric substances reached 58.4 and 80.6 mg/g mixed liquor suspended solids, respectively. Electrochemical analysis revealed increased cytochrome c content, system conductivity, and dehydrogenase activity, indicating enhanced electron transfer. These materials also modulated protein secondary structures. The ratio of α-helix to β-sheet plus random coil in loosely bound and tightly bound extracellular polymeric substances peaked at 1.1 and 0.6, respectively. This structural shift improved quorum sensing, pollutant adsorption, and stress resistance. Microbial community analysis revealed increased diversity and enrichment of functional taxa, including Acinetobacter, Pseudomonas, Comamonas, Methanosarcina, and Methanobacterium, with upregulated genes involved in organic pollutant degradation. This study elucidates the mechanisms by which material amendments enhance the anaerobic treatment of coal chemical wastewater. These findings provide valuable insights into energy recovery and industrial wastewater management.