Enhanced Phenol Biodegradation and Methanogenesis by Conductive Carbon-Based Materials in Anaerobic Systems

Phenol is a pervasive organic contaminant in industrial wastewater. This study elucidates the mechanisms of methanogenic phenol biodegradation in systems supplemented with granular activated carbon (GAC), graphite felt (GF), or their quinone-functionalized variants (GAC-Q and GF-Q). Batch assays were conducted with 10 g L–1 of each material at initial phenol concentrations of 50, 100, and 500 mg L–1. Carbon-amended systems achieved phenol removal efficiencies of 93–99%, representing a ∼50% increase over the control, suggesting that adsorption facilitated subsequent biodegradation. Methane production exhibited material-dependent responses: GF and GF-Q enhanced methanogenesis up to 40% at low phenol concentrations, whereas GAC and GAC-Q achieved the highest methane production rates at 500 mg L–1 phenol. Microbial analysis revealed a metabolic shift toward microorganisms previously involved in direct interspecies electron transfer (DIET), driven by the enrichment of electroactive taxa: strong enrichment of Syntrophorhabdus (26–46%) across all cultures and moderate enrichment of Mesotoga (1.2–4.4%) exclusively in carbon-supplemented treatments. These bacteria co-occurred with enriched methanogens, including Methanosaeta and Methanobacterium. Overall, our results suggest that phenol removal resulted from the combined effects of microbial degradation, adsorption, and potentially enhanced extracellular electron transfer associated with the carbon-based materials.