Sustainable Anaerobic Digestion of Phenol-Rich Wastewater: Enhancing Methane Production and Microbial Stability with Cosubstrate and Powdered Activated Carbon

This study evaluated the synergistic effects of cosubstrate supplementation and powdered activated carbon (PAC) addition on enhancing anaerobic digestion (AD) performance under phenol-rich conditions. Batch experiments demonstrated that cosubstrate addition significantly improved methane production, with an optimal phenol-to-co-substrate ratio of 20:80 yielding 160 ± 14 mL CH4 and 81 ± 7 mL/g COD. PAC addition further increased methane yield by 153% and COD removal efficiency by 158%, highlighting its role in facilitating direct interspecies electron transfer (DIET) and stabilizing microbial activity. Continuous operation using upflow anaerobic reactors (UARs) showed that PAC addition enhanced methane production, reaching 6,328 mL/d and 348 mL/g COD, compared to 5,560 mL/d and 305 mL/g COD without PAC. Microbial community analysis revealed greater methanogenic diversity with PAC addition, including enrichment of Methanolinea sp. and Methanosaeta harundinacea, which are involved in hydrogenotrophic and acetoclastic methanogenesis, respectively. Syntrophic bacteria such as Syntrophorhabdus sp. were also enriched, contributing to the degradation of organic acids and improved reactor stability. These findings demonstrate that cosubstrate supplementation mitigates phenol toxicity, while PAC enhances syntrophic interactions and microbial resilience. This dual strategy presents a novel and systematically validated approach to enhancing biogas recovery and operational stability in AD systems treating phenol-rich industrial wastewater.