Magnetite-mediated microbial community succession enhances methanogenic degradation of benzoate under stepwise...

Benzoate occurs widely in phenolic industrial wastewaters where elevated sodium concentrations frequently coexist and inhibit methanogenic activity in anaerobic digestion (AD). Short-term assays confirmed lower salinity tolerance for methanogenic benzoate degradation than for aceticlastic methanogenesis (IC₅₀: 4.0 and 8.1 g Na⁺/L, respectively). Accordingly, long-term benzoate-fed sequential AD batch tests with and without magnetite particles (MP) were conducted under stepwise salinity increases (1-15 g Na⁺/L) to evaluate salinity-induced destabilization of benzoate digestion and the potential for MP-mediated mitigation. Stepwise salinity increases markedly impaired methanogenic benzoate degradation in the non-amended control: lag time increased up to 67 d, the benzoate-degradation-rate (BDR) and methane-production-rate decreased by 50-95% and 49-68%, respectively, across 10-15 g Na⁺/L relative to the baseline condition at 1 g Na⁺/L. In the MP-amended condition, salinity inhibition was substantially alleviated, with the lag phase shortened by 97% and BDR maintained at 52.1 ± 4.6 mg/L/d even at 15 g Na⁺/L (∼8-fold higher than the control). This kinetic improvement under MP coincided with dominance of Syntrophus, OPB41, and Methanothrix, alongside predicted enrichment of electron-transfer/redox functions. These findings demonstrate the potential of MP to enhance the AD of benzoate under salinity stress, providing a basis for developing sustainable strategies to valorize saline, aromatic industrial wastewaters.