Mitigating combined antibiotic inhibition in anaerobic digestion of aquaculture wastewater using zero-valent...

The widespread coexistence of veterinary antibiotics in aquaculture wastewater constitutes a significant environmental hazard, severely inhibiting anaerobic digestion (AD) by disrupting microbial metabolism and electron transfer pathways. This study focuses on the realistic co-occurrence effects of oxytetracycline (OTC) and sulfamethoxazole (SMX), revealing that their interaction exhibits distinct antagonistic characteristics. To mitigate this complex inhibition, a zero-valent iron-modified biochar (ZVI-BC) was prepared via facile high-energy ball milling. This mechanochemical modification caused the micropore volume ratio to surge from 6.7 % to 52.5 %, creating a multifunctional material capable of alleviating antibiotic shock through enhanced adsorption and pH buffering. Experimental results indicated that the coexistence of OTC and SMX markedly destabilized AD, leading to a 54.50 % reduction in COD removal and severe acidification. However, the addition of ZVI-BC (optimal dosage 10 g·L^-1) effectively mitigated this toxic stress, enabling the system to operate stably for 32 days with a cumulative methane yield of 2571 mL. Mechanistic analyses revealed that ZVI-BC functioned through synergistic pathways: reducing antibiotic bioavailability via microporous adsorption and facilitating interspecies electron transfer (IET) via zero-valent iron. Crucially, FAPROTAX prediction provided novel metabolic insights, confirming that ZVI-BC successfully maintained the acetoclastic methanogenesis pathway and restructured the microbial community toward increased resilience (e.g., enrichment of Methanothrix). These results demonstrate that ball-milled ZVI-BC is a cost-effective strategy for safeguarding anaerobic digestion systems against combined antibiotic stress.