Sustainable Valorization of Seawater Aquaculture Waste via Corn Straw Biochar: Enhancing Methane Production, Shaping Microbial Communities, and Reducing Antibiotic Resistance Genes

To promote the sustainable management of marine aquaculture waste, this study investigated the effect of corn stover biochar (300 °C, 400 °C, and 500 °C) on the mesophilic anaerobic digestion (37 ± 1 °C) of particulate matter from seawater aquaculture wastewater. Batch experiments evaluated biochar’s effects on methane production, microbial succession, and antibiotic resistance genes (ARGs), and the correlation between ARG abundance and microbial taxa. Biochar addition significantly enhanced biogas production and shortened the lag phase. During 60 h fermentation, the optimal treatment achieved a methane yield of 291 mL, which was 164.55% higher than the control. Metagenomic sequencing revealed that biochar altered microbial community structure and ARG profiles, reducing the 11 most prevalent ARG types. Glycopeptide resistance genes showed the greatest reduction (15.02%). Correlation analysis identified Enterococcus, Peptostreptococcus, and Clostridium as major ARG hosts, accounting for 64.78–69.81% of total ARG abundance in the control and 68.14–76.17% in the biochar-amended group, confirming that Firmicutes are key potential ARG carriers in marine aquaculture particulate waste. From the perspective of sustainable development, biochar addition improves energy recovery from aquaculture waste and mitigates ARG dissemination risk. This study provides practical guidance for material selection and process optimization in sustainable aquaculture biogas projects, supporting the transition toward a circular bioeconomy.