Mechanistic insights into promoted biogas production and reduced antibiotic resistance genes’ risks of dry anaerobic digestion of organic wastes with biochar addition

Abstract To explore the bioaugmentation mechanism of biogas-production promotion and risk reduction of antibiotic-resistance genes (ARGs) in the anerobic co-digestion of cattle manure and rice straw with biochar addition, the performances of digestion and productivity with different amounts of biochar additions (0, 1.25, 3.75 and 5 g·L⁻¹ slurry) were studied. The results indicated that, biochar addition could effectively promote biogas production, and the cumulative methane (CH4) yields from the treatments with 3.75 g·L⁻¹ slurry and 5 g·L⁻¹ slurry biochar additions were18.7 times and 14.8 times of CK (0 g·L⁻¹ slurry), respectively. Combined with Fourier transform infrared spectroscopy (FTIR) analysis and high-throughput sequencing-based microbial community quantification, the methanogenesis was enhanced through three possible pathways: (1) the porous structure and aromatization characteristics of biochar could promote destruction of cellulose bundle structure, thereby promoting the hydrolysis of lignocellulosic substrates; (2) Biochar regulated volatile fatty acid (VFA) concentrations within an optimal range, enhancing the buffering capacity of the anaerobic digestion system; (3) The low-dose biochar (1.25 g·L⁻¹ slurry) achieving the optimal ARG risk mitigation by suppressing the primary ARG host Bacteroidota. Graphical Abstract