Enhancement effect of biochar addition on the mixed anaerobic digestion of pig manure and corn straw under biogas slurry circulation

Based on the semi-continuous anaerobic digestion (AD) reactor, the effects of biochar addition on the internal environmental changes and gas production characteristics of AD were studied under the condition of biogas slurry recirculation. The results showed that the addition of biochar enhanced the degradation and metabolic pathways of acetate and propionate, thereby reducing the concentrations of volatile fatty acids (VFAs), total ammonia and chemical oxygen demand. The buffer system formed by the combination of NH4+ and VFAs of C2-C5 was also enhanced, thereby maintaining pH stability and effectively mitigating inhibition of gas production. The addition of biochar effectively increased the relative abundance of Bacteroidetes, Chloroflexi, Spirochaetota and Synergistota, and enhanced the tolerance of archaea Methanosarcina. This study provides scientific support for the application of biochar to solve the system inhibition in mixed substrate semi-continuous AD process and provides technical support for the stable operation of biogas project.