Biochar enhanced anaerobic co-digestion of poultry litter and wheat straw: Performance, microbial analysis, and multiple factors ' interaction

Amendment of anaerobic co-digestion (Co-AD) of poultry litter (PL) and agricultural straw using biochar has rarely been practiced. This study conducted two sequential experiments to evaluate the effect of adding alkaline biochar on improving the batch Co-AD of PL and wheat straw. The feasibility experiment identified the advantages of adding biochar by the improved observed cumulative methane yield (CMYo, mL CH4/g VSsubstrate) of 9.7%; the increased removal rates of the substrate total solids (TSsubstrate) and volatile solids (VSsubstrate) of 15.2% and 14.2%, respectively; the enhanced abundance of both hydrolytic bacteria and methanogens, including hydrogegenotrophic Methanobacterium and, especially, the acetolactic Methanosaeta; and the 37.3% higher abundance of the methanogenic pathways, compared to the control. The interaction experiment showed that biochar dosage (BD) interacted with the initial substrate carbon-to-nitrogen ratio (C/N) and total solids level (TS). The developed mathematical models for CMYo and VSsubstrate removal by response surface methodology were significant, which predicted the optimal conditions being initial substrate C/N ratio 29.93 and TS 6.98%, and BD 9.98% substrate. The optimized CMYo and VSsubstrate removal were 17.7% and 22.1% higher, respectively, than those of the Control. These results support the utilization of biochar in improving the Co-AD of agricultural wastes.