Optimising organic composition of feedstock to improve microbial dynamics and symbiosis to advance solid-state anaerobic co-digestion of sewage sludge and organic waste

This study provided new insight to the underlying mechanisms, by which organic compositions, including protein, fat, degradable carbohydrates and lignocellulose, regulate the performance of solid-state anaerobic digestion (SSAD) for synergistic treatment of organic wastes. Results show that the feedstock with a balanced composition of protein, fat, degradable carbohydrates and lignocellulose could maintain SSAD homeostasis to enhance methane (CH4) production by 14–487%. On the other hand, organic waste with a high content of degradable carbohydrates and fat at 39 and 14%, respectively, showed an initially high CH4 production at the beginning but a lower overall CH4 production. This was because of the accumulation of volatile fatty acids (VFAs) and ammonium nitrogen (NH4+-N) at up to 17.3 and 7227.7 mg·L−1, respectively, leading to anaerobic activity inhibition. Microbial dynamic and modular network analyses indicated that the balanced feedstock secured stepwise biodegradation of different organic substances to reduce the relative abundance of hydrolytic bacteria (e.g. Rikenellaceae_RC9_gut_group and Tepidimicrobium), thus alleviating VFAs and NH4+-N stresses. In particular, fat in the balanced feedstock could not only enrich the phylum Firmicutes for macromolecular biodegradation and genes for VFAs production, but also inhibit relative oxidizers (e.g. Synergistes and Acinetobacter) to facilitate propionate and acetate production to strengthen acetotrophic methanogenesis for effective CH4 yield. Results in this study show that a balanced organic composition could regulate microbial dynamics and symbiosis to advance SSAD homeostasis and methanation in synergistic organic waste treatment.