Enhancing Anaerobic Digestion of Kitchen Waste via Functional Microbial Granular Sludge Addition

Given the sustainable increase in kitchen waste production, the treatment of organic waste is quite important for both alleviating environmental risks and recovering biomass energy. Anaerobic digestion (AD) could achieve the goals of both organic stabilization and the green energy production of biogas. However, AD conducted at a high organic loading rate can easily suffer from low treatment efficiency due to the accumulation of volatile fatty acids and an imbalance in the microbial community. This study investigated the functional microbial enhancement strategy for enhancing AD performance. The results suggested that adding 10 g of granular sludge every 5 days could enhance AD efficiency. In that case, the daily average methane production rate was increased by 43.21% compared to that in the control group, and the pH and ammonia nitrogen concentration were maintained at the optimal level. Humic acid production was strengthened; it served as an electron shuttle, which facilitated direct interspecies electron transfer. Both Cloacimonadota and Methanobacterium were enriched in the system inoculated with the granular sludge. Metabolomics indicated that the acetyl–CoA conversion was strengthened, and that energy metabolism (complex I and archaeal ATPase) was also enhanced. The granular sludge inoculation also activated the archaeal genetic information processing system. This technology could promote the generation of green energy, which is more conducive to sustainable resource development. This study provides the theoretical basis for a microbial enhancement strategy that can enhance kitchen waste AD.