Improving high-solids anaerobic digestion of source-separated organics with nanobubble water supplementation: Significance of microbial community dynamics

High-solids anaerobic digestion (HSAD) of source-separated organics (SSO) is a key strategy for sustainable waste management and energy recovery, but its intensification through advanced technologies is vital to enhance energy recovery and process stability. This study investigated the impact of nitrogen nanobubble water (N 2 -NBW) supplementation on HSAD of SSO with percolate recirculation. Two bench-scale HSAD reactors were operated under mesophilic conditions, one supplemented with N₂-NBW in the percolate tank, while the control operated without NBW addition. The N₂-NBW-amended reactor achieved ~43 % higher cumulative methane yield than the control along with improved methane content, and reduced hydrogen sulfide (H 2 S) levels. Although total volatile fatty acids (VFAs) levels were similar between systems by day 28, the N 2 -NBW reactor maintained a relatively lower VFA-to-alkalinity (VFA/Alkalinity) ratio (0.33 vs. 0.40) and higher alkalinity (22,540 vs. 18,824 mg CaCO 3 /L), indicating improved buffering capacity. Microbial community analysis revealed an increased abundance of Methanosarcina and vadinCA11 , indicating the development of a more resilient microbial community. These findings demonstrate that N 2 -NBW is a promising intensification strategy for enhancing HSAD efficiency and resilience. • N 2 -NBW was applied to high-solids anaerobic digestion with percolate recirculation. • Methane yield increased by ~43 %. • Improved biogas quality with reduced hydrogen sulfide and increased methane content. • Enhanced enrichment of syntrophic microbial communities.