Role of biogas stirring in alleviating acidification and promoting methanogenesis during the anaerobic digestion of food waste: Macroscale and microscale perspectives

Anaerobic digestion (AD) represents an important solution for reducing the annual increase in global food waste, by facilitating the recycling of food resources. In the present study, we introduce a biogas stirring reactor (RB) to address the over-acidification in AD systems, enhancing methanogenic efficiency. Compared with the mechanical stirring reactor (RM), the RB exhibited higher methane yields (219 ± 17 mL CH₄/g volatile solids (VS)_added/d) and stable pH values (7.0 ± 0.2) during the steady-state phase. Computational fluid dynamics analysis highlighted the superior vertical mixing and flow velocity in RB, which reduced the sludge particle size (359 μm in RM vs. 100 μm in RB) and extracellular polymeric substance content (283 mg/g VS in RM vs. 126 mg/g VS in RB), thereby enhancing microorganism interactions and AD efficiency. Notably, biogas stirring enriched hydrogenotrophic methanogens, particularly, Methanobacterium, rebalancing the AD process. Microbial community analysis confirmed the positive impact of biogas stirring on hydrogen utilization by microorganisms. Our findings highlight the effectiveness of biogas stirring in enhancing the methane yield and present a viable approach for managing over-acidification in AD systems.