Optimizing carbon source strategy for denitrification using food waste fermentation liquid: Synergistic mechanisms of...

Food waste fermentation liquid, rich in volatile fatty acids (VFAs) and carbohydrates, serves as a sustainable electron donor for biological nitrogen removal. However, the compositional fluctuation of fermentation liquid often leads to unstable denitrification, and the mechanistic influence of mixed VFA-saccharide interactions on microbial ecology remains poorly understood. In this study, four carbon-source systems-three simulating typical mixed fermentation products (acetate + sucrose, propionate + sucrose, butyrate + sucrose) and one single-carbon control (acetate alone)-were systematically evaluated in sequencing batch reactors (SBRs). Results indicated that the butyrate-sucrose system (A3) exhibited superior performance, achieving a nitrate removal efficiency of 98.5%, which was 13.5% and 8.2% higher than that of the acetate-sucrose (A1) and propionate-sucrose (A2) systems, respectively. Furthermore, A3 maintained the lowest nitrite accumulation (<0.5 mg/L). Mechanistically, A3 facilitated the selective enrichment of functional genera Ferruginibacter and Terrimonas. PICRUSt2 functional predictions revealed that this specific combination significantly enhanced KEGG pathways related to membrane transport (ABC transporters) and energy metabolism, suggesting a synergistic effect that accelerates electron transfer and metabolic turnover. This study demonstrates that regulating acidogenic fermentation towards a butyrate-dominant composition is a promising strategy to maximize the utility of food waste as a carbon source, ensuring robust nitrogen removal in wastewater treatment.