Synergistic aerobic-anoxic denitrification for nitrogen removal mediated by multi-functional microorganisms in an aerobic system

Synergistic aerobic and anoxic denitrification mediated by multiple functional microorganisms effectively prevents nitrite accumulation, maintains the structural stability of microbial communities. However, current research on the synergistic nitrogen removal mechanisms of multiple bacterial communities under aerobic conditions remains insufficient. In this study, a multi-cycle dissolved oxygen (DO) gradient environment was constructed to acclimate functional microorganisms for practical municipal wastewater treatment. The results demonstrated that the system achieved stable removal efficiencies of 90%, 95%, and 60% for COD, NH 4 + -N, and TN, respectively, under fluctuating actual influent conditions. Bacterial genera with aerobic and anaerobic denitrification capabilities, including Hydrogenophaga and Flavobacterium , were effectively enriched. The process of nitrogen migration and transformation under the influence of multiple bacterial communities was clarified. Ammonium nitrogen was first converted via autotrophic nitrification, and total nitrogen was subsequently eliminated through the synergistic coupling of aerobic denitrification and microscale anoxic denitrification inside activated sludge flocs. Increased extracellular polymeric substances (EPS) content and enlarged sludge particle size further facilitated the formation of internal anoxic zones. Functional gene prediction and metabolic pathway analysis revealed that there were both conventional anoxic denitrification and aerobic denitrification pathways within the system. The research results can provide theoretical and technical references for the dual nitrogen removal mechanism in the activated sludge system.