Novel Strategy for Aerobic Granular Sludge toward Advanced Nutrient Removal and Structural Stability: Leveraging Intracellular Carbon Source Competition and Microbial Community Assembly

The pursuit of high efficiency and stable performance has always been the central focus of the aerobic granular sludge (AGS) process. Herein, we propose a novel operational strategy that synergistically integrates unbalanced substrate feeding (i.e., an initial pulse-feeding phase followed by a slow-feeding phase) with a stepwise dissolved oxygen (DO) regulation regime shifting from high to low levels. Compared with the conventional slow-feeding mode, this strategy exhibited superior performance in both pollutant removal and granular stability. The removal efficiencies of total nitrogen, total phosphorus, and chemical oxygen demand reached a high level of 89.94%, 99.04%, and 94.21%, respectively. Unbalanced influent loading enhances the intracellular carbon storage efficiency of microorganisms, further promoting the enrichment of slow-growing bacteria (PAOs and GAOs). These bacteria enhance C and P removal as well as the gel strength of granules. Low DO regulation achieves efficient simultaneous nitrification and denitrification as well as advanced nitrogen removal, accompanied by an increase in the abundance of nitrogen-removing microbial communities. Moreover, even under the stress of substantial fluctuations in influent C/N ratios, AGS cultivated by the novel strategy still maintains excellent organic matter removal performance and structural stability.