A new strategy for self-bio-driven granular sludge in a continuous-flow reactor: Applying spherical pelletizing granular sludge as a nucleus

Aerobic granular sludge (AGS) shows potential for wastewater treatment, but its practical implementation is challenging due to the complex and time-consuming startup process. This research presents a novel approach for initiating a self-bio-driven, and direct start continuous-flow aerobic granular sludge system (AGSB) using spherical pelletizing granular sludge (SPGS) as an inoculum. The optimal preparation conditions for SPGS are a moisture content of 73% and a particle size of 2 mm, which aided pollutant removal efficiency and beneficial sludge traits in AGSB. Intermittent aeration mode maintained larger particle sizes (1.8 mm) and superior settleability (SVI30/SVI5>1), enabling efficient pollutant elimination with 92% chemical oxygen demand (COD) and 61% total nitrogen (TN). The microbial population secreted considerable extracellular polymeric substances (EPS), primarily proteins and beta-polysaccharides. The self-bio-driven process relied on the underlying mechanisms of low interfacial free energy (-24 mJ/m(2)) and total potential energy barrier (29.56 kT). Metagenomic analysis of mature SPGS-aerobic granular sludge (SPGS-AGS) with different particle sizes revealed a more diverse microbial community structure and functional genes within the particle diameter range of 0.2-1.4 mm, showcasing complete nitrification, denitrification, and anaerobic nitrate reduction as key nitrogen metabolism pathways.