Aerobic granular sludge: Formation mechanism, accelerating granulation strategies, and emerging applications

Industry, pharmaceuticals and catering all generate large amounts of complex wastewater that urgently requires effective treatment. Aerobic Granular Sludge (AGS) has emerged as a transformative technology in sustainable wastewater treatment, characterized by its compact structure, high biomass retention and multiple pollutants removal capability. The unique spatial layered structure allows AGS to simultaneously remove COD, nitrogen, phosphorus and other pollutants from wastewater in a single reactor. This paper analyzed 3289 retrieved articles and found that research hotspots in the past 15 years cover both macroscale applications and molecular mechanisms related to AGS. There is no unified view on the formation mechanism of AGS. The connections and differences between the mechanisms of various strategies to accelerate AGS granulation are still unclear. Based on relevant studies in the past 25 years, this paper proposes a 6-step granulation mechanism of AGS, including 6 processes from nucleus formation to AGS fragmentation. It comprehensively summarizes the influencing factors in the granulation process, the mechanisms of 4 strategies to accelerate granulation, their connections and the latest knowledge. It emphasizes the crucial role of AGS in integrating the treatment of emerging pollutants in wastewater and resource recovery. This work is of great significance for developing efficient and sustainable wastewater treatment systems.