Rapid formation of aerobic granular sludge by bioaugmentation technology: A review

Aerobic granular sludge (AGS) is the most promising technology to upgrade the most widely applied conventional activated sludge (CAS) due to its overwhelming advantages. Long start-up period is still one of the major challenges limiting the commercialization of AGS in wastewater treatment plants (WWTPs). This review summarized the main strategies adopted in the recent works about accelerating the formation of AGS, including manipulating operation parameters, dosing additives, seeding granular sludge, and inoculating special microorganisms. Although bioaugmentation technology has shown great potentials in accelerating granulation, it was inadequate summarized and underestimated in the previous reviews. In this review, bioaugmentation technology was mainly focused on and divided into two categories based on the inoculated microorganisms: (1) Flocculating bacteria; (2) Filamentous fungus (the form of spores/pellets). In parallel, some cases that inoculating pure fungal pellets (also named as mycelial pellets) and pellet-bacteria system (functional bacteria immobilized with fungal pellets) for wastewater treatment, has not been mentioned in AGS related reviews, however, the pure-culture fungal pellets was inevitable to adsorb various microorganisms during the long-term operation in the open environment exposed to the influent and air. Therefore, here we concluded it as a kind of AGS precursor and also summarized fungal pellets technology in this review. Comparison analysis was also performed among different bioaugmentation technology for rapid AGS cultivation, with future research perspectives being prospected.