Reducing the startup time of aerobic granular sludge reactors through magnesium and PAC augmentation

One of the main challenging issues for the aerobic granular sludge technology is the long startup time in wastewater treatment practice. This study presents a strategy to reduce the time required for granulation. The effects of magnesium and PAC augmentation on aerobic granulation in SBR were investigated using synthetic wastewater. Morphological variation of granular sludge in the reactor was observed and results revealed that augmentation with 20 mg/L Mg²⁺ and 1 g/L PAC in R2 significantly reduced the startup time of sludge granulation from 28 days to 14 days, at the same time, the mean diameter of the granules in R2 was 2.5 mm after the granulation, which was consistently larger than that (1.5 mm) in R1. The PAC may play a role of nucleus for the granulation of aerobic sludge. The addition of PAC enhanced the settleability of floes, enhanced granule strength and specific gravity, slowed down the sludge growth rate and yield rate, moderated the sludge concentration and size, and reduced the dispersed tread of size distribution.