Regulation of aerobic granular sludge reformulation after granular sludge broken: Effect of poly aluminum chloride (PAC)

• The effects of PAC on the re-formation of broken aerobic granular sludge were investigated.
• Charge neutralization and bridging induced by PAC improved the sludge surface properties.
• The protein in the EPS correlated well with the surface property and settling ability of sludge.
• The re-formed granules cultivated with PAC showed better characteristics.
• PAC treatment accelerated the re-formation process of crush granular sludge.

The present study focuses on the effect of poly aluminum chloride (PAC) on the re-formation of aerobic granular sludge after its rupture. The morphological changes, physical characteristics such as SVI, mechanical strength and surface properties of aerobic granular sludge during the re-formation process of broken granules were investigated. Moreover, components (protein (PN), polysaccharides (PS)) and distributions (soluble, loosely-bound (LB), tightly-bound (TB)) of extracellular polymeric substances (EPS) in sludge flocs were taken into consideration. It was found that the effect of charge neutralization and bridging induced by PAC treatment improved the surface properties of sludge, the re-formed granules had a larger size, more compact structure and that the removal performance of pollutants after chemical coagulation had improved. The results of correlation analysis demonstrated that PN in EPS correlated well with the surface characteristics and settling ability of sludge flocs, and PAC treatment strengthened the influence, further accelerated the reformation of granular sludge.