Study on the process of aerobic granule sludge rapid formation by using the poly aluminum chloride (PAC)

• The effect of PAC on aerobic sludge granulation was investigated.
• The process for aerobic sludge granulation is greatly accelerated by cultivating with PAC.
• PAC addition promoted the aggregation of microorganisms and extracellular polysaccharides.
• Aerobic granules cultivated with PAC showed better characteristics.

Two sequencing batch reactors (SBRs) were concurrently operated to investigate the effect of PAC augmentation on aerobic sludge granulation. The result showed that dosing 500 mg/L PAC in R1 could create a strengthening process for sludge granulation, the sludge granulation time significantly decreased from 17 days to 7 days, and the mean diameter of granules in R1 was 3.2 mm after the granulation, which was consistently larger than that (2.7 mm) in R2 (control). PAC-fed granules showed better performance in the terms of settling property, compactness, mechanical strength, and higher extracellular polysaccharide content was also found. Due to the granules cultivated in R1 had more biomass, more substrate was degraded in one cycle. However, for chemical oxygen demand (COD) and ammonia–nitrogen removal efficiency, no significant difference had been discovered between the two kinds of granules. The results demonstrated that PAC enhanced the sludge granulation process in the sequencing batch reactor.