To investigate the effect of aluminum additive on the formation of granular aerobic sludge

PAC and aluminum sulfate were added into different SBR reactors to strengthen the granular sludge during the period of 10th to 16th day

and the chemical characteristics of granules cultivated with different coagulants were analyzed. Meanwhile the content and distribution changes of aluminum in the sludge were evaluated. Experimental results showed that aluminum coagulants additive could significantly accelerate the formation of granules and influence the chemical structure of sludge EPS. Once dosing terminated

the quality of Al in the granules cultivated with PAC decreased from 30.46% to 0.43% during the 16th to 29th day operation. Meanwhile

for the aluminum sulfate enhanced granules

the Al content decreased from 45.69% to 13.29%. Hydrolysis products of PAC mainly distributed in the periphery of flocs and the aluminum content of sludge was eventually below the limit of detection after granulation. However

aluminum sulfate fully contacted with flocs after polymerization and hydrolysis

and then concentrated in the center of granular after maturation. Above results demonstrated that aluminum coagulants played different roles in the granulation process. For PAC

the promotion of EPS secretion enhanced the aerobic granulation and then the microorganism aggregated; while a nucleation is formed after aluminum sulfate additive

leading to an increasing of EPS content