[Experimental and modeling research on the settlement of aerobic granular sludge]

Settling process of mature aerobic granules cultivated in sequencing batch reactor was investigated in this study. With the increase of settling height, the concentration of suspended solids increased from 0.24 mg x L(-1) to 6.07 mg x L(-1), mean size increased from 450 microm to 550 pm and roundness of granules increased by 12.67%. This indicated that big and regular granules have high settling velocity and can remain in the reactor after settling selection. A new parameter, selective coefficient is introduced based on the theory of selective pressure and settling experiments. Both experimental and simulated results showed that the selective coefficient increased with the increase of granule size and density, at any settling height. With the increase of settling height, selective coefficient of granules with radius above 600-800 microm increased, while that of smaller granules decreased. At high exchange ratio, bigger granules have higher selective coefficient and can accumulate more than smaller ones. At lower exchange ratio, the granulation process will slow down. Results of this study can provide foundation and instruction for the cultivation and stability of aerobic granular sludge reactors.