Impact of carrier structure on the start-up of aerobic granular sludge process

Aerobic granular sludge (AGS) has the advantages of high biomass retention, compact structure, rapid settling, and strong resistance to shock loads, while its start-up period is realtively long, restricting its wide application. Carrier-based incubation can accelate the formation of stable AGS. This study investigated the AGS formation process in four carries with different physical structures. The experimental results demonstrated successful AGS formation in all carriers, with the exception of the carrier exhibiting the lowest porosity. The formed AGS removed over 90% of chemical oxygen demand in the influent, at an organic loading rate of 3.5 ± 0.2 kg COD/m³/d. Interestingly, the carrier with the largest single-hole volume (294.3 mm³) produced AGS of the largest size. However, its settleability was lower than that of AGS in the other two systems due to its loose structure. In addition, the experimental results showed that the formed AGS can remove over 80% of total nitrogen and over 45% of total phosphate in the influent in an aerobic bulk liquid condition, suggesting a multilayer structure of AGS including all required functional microorganism. Overall, the findings of this study provide some insight into the start-up of AGS process in a relatively short period using different carriers.