Pilot-scale demonstration of aerobic granular sludge augmentation applied to continuous-flow activated sludge process for the treatment of low-strength municipal wastewater

This study investigated the application of aerobic granular sludge (AGS) augmentation strategy to continuous-flow activated sludge (AS) process (mainstream) for the treatment of low-strength municipal wastewater using a pilot-scale demonstration plant. A sidestream sequencing batch reactor (SBR) was adopted for AGS production, and the AGS produced was supplied to a mainstream reactor. In the sidestream, a simultaneous feeding and drawing SBR was operated. AGS rapidly formed in terms of sludge volume index (SVI) and AGS fraction and stabilized (SVI30: 62 ± 5 mL g−1, AGS fraction: 40–60 %). The installation of a novel SBR cycle, with alternately repeated steps of short and long aeration times, further improved the settleability (SVI30: 47 ± 6 mL g−1) and contributed to an increase in AGS production by ∼50 %. AGS augmentation increased the AGS fraction (20–30 %) in mainstream, and SVI30 improved to <100 mL g−1. As the organic loading rate (OLR) to the mainstream increased, the AGS fraction increased to ∼50 %, suggesting the growth of AGS in mainstream. Despite the OLR variations, the stable settleability (<100 mL g−1 of SVI30) and relatively high retention of the MLSS enabled stable removal of tBOD and ammonium (94 ± 4 and 98 ± 1 %, respectively). This is the first study that demonstrated the potential use of AGS augmentation strategy in a continuous-flow process at the pilot scale for the treatment of low-strength municipal wastewater.