Development of Arcella vulgaris induced granule formation in an SBR.

This study reports aerobic granular sludge formation in a sequencing batch reactor (SBR) treating municipal wastewater at technical scale. An increase in temperature caused a massive increase in Arcella vulgaris abundance in the activated sludge. Next, the observed relative abundance of Arcella vulgaris gradually diminished, which may have occurred as a result of these microorganisms serving as a scaffolds for granule formation and subsequently being hidden in the granules. As a result of granule formation, biomass concentration in the SBR chamber increased from 5.9 ± 0.8 g MLSS/L to 9.1 ± 0.7 g MLSS/L; the sludge volume index (SVI) decreased from 135 ± 26 mL/g MLSS to 46 ± 16 mL/g MLSS. At the beginning of the period with mature granular sludge, crawling ciliates, attached ciliates and free-swimming ciliates co-dominated. Then a massive development of Aspidisca cicada resulted in crawling ciliates becoming the dominant group. The sludge biotic index (SBI) ranged from 9 to 10, which indicated first-class sludge quality. [ABSTRACT FROM AUTHOR]