The impact of organic loading rate on the cultivation and stability of aerobic granular sludge in continuous flow reactor

Abstract

To investigate how organic loading rate (OLR) affects the formation of aerobic granular sludge (AGS) in continuous flow system, the effect of OLR adjusted by hydraulic retention time (HRT) and influent chemical oxygen demand (COD) on pollutant removal, granulation efficiency and microbial community were comprehensively analyzed. The results showed that increasing OLR by decreasing HRT led to significant filamentous sludge bulking and biomass loss. Conversely, gradually increasing the OLR to 0.19 kg·(kg·d)⁻¹ by adjusting influent COD improved the granulation efficiency from 3.00% to 28.40% with the average particle size of 193.60 μm at the 60th day. However, excessive OLR would promote filamentous bacteria to use the residual COD in the oxic tank. Organic matter utilization path analysis showed that the COD utilization enhanced by phosphate accumulating organisms (PAOs), glycogen accumulating organisms (GAOs) and adsorption (44.85 ± 2.50%) during anaerobic phase when influent COD was 350 mg L⁻¹. And the relative abundance of PAOs and GAOs increased to 4.14% and 3.18%, respectively. This was the main cause of granulation. Furthermore, strategies to enhance granulation in continuous flow systems were proposed: Increase the volume of anaerobic tank or introduce intermittent mixing to keep more influent organics is used by bigger biomass before entering the oxic tank.