The compensation of micro-carriers on hydraulic shear force during aerobic sludge granulation

Abstract

Hydraulic shear force (HSF) is of great importance in granulation and treatment performance of aerobic granular sludge (AGS) process. High HSF has been shown to be conductive to granulation, which could be obtained by high superficial gas velocity (SGV). Micro-carriers could influence the flow regime in reactors. Thus, AGS system with micro-carriers addition could obtain higher HSF. In this paper, impact of SGV on granulation under micro-carriers enhancement was comparatively evaluated by keeping SGV at 0.6 cm/s (R1) and 1.2 cm/s (R2), respectively. Results showed that sludge granulation and nutrient removal performance was greatly enhanced by micro-carriers under low SGV. However, microorganisms were suppressed inside micro-carriers under high SGV, although the extracellular polymeric substances (EPS) contents in R2 were higher. The gas holdup in R2 was 1.32 times higher than traditional AGS system, resulting in excessive collision and velocity field difference. Overall, addition of micro-carriers could compensate the HSF under low SGV, which is of great significant in reducing the energy consumption of AGS system.