Effects of impeller types on gas-liquid mixing and oxygen mass transfer in aerated stirred reactors

Abstract

Aeration and stir are vital steps in wastewater treatment plants (WWTPs) to enhance dissolved oxygen (DO) concentration in water. In laboratories, aerated stirred reactors (ASRs) are commonly utilized to cultivate activated sludge and degrade pollutants in sewage. The performance of the ASR depends mainly on the gas-liquid distribution and hydrodynamics. The current study investigated a lab-scale ASR using computational fluid dynamics (CFD) modeling and simulation. The experimental data were used to validate the CFD model. Then, the validated model was used to investigate the effect of impeller types on gas-liquid mixing quality and oxygen mass transfer efficiency. This investigation aimed to select suitable and efficient impeller types for different needs in ASRs. The predictions suggested the Pitched 30° impeller is excellent in mass transfer and gas-liquid mixing besides needing more power. Simulation results of oxygen transfer shown that the gas holdup and bubble diameter mainly determined the oxygen mass transfer coefficient in ASRs. Rushton impeller and Folded impeller offer good oxygen transfer but also higher power consumption. Pitched 45° impeller and Pitched 60° impeller offer more uniform gas holdup than other impellers and have lower energy consumption.