Stirred tank reactor with dual impeller Rushton turbine for application of wastewater treatment - Process optimization and CFD simulation

The treatment of industrial wastewater by economical and efficient methods is being explored to improve treatment efficiency and costs. Wastewater treatment via biological methods to reduce carbonaceous matter is common in the form of an activated sludge process (ASP). In the current work, the aerobic decomposition of waste was carried out in a reactor with constant stirring with a Rushton type turbine. The optimum values of the flow rate of air were obtained for two reactor impeller configurations for better waste degradation. The extent of degradation in the stirred tank reactor was studied for different values of impeller clearances. Two configurations, C1 and C2, were investigated. It was observed that under a continuous air supply for 36 hours, the impeller configuration C2 provided 80% degradation compared to 74.4 % for C1. Increased values of superficial gas velocity (UG) and impeller speed resulted in decreased degradation due to shear stress on microorganisms for two impeller configurations. The hydrodynamic study confirmed that the impeller configuration C1 required less power consumption than C2 for the same operating condition. The k-epsilon turbulent model and the population balance model were used in combination. The models were validated with the experimental results of the hydrodynamic parameters for the values of operating parameters over a considerable range. The forecasting of mass transfer coefficients from different models was compared with practically determined values for the two configurations of impeller positions in the tank.