Simulation of Countercurrent Operation of Two-Stage Hybrid PAC-Submerged Membrane System for Trace Organics Removal

Abstract

A countercurrent two-stage hybrid powdered activated carbon-submerged membrane (PAC-SM) system for atrazine removal was simulated numerically in the present work. The simulation of the system performance at different operating conditions confirms that the adsorption capacity of the powdered activated carbon (PAC) can be further utilized and a stable product water quality can be maintained in the countercurrent two-stage mode as compared with the concurrent single-stage operations. For instance, the utilization of the PAC adsorption capacity was enhanced by 28% in the countercurrent two-stage operation at a flux of 60 L/m2h, and 21% of enhancement was obtained at a flux of 100 L/m2h by more frequent PAC replacement. Therefore, the adsorption capacity utilization is also dependent on the membrane filtration flux. Moreover, if the final effluent concentration was controlled at a higher level (e.g., C2*=0.1 instead of C2*=0.05), a further 5% of the PAC adsorption capacity can be utilized. In addition, reducing the replacement rate (RR) will make the operation similar to a system with continuous PAC dosing (pseudo-steady-state) by presenting nearly constant product water quality. This study sheds some light on the performance of a countercurrent multistage hybrid PAC-SM system for its further applications and system optimization.