Synergistic effect of air sparging in direct contact membrane distillation to control membrane fouling and enhancing flux

In this paper, we present the synergistic effect of air sparging in reducing membrane fouling and enhancing water vapor flux in direct contact membrane distillation (DCMD). This air sparged-DCMD (or AS-DCMD) was tested with water containing saturated CaSO₄ and simulated flue gas desulfurized (FGD) water. Polytetrafluoroethylene (PTFE) and carbon nanotube immobilized membrane (CNIM) were used in this study. The permeate flux was found to be as much as 10% higher in AS-DCMD mode compared to conventional DCMD for both membranes. The morphology of foulants deposited on the membrane were analyzed by SEM and were found to significantly different in the presence of air sparging, as the sparging altered the colloidal behavior of the precipitating salts and the amount of salt deposited during AS-DCMD was 65% lower than that observed during DCMD. Relative flux reduction measured as the drop in flux due to fouling was measured using simulated flue gas desulfurization water from coal power plants (nearly saturated with CaSO₄), and an 32% improvement was observed when compared to DCMD. AS-DCMD appears to be particularly suitable for desalting high salt concentration brine where both the lower flux and fouling can be important considerations.