Influence of hydraulic pressure on pore wetting of direct contact membrane distillation (DCMD)

This paper presents the experimental results on the effect of hydraulic pressure on the wetting of membrane distillation (MD) membranes. Using CaSO4 as a model foulant, a series of MD experiments were carried out by adjusting the feed and distillate pressure between 0.1 and 0.7 bar. The flux, electric conductivity of the distillate, rejection, and recovery was measured in each experiment. The rate of the conductivity increase (dE(c)/dt) and the liquid entry pressure (LEP) were also estimated as quantitative measures for wetting propensity. Results showed that there was no wetting due to scale formation without the application of the external hydraulic pressure. As the feed pressure exceeds the distillate pressure, the wetting was accelerated. The recovery was higher when the distillate pressure was higher than the feed pressure. The rejection maintained high when the feed pressure was equal or less than the distillate pressure. The wetting by net pressure lower than the LEP is attributed to the existence of relatively large pores in the MD membrane.