Flux stabilization in membrane distillation desalination of seawater and brine using corrugated PVDF membranes

Abstract

Due to its tolerance of high salinities, membrane distillation (MD) is promoted for desalination of challenging high salinity seawater and for brine recovery and reduction in seawater desalination plants. In these applications, fouling of MD has recently been shown to become more pronounced, although much less than for reverse osmosis. In this study, a two-layer corrugated composite flat sheet polyvinylidenefluoride (PVDF) membrane was fabricated, characterized and tested in a lab-scale direct contact MD (DCMD) system for improved flux stabilization. The first membrane layer was used to control the pore size while the second was devoted for formation of surface corrugation and enhancing hydrophobicity. Tested using seawater and concentrated brine against a non-corrugated composite membrane, the corrugated composite membrane showed much higher flux stability identified by only 10.7% reduction in permeate flux after 103h of operation, compared to 66.6% reduction for the non-corrugated membrane. DCMD experiment with concentrated brine proved the effectiveness of corrugations even at high brine concentrations, where the corrugated membrane performed as well as it did with seawater, while the non-corrugated membrane showed even worse performance reaching almost zero flux after 93h of operation. SEM images of the post-MD membranes also confirmed the advantage of corrugations over the flat surface, where the corrugated membrane experienced small amount of salts deposition leaving most of the membrane pores open while the non-corrugated membrane experienced severe scaling and salt depositions forming a thick layer at the membrane surface, blocking most of its pores.