Performance Restoration of Membranes Degraded by Fouling and Wetting in Membrane Distillation

Abstract

Membrane distillation (MD) is a promising technology for desalination due to its ability to produce high-purity water using low-grade or waste energy. However, despite its potential, MD still faces challenges such as membrane fouling and wetting, necessitating continued research and development. In this study, restoration protocols were developed and evaluated at different stages of CaSO4 - induced fouling and wetting in a lab-scale direct contact MD system. During the early stage of fouling, flushing with deionized water restored membrane performance without noticeable difficulty. However, when fouling progressed to the point immediately before a significant decline in distillate flux, complete recovery of both distillate flux and cumulative volume was achieved only through cleaning using high concentration of citric acid. At the stage of severe fouling and complete pore wetting, even strong acid cleaning was unable to fully restore membrane performance. In addition, when the fouling layer was allowed to dry prior to cleaning, the effectiveness of citric acid cleaning was substantially reduced, even when the cleaning was applied before the onset of severe fouling. These findings emphasize the importance of timely chemical cleaning before advanced fouling or membrane drying occurs in order to maintain stable long-term performance in MD operations.