Restoration of the Performance of Membranes Fouled and Wetted in a Pilot-scale Membrane Distillation Process

Objectives : The fouling and wetting of membranes in membrane distillation processes can significantly reduce membrane performance, thereby affecting overall process efficiency. The purpose of this study is to develop methods for restoring the performance of membranes used in a membrane distillation pilot plant operated in the Middle East by testing and optimizing various cleaning methods. This aims to maintain the long-term performance and improve the operational efficiency of the pilot plant through the reuse of restored membranes.Methods : To analyze the main fouling substances on the hollow fiber membranes collected from a module operated in a pilot plant, FTIR, XRD, and SEM analysis techniques were employed. A lab-scale module was fabricated using the collected membranes, and cleaning methods were applied. Citric acid was used for cleaning to restore membrane performance, which was evaluated by measuring water permeability and conductivity before and after cleaning.Results and Discussion : FTIR and XRD analyses revealed that the main fouling substances on the membranes used in the pilot plant were NaCl, CaCO<sub>3</sub>, and CaSO<sub>4</sub>. SEM and ICP analyses confirmed that the membranes near the feed inlet of the module experienced severer fouling compared to those near the outlet. The cleaning method involving pump circulation after inducing artificial wetting was found to be the most effective for restoring membrane performance. Notably, when a high concentration of citric acid was used, almost all fouling substances on the membrane surface were removed, restoring membrane performance to nearly its original state.Conclusion : The cleaning method involving artificial wetting followed by pump circulation was determined to be the optimal method for successfully restoring the performance of membranes fouled and wetted in membrane distillation processes.