Identifying pore wetting thresholds of surfactants in direct contact membrane distillation

Abstract

Direct contact membrane distillation (DCMD) is a potential on-site water treatment option for water reuse at solar energy facilities that require water for cooling and cleaning of panels/mirrors. Surfactants, which are often used as part of panel washing, can negatively impact the hydrophobic DCMD membranes and diminish the quality of the treated water. In this work, surfactant effects on DCMD were evaluated to assist in developing standard operating procedures for the reuse of wash waters by on-site DCMD systems. A non-ionic surfactant and an anionic surfactant were tested in a bench-scale DCMD system using commercially available hydrophobic membranes of varying materials and pore sizes. The surfactant concentration at which pore wetting occurred was determined using a novel graphical method developed for this work and verified analytically. All membranes evaluated had reduced hydrophobicity after being exposed to the surfactants, and all membrane materials evaluated were determined to have lower pore wetting concentrations for the non-ionic surfactant than of the anionic surfactant. Pore size had no significant effect on pore wetting concentrations. Overall, it was determined that the membrane material had the most significant effect on membrane performance, with PTFE membranes being able to tolerate higher concentrations of both surfactant types before pore wetting.