Surfactant pretreatment as a novel fouling mitigation strategy for membrane distillation

Abstract

Membrane distillation (MD) has emerged as a promising thermal desalination technology for hypersaline wastewater reclamation. However, the practical implementations of MD face a critical challenge of membrane fouling. Conventional strategy to address membrane fouling is to emphasize the progress in developing composite MD membranes, but these membranes are commercially unavailable. In this study, we introduce a new operation strategy to mitigate fouling by using surfactant pretreatment. We demonstrate that after being pretreated by 0.05 mM Triton X-100 feed solution for 10 min, a commercial polyvinylidene fluoride (PVDF) membrane can exhibit outstanding fouling resistance in MD process. Further, we elucidate the underlying working mechanism using quartz crystal microbalance (QCM) experiments, oil contact angle measurements, and force spectroscopy determinations. Specifically, in the pretreatment process, the amphiphilic surfactant adsorbs onto the hydrophobic membrane, altering the membrane surface to be hydrophilic. During the MD operations, a hydration layer forms on the hydrophilic surface, eliminating the foulant-membrane interaction and thereby achieving fouling mitigation. For effective fouling mitigation, a surfactant exhibiting a moderate hydrophilic-lipophilic balance (HLB) value (e.g., Triton X-100 with an HLB of ∼14) is required. As an easy-to-implement but effective strategy to mitigate membrane fouling, surfactant pretreatment can substantially improve the fouling resistances of commercial hydrophobic membranes, greatly facilitating the practical applications of MD and membrane contactor technologies.