Distinct membrane fouling mechanisms in vacuum membrane distillation: Interaction energy analysis with the XDLVO approach

In this study, organic solutions (30–120 mg/L HA, BSA or SA) and composite solutions (5.93–10.15 wt% inorganic salts with 75 mg/L HA, BSA or SA) were used to investigate the membrane fouling behavior in the vacuum membrane distillation (VMD) system. The different permeate flux attenuation and fouled membrane morphology implied distinct membrane fouling mechanisms during VMD process. Furthermore, we employed the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory as an effective approach to analyze membrane fouling mechanisms. The results showed that the total interaction energy was negative (attraction) within the separation distance of 1–2 nm by applying the XDLVO approach, indicating that a pristine membrane was more prone to fouling. Finally, we elucidated distinct membrane fouling mechanisms in the VMD system. The inorganic feed solution readily induced inorganic fouling on the membrane surface and pore wetting, while organic feed solution and combined feed solution did not cause membrane wetting, conversely, only organic fouling and combined fouling were identified on the membrane surface. This study was expected to facilitate understanding of membrane fouling mechanisms in the VMD process.