Effect of Ca 2+ on organic fouling of hydrophobic polytetrafluoroethylene membrane during membrane distillation process: An especial interest in intermolecular interactions

Abstract

The growing attention to membrane distillation (MD) processes from various disciplines raises the demand for in-depth research on MD membrane fouling. This study investigates the role of salt ions, such as Ca 2+ , in organic fouling of direct contact membrane distillation (DCMD). The differently charged lysozyme (LYS), sodium alginate (SA), and bovine serum albumin (BSA) were chosen as model organic foulants. The fouling data showed that Ca 2+ obviously aggravated the flux decline rate from 0.55 ~ 0.67 to 0.35 ~ 0.61. The scanning electron microscopy coupled with energy dispersion spectrometry (SEM-EDX) analysis further displayed that Ca 2+ could cause higher mass deposition on the membrane surface and correspondingly severe fouling behavior. Through the gel permeation chromatography (GPC) analysis, obvious binding interactions between foulants were observed as a result of the decisive role of Ca 2+ , finally leading to the significant changes of zeta potential and particle size of feed solutions. The zeta potential obviously decreased with a trend towards the neutral state, and the particle size increased except for the individual LYS. Additionally, the interfacial interaction analysis was applied to study the foulant-membrane and foulant-fou-lant interaction energy, and the results showed that Ca 2+ significantly decreased the repulsive electrostatic interaction energy between foulants and membrane surface, leading to a severe foulants deposition and membrane fouling.