Effect of post-treatment on permeance and fouling of nanofiltration membrane

View large Download slide View large Download slide Close modal The effects of two post-treatments with CaCl 2 and NaOH on nanofiltration (NF) membranes were investigated according to the physicochemical properties and antifouling performance. The membrane post-treated with NaOH (NF-OH − ) exhibited enhanced hydrophilicity and greater negative surface charge, accompanied by collapsed nodular structures. Compared with the pristine NF membrane, NF-OH − demonstrated a 50% increase in permeance, but showed compromised separation performance, with SO 4 2 − rejection of 97.3% and Cl − / SO 4 2 − separation factor of 46. In contrast, the CaCl 2 -treated membrane (NF-Ca 2+ ) displayed improved hydrophilicity with reduced negative charge and denser nodular morphology. While NF-Ca 2+ achieved 25% higher permeance than the pristine membrane, it maintained comparable SO 4 2 − rejection and Cl − / SO 4 2 − separation factor. Fouling experiments using biological treatment effluent of leachate revealed that NF-OH − showed greater fouling propensity and lower cleanability than the other two membranes. This is likely due to the stronger negative charge and smoother surface morphology of the NF-OH − membrane, which promoted foulant adhesion while limiting surface turbulence. Conversely, the NF-Ca 2+ membrane demonstrated superior antifouling characteristics and higher permeance recovery, attributable to its reduced negative surface charge and denser nodular morphology. These findings underscore the critical influence of surface charge and nanostructure on the filtration and antifouling behavior of NF membrane. Permeance of nanofiltration (NF) membranes increased by 26–50% after post-treatments. Surface nodulars increased on NF-Ca 2+ , but collapsed on NF-OH − . NF-Ca 2+ became less negatively charged, while NF-OH − became more negatively charged. NF-OH − was more prone to fouling and harder to recover during fouling tests. Surface charge and morphology changes significantly impact membrane performance.