Temperature-dependent alkaline cleaning of nanofiltration membranes fouled by organic contaminants

Nanofiltration (NF) is increasingly used in water treatment for its high membrane fouling issues. Alkaline chemical cleaning is generally applied to mitigate organic fouling of NF membranes, while the role of temperature in governing the cleaning process has not yet been systematically elucidated. This study compared the fouling behaviors of four organic model foulants on NF membranes, and evaluated the impact of alkaline cleaning temperatures (pH 11, 10–55 °C) through measurements of membrane flux recovery and characterizations of residual foulants after cleaning. Results showed that for the fouling solely by three negatively charged foulants (fulvic acid, bovine serum albumin, and sodium alginate), membrane cleaning temperature at 25 °C was basically effective, while a higher temperature like 40 °C was more advantageous in multiple cycles of fouling and cleaning. The positively charged lysozyme caused the most severe irreversible fouling that could not be removed by alkaline cleaning. For the composite fouling jointly caused by various foulants, the chemical cleaning efficiency was lower compared to that for the single foulants, implying the need to develop enhanced cleaning approaches during long-term operations. This study highlights the significance of chemical cleaning temperatures during membrane fouling control, offering implications for practical engineering applications.