Fouling behavior and cleaning strategies of polyester and polyamide loose nanofiltration membranes in textile wastewater treatment

Abstract

Loose nanofiltration (LNF) membranes based on interfacial polymerization (IP), such as polyester (PE) and polyamide (PA), are widely used in textile wastewater treatment. However, membrane fouling is unavoidable due to dye accumulation and salt scaling, resulting in a reduced membrane performance and reduced service life. Herein, we investigate the fouling behavior of two representative PE and PA LNF membranes, synthesized using quercetin and arginine as aqueous monomers via the IP technique, respectively. When the concentration factor (the ratio of the initial feed volume to the final concentrated volume) of the feed solution reaches 10 through the continuous process, comparing the fouling behavior of the PE and PA membrane, the water flux and Congo red/NaCl selectivity of the PE membrane decreased by 62.8 % and 26.9 % respectively, and that of the PA membrane decreased by 55.5 % and 13.9 %. The severe fouling of the PE membrane was mainly because of the large pore size and rough surface. Then, four cleaning agents were employed (NaOH, HCl, NaClO, and acetone solution) to clean the PE and PA membranes. A NaClO solution (300 ppm) was most effective for cleaning the PE membrane, while a pH 11 NaOH solution worked best for the PA membrane. Finally, cleaning strategies for the fouled PE and PA LNF membranes after textile wastewater treatment are proposed. Through the batch process involving both fouling and cleaning, when the concentration factor of the feed solution reaches 10, the cleaning efficiency of the PE membrane and the PA membrane are respectively 12.3 % and 5.9 % higher than that of the continuous process. This study highlights the importance of selecting appropriate cleaning agents and optimizing the cleaning strategy in maintaining the long-term stability and performance of LNF membranes, providing theoretical guidance for the cleaning of loose PE and PA membranes.