Antifouling enhancement of thin-film composite polyamide reverse osmosis membrane by surface immersion deposition and in-situ crosslinking method with NaAlg-GA hydrogel

Abstract

In order to optimize antifouling performance to organic foulants, a commercial polyamide reverse osmosis membrane of composite polyamide material was modified by surface gelation using sodium alginate (NaAlg) as surface coating agent, which was widely known as a natural polymer and environmentally friendly materials. NaAlg-GA hydrogel layer was successfully deposited on commercial membrane surface by combining immersion coating with in-situ crosslinking method and the chemical structure was verified by FT-IR spectroscopy. SEM and AFM was adopted to analyze the changes of morphology and roughness. Zeta potentiometer, and contact Angle analyzer were all used to analyze the hydrophilicity and charge property of relevant NaAlg modified membranes in detail. Specific separation performance was also evaluated by cross-flow filtration tests. Results from above experiments confirmed that NaAlg modified membranes exhibited a surface with more hydrophilic, smoother and more regular, denser negative charge, slightly improved selectivity and lower permeability. Long-term monitored the performance of 100 ppm NaAlg modified membrane, it was found that the rejection rate fluctuated between 98.96% and 99.17%, and the flux ranged from 25.15 ∼ 26.06 L/m2 h during the whole test period, which fully proved that modified membrane had good durability. BSA pollution experiment results showed that the flux attenuation rate of 100 ppm NaAlg modified membrane decreased from 40.87% to 25.01%, and flux recovery rate of contaminated membrane after washing was as high as 90.8%. In addition, the flux of 100 ppm NaAlg modified membrane exceeded that of unmodified membrane after filtrating 20 h. Moreover, with the extension of time, the cumulative flux loss of modified membrane caused by additional resistance at the initial filtration stage would soon be compensated, and it completely exceeded that of unmodified membrane after 40 h. All above results showed that NaAlg-GA hydrogel layer can effectively improve the antifouling performance.