pH-responsive polyacrylic acid chemical cross-linking for end-of-life reverse osmosis membrane rejuvenation

An in-situ chemical cross-linking rejuvenation technique for reverse osmosis (RO) membranes was developed and investigated utilizing pH-responsive polymer with multiple carboxyl groups to improve the salt rejection and performance stability of end-of-life RO membranes. Polyacrylic acid (PAA) was used as a rejuvenating agent to cross-link with amino groups on the degraded RO membrane through EDC/NHS activated reaction. Indicated by ATR-FTIR, XPS, Zeta potential and SEM analyses, the covalent bonds between carboxyl groups and amino groups were generated on the PAA-rejuvenated membrane. The end-of-life RO membrane elements with an average NaCl rejection of 92.68 % could be recovered to 97.26 % by PAA rejuvenation. As a result of pH responsivity, PAA-rejuvenated membranes exhibit excellent rejection stability after continuous 12 cycles of alkali and acid alternate cleaning. The adjustable salt rejection and the durability of PAA-rejuvenated membrane elements were validated in real water tests for 185 days at a coal mine water treatment plant, indicating the practical application potentiality. The effects of initial end-of-life RO membrane condition on PAA rejuvenation are also provided.