Investigating the influence of polymaleic acid on reverse osmosis membrane performance to mitigate gypsum scaling

Polymaleic acid (PMA) is widely recognized and utilized as an anti-scaling agent in reverse osmosis (RO) applications, however, the specific impacts of PMA on RO membrane scaling and cleaning performance remain underexplored, particularly related to comparing the addition of PMA to the feed solution and its immobilization on membrane surfaces. To address this knowledge gap, this study compared bare membranes alone with membranes coated (ESPA2-PMA) and bare membrane exposed to PMA in the feed solution (ESPA2-PMA_Solution), with all membranes tested under dynamic RO scaling, cleaning, and re-scaling conditions. Initial scaling experiments showed that both PMA applications presented reduced flux declines relative to the unmodified membrane. PMA in solution demonstrated the highest scaling resistance, maintaining up to 70 % of the initial flux after 6 h, while the coated membrane showed moderate improvement. X-ray photoelectron spectroscopy (XPS) analysis revealed that PMA's form—coating versus solution—significantly influenced calcium (Ca) binding modes and gypsum crystal formation process. After cleaning, the membranes treated with PMA in solution had the lowest water recovery, suggesting strong scaling prevention but reduced cleaning efficiency, likely due to Ca bridges forming between gypsum crystals and the membrane surface, which impacted the cleaning process. Rescaling experiments confirmed consistent trends in fouling resistance and cleaning durability. These findings underscore PMA's potential both as a membrane coating and as a feed additive, presenting an effective strategy to minimize gypsum fouling and enhance RO membrane longevity in desalination systems. • PMA in solution exhibits higher scaling resistance but lower cleaning efficiency. • PMA coating improves scaling resistance and maintains better cleaning efficiency. • XPS confirms distinct Ca-binding modes affecting cleaning and re-scaling performance. • Rescaling confirms consistent flux decline trends and surface coverage patterns. • PMA-coated membranes retain greater stability than unmodified ones after cleaning.