Temperature-dependent performance of citric acid and EDTA cleaning sequences in fouled RO membranes

This study optimized chemical cleaning operating conditions for raw water containing humic acid and inorganic salts in a RO process. Filtration and cleaning were performed under identified temperature conditions at 5°C, 15°C, 30°C, and 45°C, respectively. After 24 hours of filtration, it was confirmed that the fouling layer on the membrane surface gradually thickened from 4.03 μm to 6.54 μm as the temperature increased. Additionally, the cleaning efficiency according to the sequence of the two cleaning agents used in the study, citric acid and EDTA∙4Na, showed higher cleaning efficiency when citric acid was used first under all temperature conditions. It was determined that complexes of organic matter and divalent cations formed a fouling layer first and that citric acid effectively removed the deposited inorganic salts. The flux recovery rate (FRR) gradually decreased, and the membrane surface became hydrophobic after cleaning it three times. The cleaning cycle and frequency should be appropriately established for a stable RO process since multiple cleanings change the membrane surface characteristics. • Increased temperature intensifies membrane fouling by forming a thicker cake layer. • Using citric acid first improves flux recovery by effectively removing the foulants. • The necessity to optimize the cleaning frequency and cycle duration was highlighted.