Physicochemical autopsy and sequential cleaning optimization of seawater reverse-osmosis membranes: a study from Beni Saf desalination plant, Algeria

This study focused on the fouling of two seawater reverse osmosis (SWRO) membranes at the Beni Saf Water Company desalination plant in Algeria, which has a daily capacity of 200 000 m3 and a recovery rate of 45% using 17 920 membranes. Approximately 3 234 membranes are replaced annually due to fouling. A detailed study of the fouling agents of the two membranes was conducted using various analytical techniques, such as moisture analysis, loss on ignition (LOI), determination of calcium carbonate (CaCO3) content, x-ray fluorescence (XRF), x-ray diffraction (XRD), and Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR). Surface characterization was also performed using scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy (SEM-EDS), FTIR-ATR, and XRD. The LOI analysis indicated that more than 30% of the fouling material was organic in nature. FTIR-ATR identified the presence of –OH groups, phenolic C–O groups, and amide bonds, suggesting the accumulation of organic substances such as proteins, humic substances, and polysaccharides. Additionally, SEM-EDS, XRF, and XRD revealed relatively high concentrations of silica, primarily in the form of quartz, confirming the formation of an organo-inorganic complex on the membrane surface. Based on these findings, a sequential chemical cleaning protocol was developed, incorporating alkaline (NaOH), metal chelator (EDTA), surfactant (SDS), oxidant (H2O2), and sulfuric acid (H2SO4), each followed by rinsing with deionized water (DI). This cleaning regime effectively removed fouling from the membrane surface, resulting in an average weight loss of 15% for one membrane and 14% for the other.