Iron fouling prevention and membrane cleaning during reverse osmosis process

Abstract

Fouling inhibition is one of the most important challenges in membrane processes. Manifesting under several forms and origins, fouling significantly reduces the performance of membranes during water desalination process. Despite its low concentration, iron is considered as one of the most common inorganic pollutants that generate oxides and hydroxides causing membrane fouling. In the current work, reverse osmosis (RO) membrane fouling caused by iron precipitation was investigated. Herein, the mechanism of iron salt crystallization by oxidation technique was experimentally studied. In addition, the regeneration of a fouled RO membrane by iron precipitation was carried out. Analysis with scanning electron microscopy, infrared (IR) and X-ray diffraction (DRX) spectroscopy has been performed to identify deposits. It was shown that the collected deposit is essentially the lepidocrocite (γ-FeOOH). RO membrane regeneration was carried out using citric acid as a cleaning reagent with a concentration of 0.01%. The efficiency of the treatment was tested through the assessment of the recovery ratio, pressure drop and iron accumulation. In addition, complexation–filtration using citric acid was tested to remove iron during pretreatment step to inhibit membrane fouling. IR and DRX data showed the complex iron citrate (Fe–citrate) was found in the RO retentate, which proves that the complexation–filtration process was clearly efficient.