Characterization of fouling for a full-scale seawater reverse osmosis plant on the Mediterranean sea: membrane autopsy and chemical cleaning efficiency

Abstract

Membrane fouling is a serious problem facing most reverse osmosis plants used for the remediation and desalination of surface and ground waters. Herein, the fouling and cleaning behaviors of RO membranes, of full-scale seawater reverse osmosis (SWRO) plant after eight months of operation, were thoroughly investigated via membrane autopsies and foulants' characterization. Various techniques were applied to characterize the fouling layers; i.e., X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), energy dispersion X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence spectrometry (XRF) and thermogravimetric analysis (TG). The FESEM analysis of the membrane coupons revealed the presence of heterogeneous fouling layer with particles embedded in an amorphous matrix. The main elements detected with EDX were Si, Al, and Fe. However, FTIR spectra revealed the contribution of polysaccharides, proteins, and aromatic compounds to the fouling layer. Moreover, the normalized permeate flow rate, and differential pressure, as representatives of the plant performance, were monitored during the eight months’ study period. Based on the membrane autopsy results, membranes were regenerated by chemical cleaning with a commercial Hydrex® 4730 alkaline product; after that, Zeta potential and contact angle measurements were applied to investigate the surface charge and hydrophilicity of the surface of virgin, fouled, and cleaned RO membranes.