Quantitative analysis of the irreversible membrane fouling of forward osmosis during wastewater reclamation: Correlation with the modified fouling index

In this study, the fouling behavior in the long-term performance of the forward osmosis (FO)-based osmotic dilution process was systematically explored by assessing the impact of irreversibility. The effects of physical cleaning, scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) analyses, and foulant distributions were systematically investigated to control irreversible organic foulants on the membrane surface. It was observed that specific foulants in the secondary wastewater effluent impeded the long-term performance of FO fouling reversibility and final flux. A strong correlation between irreversible foulant concentrations, especially that of protein-like biopolymer, and physical fouling reversibility was observed, which caused continual irreversible fouling in the FO process. Multiple modified fouling indexes (MFIs) were measured to evaluate the fouling potential of the feed water with size fractionation. It was confirmed that the MFI-UF employing a 300 kDa ultrafiltration (UF) membrane is an appropriate water quality index for studying irreversible membrane fouling. It is expected that the application of MFI in predicting the fouling potential of FO intake water will significantly contribute toward the development of operational guidelines for FO plants.