Performance of different pretreatment methods on alleviating reverse osmosis membrane fouling caused by soluble microbial products

Abstract

Soluble microbial products (SMP) are one of the main causes of reverse osmosis (RO) membrane fouling in wastewater reclamation, and coagulation and adsorption are commonly used to prevent such fouling. However, the mechanism by which typical coagulants and adsorbents affect the RO membrane fouling caused by SMP remains unclear. In this study, two bacterial strains isolated from fouled RO membranes in a full-scale wastewater reclamation plant were used to produce SMP. Both bacterial strains were found to generate high SMP yield (0.23–0.25 g/g), which caused severe RO membrane fouling. Coagulation by polyaluminum chloride (PACl) and ferric chloride (FeCl3) and adsorption by granular activated carbon (GAC) were applied as pretreatment methods to alleviate the membrane fouling caused by SMP. Compared with PACl, FeCl3 performed better in removing SMP, decreasing fluorescence intensity, and reducing molecular weight (MW). GAC preferentially adsorbed protein and humic substances in SMP and unselectively and efficiently removed fluorescent compounds; however, it could only remove a limited amount of the high-MW compound. The RO membrane fouling potential of treated SMP was investigated, and FeCl3 and GAC were found to effectively alleviate the fouling. In addition to a decrease in the dissolved organic carbon content of SMP, a decrease in specific fluorescence intensity, MW, and polysaccharide content caused by coagulation or adsorption could result in lower RO membrane fouling.