Surface charge regulation of reverse osmosis membrane for anti-silica and organic fouling

Dissolved silica and organic matter are major foulants in reverse osmosis (RO) in brackish water treatment. Though the mechanism of inorganic and organic fouling has been clear, combined silica-organic fouling-resistant membrane have been poorly investigated. In this study, we fabricated membranes with different surface charge. More negatively surface charged membrane (-COOH), acrylic acid (AA) membrane was fabricated through redox free radical grafting method. Ethylamine (EA) and ethylenediamine (ED) membranes with neutral or less negative surface charge were fabricated through -CH3 or -NH2 functional groups grafting. The surface modified membranes were characterized in terms of physicochemical properties and antifouling performance. Compared with the pristine membrane, all the modified membranes possessed better salt rejection without sacrificing water permeability. The AA membrane also showed better antifouling property and higher water flux recovery after physical rinsing. On the other hand, fouling on the EA and ED membranes were aggravated. Unlike the gel-like foulant structure on the EA and ED membrane surfaces, the AA membrane presented more disordered granular structure. Analysis of fouling layer has also proved that there was less silica scaling and organic foulants on the AA membrane surface. Despite the outstanding hydrophilicity of the AA membrane, its antifouling property was mainly attributed to the more negative surface charge, according to regression between flux decline and membrane characteristics. Importantly, we proposed that electrostatic interaction was the dominant fouling mechanism in the combined silica-organic fouling. With more negative surface charge, the AA membrane was prone to prevent foulants from depositing and aggravating, so as to mitigate membrane fouling. Our research provides a simple and practical approach to RO membrane fabrication for anti-inorganic and organic.