Reverse osmosis silica fouling control with reactive micromixing

Abstract

Silica fouling is a major challenge in groundwater reverse osmosis (RO) desalination. Dissolved silica, upon concentration during RO, forms a difficult-to-clean glassy foulant layer on membranes, limiting recoveries from brackish groundwater desalination systems. Further, dissolved silica interacts strongly with organic matter to enhance fouling and degrade membrane performance. In this work, we demonstrate an innovative coating approach employing catalytic metal oxides on polyamide RO membranes using polydopamine (PDA) that greatly mitigates fouling and alleviates concentration polarization (CP). By injecting hydrogen peroxide (H2O2) into the feed, oxygen (O2) bubbles were formed through the catalytic disproportionation of manganese dioxide (MnO2). The produced O2 bubbles increased turbulence in the boundary layer, which reduced both CP and silica fouling. Fouling was further reduced in the presence of humic acid, likely because of enhancement of the catalytic action of MnO2 in the presence of humic acid. Compared to other silica scaling control methods, which require high energy consumption, the use of H2O2 to generate bubbles consumes much less energy. Overall, PDA-encapsulated catalytic MnO2 particles in the presence of H2O2 increased the effectiveness of thin-film composite desalination membranes without impacting their integrity in short-term tests, indicating its potential for improving energy efficiency in RO systems.