Enhancing boron rejection of reverse osmosis membranes via electrochemical method

Abstract

With intensifying global water scarcity, it is pressing to find new and novel ways to retrieve freshwater to meet growing water demands. The reverse osmosis (RO) desalination technology is increasingly adopted in many countries due to its large volume of purified water production per unit area. Despite its high ionic rejection performance in general, it is not the case for contaminants which have similar properties to the water molecule – small and uncharged. Boron exists as boric acid (B(OH)3) in seawater. It requires at least a two-pass configuration in a conventional treatment plant to meet the World Health Organization (WHO) water quality standards. Its removal can be enhanced under higher pH conditions, where the small and uncharged boric acid transforms into a bigger and negatively charged borate ion (B(OH)4-). This process usually occurs in the second pass, where boron is more efficiently removed. However, it requires high chemical, operational and capital costs. Introducing electrochemistry into the RO desalination process can overcome the existing limitations in conventional processes. Previous works had modified the membrane surface to make it electrically conductive, but is limited by the coating consistency and integrity. In this project, boron rejection via the use of commercial RO membranes is enhanced via an electrochemical method. The effect of applied potential differences on pH, rejection and flux are analysed. Some results produced are in line with existing trends and can be further improved.