Forward osmosis treatment for volume minimisation of reverse osmosis concentrate from a water reclamation plant and removal of organic micropollutants

Abstract

Reverse osmosis concentrate (ROC) produced in water reclamation and desalination plants can endanger the environment if it is not treated before discharge. Volume minimisation of ROC can help in its easy disposal. The study examined the use of forward osmosis (FO) with and without granular activated carbon (GAC) fixed-bed adsorption pretreatment for volume minimisation of ROC and removal of organic micropollutants. Five repeated FO steps using 2 or 3M NaCl as the draw solution reduced the volume of ROC to 8%. With each successive step the flux decreased due to membrane fouling and scaling caused by increased concentrations of organics and inorganics resulting from volume reduction of ROC. However, flux decline was arrested in the second or third step by reducing the pH of the feed solution from 7.0 to 5.0. FO treatment rejected 9 of the 18 organic micropollutants at >82% and GAC treatment removed 15 of them at >82%. GAC pre-treatment followed by FO treatment removed almost all the organic micropollutants from the ROC. GAC pretreatment also reduced total organic carbon concentration in ROC by adsorption, thus controlling membrane fouling.