Status of hybrid membrane–ion-exchange systems for desalination: a comprehensive review

Recently, water scarcity, world population rise and urbanization are causing desalting of seawater. Membrane separation processes such as reverse osmosis are applied for desalination over the conventional mass transfer techniques. For instance, reverse osmosis accounts for the treatment of nearly 1% of the world water supply and its applications are increasing with time. However, cost, technical management and efficiency are challenging aspects. Hence, membrane fouling, direct and indirect investment costs, and permeate quality are the major hurdles encountered. Toward solving these problems, various studies are being conducted including varying membrane operating conditions and separation methodologies whereby ion-exchange–reverse osmosis hybrids and the coupling of two or more other membrane filtration techniques can be mentioned. Apparently, most of the hybrid techniques targeted for the selective removal of a pollutant. Hence, ion exchange–reverse osmosis is the most applied hybrid process particularly for boron removal due to its public and environmental health impact. Despite that, there is no current and comprehensive review that bridged the piece by piece and fragmented reports. In this review, desalination–ion-exchange coupling with other membrane filtration is explored in detail and the recent advances in composite membrane material synthesis are uncovered. Further, the status, cost and future potential of hybrid membranes are discussed and gaps are identified for future research.