Desalination and Demineralization in Water and Used Water Purification, Nanofiltration, Reverse Osmosis, Electrodialysis Reversal, Ion-Exchange, and Electrodeionization

The following chapter provides an overview of desalination and demineralization technologies, such as ion exchange (IE), reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and electrodeionization (EDI). Desalination and demineralization describe processes in which dissolved salts are removed from seawater, brackish, or used water, thus producing fresh water. The presented technologies are interlinked with other chapters, therefore providing a more comprehensive explanation. RO and NF comprise membranes for the retention of salts. While RO is unselective and can achieve a high salt rejection, NF only attains a partial desalination, as the rejection of monovalent ions is not as efficient. ED is also a membrane technology; however, it integrates an electric process. In this framework, by applying an electric current, the ions migrate towards the respective electrodes and are retained by ion exchange membranes, thus achieving the separation of different salts. In contrast to membrane technologies, IE accomplishes the removal of dissolved ions with ion exchange resins. These resins include diverse functional groups which swap out the dissolved ions with H+ and OH−. Finally, EDI is a combination of ED and IE. This technology is mainly employed for the production of ultrapure water and although the salt rejection is not as high as in conventional IE, the continuous operation makes it a technology worth considering. RO and EDR gradually gained importance reasoning to less energy demand in water production. Requirement of high quality water in industries gave more importance to the development of IE processes aiming to produce very high quality water demanded by few industries. The implementation of different desalination and demineralization technologies is illustrated with three different case studies.