Abstract: A method of providing ultrapure water from feed water containing hardness forming ions, comprising at least the steps of passing the feed water successively through: (i) providing a feed water stream containing hardness forming ions: (ii) passing the feed water stream through a reverse osmosis (RO) unit to remove at least some ionic contamination to provide a RO permeate water stream: (iii) passing the RO permeate water stream though a capacitive de-ionisation (CDI) unit to remove at least some of the ions to provide a post-CDI stream: and (iv) passing the post-CDI stream through an electrodeionisation (EDI) unit to remove at least some of the ions and carbon dioxide and to provide an ultrapure water stream for dispense or storage. In this way, the capacitive deionisation provides a wholly or substantially continuous process for removing a proportion of unwanted ions, especially the hardness forming ions, from the feed water prior to the use of electrodeionisation.

Abstract: An electrodeionisation apparatus comprising a first deionising flow path and an integral second deionising flow path is described. The outflow from the first path is held in a holding tank prior to passage through the second flow path, and the outflow from the second path is available for use. Optionally, the second path outflow is partly or fully returned to the holding tank. Me recirculation of the already purified water in the holding tank maintains the water in the holding tank at a higher standard than otherwise “standing” purified water. The water in the holding tank could be separately made available for use. The apparatus requires the use of only a single pair of electrodes and hence one power supply. Moreover, the ion exchange materials in the first deionising flow path can be regenerated when water is not flowing through them such that they have a greater capacity for deionisation when required.

Abstract: An electrodialysis apparatus and method for purifying water. An electrodialysis apparatus including an anode and anode chamber, a cathode and cathode chamber, and a desalting stream flow path comprising a first portion juxtaposed to the anode and a second portion juxtaposed to the cathode is described. By passing water through the apparatus, purified water is produced.