Electrodeionization
Electrodeionization (EDI) is a continuous process that removes dissolved salts and other ionised and ionisable substances from water. In process water treatment, EDI is used after reverse osmosis as a final polisher to achieve the highest water qualities.
Functional principle
An elektrodeionisation module, also called EDI module, is made up of several chambers separated by ion-selective membranes and arranged between a cathode and an anode. In order to improve ion transport, the chambers are filled with mixed-bed resin.
The driving force for ion transport is a DC voltage. Depending on their charge, the cations are transported in the direction of the cathode and the anions in the direction of the anode.
Through the arrangement of the membranes, product channels are created, from which the cleaned water is brought together as a diluate. The concentrated ions are discharged via the wastewater channels of the EDI module (concentrate).
Usage possibilities
The electrodeionisation process is used for the fine cleaning of demineralised water. Conductivity of ≤ 0.056 µS/cm (at 25°C) can be achieved. As a continuous process without the need for regeneration chemicals, EDI is ideal for the post-treatment of permeate from reverse osmosis systems.
The modular design enables space-saving mounting on plant framework. EDI is basically a chemical-free process and only requires an electrical current for the application of a DC voltage.
Through the discharge of dissolved salts via the concentrate, wastewater amounting to approximately 5-10% of the inflow stream is produced. This wastewater can be returned to the reverse osmosis inflow if discharge is not desired and water requirements are to be minimised.
