Electrodeionization

In electrodeionization (EDI), water is deionised using electric current, ion-exchange membranes and resin. EDI is typically used for the final polishing of water after the reverse osmosis stage when there is a need for very low conductivity of the water (below 0.1 μS/cm). Very low conductivity water is required, for example, for steam turbines in electric power plants and in the production of various semiconductor components (e.g. production of solar panels).

Equipment and system principle

An electrodeionization system consists of an EDI cell (basically an encased unit containing ion-selective membranes and mixed bed ion-exchange resin), a DC power supply unit and piping with the necessary regulators and sensors to control the flow of water within the EDI cell.

Within the EDI cell, the water is divided into final product water (diluate), concentrate and electrolyte (the residue water streams that include filtrated substances). The concentrate and electrolyte can be collected and re-used elsewhere in the process. With EDI, the yield is typically between 90–95%.

Required information for system design

To complete a water treatment system design, a raw water analysis is needed together with information about the required water flow/capacity of the system and the required water quality after treatment or information about the use of the water produced. If the equipment being installed in an existing space, information about the available drainage and room dimensions is also good to know.