A common definition for deionised and ultra-pure water (e.g. compared to RO water) is that the water has been treated with one or more additional desalination stages/technologies after single-stage RO. Deionised water is used, for example, in turbine power plants, laboratories and semiconductor production where water from a single-stage RO system is not pure enough.
A DI water system consists typically of a pre-treatment stage (e.g. multimedia filtration and softening – based on raw water quality), a reverse osmosis stage and one or more additional treatment stages/technologies to meet the required water quality. In some cases, second-stage reverse osmosis is enough. When ultra-pure water is needed (conductivity below 0.1 μS/cm), the system is usually completed with membrane degasification and electrodeionisation (EDI) stages. In addition, a mixed-bed filter can act as the final confirming/backup stage. Automation control systems have a critical role in deionised water treatment. As DI water systems consist of several treatment stages, it is crucial that the process works together and can be monitored and controlled continuously in real time.
Required information for system design
To complete a DI water system design, a raw water analysis is needed together with information about the required water flow/capacity of system and the required water quality after treatment or information about the use of the water produced. If the equipment is being installed in an existing space, information about available drainage and room dimensions is also good to know.