DI Water Systems

DI Water Systems

Deionisation of water, usually RO water, uses synthetic resins to remove ions.

Some of the uses of Type 2 (General Grade) DI Water produced from this technology are:

  • Buffer make up
  • Media production
  • Sample dilution and reagent preparation
  • General Chemistry

Type 2 Water Diagram

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In the Triple Red Water Technology range, there are a number of systems which provide DI water and the choice depends on the amount of water required. Water is produced into a reservoir which allows it to be drawn off in volumes, or for many points of use around a building.

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How does Deionisation Work?

Deionisation uses synthetic ion-exchange resins to chemically remove ions from feed water. As the water passes through the ion exchange resin beads, hydrogen and hydroxide ions are chemically exchanged with dissolved minerals to form water. Deionisation resin beds or columns are made from cation-exchange resins and anion-exchange resins either in separate beds or packaged together. Different technologies are referred to as co-current, counter-current and mixed bed. Most commercial resins are made of polystyrene sulphonate and oppositely charged ion exchanging sites are introduced after polymerisation. Cation-exchange media use sulphonic acid groups to exchange a hydrogen ion for any cations they encounter (e.g. Na+, Ca++, Al+++) and anion-exchange resins use quaternary amino groups such as polyAPTAC to exchange a hydroxyl for any anions (e.g. Cl-, NO3 - , SO4 -- ). When the hydrogen ion from the cation exchanger unites with the hydroxyl ion of the anion exchanger pure water is formed.

Once all of the ion exchange sites on the resin have been filled by contaminants in the water, the resin will become exhausted. Resins may be regenerated by chemically rinsing in strong acids and bases to recharge the beads. Regeneration may be carried out when large cylinders of resin are used in industrial applications. In laboratory water systems, cartridges are discarded once exhausted. Choosing a water system with high capacity, longer lasting deionisation packs will impact greatly on running costs. Deionisation is the only technology which produces the resistivity requirement for Type 1 ultrapure reagent grade water. The electrical resistivity of ultrapure water is 18.2 M‑-cm. This low conductivity can only be achieved with water dissociation equilibrium which requires the production of H+ and OH− ions in the presence of dissolved monatomic gases.

How does Electrodeionisation (EDI) Work?

RO/EDI systems feature an EDI module that consists of ion exchange resins used in single beds for enhanced water purification. Microbiological analysis of product water shows a high decrease in proliferation of bacteria due to the high pH swing between the 2 cells and direct contact of resin and electrodes. Furthermore, an intermediate pH shift has a positive effect on the separation of SiO2 (Silicon Dioxide) and CO2 (Carbon Dioxide). We also see a remarkable reduction in the number of bacteria with high colony forming unit (CFU) counts from the feedwater, as electrodes in the water make it unsuitable for bacteria to live.

Learn more about our DI Water Systems