Electrodeionization (EDI) Systems: Design Principles and Maintenance Techniques for Ultrapure Water Treatment

A popular water treatment process, EDI System’s main function removing ions from the water source. This new technology replaces the traditional ion exchange systems which are simple to operate, have stable water quality, and low operating costs.

Figure 1 EDI system

EDI is a highly sensitive ultrapure water deionization system. The operating life of an EDI system is typically between three and five years, depending on the quality of the entering water. The water quality can be stabilized at no less than 15 megaohms, and as high as 17 megaohms under ideal conditions.

Chemical cleaning of the EDI system is required whenever the water quality or production rate of the system begins to deteriorate (the cleaning cycle is typically every six months). Contact the manufacturer for in-depth troubleshooting and tailored solutions if the cleaning effect is unsatisfactory.

Water Quality Specifications for EDI Equipment

Pharmaceutical Grade Purified Water

1. Total exchangeable anions, calculated as CaCO3: <25ppm
2. Conductivity: <20uS/cm
3. pH: 6.09.0
4. Temperature: 535°C
5. Inlet pressure: <4bar (60psi)
6. Hardness (calculated as CaCO3): <0.5ppm
7. Organic matter (TOC): <0.5ppm
8. Oxidants: Cl2<0.05ppm, O3<0.02ppm
9. Multivalent metals: Fe<0.01ppm, Mn<0.02ppm
10. H2S: <0.01ppm
11. Silica: <0.5ppm
12. Color: <5APHA
13. Total amount of carbon dioxide: <5ppm
14. SDI 15min: <1.0

Preventative Maintenance for EDI

Electrodeionization (EDI) Unit2

1. Pressure gauges should be calibrated every 12 months.
2. Conductivity probe and flow meter should be cleaned and calibrated every 3 months.
3. Check the recovery rate at least weekly, and regularly record flow and pressure. Periodically check the incoming water quality, module screws, and end plate distances, check for leaks, ensure good module grounding, and check for loose electrical connections.
4. Module cleaning and disinfection is required for the following reasons: hardness scaling (mainly in the concentrate chamber and cathode), inorganic fouling of ion exchange resins and membranes, organic fouling of ion exchange resins and membranes, and microbial contamination of modules, system piping, and other components.

EDI Regeneration

During normal operation, the EDI system does not need any further dosing or regeneration from the operator because it is an autonomous regeneration system. However, the control system must be switched to automated regeneration or manual dosing for acid washing if problems arise when the water quality and quantity significantly change.

1. Hydrochloric acid circulates in the concentrate pipeline. The cleaning pump sends the acid solution into the module through the concentrate pipeline and back to the cleaning tank without going through the concentrate circulation pump.
2. Connect the cleaning ports of the concentrate outlet (Cout) and electrodeionization water (Eout) to the cleaning tank, and connect the cleaning port of the concentrate inlet (Cin) to the cleaning pump to prevent the chemical from splashing out.
3. Add 400L of reverse osmosis product water (or better quality water) to the cleaning tank. Slowly add 16.8L or 19.8kg.

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