Ultrapure Water Systems: Design Principles and Maintenance Techniques

Electrodeionization technology is a commonly used method for producing ultrapure water in water treatment. In recent years, EDI technology has been increasingly used in power generation, electronics, pharmaceutical, and other industries.

So how does the EDI system achieve the production of ultrapure water? How to maintain electrodeionization systems?

1. What is Electrodeionization?

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.

EDI is a highly sensitive ultrapure water deionization system. The operating life of an electrodeionization 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 electrodeionization system is required whenever the water quality or production rate of the system begins to deteriorate (the cleaning cycle is typically every 6 months). Contact the manufacturer for in-depth troubleshooting and tailored solutions if the cleaning effect is unsatisfactory.

Electrodeionization Unit2

2. What is Ultrapure Water?

The standard for ultrapure water is that the water resistivity is 18.2 MΩ.cm. As high-purity water, ultrapure water contains almost no impurities, bacteria, viruses, minerals, etc.

Ultrapure water can be divided into first-level ultrapure water, second-level ultrapure water, and third-level ultrapure water. Widely used in laboratories, semiconductors, biopharmaceuticals, chemical industry, and other fields.

Ultrapure water for laboratory use:
-Grade 1 water: It can be obtained by using second-grade water. Basically does not contain dissolved ions, impurities, and organic matter.
-Grade 2 water: Contains trace amounts of inorganic, organic, or colloidal impurities.
-Grade 3 water: used for general laboratory experimental work.

Pharmaceutical Water Purification System

3. How does EDI System Work?

EDI ultrapure water system consists of a cation exchange membrane, concentrated water chamber, anion exchange membrane, fresh water chamber, and positive and negative electrodes. The ion exchange resin forms a single treatment unit, the freshwater chamber, between the anion and cation exchange membranes. In addition, the units are separated from each other by a mesh which is the concentrated water chamber.

Under the action of a DC electric field, the cations and anions carried by the ion exchange resin present in the fresh water chamber will move directionally through the partition plate, migrating in the negative and positive directions, respectively, and entering the concentrated water chamber to form concentrated water.

At the same time, the cations and anions in the EDI feed water are exchanged with the hydrogen ions and hydroxide ions in the ion exchange resin to form ultrapure water. Thus achieve the purpose of water purification by using the selective permeation of ions through the exchange membrane, the EDI device will eventually split the feed water into three independent water streams: pure water, concentrated water, and extreme water.

The electrodeionisation plant can be divided into thin chamber EDI plant and thick chamber EDI plant. Compared with the traditional ion exchange technology, the resin in the EDI membrane stack is continuously regenerated by water electrolysis, so acid and alkali chemical regeneration is not required. Therefore, the EDI water system gradually replaces the mixed bed as the fine treatment equipment used, widely in the pharmaceutical, electronics, electric power, chemical industry, and other industries.

4. Water Quality Specifications for EDI Equipment

Figure 1 EDI system

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

5. 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 are 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.

6. How to Regenerate EDI Systems?

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.

7. EDI Water Purification Features:

(1) Continuous operation, stable product water quality
(2) Fully automatic control system
(3) The entire process does not require acid-base regeneration
(4) No shutdown due to regeneration
(5) Saves recycled water and recycled sewage treatment facilities
(6) The water produced is of high quality.

8. Electrodeionization (EDI) Systems Applications:

* Chemical water treatment for power plants
* Ultrapure water for electronics and semiconductor industries
* Preparation of food, beverages, and drinking water
* Preparation of ultrapure water in the laboratory
* The pharmaceutical industry processes water
* Desalination of sea water and brackish water

9. Final Words

NEWater has been in the ultrapure water treatment industry for 20 years. We ensure the quality and longevity of our products while demonstrating our level of expertise to our customers. Whether it’s the design of an ultrapure water system or the supply of an electrodeionisation module, just call NEWater!

We provide you with electrodeionisation process manuals, equipment operation, and maintenance training, equipment pipework installation drawings, and electrical circuit diagrams. Worldwide shipping and a one-year quality guarantee.

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