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Understand the Basics of Electrodialysis Reversal (EDR): A Complete Guide

Electrodialysis Reversal (EDR) is a process that is used for separating ions from a solution using electrical potential. It is an effective method for purifying water and removing ions from saline solutions, making it a crucial process in various industries such as food and beverage, pharmaceuticals, and chemical manufacturing.

In this comprehensive guide, we will take a closer look at the basics of electrodialysis reversal, how it works, and its numerous applications.

Article Outline

What is Electrodialysis Reversal (EDR)?

Electrodialysis Reversal (EDR) is a separation technique that uses electric fields to move ions through a semi-permeable membrane.

The ions are separated based on their electrical charge, with positively charged ions moving towards the negatively charged electrode and negatively charged ions moving towards the positively charged electrode.

The process is carried out in a series of cells or stacks, with each cell consisting of alternating anion and cation exchange membranes.

How Does Electrodialysis Reversal (EDR) Work?

The process of electrodialysis begins with the introduction of a saline solution into the first cell of the stack. A direct current is then applied to the electrodes, causing the positive and negative ions in the solution to be drawn towards the respective electrodes.

Electrodialysis Reversal Working Principle Scheme Design
Electrodialysis Reversal Working Principle

The ions are transported through the semi-permeable membranes and collected at the electrodes, resulting in a separation of the ions in the solution. The separated ions are then passed through the subsequent cells, with each cell contributing to the overall ion separation process.

Electrodialysis Reversal Main Advantage: Flow and Polarity Reversal

Electrodialysis current reversal reduces clogging of membranes, as salt deposits in the membrane gets dissolved when the current flow is reversed.

Electrodialysis reversal causes a small decrease in the diluted feed quality and requires increased design complexity, as reversible valves are required to change the flow direction of diluted and concentrated streams.

However, it greatly increases ion exchange membranes durability, and membrane cleaning prevents electrical resistance increase of membrane as deposits accumulate in the membrane pores. Electrodialysis membranes can last about 10 years with the proper maintenance, a great advantage compared to RO membranes that on average need replacement every 1.5 years.

The polarity reversal of EDR alternately exposed membrane surfaces and the water flow paths to concentrate with a tendency to precipitate scale and desalted water that tends to dissolve scale.

These feature allows the process to operate with supersaturated concentrate streams up to specific limits without chemical additions to prevent scale formation.

The Role of Electrodialysis Semi-Permeable Membranes

The semi-permeable membranes play a crucial role in the electrodialysis process. These membranes allow the ions to pass through, while preventing the movement of other components in the solution.

The electrodialysis membranes (or sheets) come in different kind, depending on their functionality:

Anionic, Cationic, Bipolar Electrodialysis Membrane Sheets Features
Anionic, Cationic, Bipolar Electrodialysis Membrane Sheets Features

The membranes used in electrodialysis are typically made of ion exchange resins, which have a high ionic conductivity and a low resistance to the flow of ions. This ensures that the ions are efficiently transported through the membranes, leading to a high degree of separation efficiency. More scientific studies about these membranes can be found at: Ion-Exchange Membrane Separation Processes

For more technical information about our membranes for electrodialysis reversal you can get in touch with our team in the contact us section of our website.

The Importance of Testing Electrodialysis Reversal on Feed Water

Testing is one of the most important processes to understand the efficiency and efficacy of Electrodialysis Reversal (EDR) with the correct test equipment, lab scale pilot plant, or bench tests.

A pilot plant is a larger-scale system that mimics an industrial electrodialysis process, allowing for the testing and optimization of the process parameters. A demo unit, on the other hand, is a smaller-scale system that can be used for educational purposes or for showcasing the technology to potential clients.

Applications of Electrodialysis Reversal (EDR)

Electrodialysis Reversal (EDR) has a wide range of applications, with the most common being in the purification of water and the removal of ions from saline solutions. Some of the other applications of electrodialysis include:

  • Large scale brackish and seawater desalination and salt production

  • Small and medium scale drinking water production (e.g., towns & villages, construction & military camps, nitrate reduction, hotels & hospitals)

  • Water and wastewater reuse (e.g., desalination brine treatment, industrial laundry wastewater, produced water from oil/gas production, cooling tower makeup & blowdown, metals industry fluids, wash-rack water)

  • Pre-demineralization (e.g., boiler makeup & pre-treatment, ultrapure water pre-treatment, process water desalination, power generation, semiconductor, chemical manufacturing, food and beverage)

  • Food processing

  • Agricultural water (e.g., water for greenhouses, hydroponics, irrigation, livestock)

  • Glycol desalting (e.g., antifreeze / engine-coolants, capacitor electrolyte fluids, oil and gas dehydration, etc.)

  • Glycerine purification

  • Acid and base regeneration from salts

  • Recovery of valuable dissolved substances or ions from wastewater

  • Lithium recovery from battery recycling processes

  • Zero Liquid Discharge (ZLD)

Desalination of Seawater by Electrodialysis

Electrodialysis is widely used in the desalination of seawater or brackish waters, with the process allowing for the removal of ions such as sodium and chloride, resulting in the production of high-purity water. The process is energy-efficient and cost-effective, making it a popular choice for large-scale desalination projects.

Production of High-Purity Water for Industrial Processes

High-purity water is a critical component in many industrial processes, and electrodialysis is an effective method for producing it. The process removes impurities such as ions and other contaminants, resulting in water that is pure enough for use in applications such as power generation, pharmaceuticals, and electronics manufacturing.

Removal of Ions from Food and Beverage Products

Electrodialysis is also used in the food and beverage industry for the removal of ions from products such as cheese, wine, and fruit juices. The process helps to preserve the quality and taste of the products, while also improving their shelf life. This makes electrodialysis an important tool for the food and beverage industry, helping to ensure that products are of the highest quality for consumers.

Purification and Filtration of Wastewater

Electrodialysis can also be used in the purification and filtration of wastewater, helping to remove ions and other contaminants that may be present. The process helps to improve the quality of the wastewater, making it safer for discharge into the environment or to concentrate it to reduce the disposal costs of factories.

These features make electrodialysis reversal an important tool in the protection of the environment, helping to reduce the impact of human activity on the natural world.

Concentration of RO Reject and Brine

The brine that is generated during the RO process has a high salt concentration and obviously it cannot be discharged into the environment. This RO reject or brine can be further concentrated by Electrodialysis Reversal and water can be extracted from it. Typical salt concentrations from the EDR process brine can reach salinity levels up to 300,000ppm. More info can be found at: Electrodialysis Reversal (EDR) For RO Reject and Brine Concentration

For more applications of electrodialysis reversal, please visit: Applications of Electrodialysis Reversal | DESALT EDR (


Frequently Asked Questions About Electrodialysis Reversal

What is the efficiency of electrodialysis?

The efficiency of electrodialysis depends on a number of factors, including the type of solution being processed, the type of semi-permeable membranes used, and the electrical potential applied. Generally, the efficiency of electrodialysis is high, with most systems achieving over 90% ion separation efficiency.

What are the advantages of electrodialysis compared to other separation methods?

Electrodialysis has several advantages compared to other separation methods, including:

  • Energy consumption and efficiency: Electrodialysis requires less energy than other separation methods, making it a more cost-effective option

  • Modularity: electrodialysis membrane stacks can be easily assembles and installed in pre-built modules

  • Environmental friendliness: The process does not generate harmful by-products neither needs chemicals to operate, making it a more environmentally friendly option

  • Flexibility: Electrodialysis can be used for a wide range of applications, making it a versatile and flexible option

  • High separation efficiency: Electrodialysis typically achieves high separation efficiency, resulting in highly purified products

  • Ion selectivity: electrodialysis membranes stacks can be designed to recover or remove specific ions from the feed liquid

Is Reverse Electrodialysis suitable for treating and concentrating all types of RO reject?

Yes, Reverse Electrodialysis equipment can be customized to treat and concentrate RO reject from a variety of sources and with varying levels of dissolved solids.

How much energy does a system like DESALT electrodialysis consume compared to other technologies?

DESALT electrodialysis consumes less energy than thermal evaporation and other technologies commonly used for concentrating RO reject.

What are the main benefits of an electrodialysis reversal equipment such as DESALT?

The main benefits of DESALT electrodialysis reversal equipment include high salt rejection rates, low energy consumption, scalability, and ease of operation and maintenance.

How does electrodialysis reversal equipment compare to other concentration technologies?

An electrodialysis reversal equipment offers several advantages over other concentration technologies, including lower energy consumption, reduced environmental impact, and a lower total cost of ownership.

What industries can benefit from an electrodialysis reversal equipment?

An equipment such DESALT electrodialysis reversal can be used in a variety of industries, including water treatment, food and beverage, and chemical processing. Also, the equipment can be used in any application that require RO reject concentration.



Electrodialysis is an effective method for separating ions from a solution, making it a crucial tool in a wide range of industries. The process is energy-efficient, environmentally friendly, and highly effective, making it an attractive option for a variety of applications.

Whether it's used for desalination, the production of high-purity water, or the purification of wastewater, electrodialysis is a valuable tool that helps to ensure that the products we use are of the highest quality and purity.

In this complete guide to electrodialysis, we've explored the basics of the process, how it works, and its numerous applications. With its numerous advantages, electrodialysis is sure to continue playing an important role in the purification of water and the removal of ions from saline solutions for years to come.

For more information about Electrodialysis Reversal you can get in touch with our team.


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