What Is Electrodeionization?
What Is Electrodeionization?
Electrodeionization (EDI) is a method of purifying water without chemicals by using electricity, ion exchange membranes, and resin. It is often used as a final step to remove impurities after reverse osmosis (RO).
Continuous electrodeionization (CEDI) units are available, which use an electric current to continuously regenerate the resin. EDI can achieve very high purity, with a conductivity below 0.1 μS/cm. The process includes electrodialysis, ion exchange and regeneration.
In electrodialysis, a voltage is applied to direct ions to electrodes with opposite charges, while in ion exchange, salts in the water adsorb onto the resin and are replaced by hydroxyl anions and hydrogen cations.
The regeneration is done continuously by hydrogen ions and hydroxyl groups, through the process of water splitting that occurs in the anode and cathode when voltage is applied.
History Of Electrodeionization
Electrodeionization, a technology developed in the late 1950s to eliminate or reduce the concentration polarization in electrodialysis systems, was initially limited in application due to its low tolerance for hardness and organics.
In the 1970s and 1980s, reverse osmosis became the preferred method for high TDS waters, leading to the use of electrodeionization as a polishing technology in packaged RO and EDI systems. In the 1980s and 1990s, companies such as Millipore, Ionpure, HOH Water Technologies, and Ionics Inc. developed electrodeionization devices, but they were large, costly, and unreliable.
In 1995, Glegg Water Conditioning introduced the E-Cell brand, which was more affordable and reliable due to its modular design. Competitors such as Electropure and SnowPure soon followed with similar designs.
Today, the technology is widely available from many water treatment companies, but it should only be used by experts who understand its limitations and use high-quality products.
How Does Electrodeionization Work?
The EDI module uses ion exchange resins and membranes to remove impurities from water. An electrical field is applied to force ions through the resins and across the membranes, where they are collected into a concentrate stream.
The purified water can be used directly or undergo further treatment. The module continuously regenerates itself by exchanging ions and flushing waste to a separate chamber.
The limitations of EDI are different from traditional ion exchange, as it is limited by the maximum rate of ion arrival rather than the total number of ions taken up by the resins. EDI is often used in conjunction with reverse osmosis and degassing for very hard water.
Advantages Of Electrodeionization
The main advantages of using electrodeionization chemical cleaning include:
- The absence of contaminant accumulation due to the continuous regeneration of ion-exchange beds, which prevents exhaustion in contrast to batch mode operation.
- The use of no chemicals in the process, making it safe and environmentally friendly.
- The removal of virtually all ions within the water, making it suitable for high-stakes applications such as pharmaceutical production.
- The ability to recycle or repurpose the collected ions.
Limitations Of Electrodeionization
Electrodeionization (EDI) is a continuous electrochemical process used to remove ions and other impurities from water. However, despite the many benefits of EDI, it also has some limitations that should be taken into consideration.
Electrodeionization, while having its advantages, also has several downsides. These include being limited to only removing ions, requiring additional purifying processes to remove other contaminants, incurring costs for membrane replacement, consuming a continuous stream of electricity, and having performance that may vary depending on the composition of the feed water.
Applications Of Electrodeionization
EDI is a useful technology for applications that require efficient and safe removal of water impurities without the use of harmful chemicals.
Examples include the recycling of residual water in the food and beverage industry, chemical production, biotechnology, electronics, cosmetics, laboratories, and the pharmaceutical industry.
Additionally, EDI units are reliable and provide customers with high-quality production water for use in power plant boilers or microchip rinsing. The water produced by EDI meets or exceeds customer specifications and, when necessary, cleaning the system can fully restore product quality.