Electrodialysis using ion exchange membranes
Ion Exchange Membrane for Electrodialysis: Purifying Water
Issues surrounding water have increasingly become serious worldwide caused by drought and other meteorological phenomena as well as rise in salt content in groundwater. However, securing good quality water is important from the perspective of people's health and sanitation.
AGC Inc. has developed the ion exchange membrane SELEMION™, a FORBLUE™ family product, for electrodialysis. Electrodialysis can separate organic materials from salt efficiently because it only permits ionic materials to pass through the ion exchange membrane. Although electrodialysis process is already widely utilized in food industries, AGC Inc. succeded to apply and develop the essence of electrodialysis for water purification.
Essentially, the technology provides desalination and nitrate removal from groundwater for generating drinking water. It’s ideal for use in places where water resources depend on limited groundwater. It can be applied to increase supply of drinking water in areas with insufficient power infrastructure.
I. High Water Reuse Ratio
The water reuse ratio of the electrodialysis method is nearly 90 percent, although it depends on the composition such as hardness component of supplied water. This allows for the effective use of groundwater.
II. Energy Efficiency
The electrodialysis method requires less power than other water purification technologies. Also, it can be used in conjunction with solar panel systems. Thus, it is possible to install the system on-site with limited power sources.
III. Low Operational Cost
Operational costs are about the same or less than the conventional RO process. This is because a high-pressure pump is not needed.
Selemion™ can be used in a variety of ways in many applications, such as:
・Table salt production
・Demineralization in food industries
・Industrial wastewater reclamation
・Desalination (tap water)
・Electro organic synthesis
・Desalination and nitrate removal of groundwater for drinking water.
・This technology is applicable in areas where water resources depend on limited groundwater, not on sea water or river.
・Supply of drinking water in areas with insufficient power infrastructure.
[Description of electrodialysis]
An electrodialyzer is composed of anion and cation exchange membranes stacked alternately with thin spacers between them and a pair of electrodes at both ends.
In an electrodialyzer, two types of chambers are placed between a pair of electrodes. One is a desalination (D) chamber partitioned with an anion-exchange membrane on the anode side and a cation-exchange membrane on the cathode side. The second is a concentration (C) chamber partitioned with a cation-exchange membrane on the anode side and an anion-exchange membrane on the cathode side.
Saline water is desalinated in the D chamber and is concentrated in the C chamber, as a result of the electrical potential (see Figure 1).
Figure 1. Cross section image of an electrodialyzer
Photo 1. Ion-exchange membranes
Left side: Cation-exchange membrane
Right side: Anion-exchange membrane
1. High water reuse ratio
・The water reuse ratio of the ED (electrodialysis) process is higher than other technologies. Thus, this technology can contribute to the effective use of groundwater.
2. Energy saving
・The ED process requires less power compared with other water purification technologies.
・Although, there are no previous cases yet, because the ED process is powered by direct current, it can be used with solar panel systems, making it possible to install the system on sites with limited power sources.
・Ion exchange resin used in water-softening equipment loses performance as hard minerals build up during use. However the ED process requires no regeneration process to remove hard substances to recover performance, meaning that the amount of chemicals used can be cut significantly.
3. Low operational cost
・The operation cost is roughly the same or less than the conventional RO process since a high-pressure pump is not required.
・The water reuse ratio of this method (electrodialysis method) is close to 90% (This value depends on the composition such as hardness component of water supplied and the target composition of water.)
・The degree of desalination is adjustable.
In the late 1990’s, these systems were installed at more than 10 sites in the Middle East. These projects were related to well water.
We regularly replace membranes used in these systems even after installation. Membrane replacement frequency is roughly once every 4 years, but it depends on the usage situation. As annual maintenance can also serves as operational inspection, an option to replace 25% of the membrane every year is also available.
Without proper operation and maintenance (daily and regular), there is a possibility that the performance of the system can not be demonstrated to its full capacity.
In order to avoid this risk, we will work with local partner companies not only to install these systems, but also to build maintenance systems.
Part of maintenance and technical service will be conducted under the guidance of a local company, such as a water engineering company. The biggest risk is that users might operate the system without fully understanding the operation method resulting in damage to membranes. In order to avoid this risk, we also want to perform proper operation and maintenance locally.
The complexity of any electrodialysis water treatment system depends on its conditions and goals, so please make inquiries first.
※This innovation seed information is reprinted with permission from UNIDO ITPO Tokyo’s STePP website.