Electrodialysis (ED) or Electro Dialysis is a water treatment process. How does it work? What are the most suitable applications for this treatment technology?
Please continue reading this article to find out.
WHAT IS ELECTRODIALYSIS (ED)?
Electrodialysis (ED) is a membrane-based process involving transport of ions through semipermeable membranes using an applied electric field.
HOW DOES ELECTRODIALYSIS PROCESS WORK?
The electrodialysis process utilizes an electrodialysis stack built on the filter press principle. The stack consists of 200–400 alternate cationic and anionic membranes between two electrodes; the aqueous feed solution flows through the cells between each pair of membranes.
When an electrical potential difference is applied between the two electrodes, positively charged cations in the feed solution move toward the cathode. These ions easily pass through the negatively charged cation exchange membranes, but are retained by the positively charged anion exchange membranes. Similarly, negatively charged anions migrate towards the anode, pass through the anion exchange membrane and are retained by the cation exchange membrane. As shown in the picture below.
Because of the arrangement of ion-selective membranes, the migrating ions become concentrated in each alternate cell in the stack. Thus, ions removed from the aqueous feed solution are concentrated into two separate streams.
The electrodialysis process can be operated as continuous production or batch production. In a continuous process, feed is passed through a sufficient number of stacks placed in series to produce the final desired product quality. In batch processes, the diluate and/or concentrate streams are re-circulated through the electrodialysis systems until the final product or concentrate quality is achieved.
ELECTRODIALYSIS PROCESS APPLICATIONS
Electrodialysis process of water is used for different applications. The main application of electrodialysis has historically been the desalination of brackish water or seawater as an alternative to RO for potable water production and seawater concentration for salt production.
The electrodialysis process is used for many different applications:
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 reuse (e.g., desalination brine treatment, industrial laundry wastewater, etc.)
Pre-demineralization (e.g., boiler makeup & pre-treatment, ultrapure water pre-treatment for electro deionization, etc.)
Food processing industries
Agricultural water (e.g., water for greenhouses, hydroponics, irrigation, livestock, etc.)
Glycol desalting (e.g., antifreeze / engine-coolants, capacitor electrolyte fluids, oil and gas dehydration, etc.)
THE ADVANTAGES OF ELECTRODIALYSIS WATER TREATMENT PROCESS
The main benefit of electrodialysis process is the high recovery rate, especially for applications where the water recovery is required.
The ED system works at very low pressure, thus the effect of fouling is not significant and consequently no hard chemicals are required to clean the membranes.
Furthermore, the electrodialysis process works without phase change, which results in relatively low energy consumption.
IS ELECTRODIALYSIS WATER TREATMENT COST-EFFICIENT COMPARED TO REVERSE OSMOSIS?
In normal potable water production without the requirement of high recoveries, reverse osmosis is generally believed to be more cost-effective when total dissolved solids (TDS) are 3,000 parts per million (ppm) or greater, while electrodialysis is more cost-effective for TDS feed concentrations less than 3,000 ppm or when high recoveries of the feed are required.
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FAQs ABOUT ELECTRODIALYSIS (ED)
What is the Electrodialysis process?
Electrodialysis is a separation process using ion-exchange membranes and an electrical potential as a driving force.
What is Electrodialysis primarily used for?
Electrodialysis is primarily used for water desalination, table salt production, and in the food industry.
How much does the Electrodialysis process cost?
Typically, the electrodialysis water treatment cost ranges from $0.32/m3 to $6.32/m3, depending on concentrate disposal cost and water recovery.
Which membrane is used in Electrodialysis?
The ion permeable membranes used in electrodialysis are essentially sheets of ion-exchange resins. The membranes normally are copolymers of styrene and divinylbenzene.
What is Reverse Electrodialysis?
Reverse electrodialysis (RED) allows for the capture of energy from salinity gradients between salt and fresh waters generating clean energy out of desalination’s concentrate effluents.
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