Electrodialysis Reversal (EDR) is an advanced electrochemical water treatment tech and process that uses electric fields and special membranes to remove ions (salts, minerals) from water, featuring automated polarity switching (reversal) for a "self-cleaning" effect, preventing fouling, increasing water recovery (up to 94%), and tolerating challenging feedwaters like those high in silica or suspended solids, making it great for desalination, water reuse, and industrial processes, it is used primarily to desalinate brackish water and treat industrial wastewater. It is a variation of standard Electrodialysis (ED) that incorporates a "self-cleaning" mechanism to prevent membrane fouling.
The process relies on the movement of dissolved salt ions through selective membranes using an electric current as the driving force.
Ion Migration and Movement: When a direct current (DC) is applied, positively charged ions (cations) move toward the negative cathode, and negatively charged ions (anions) move toward the positive anode.An electric current pulls charged ions (like Na⁺, Cl⁻) through ion-exchange membranes (anion/cation selective) into concentrated streams, leaving purified water (dilute stream) behind.
Selective Membranes: The system uses alternating layers of Cation Exchange Membranes (CEM) and Anion Exchange Membranes (AEM). CEMs only allow cations to pass, while AEMs only allow anions to pass.
Polarity Reversal: The system periodically reverses the direction of the electric current , effectively switching the function of the membranes and flushing away foulants, reducing scaling and organic buildup. Periodically (usually 3–4 times per hour), the electrical polarity of the electrodes is reversed.
This reverses the direction of ion movement.
The channels that were previously "concentrating" salt become "diluting" channels.
This action helps dissolve and flush out scale or mineral deposits that have started to build up on the membrane surfaces, acting as a built-in cleaning cycle.
Self-Cleaning: The polarity reversal significantly reduces the need for chemical antiscalants and frequent manual cleaning, and reduce chemical cleaning needs and downtime.
High Water Recovery: EDR can often recover up to 90–94% of the feed water, leaving very little brine waste.
Durability: EDR membranes are rugged and can last 10–15 years, much longer than typical RO membranes.
Tolerance: It handles water with high levels of silica, suspended solids, and organic matter better than pressure-driven membrane systems.
No High Pressure: Since it uses electricity rather than pressure to move ions, it doesn't require high-pressure pumps, which reduces mechanical wear.
Fouling Resistance: Tolerates higher levels of silica, moderate suspended solids, and organic matter better than other methods like Reverse Osmosis.
Chlorine Tolerant: Membranes can withstand chlorine, useful for disinfection.
Versatile: Controls salt removal by adjusting electrical input.
Desalination and Brackish Water Treatment: For drinking water.
Water Reuse: Treating municipal and industrial wastewater.
Industrial Processes:food/beverage, chemical manufacturing,cooling tower blowdown recovery, boiler feed water pretreatment.
Resource Recovery: Extracting valuable minerals like lithium or concentrating brine.
Wastewater:Treating textile dyes, mining brine, and metal finishing rinse water.
Food and Beverage:Demineralization of whey, deacidification of fruit juices, and wine stabilization.
While RO is the most common desalination technology, EDR is often preferred when:
The water has high scaling potential (e.g., high calcium or sulfate).
Selective ion removal is needed (specific membranes can target certain ions).
The Total Dissolved Solids (TDS) are in the low-to-moderate range (usually below 3,000–5,000 ppm), where EDR is often more energy-efficient.
Mechanism: EDR uses electricity; RO uses high pressure.
Fouling: EDR handles fouling better; RO is more sensitive.
Water Quality: EDR is great for moderate salt removal; RO often provides higher purity but with more brine waste.
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