What Is Electrodialysis Reversal? How “Automatic Polarity Reversal” Makes High-Salinity Water Treatment More Stable

In industrial desalination and high-salinity wastewater treatment, many projects are not really about “whether desalination is possible,” but about whether the equipment can operate stably over the long term. Traditional electrodialysis uses a direct current electric field to drive cations and anions in water to pass through ion exchange membranes with selective permeability, so that salt in the dilute compartments is continuously reduced while salt in the concentrate compartments gradually accumulates. Electrodialysis Reversal (EDR) adds periodic electrode polarity reversal and flow path switching on this basis: after the system operates for a period, the roles of anode and cathode are exchanged, and the functions of the original concentrate and dilute compartments are switched accordingly, making it difficult for deposits that tend to form on membrane surfaces to remain for long. It is not “a completely different membrane process,” but an engineered solution that strengthens the long-term operational stability of electrodialysis, especially suitable for scenarios with significant raw water quality fluctuations, high scaling risk, or the need for high recovery.

1.Why Does Polarity Reversal Improve Operational Stability?

The core value of EDR comes from the periodic interruption of concentration polarization, scaling, and fouling tendencies on membrane surfaces by “reversal.” During continuous direct current operation, certain ions accumulate near membrane surfaces, and elevated local concentrations may induce the formation of inorganic scales such as carbonates and sulfates; organic matter and colloids may also gradually attach. By periodically reversing polarity, the direction of ion migration changes, and areas previously prone to enrichment become relatively diluted zones, thereby reducing the opportunity for deposits to continue growing. Therefore, a high-quality EDR system is not just one that “can reverse polarity”; it also requires stable power control, reliable valve coordination, uniform flow channel design, membrane stacks suited to water quality, and proper pretreatment. If raw water contains high levels of suspended solids, hardness, iron, manganese, organic matter, or silica, targeted pretreatment is still required, and the polarity reversal function should not be understood as a replacement for all front-end controls.

2.Equipment Selection and Application Scenarios

From the perspective of equipment structure, the key components of an electrodialysis water treatment system include membrane stacks, electrodes, power supply, circulation pumps, valve groups, instruments, and control systems. Among them, electrodialysis membranes and spacers together determine ion migration paths and hydraulic conditions. In practical engineering, the more commonly used functional term is ion exchange membranes, including cation exchange membranes and anion exchange membranes; membrane material selection needs to comprehensively consider acid/alkali resistance, permselectivity, electrical resistance, mechanical strength, and fouling resistance. For customers, selection should not focus only on “treatment capacity” or equipment appearance; more attention should be paid to feed TDS, major ion composition, target product water conductivity, recovery rate, temperature, pH, hardness, COD, and allowable concentration factor. For example, for the same high-salinity water, water dominated by NaCl has significantly different scaling risk and operating strategy compared with water containing high levels of Ca²⁺, Mg²⁺, and SO₄²⁻. A truly reasonable solution usually requires water quality analysis first, followed by determining membrane type, number of stages, flow velocity, current density, and polarity reversal interval.

In application, EDR is commonly used in brackish water desalination, salt reduction in industrial circulating water, concentration and reuse of some high-salinity wastewater, and ion adjustment of food and chemical process liquids. It is not simply a matter of “one replacing the other” compared with reverse osmosis: RO relies on pressure to push water molecules through a membrane, while EDR mainly uses an electric field to migrate ions; the two differ in sensitivity to salinity, target separation, recovery rate, pretreatment, and energy consumption. When a project is more concerned with selective desalination, higher recovery, or reducing long-term scaling risk on membrane surfaces, EDR has clear engineering appeal. For ultra-low-salt product water or projects that also need to reject large amounts of non-ionic pollutants, it may need to be combined with RO, filtration, or other processes. Bipolar membrane electrodialysis belongs to another technical route: it uses bipolar membranes to split water into H⁺ and OH⁻ under an electric field, making it more suitable for acid/base production, salt conversion, and resource recovery, and should not be confused with EDR.

For companies evaluating electrodialysis solutions, the most important thing is not to first decide on a particular standard equipment model, but to clarify “what should be removed from the water, what should be retained, what final water quality must be achieved, and what operating costs are acceptable.” Rubri, a brand of Hefei Sinopower Technologies Co., Ltd., provides water treatment solutions covering electrodialysis, electrodialysis reversal, and related membrane separation technologies. During project discussions, membrane stack configuration, pretreatment, reversal logic, and control strategies can be matched according to raw water analysis, design capacity, target recovery, and product water specifications. More product and technical information is available at hfsinopower.com. For complex industrial water, it is recommended to provide complete ion analysis and actual operating boundary conditions before formal equipment selection, rather than judging whether the equipment is suitable based only on TDS as a single indicator.

FAQ: Customers’ Most Common Questions About Electrodialysis Reversal

1.Can EDR completely prevent scaling?

No. EDR can significantly reduce the tendency of continuous scaling and fouling on membrane surfaces, but it is not a “pretreatment-free” technology. If raw water contains excessively high hardness, sulfate, silica, iron, manganese, suspended solids, or organic matter, scaling, clogging, or membrane fouling may still occur. In engineering, softening, filtration, chemical dosing, or other pretreatment should be designed according to saturation indices, water composition, and concentration factor, and system status should be judged by changes in operating differential pressure, voltage, current, and conductivity.

2.Is my high-salinity wastewater suitable for EDR equipment?

You need to look at the complete water quality beyond salinity. It is recommended to provide at least major cations and anions, TDS, conductivity, hardness, COD, SS, pH, temperature, treatment capacity, target product water specifications, and target recovery rate. If wastewater contains large amounts of non-ionic organic matter, oils, or high concentrations of suspended solids, pretreatment is usually required first. For projects that need selective ion removal, higher recovery, or salt concentration, EDR often has high evaluation value.

3.How should I choose between EDR and reverse osmosis?

The driving forces and advantages of the two are different. RO uses pressure difference as the driving force and is good at broadly removing dissolved salts and many types of pollutants; EDR uses an electric field to drive ion migration, separates ionic substances more directly, and can reduce scaling tendency on membrane surfaces through polarity reversal. Actual selection should compare feed salinity, ion composition, target water quality, recovery rate, energy consumption, concentrate disposal method, and maintenance conditions. In some projects, a combination of RO and EDR is more reasonable.

4.How often do electrodialysis membranes need to be replaced?

There is no fixed replacement interval. The actual service life of electrodialysis membranes is affected by raw water quality, pretreatment effectiveness, operating current density, temperature, pH, cleaning frequency, mechanical assembly, and the extent of scaling and fouling. Rather than simply focusing on “how many years before replacement,” a more professional approach is to continuously track membrane stack resistance, energy consumption per unit of product water, salt removal rate, pressure drop, and cleaning recovery rate. When performance continues to decline and cannot be restored after cleaning, evaluate partial or complete replacement.