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Review

Research Progress on the Application of Electrodialysis Technology for Clean Discharge Water Treatment from Power Plants

by
Zhiwei Kang
1,
Guifeng Zhao
2,
Haoyang Xiong
2,
Kai Zhang
2 and
Peidong Su
2,*
1
Hongshaquan Energy Co., Ltd., Xinjiang Energy & Chemical Co., Ltd., Urumqi 830000, China
2
School of Chemical & Environmental Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
*
Author to whom correspondence should be addressed.
Water 2025, 17(18), 2701; https://doi.org/10.3390/w17182701
Submission received: 17 July 2025 / Revised: 1 September 2025 / Accepted: 9 September 2025 / Published: 12 September 2025
(This article belongs to the Section Wastewater Treatment and Reuse)
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Abstract

The increasing global demand for sustainable water management in coal-fired power plants highlights the critical challenges of high-salinity wastewater treatment, where electrodialysis technology emerges as a promising technology for salinity removal. This paper systematically investigates the application status, technical principles, advantages, and challenges of electrodialysis (ED) in clean water treatment for coal-fired power plants, and its future development potential is also discussed. As an efficient membrane-based desalination technology, ED could effectively remove chloride ions, sulfate ions, and other dissolved salts from clean water, significantly reducing conductivity and enabling both water reuse and salt recovery. Studies indicate that through optimized operational parameters and system design, ED systems can achieve over 90% desalination efficiency and concentrate salts to levels exceeding 12%, delivering notable economic and environmental benefits. However, practical implementation still faces challenges such as membrane fouling and high energy consumption. Advances in novel membrane materials, system integration, and intelligent control technologies are expected to broaden ED’s applicability in power plant water treatment. This study serves as a valuable technical reference for advancing clean water purification and resource recovery in the energy sector, and the findings will contribute to informed decision-making for sustainable water treatment solutions.

1. Introduction

Coal-fired power plants, as the primary source of electricity supply in China, generate substantial amounts of industrial wastewater during operation. According to statistics from the China Electricity Council, the annual wastewater discharge from coal-fired power plants nationwide exceeded 2.5 billion tons in 2022, with clean discharge water accounting for approximately 40% [1]. Clean discharge water (which usually includes (1) circulating cooling water system discharge, (2) boiler makeup water system discharge, (3) thermal system drain water, (4) rainwater drainage, and (5) auxiliary system drainage) primarily originates from circulating cooling water system drainage, reverse osmosis concentrates from boiler feedwater treatment systems, and equipment rinsing water [2,3]. It is characterized by relatively stable water quality and low suspended solids content, but contains high levels of total dissolved solids (TDS), typically ranging from 1000 to 5000 mg/L. The main components include soluble salts such as chloride ions, sulfate ions, sodium ions, and calcium ions [4,5]. The presence of these dissolved salts can adversely impact power plant water systems in multiple ways: Firstly, high concentrations of chloride ions (>250 mg/L) can significantly accelerate pitting corrosion and stress corrosion in metal pipelines. Secondly, calcium and magnesium ions tend to form scale deposits on heat exchange surfaces, thereby reducing the efficiency of heat transfer. Furthermore, excessive salinity in discharged water can negatively affect the ecological environment of receiving water bodies [6,7,8]. With the progressive implementation of the “Guidelines for Best Available Techniques of Pollution Prevention and Control for Thermal Power Plants” (HJ-BAT-001) and the “Water Pollution Prevention and Control Action Plan” [9,10], the water quality requirements for power plant effluents have become increasingly stringent. Traditional treatment methods involving simple sedimentation followed by direct discharge can no longer meet current environmental protection standards [11].
Table 1 comprehensively compares the energy consumption profiles, merits, and limitations of mainstream desalination technologies. Electrochemical processes like conventional electrodialysis exhibit superior energy efficiency (0.4–8.7 kWh/m3) but encounter performance constraints related to membrane durability [12,13]. Thermal-based methods, including multi-stage flash (MSF) (14–25 kWh/m3) and multi-effect distillation (MED) (7–25 kWh/m3), demonstrate established operational reliability despite their significant energy demands and scaling vulnerabilities [14]. Emerging hybrid configurations, such as membrane distillation, present distinctive capabilities for hypersaline treatment (22–67 kWh/m3) but require optimization to improve recovery rates. The apparent duplication of conventional electrodialysis data points to possible tabulation inconsistencies that should be addressed [15]. This systematic evaluation reveals critical performance trade-offs between energy intensity and process stability, emphasizing the importance of technology matching based on feedwater characteristics and operational requirements in desalination system design. The findings contribute to informed decision-making for sustainable water treatment solutions.
Electrodialysis (ED), as a mature membrane separation technology, demonstrates unique advantages in industrial wastewater treatment [16,17,18]. Compared to pressure-driven membrane technologies such as reverse osmosis (RO), ED exhibits the following distinctive features: lower operating pressure (typically < 0.3 MPa), relatively lenient feed water quality requirements, selective separation of specific ions, and the ability to produce highly concentrated brine suitable for resource recovery. Particularly noteworthy is ED’s optimal economic efficiency when treating wastewater with medium salinity (1000–10,000 mg/L TDS), which aligns perfectly with the typical water quality characteristics of power plant clean discharge water [13].
From a sustainable development perspective, the application of ED technology in treating power plant clean discharge water delivers triple benefits: (1) environmental benefits: enables near-zero liquid discharge (ZLD) of wastewater, significantly reducing pollution to natural water bodies; (2) economic benefits: recovered water can be reused in circulating cooling water systems, while salts in the concentrated brine can be extracted to produce industrial-grade sodium chloride and other products; (3) social benefits: the widespread adoption of this technology facilitates the green transformation of the power industry and contributes to achieving the “dual carbon” goals (carbon peak and carbon neutrality). Therefore, in-depth research on the application of ED technology in power plant clean discharge water treatment holds significant theoretical and practical value.
Research on ED technology originated in the 1950s, with developed countries such as the United States and Japan taking leading positions in the development of membrane materials and engineering applications. In recent years, projects such as “Zero Brine”, funded by the European “Horizon 2020” program, have successfully applied ED technology for salt recovery from industrial wastewater [16]. In China, research institutions, including North China Electric Power University and Zhejiang University, have achieved a series of innovative results in power plant wastewater treatment. However, systematic research on ED technology specifically for treating power plant clean discharge water remains insufficient, particularly lacking in-depth analysis of long-term operational stability and economic evaluation.
This study aims to systematically investigate the application of ED technology in treating clean discharge water from coal-fired power plants, addressing critical gaps in long-term operational stability and comprehensive economic evaluation. By analyzing ED’s performance in desalination, resource recovery, and system optimization, the research provides both theoretical insights and practical solutions to achieve near-zero liquid discharge, supporting the power industry’s transition toward sustainable water management and alignment with China’s “dual carbon” goals. The findings will serve as a valuable reference for advancing ED implementation in industrial wastewater treatment, offering environmental benefits through pollution reduction, economic advantages via water reuse and salt recovery, and social value by promoting green energy development.

2. Methods and Materials

2.1. Materials for the Electrodialysis System

The core of electrodialysis is the selective permeability of ion-exchange membranes. Typically, cation-exchange membranes (CEM) contain negative groups such as sulfonic acid groups (-SO3H), allowing only cations (such as Na+, Ca2+) to pass through. Anion-exchange membrane (AEM) contains positively charged groups such as quaternary ammonium groups (-NR3+), allowing only anions (such as Cl−, SO42-) to pass through [19,20,21]. The general composition of an electrodialysis system mainly includes a membrane stack (consisting of 50–300 pairs of CEM/AEM alternately arranged to form a concentrated water chamber and a fresh water chamber), a DC power supply (providing 100–600 V voltage, current density 10–50 mA/cm2), a fluid transport system (including inlet pumps, circulation pumps, etc., to ensure uniform water flow distribution), and a control system (based on PLC/DCS real-time adjustment of voltage, flow rate, and other parameters to optimize operating efficiency) [22,23]. The process of electrodialysis technology in clean discharge water treatment from power plants is illustrated in detail in Figure 1.

2.2. Optimization of Pretreatment Process

The clean wastewater from power plants needs to be pretreated to reduce the risk of membrane fouling and improve the efficiency of electrodialysis. Under normal circumstances, the main pretreatment methods include (1) pH adjustment (using an automatic dosing system (such as NaOH/H2SO4) to stabilize the pH at 6.5–7.5) [25]; (2) hardness removal (adding Na2CO3 and NaOH to make Ca2+ < 50 mg/L and Mg2+ < 30 mg/L) [26,27]; and (3) suspended solids removal (through multi-media filtration, such as using smokeless coal (0.8–1.2 mm) + quartz sand (0.5–0.8 mm) double-layer filter media, with a filtration speed of 8–10 m/h) [28]. Finally, when COD > 50 mg/L, organic matter can be removed through activated carbon adsorption or advanced oxidation.

2.3. Optimization of the Electrodialysis System

The optimization of electrodialysis systems first involves innovative membrane stack structures, such as constructing an anion-exchange resin coupled with three-chamber electrodialysis (RTED). Wave-shaped mesh can also be used to optimize the channel structure, increase the maximum current density by 20–30%, and reduce concentration polarization. Another way is to improve the reaction efficiency of the system by coupling electrodialysis nanofiltration (NF-ED) [29,30]. NF membrane preferentially intercepts divalent ions (such as SO42−, Ca2+), and the permeate (containing Na+, Cl−) enters ED for further desalination. System optimization can also be achieved through electrodialysis extraction coupling.
As shown in Figure 2, the core components of the system include ion-exchange membranes—specifically, the cation-exchange membrane, which permits the passage of cations, and the anion-exchange membrane, which allows anions to pass—arranged alternately to form distinct chambers. The electrodes consist of an anode on the left and a cathode on the right, providing the electric field required for ion migration. The chambers are functionally divided into the anode chamber, concentrate chambers (where ions are enriched), dilute chambers (where ions are removed to achieve desalination), a NaOH chamber, and the cathode chamber. An electrolyte solution circulates through the chambers, and under the applied electric field, ions—such as those in the MDEA solution—migrate through the respective membranes: cations (e.g., Na+) pass through CEM, while anions migrate through AEMs. This process results in ion enrichment in the concentrate chambers (yielding concentrated methyldiethanolamine (MDEA) solution) and ion depletion in the dilute chambers (with diluted MDEA solution collected in the dilute tank). The NaOH solution helps maintain ionic balance within the system, potentially aiding in pH regulation, and is circulated between the NaOH chamber and its storage tank [31,32,33].
This setup is designed for the regeneration of MDEA, a common absorbent in processes such as gas decarbonization. Through electrodialysis, rich MDEA solution is regenerated, while lean MDEA solution is further treated. The use of NaOH supports the electrochemical environment, making this a representative electrochemical method for chemical separation and solvent purification. In summary, this electrodialysis system utilizes an electric field and selective ion-exchange membranes to enable ion transport for the concentration or dilution of solutions such as MDEA. It demonstrates significant potential for applications in chemical separation and solvent regeneration.

3. Principles of Electrodialysis Technology

3.1. Fundamental Components of Electrodialysis Systems

The complete ED system consists of several key subsystems [34]. (1) the membrane stack assembly, comprising 50–300 pairs of ion-exchange membranes, spacers, and electrodes arranged in a “sandwich” laminated structure. The spacers, typically made of 0.5–2.0 mm thick polypropylene mesh, serve dual functions as both water flow channels and turbulence promoters to prevent concentration polarization. (2) The DC power supply system, including rectifiers and transformers, typically delivers an output voltage of 100–600 V while maintaining current density at 10–50 mA/cm2. Advanced pulse power technology can reduce electrode polarization and achieve over 15% energy savings. The fluid delivery system incorporates feed pumps, concentrate/dilute circulation pumps, and electrode rinse pumps, all equipped with variable frequency control to accommodate different processing loads. Special attention must be paid to ensuring uniform flow distribution during system design to avoid “dead zones” that may lead to localized scaling. Finally, the automated control system, based on PLC or DCS platforms, monitors and adjusts more than 30 parameters in real time, including voltage, current, flow rate, and pressure. The intelligent control system can automatically detect membrane fouling levels and initiate cleaning procedures.
The schematic in Figure 3 illustrates the key components and functional zones of an ED system, which is driven by a DC power supply. The system comprises two primary electrode chambers: the anode chamber, housing the positive electrode (anode), and the cathode chamber, containing the negative electrode (cathode). Between these chambers, ion-exchange membranes are strategically arranged, including a CEM and an AEM, which facilitate selective ion transport. The concentrate chamber, positioned adjacent to the CEM, serves as the zone for ion enrichment, while the dilute chamber, situated next to the AEM, functions as the region for ion depletion. The feed solution (influent) enters the system, and the processed streams exit through the concentrate outlet (enriched in ions) and the dilute outlet (depleted in ions) [35,36]. This configuration highlights the ED system’s capability for efficient ion separation and concentration gradient generation.

3.2. Selective Permeability of Ion-Exchange Membranes

Ion-exchange membranes serve as the core components of ED systems, with their performance directly determining treatment efficiency. At the microscopic level, these membranes consist of three fundamental elements: a polymer matrix, functional groups, and cross-linking agents [37]. Cation-exchange membranes contain negatively charged groups such as sulfonic acid (-SO3H) or carboxylic acid (-COOH), permitting exclusive passage of cations. Conversely, anion-exchange membranes incorporate positively charged groups like quaternary ammonium (-NR3+), allowing only anions to permeate. This selective transport mechanism originates from Donnan equilibrium effects and electrostatic repulsion forces. Recent advancements demonstrate that incorporating zwitterionic groups or constructing gradient pore structures can significantly enhance membrane ion selectivity [38]. For instance, block-type ion-exchange membranes fabricated via graft polymerization achieve a Cl−/SO42− selectivity coefficient of 5.8, substantially surpassing conventional homogeneous membranes (~2.5). Furthermore, surface modification techniques, including plasma treatment and nanocoatings, effectively improve membrane antifouling properties.
As shown in Figure 4, the system incorporates alternating CEM, which allows only cations such as Na+ to pass, and AEM, which permits only anions such as Cl− to pass. These are arranged in repeated membrane pairs that define separate flow channels. Electrodes—an anode on the left and a cathode on the right (though the diagram appears to mislabel the cathode as “Anode”)—apply a direct current electric field to enable directional ion transport. The feed wastewater enters through the inlet and is separated into two streams: a freshwater outlet where ions are removed, and a concentrated water outlet where ions are accumulated. An electrode rinse solution circulates through the electrode compartments to prevent the buildup of reaction products that could impair system performance.
Under the influence of the electric field, cations (e.g., Na+) migrate toward the cathode through CEMs, while anions (e.g., Cl−) move toward the anode through AEMs, both converging into the concentrate channels. Consequently, the dilute stream becomes ion-depleted, producing fresh water, while the concentrate stream is enriched with ions, yielding concentrated brine. ED is widely used in applications such as brackish water desalination, industrial wastewater recycling for water recovery and pollutant concentration, and as a pretreatment step in seawater desalination. Recognized for its relatively low energy consumption and modular design, electrodialysis exemplifies an efficient electrochemical separation strategy aimed at supporting water reuse and reducing waste volume. In essence, this system employs an electric field and selective ion-exchange membranes to redirect ions from wastewater, separating it into a purified stream and a concentrated brine, making it a vital technology in modern electrochemical water treatment.

3.3. Ion Migration in the Electrodialysis Process

Under the influence of a direct current electric field, ion migration follows the Nernst–Planck equation [38]:
J i x =   − D i ∂ C i x ∂ x   −   z i F RT D i C i   ∂∅ x ∂ x   +   C i v ( x )
In the above equation, the first term on the right side represents the diffusion term, the second term denotes the migration term, and the third term corresponds to the convection term, where i indicates the ith species, Ci represents concentration, Di stands for diffusion coefficient, ∅ signifies electrical potential, and v(x) denotes liquid flow velocity. In practical operation, the following influencing factors must be considered: (1) concentration polarization: when current density exceeds the limiting current density, an ion depletion layer forms at the membrane surface, causing water dissociation into H+ and OH- ions, which not only increases energy consumption but also deteriorates membrane performance. Optimizing flow channel design (e.g., using curved spacer networks) can enhance the limiting current density by 20–30%. (2) Non-ideal transport phenomena: including co-ion transport, osmotic water transport, and electro-osmotic drag. Research shows that under typical operating conditions, approximately 5–15% of current is lost due to these non-ideal effects. (3) Electrode reactions: oxidation occurs at the anode (2H2O → O2↑ + 4H+ + 4e−), while reduction takes place at the cathode (2H2O + 2e− → H2↑ + 2OH−). These reactions induce pH variations in electrode compartments, necessitating regulation through electrode solution circulation systems.

4. Application of Electrodialysis Technology in Power Plant Clean Discharge Water Treatment

4.1. Pretreatment Process Optimization

To address the specific characteristics of clean discharge water from power plants, a tailored pretreatment process is essential to ensure downstream system reliability and efficiency. In Table 2, different pretreatment units and their function for clean discharge water treatment are listed in detail. This process typically integrates several sequential water conditioning units: (1) pH adjustment is performed using an automated dosing system to maintain the influent within the optimal range of 6.5–7.5; operational data from a 600 MW unit indicate that sustaining pH at 7.2 ± 0.3 can prolong the membrane service life by up to 30%. (2) Hardness removal is achieved through combined chemical softening with Na2CO3 and NaOH, effectively reducing Ca2+ to below 50 mg/L and Mg2+ below 30 mg/L. (3) Suspended solids are removed via multi-media filtration, utilizing a dual-layer configuration of anthracite (particle size 0.8–1.2 mm) and quartz sand (0.5–0.8 mm) at filtration rates of 8–10 m/h. (4) Precision filtration is ensured using 5 μm cartridge filters equipped with automatic backwashing triggered when the differential pressure exceeds 0.1 MPa. (5) Activated carbon adsorption employs coal-based activated carbon with an iodine value ≥ 950 mg/g and a minimum contact time of 15 min to effectively remove organic contaminants. (6) For water with elevated chemical oxygen demand (COD > 50 mg/L), an advanced oxidation process based on UV/O3 combination is implemented, achieving 70–85% oxidation efficiency [39,40]. This integrated pretreatment strategy significantly mitigates fouling and scaling risks, enhances the overall efficiency of subsequent desalination processes, and improves the economic and operational sustainability of the water treatment system.

4.2. Optimization of Electrodialysis Reaction Systems

4.2.1. Construction of Multifunctional Electrodialysis Membrane Stacks

In ED technology, conventional membrane stacks typically employ an alternating arrangement of anion-exchange membranes and cation-exchange membranes to form a series of electrode, concentrate, and diluate compartments. While this classical configuration has been widely adopted, it suffers from several inherent technical limitations, such as high energy consumption, low current utilization efficiency, limited desalination performance, and elevated system resistance. These shortcomings become particularly pronounced when treating complex industrial effluents or in applications requiring high recovery rates.
In response to these challenges, researchers have developed innovative membrane stack architectures aimed at overcoming the drawbacks of traditional designs. Recent advances include the incorporation of bipolar membranes, selective layered configurations, and hybrid setups integrating monovalent-selective membranes. These novel designs not only enhance the adaptability of ED systems to wastewater streams with varying compositions—such as those containing high salinity, organic matter, or multicomponent ion mixtures—but also significantly improve energy efficiency through reduced ohmic resistance and optimized current pathways. Furthermore, such innovations open new pathways for resource recovery, enabling the extraction of valuable acids, bases, or specific salts from waste streams, thereby supporting circular economy approaches in water treatment [41].
A case in point is the treatment of N-methyldiethanolamine wastewater. The research team led by Zhang et al. [42] developed a novel resin-coupled three-chamber electrodialysis (RTED) system. Experimental results demonstrate that this system achieves 93.84% removal efficiency for heat-stable salts (HSS), representing a 7.88 percentage-point improvement over conventional three-chamber ED and a 28.57 percentage-point enhancement compared to two-chamber ED systems. Notably, the RTED system maintains high removal efficiency while significantly reducing the loss rate of active MDEA components. Furthermore, the innovative design incorporating anion-exchange resins in the diluate compartment effectively mitigates membrane fouling issues. This technological breakthrough provides an innovative solution for industrial wastewater treatment.
As shown in Figure 5, the core operational principle combines electrically driven ion transport with selective ion adsorption for efficient separation. The key components consist of ion-exchange membranes—CEMs that permit cation passage and AEMs that allow anion transfer—which partition the unit into functional chambers. Electrodes, including the anode on the left and the cathode on the right, provide the electric field necessary for ion migration. The chambers include a concentrate cell for ion enrichment, a dilution cell equipped with anion-exchange resin to enhance anion adsorption and exchange, and a NaOH chamber to maintain alkaline conditions and support ion mobility. Storage tanks are provided for concentrated MDEA, diluted MDEA, NaOH solution, and electrode rinse liquid, enabling continuous recirculation of fluids throughout the system [43,44].
During operation, ions from the MDEA solution migrate under the applied electric field: anions pass through AEMs while cations move across CEMs. The anion-exchange resin in the dilution cell further enhances the removal of anions, significantly improving the degree of desalination and dilution in this compartment. Simultaneously, the concentrate cell accumulates ions, yielding a concentrated MDEA stream. Solutions are continuously circulated between their respective chambers and external tanks, with the electrode rinse stabilizing the electrochemical reactions at the electrodes. This integrated system is particularly valuable for regenerating MDEA—a common absorbent in applications such as decarbonization—enabling simultaneous dilution of spent solution for reuse and concentration of valuable components for recovery. By synergizing electrodialysis with resin adsorption, the process enhances separation efficiency, reduces energy consumption, and represents a sophisticated hybrid electrochemical–ion-exchange approach to solvent purification and resource recovery in industrial gas treatment processes [45].

4.2.2. Coupling of Electrodialysis with Nanofiltration

The development of high-efficiency, low-energy desalination technologies for resource recovery from power plant clean discharge water containing mixed mono- and divalent ions has become a key research focus. Nanofiltration (NF), as a pressure-driven membrane separation technology, demonstrates exceptional separation performance in complex wastewater systems due to its unique size-sieving effect and Donnan exclusion mechanism, enabling selective retention of divalent ions. The integration of NF with ED technology not only effectively mitigates scaling issues in ion-exchange membranes but also significantly enhances water recovery rates, offering innovative solutions for resource-oriented treatment of high-salinity wastewater. For instance, Ye et al. [46] successfully achieved efficient separation of dyes and salts using an ED process incorporating loose NF membranes. The experimental results demonstrated remarkable dye rejection rates of 99.4%, alongside 98.9% desalination efficiency, presenting a viable approach for textile wastewater reclamation.
Furthermore, the NF-ED integrated system proposed by Zhang et al. [47] optimizes the treatment process through (1) primary separation of mono- and divalent ions by NF, followed by (2) directed routing of permeate and concentrate streams to the ED system for metathesis reactions, ultimately producing high-value salts (e.g., CaCl2 and Na2SO4) to achieve wastewater resource utilization. Compared to conventional reverse osmosis processes, the NF-ED system exhibits superior performance in freshwater recovery rate, resource recovery efficiency, energy consumption control, and membrane fouling mitigation, establishing a novel pathway for sustainable treatment of high-salinity industrial wastewater.

4.2.3. Integration of Electrodialysis with Extraction

Compared to conventional solvent extraction processes, the combination of extraction with electrodialysis technology offers distinct advantages: significantly reduced organic solvent loss, lower membrane fouling risks, and substantially improved recovery efficiency of target products, thereby enhancing the overall economic viability of the process [48]. Buchbender et al. [49] developed a multistage countercurrent extraction–electrodialysis integrated process, employing a mixed solvent system of di(2-ethylhexyl) phosphate and isododecane for selective extraction of γ-aminobutyric acid (GABA) from fermentation broth, followed by efficient separation and recovery of GABA salts through bipolar membrane electrodialysis (BMED).
In the field of lithium resource extraction, Zhao et al. [50] innovatively proposed a Sandwich Liquid Membrane Electrodialysis (SLMED) technology that combines the advantages of liquid membrane permeation (LMP) and electrodialysis. As shown in Figure 6, the hybrid system addresses the key challenges in lithium extraction from salt lake brines, particularly those with high Mg2+/Li+ ratios, which are notoriously difficult to separate due to their similar ionic radii and chemical properties. The core structure of the SLMED system, as illustrated in Figure 7, features a unique configuration where two cation-exchange membranes sandwich a Li+-loaded organic liquid membrane. The liquid membrane employs a synergistic system consisting of tributyl phosphate (TBP) as the extractant and ClO4− as the counterion, which selectively facilitates the transport of Li+ ions while effectively blocking Mg2+ and other interfering cations.
The experimental results demonstrate that the SLMED technology achieves remarkable efficiency and selectivity in lithium enrichment. Under optimized conditions, the system exhibits high Li+ recovery rates and significant rejection of Mg2+, even in brines with Mg2+/Li+ ratios exceeding 100:1. The process operates at relatively low energy consumption compared to conventional methods such as evaporation or solvent extraction, making it both economically viable and environmentally sustainable. Furthermore, the use of a liquid membrane eliminates the need for additional chemical reagents or complex pretreatment steps, reducing secondary pollution risks [51,52].
The success of SLMED highlights the broader potential of extraction–electrodialysis hybrid technologies in the recovery of high-value substances from complex solutions. These systems not only enhance resource utilization efficiency but also minimize environmental impacts by reducing energy demands and chemical waste. Future research could explore the adaptation of this technology for other critical metal separations, such as cobalt, nickel, or rare earth elements, further advancing sustainable resource recovery processes.

4.3. System Design and Operational Optimization

Taking a clean discharge water treatment project at a 2 × 1000 MW power plant as an example, the key design parameters of the electrodialysis system are showing in Table 3:
Operational data demonstrate that after six months of continuous operation, the system achieved an average desalination rate of 92.3%, with product water conductivity stabilized at 200–300 μS/cm, meeting the requirements of GB/T 19923–2005 [24] The concentrated brine reached a TDS concentration of 12.5%, making it directly suitable for use in the chlor-alkali industry.
ED technology, coupled with other treatment processes, can significantly enhance system efficiency and expand application scenarios across various industries.Figure 8 illustrates the typical integration workflow of ED with other technologies.
For desalination applications, the ED-RO integrated system demonstrates remarkable advantages. The electrodialysis unit serves as a pretreatment step to reduce feedwater salinity below 1%, which substantially decreases membrane fouling potential in subsequent reverse osmosis treatment. This combined approach not only improves freshwater recovery rates but also enables byproduct recovery, as the concentrated brine stream can be further processed to produce industrial-grade salts. This dual-purpose system has proven particularly effective for seawater desalination and high-salinity wastewater treatment projects. In large-scale desalination plants, the ED-MSF (Multi-Stage Flash) hybrid configuration offers superior energy efficiency. The electrodialysis pretreatment unit lowers the salt load entering the thermal desalination system, while waste heat from the MSF process can be utilized to preheat the ED feedwater [53,54]. This energy cascade utilization strategy can reduce overall energy consumption by 20–30% compared to standalone systems, making it an attractive solution for coastal mega-cities with high water demand.
For industrial wastewater treatment and resource recovery, the ED-BMED (Bipolar Membrane ED) integrated system represents a breakthrough in circular economic applications. The process first concentrates salt-containing wastewater through conventional electrodialysis, then employs bipolar membrane technology to electrochemically convert the salts into marketable acid and alkali products. This innovative approach not only achieves zero liquid discharge but also transforms waste streams into valuable commodities, with typical conversion efficiencies exceeding 85% for common salts like NaCl. In ZLD systems, the ED-evaporation crystallization combination delivers unprecedented energy savings. By preconcentrating wastewater to over 20% TDS using electrodialysis prior to thermal evaporation, the system reduces evaporator load by 60–70%, dramatically lowering both capital and operational expenses [55,56]. Field data from coal chemical plants show that this hybrid configuration can cut ZLD operating costs by 40% compared to conventional thermal-only systems. For ultrapure water production, the ED-ion exchange integrated process revolutionizes traditional approaches. The electrodialysis unit replaces approximately 50% of the ion-exchange capacity, reducing chemical consumption for resin regeneration by 30–50% while maintaining product water quality below 0.1 μS/cm conductivity. This hybrid system has become the industry standard for semiconductor and pharmaceutical water treatment, where both water purity and operational cost are critical factors.
In Table 4, the comparative analysis of ED and its hybrid configurations reveals critical trade-offs between desalination efficiency, energy consumption, and operational feasibility. Conventional ED remains the most energy-efficient (0.4–8.7 kWh/m3) and widely applicable method, particularly for brackish water desalination, due to its low chemical demand and adaptability. However, its limitations in selectivity and susceptibility to membrane fouling restrict its use in high-salinity or complex feedwaters. Reverse electrodialysis (RED) further reduces energy demand (0.1–2.5 kWh/m3) by harnessing salinity gradient power, but its low desalination rate (30–60%) and limited driving force hinder large-scale deployment.
Hybrid systems, such as nanofiltration-integrated ED (NF-ED) and selective-layer MED (SLMED), demonstrate improved desalination performance (70–95% salt removal) and recovery rates (70–90%) by combining membrane selectivity with enhanced ion separation [57,58]. However, these systems incur higher operational complexity and costs. Bipolar membrane ED (BMED) achieves exceptional salt removal (80–98%) and enables concurrent acid/base production, but its high voltage requirements and membrane degradation pose sustainability challenges. At the high-performance end, membrane distillation-coupled ED (MD-ED) delivers near-complete desalination (90–99%) and high recovery (80–95%), making it suitable for hypersaline brines. Yet, its energy intensity (10–30 kWh/m3) and thermal management needs limit economic viability without renewable energy integration. Capacitive deionization (CDI)-ED offers a middle ground with moderate energy use (1.5–10 kWh/m3) and antifouling properties but remains constrained by electrode stability in high-salinity environments [59,60].
The successful implementation of these hybrid systems requires careful attention to three key aspects: (1) Comprehensive pretreatment, including filtration and softening to protect ED membranes; (2) sophisticated energy integration strategies to maximize thermodynamic efficiency; (3) advanced control systems to optimize operating parameters across different treatment units. The growing adoption of these coupled technologies demonstrates their potential to address increasingly complex water treatment challenges while improving sustainability and cost-effectiveness across multiple industries.
The successful implementation of hybrid ED water treatment technology relies on three key elements: comprehensive pretreatment, efficient energy integration, and intelligent control systems, which collectively provide significant advantages and broad feasibility. In terms of pretreatment, filtration and softening processes effectively remove suspended solids and hardness ions, significantly extending the lifespan of ED membranes and reducing maintenance costs. This step, which leverages mature and cost-effective technologies, not only minimizes the frequency of chemical cleaning but also expands the application of ED in treating highly polluted or high-hardness wastewater. Energy integration strategies, such as waste heat recovery, pressure exchange, or the use of renewable energy, dramatically reduce system energy consumption. The modular design of ED facilitates integration with solar or cogeneration systems, enhancing thermodynamic efficiency while aligning with carbon neutrality goals [61,62]. Over time, energy savings and government subsidies can offset initial investments. The intelligent control system utilizes real-time monitoring and AI algorithms to dynamically optimize operational parameters, enabling precise resource utilization and fault prediction. Its foundation in industrial IoT lowers deployment barriers, further improving system stability and automation.
Compared to traditional RO or ion-exchange technologies, hybrid ED systems excel in energy efficiency, tolerance, and flexibility. Their low-pressure operation reduces energy consumption by 30–50%, making them ideal for energy-sensitive scenarios. The modular design allows for easy scaling or integration with other technologies, adapting to distributed water treatment needs [63,64]. Additionally, the potential for brine resource recovery reduces reliance on chemicals, aligning with circular economy principles. These advantages position hybrid ED systems as highly competitive in treating high-salinity wastewater, zero liquid discharge, and renewable energy-coupled applications, enhancing both processing efficiency and cost-effectiveness while boosting corporate sustainability profiles. With advancements in digital and green energy technologies, hybrid ED systems will further drive the water treatment industry toward high-efficiency, low-carbon solutions, offering a sustainable approach to addressing complex water quality challenges.

5. Conclusions

Electrodialysis technology demonstrates significant technical advantages and application potential in treating clean discharge water from coal-fired power plants. By leveraging the selective separation capability of ion-exchange membranes, ED can effectively remove dissolved salts (desalination rate ≥90%), achieve near-zero liquid discharge, and enable water reuse in circulating cooling systems while facilitating resource recovery from concentrated brines. Tailored to the water quality characteristics of power plant clean discharge water (TDS 1000–5000 mg/L), ED systems maintain long-term stable operation with balanced environmental and economic benefits through (1) optimized pretreatment processes (pH adjustment, hardness removal, precision filtration); (2) innovative membrane stack designs (resin-coupled three-chamber ED, NF-ED hybrid systems); and (3) operational parameter control (pulsed power supply, electrode reversal). Furthermore, integration with nanofiltration and extraction technologies expands its applications in complex wastewater treatment and resource recovery.
Looking ahead, further advancements in ED technology will focus on three key directions: (1) Development of smart selective membranes with enhanced ion selectivity, antifouling properties, and adaptive permeability to improve separation efficiency for specific ions (e.g., Li+, heavy metals). (2) Integration with electrochemical and resource recovery processes, such as lithium extraction (Li+ selective ED), bipolar membrane electrodialysis (BMED) for acid/base production, and hybrid systems combining ED with crystallization or adsorption to maximize resource valorization. (3) Digitalization of ED control systems, including AI-driven optimization of operational parameters (voltage, flow rate), real-time fouling monitoring, and smart management of ED battery configurations to enhance energy efficiency and adaptability to fluctuating feedwater conditions. These innovations will solidify ED’s role as a cornerstone technology for sustainable water management, supporting the power industry’s green transition and the broader “dual carbon” objectives.

Author Contributions

H.X. and Z.K. designed the experiment. K.Z. and P.S. supervised the project and oversaw all the research phases. H.X. and G.Z. performed the full experiments and analyzed the characterization data. G.Z. and Z.K. helped to enhance the figures and revised the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Fundamental Research Funds for the Central Universities (2023ZKPYHH04, 2024ZKPYHH08) and Basic Research Business Expense Project for New Teachers at China University of Mining and Technology (Beijing) (2023XJHH02).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors upon request.

Conflicts of Interest

Author Zhiwei Kang was employed by the company Hongshaquan Energy Co., Ltd., Xinjiang Energy & Chemical Co., Ltd., China. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Flowchart for the methodology used in this article [24].
Figure 1. Flowchart for the methodology used in this article [24].
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Figure 2. Basic process schematic of RTED for treating MDEA solution (reproduced according to Ref. [19], copyright to Elsevier) (with the selective permeability of CEM and AEM ions in the solution migrating selectively. The system consists of an anode chamber, a concentrate chamber, a dilute chamber, a NaOH chamber, and a cathode chamber. MDEA solution undergoes processing: concentrated MDEA solution is involved, and NaOH solution from the NaOH solution tank, along with electrolyte solution, participates in electrodialysis. Through the selective migration of ions facilitated by the membranes, the solution is separated and purified, achieving the treatment of MDEA solution via electrodialysis.
Figure 2. Basic process schematic of RTED for treating MDEA solution (reproduced according to Ref. [19], copyright to Elsevier) (with the selective permeability of CEM and AEM ions in the solution migrating selectively. The system consists of an anode chamber, a concentrate chamber, a dilute chamber, a NaOH chamber, and a cathode chamber. MDEA solution undergoes processing: concentrated MDEA solution is involved, and NaOH solution from the NaOH solution tank, along with electrolyte solution, participates in electrodialysis. Through the selective migration of ions facilitated by the membranes, the solution is separated and purified, achieving the treatment of MDEA solution via electrodialysis.
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Figure 3. Key components and functions of the ED system.
Figure 3. Key components and functions of the ED system.
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Figure 4. Schematic diagram of the electrodialysis process based on ion-selective migration (driven by the electric field from the power supply, and leveraging the selective permeability of CEM and AEM). Cations like Na+ in wastewater migrate toward the cathode via CEM, while anions such as Cl− move toward the anode via AEM. This purifies water in some regions into fresh water exiting through the Fresh Water Outlet, and enriches ions in water into concentrated water discharged from the Concentrated Water Outlet. With the electrode rinse solution involved, wastewater enters through the Wastewater Inlet and concentrated water via the Concentrate Inlet, thus achieving ion separation and purification in solution through electrodialysis.
Figure 4. Schematic diagram of the electrodialysis process based on ion-selective migration (driven by the electric field from the power supply, and leveraging the selective permeability of CEM and AEM). Cations like Na+ in wastewater migrate toward the cathode via CEM, while anions such as Cl− move toward the anode via AEM. This purifies water in some regions into fresh water exiting through the Fresh Water Outlet, and enriches ions in water into concentrated water discharged from the Concentrated Water Outlet. With the electrode rinse solution involved, wastewater enters through the Wastewater Inlet and concentrated water via the Concentrate Inlet, thus achieving ion separation and purification in solution through electrodialysis.
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Figure 5. Principle of anion-exchange resin coupled with three-chamber electrodialysis process (reproduced according to Ref. [19], copyright to Elsevier) (The system has an anode cell, concentrated cell, dilution cell, NaOH cell, and cathode cell. Concentrated MDEA and NaOH solutions are input, and through electrodialysis, MDEA solution is concentrated (in the concentrated cell) and diluted (in the dilution cell), with diluted MDEA collected and electrode liquid stored, achieving MDEA solution separation and concentration/dilution).
Figure 5. Principle of anion-exchange resin coupled with three-chamber electrodialysis process (reproduced according to Ref. [19], copyright to Elsevier) (The system has an anode cell, concentrated cell, dilution cell, NaOH cell, and cathode cell. Concentrated MDEA and NaOH solutions are input, and through electrodialysis, MDEA solution is concentrated (in the concentrated cell) and diluted (in the dilution cell), with diluted MDEA collected and electrode liquid stored, achieving MDEA solution separation and concentration/dilution).
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Figure 6. Schematic diagram of nanofiltration electrodialysis combined reaction stack process (reproduced according to Ref. [19], copyright to Elsevier).
Figure 6. Schematic diagram of nanofiltration electrodialysis combined reaction stack process (reproduced according to Ref. [19], copyright to Elsevier).
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Figure 7. Principle of sandwich liquid membrane electrodialysis system (reproduced according to Ref. [22], copyright to Wiley).
Figure 7. Principle of sandwich liquid membrane electrodialysis system (reproduced according to Ref. [22], copyright to Wiley).
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Figure 8. Typical coupled process flow diagrams integrating ED with other technologies.
Figure 8. Typical coupled process flow diagrams integrating ED with other technologies.
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Table 1. The advantages and disadvantages of different methods for clean discharge water treatment.
Table 1. The advantages and disadvantages of different methods for clean discharge water treatment.
Desalination TechnologyEnergy Consumption (kWh/m3)AdvantagesDisadvantages
Conventional Electrodialysis0.4~8.7Low energy consumption, minimal chemical usage, adaptable to varying salinity levelsMembrane fouling, poor ion selectivity
Multi-stage Flash (MSF)14~25Rapid evaporation, less prone to scalingHigh energy consumption
Multi-effect Distillation (MED)7~25Mature technologyScaling issues, high energy consumption
Membrane Distillation (MD)22~67Capable of treating high-salinity wastewater with low fouling potentialLow recovery rate, high energy consumption
Mechanical Vapor Compression (MVC)20~25Technologically matureScaling problems, high energy consumption
Table 2. Pretreatment units and their function for clean discharge water treatment.
Table 2. Pretreatment units and their function for clean discharge water treatment.
Process UnitFunction
Equalization TankServes as the preliminary storage and regulation unit for raw water, ensuring stable flow and quality for subsequent treatment systems.
High-Density TankAdds coagulants or flocculants to promote aggregation and sedimentation of suspended solids/colloids, improving water clarity.
SedimentationUtilizes gravity to settle flocs formed in the high-density tank, producing sludge at the bottom and supernatant for the next stage.
Multi-Media FilterFurther removes suspended solids, colloids, and organic matter to protect downstream membrane components from fouling.
Ultrafiltration (UF)Uses UF membranes to retain macromolecules, bacteria, and viruses, providing pretreatment for NF and RO.
Nanofiltration (NF)Softens UF-treated water by removing partial hardness ions (e.g., Ca2+, Mg2+), reducing the load on the RO system.
SWRO (Seawater RO)Treats 1% NaCl solution (from ED desalination) for further desalination, producing high-quality freshwater.
Electrodialysis (ED)Core process: Separates pretreated 4% NaCl solution into dilute (1% for RO) and concentrate (15% brine) streams.
Table 3. Key design parameters of the electrodialysis system (clean discharge water treatment in a 2 × 1000 MW power plant).
Table 3. Key design parameters of the electrodialysis system (clean discharge water treatment in a 2 × 1000 MW power plant).
ParameterDesign ValueOptimization Measures
Membrane stack configuration3-stage, 6-sectionElectrode reversal design (EDR)
Effective area per membrane pair0.5 m2Wave-shaped spacer design
Operating voltage1.2 V/cell pairPulsed power supply (duty cycle 0.7)
Recovery rate75–85%Concentrate recirculation ratio at 30%
Desalination rate≥90%Automatic current density adjustment
Table 4. Comparison of ED technologies and hybrid configurations.
Table 4. Comparison of ED technologies and hybrid configurations.
TechnologyDesalination RateAdvantagesDisadvantages
Conventional EDModerate (~50–90% salt removal)Low energy use, minimal chemicals, adaptable to salinityMembrane fouling, poor ion selectivity
Reverse ED (RED)Low (~30–60% salt removal)Energy recovery, low foulingLow driving force, limited scalability
Nanofiltration-ED (NF-ED)High (~70–95% salt removal)High selectivity, reduced foulingHigher cost, complex operation
Selective-Layer MED (SLMED)Moderate-High (~60–85% salt removal)Improved ion selectivity, stable operationModerate scaling risk
Bipolar Membrane ED (BMED)High (~80–98% salt removal)Acid/base production, high efficiencyHigh voltage required, membrane degradation
Capacitive Deionization (CDI) + EDModerate (~50–80% salt removal)Low fouling, energy-efficient regenerationLimited to high salinity, electrode degradation
Membrane Distillation-ED (MD-ED)Very High (~90–99% salt removal)Handles hypersaline brine, high purityHigh energy demand, thermal management needed
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Kang, Z.; Zhao, G.; Xiong, H.; Zhang, K.; Su, P. Research Progress on the Application of Electrodialysis Technology for Clean Discharge Water Treatment from Power Plants. Water 2025, 17, 2701. https://doi.org/10.3390/w17182701

AMA Style

Kang Z, Zhao G, Xiong H, Zhang K, Su P. Research Progress on the Application of Electrodialysis Technology for Clean Discharge Water Treatment from Power Plants. Water. 2025; 17(18):2701. https://doi.org/10.3390/w17182701

Chicago/Turabian Style

Kang, Zhiwei, Guifeng Zhao, Haoyang Xiong, Kai Zhang, and Peidong Su. 2025. "Research Progress on the Application of Electrodialysis Technology for Clean Discharge Water Treatment from Power Plants" Water 17, no. 18: 2701. https://doi.org/10.3390/w17182701

APA Style

Kang, Z., Zhao, G., Xiong, H., Zhang, K., & Su, P. (2025). Research Progress on the Application of Electrodialysis Technology for Clean Discharge Water Treatment from Power Plants. Water, 17(18), 2701. https://doi.org/10.3390/w17182701

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