Electrochemical Methods for Nutrient Removal in Wastewater: A Review of Advanced Electrode Materials, Processes, and Applications

Abstract

In response to the increasing global water demand and the pressing environmental challenges posed by climate change, the development of advanced wastewater treatment processes has become essential. This study introduces novel electrochemical technologies and examines the scalability of industrial-scale electrooxidation (EO) methods for wastewater treatment, focusing on simplifying processes and reducing operational costs. Focusing on the effective removal of key nutrients, specifically nitrogen and phosphorus, from wastewater, this review highlights recent advancements in electrode materials and innovative designs, such as high-performance metal oxides and carbon-based electrodes, that enhance efficiency and sustainability. Additionally, a comprehensive discussion covers a range of electrochemical methods, including electrocoagulation and electrooxidation, each evaluated for their effectiveness in nutrient removal. Unlike previous studies, this review not only examines nutrient removal efficiency, but also assesses the industrial applicability of these technologies through case studies, demonstrating their potential in municipal and industrial wastewater contexts. By advancing durable and cost-effective electrode materials, this study emphasizes the potential of electrochemical wastewater treatment technologies to address global water quality issues and promote environmental sustainability. Future research directions are identified with a focus on overcoming current limitations, such as high operational costs and electrode degradation, and positioning electrochemical treatment as a promising solution for sustainable water resource management on a larger scale.

1. Introduction

The runoff of excess nutrients due to fertilizer application and pollution discharge has a significant impact on ecosystems. These nutrients are primarily derived from agricultural activities and industrial emissions, mainly consisting of nitrogen (N) and phosphorus (P) compounds. These compounds originate from point sources, such as sewage treatment plant (STP) discharges, and non-point sources, like fertilizer runoff, leading to detrimental effects on aquatic ecosystems worldwide [1]. Excessive N and P lead to algal blooms by promoting the growth of photosynthetic algae and cyanobacteria, resulting in eutrophication [2,3]. This reduces oxygen concentration, degrades water quality, changes water color, harms aquatic life by creating hypoxic conditions, and disrupts the balance of aquatic ecosystems [4,5,6]. Such conditions also make water unsuitable for drinking and various other uses [7]. Therefore, removing nutrients, such as N and P, from wastewater is crucial in preventing eutrophication, protecting water quality, and maintaining biodiversity. International regulations, including the European Union’s Water Framework Directive (WFD) and the United States’ Clean Water Act (CWA), mandate stringent nutrient removal from wastewater to safeguard water quality. The WFD aims to achieve “good status” for all water bodies by 2027, necessitating comprehensive river basin management plans and measures to mitigate nitrogen and phosphorus pollution [8,9]. Similarly, the CWA establishes effluent limits on pollutants, including nutrients, to prevent water quality degradation and protect aquatic ecosystems, as enforced by the U.S. Environmental Protection Agency (EPA) [10].

One approach to meeting these goals is to leverage innovative and efficient technologies for removing contaminants from water; among these, electrochemical (EC) treatment offers several advantages over traditional treatment methods [11]. EC treatment enables on-site production of chemicals and decomposition of target pollutants simultaneously, facilitating automation, high treatment efficiency, energy efficiency, environmental friendliness, and mineralization of persistent pollutants [12,13,14]. Various EC methods are employed for the treatment of waste and industrial wastewater, including electrocoagulation, electrooxidation (EO), electrodeposition (ED), electroflotation (EF), electrodialysis (EDR), electroflocculation (EFLOC), electrophoresis (EP), and electroreduction (ER) [15,16,17,18]. These treatment processes are designed to enhance pollutant removal rates, handle more complex or persistent contaminants, improve efficiency and cost-effectiveness, and often integrate multiple stages or synergistic reactions for effective treatment [19]. The selection of the most suitable EC treatment method depends on the characteristics of the effluent, the target pollutants, and the type of electrode material used [18,20]. For instance, EC and EFLOC are more suitable for removing colloids and suspended organic matter, although they can also remove dissolved organics [21]. EF is effective for removing oils, greases, and light particles present in effluents, while capacitive deionization (CDI) is used for water desalination, EDR for removing dissolved ions, and EC advanced oxidation processes (EAOPs) for the mineralization of target pollutants [22].

EC processes are gaining attention as effective methods for the removal of key nutrients, such as N and P, which play a critical role in water quality and protecting ecosystems by effectively targeting nutrient pollution. EC generates coagulants electrochemically using iron or aluminum electrodes, which precipitate and remove phosphorus from water [23]. EO involves oxidation reactions at the electrode surface, which can oxidize ammoniacal nitrogen to nitrate or further denitrify it to nitrogen gas. Electrodialysis uses selective ion exchange membranes to separate cations and anions, effectively removing nitrogen and phosphorus from water [24]. EAOPs utilize electrochemically generated reactive oxygen species to decompose or oxidize nutrients, providing high treatment efficiency [25]. These EC nutrient treatment methods offer various advantages because they can achieve higher removal rates, especially through multistage processes or synergistic reactions, thus contributing to the reduction of nutrient-induced water pollution and sustainable water resource management [26].

Table 1. Advantages and disadvantages of electrochemical processes mainly used to remove nutrient matter.

Process	Application	Advantage	Disadvantage	Ref.
Electrocoagulation	Colloidal and suspended particles	Minimal chemical consumption Easy operation Low sludge production High removal efficiency Possibility of automation	Corrosion of the anode material Ineffective removal of complex pollutants Sludge generation	[18,29]
Electroflotation	Colloidal particles and suspended solids	Reduction in chemical consumption	Sludge generation Risk of corrosion Significant energy consumption	[30]
Electrodeionization	Ions and other charged species	Nonstop process Ultrapure water production	Formation of concentrate solution Sensitivity to feed water quality	[31]
Electrochemical Oxidation	Organic and recalcitrant compounds	Rapid reaction rate Small footprint Mineralization of organics Low need for additional chemical reagents or catalysts	High cost and safety requirements due to reactive compounds Large amount of sludge produced	[32]

provides a comparative analysis of EC methods versus traditional nutrient removal technologies, highlighting the operational and environmental benefits of EC processes [27,28].

EC processes are promising alternatives to traditional physical and chemical wastewater treatment methods, addressing several key limitations of these conventional approaches. Notable advantages include high energy efficiency, cost-effectiveness, ease of automation, and a significant reduction in chemical consumption and sludge production [11]. Moreover, EC treatment effectively reduces chemical oxygen demand (COD) and color in wastewater, enabling compliance with stringent discharge standards while also potentially yielding valuable by-products, such as metal coatings, depending on the wastewater composition [33]. A major benefit is the high selectivity for removing specific nutrients achieved by adjusting electrode materials and reaction conditions. By minimizing the use of chemicals, relying primarily on electricity, EC methods avoid secondary pollution and are compatible with renewable energy sources, such as solar photovoltaic (PV) electricity generation, a well-established, sustainable, and environmentally friendly energy source [34]. Since PV technology now produces the lowest-cost electricity in history [35], it can be used to accelerate the point at which EC wastewater treatment is economically viable. This approach is particularly promising, as wastewater treatment with EC methods can act as a dispatchable load to help manage the intermittent availability [36] of renewable energy resources.

Despite these advantages, challenges remain, including ensuring sufficient conductivity of wastewater, preventing electrode surface fouling by organic matter, and mitigating the potential formation of harmful by-products in certain processes [37]. Addressing these challenges systematically will enhance the sustainability and efficiency of electrochemical wastewater treatment. As a result, significant research efforts have been made in these areas, as reflected in Figure 1, which illustrates the increasing number of documents in the Scopus database. The search was conducted using keywords such as ‘electrochemistry’, ‘water’, ‘electrode’, ‘treatment’, and ‘wastewater’ in the title, abstract, or keywords. The search covered the period from 2014 to 2023, and the results were further classified into experimental studies and review articles. The number of experimental articles related to ‘water’ and ‘wastewater’ rose from 17 to 83 (a 68.8% increase), while review articles increased from 3 to 31 (a 101.4% increase). This trend highlights the growing interest in electrochemical methods for wastewater treatment, driven by the need for more sustainable and efficient solutions. The classification into experimental and review papers was conducted by reviewing the abstracts and determining whether the studies reported new experimental data or provided a summary of the existing literature. The numbers in Figure 1 represent the annual publication count, with each bar reflecting the number of publications each year. Similarly, when searching the Web of Science database using the same keywords, the trend from 2014 to 2023 also showed a significant increase in experimental studies. From 2014 to 2023, the number of experimental articles related to ‘water’ and ‘wastewater’ rose from 47 in 2014 to 102 in 2023, representing an increase of approximately 117.02%. This result further underscores the growing momentum in research focused on electrochemical wastewater treatment technologies.

This review examines the latest technologies and innovative electrode materials for EC nutrient removal, focusing on nitrogen and phosphorus in wastewater. It covers underlying mechanisms, real-world applications, and future research directions, highlighting the efficiency, selectivity, and sustainability of these methods. It also assesses the practical viability of EC processes, addressing challenges and proposing solutions. Furthermore, it explores the integration of methods like electrocoagulation, electroflocculation, and advanced oxidation to enhance wastewater and industrial effluent treatment, aiming to advance research maturity and promote eco-friendly alternatives for reducing environmental pollution.

2. Innovative Electrode Materials in Electrochemical Wastewater Treatment

Traditional electrodes, such as stainless steel (SS), are known for their durability and electrical properties, but they face limitations in terms of corrosion and fouling, especially in harsh environments, leading to a decline in performance and longevity [38,39]. This has driven innovation in advanced materials, including alloyed electrodes and surface-coated electrodes. The development of innovative electrode materials is essential for advancing EC wastewater treatment technologies, as it overcomes the inherent limitations of traditional electrodes and provides a foundation for developing more sustainable and high-performance treatment systems across diverse wastewater streams [40]. Thus, despite the numerous advantages of EC methods, these limitations and others hinder their industrial applications. Key issues include the high costs and short lifespans of some electrode materials, as well as low current efficiency under specific conditions. An ideal anode material should be cost-effective, exhibit physical, chemical, and mechanical stability in the electrolyte medium, and have high activity for organic oxidation and low activity for side reactions, such as oxygen evolution (OER) [41].

According to Anglada et al. [42], an ideal electrode material should possess: (1) high physical and chemical stability and high resistance to erosion, corrosion, and the formation of passive layers; (2) sufficient electrical conductivity; (3) high catalytic activity and selectivity; and (4) low cost and high durability (i.e., long service life) [41]. Significant progress has been made in developing better electrode materials that meet these criteria. Numerous materials have been tested [43], including polypyrrole, granular activated carbon (GAC), activated carbon fiber (ACF), glassy carbon (GC), graphite, platinized titanium (Pt/Ti), massive platinum (Pt), pure and doped lead dioxide (PbO₂), and mixed metal oxides (MMOs) of titanium (Ti), ruthenium (Ru), iridium (Ir), tin (Sn), tantalum (Ta), and antimony (Sb).

In EC wastewater treatment, a variety of electrode materials are utilized, including platinum (Pt), dimensionally stable anodes (DSAs), boron-doped diamond (BDD), graphite, and emerging materials like metal–organic frameworks (MOFs), each offering unique advantages in terms of efficiency, stability, and versatility. These materials possess unique characteristics and advantages, making them applicable to various EC treatment processes. Pt is widely used in pretreatment and synthesis processes due to its excellent chemical resistance and significant electrocatalytic activity in the EO of organic pollutants [44]. DSAs are typically Ti substrates coated with metal oxides or MMOs. Research has developed new coatings for various EC applications. Anodes coated with RuO₂ and TiO₂ are used in the chloralkali industry, while anodes coated with iridium dioxide (IrO₂) promote oxygen evolution reactions (OERs) in acidic media. Iridium oxide (IrOx) and Ti/IrOx–Ta₂O₅ electrodes, however, are relatively expensive and do not allow for the complete mineralization of organics [45].

BDD electrodes, known for their high durability and reactivity for the oxidation of organics, are among the most efficient anode materials. Numerous studies have reported that BDD anodes enable complete mineralization of a wide range of contaminants, including ammonia, cyanide, phenol, aniline, hydrocarbons, dyes, surfactants, pharmaceuticals, and pesticides [46,47]. Graphite electrodes are also widely employed due to their low cost, large surface area, excellent electrical conductivity, and chemical stability. They tend to have lower durability at high anodic potentials, however, leading to surface corrosion. Despite this limitation, graphite electrodes are effective in three-dimensional EC reactors (e.g., packed bed, fluidized bed, porous electrodes) for organics treatment [48]. Emerging materials like MOFs have garnered attention due to their high surface area, structural diversity, high catalytic activity, and functionalization potential. MOFs exhibit excellent performance in EC oxidation and reduction of both organic and inorganic pollutants. Particularly in EAOPs, MOFs show high efficiency in treating recalcitrant pollutants, representing a promising direction for future electrode innovations [49].

In EC wastewater treatment, electrode selection is critical because of its direct impact on performance and longevity. The electrode choice is specific to each EC process, and it is important to select the right electrode for optimal performance. Therefore, categorizing electrode innovations by treatment method and selecting the ideal electrode for each application are essential for optimizing outcomes. In EO, BDD anodes are highly effective due to their durability and reactivity, enabling the complete mineralization of various organic contaminants, including ammonia, phenol, dyes, and pesticides. Graphite cathodes are also used in EO for their low cost, large surface area, and excellent electrical conductivity, though they have lower durability at high anodic potentials [12]. For electro-Fenton processes, DSA and BDD anodes are commonly employed to drive strong oxidation reactions, particularly when treating recalcitrant pollutants, while carbon felt and graphite cathodes are favored for their ability to promote hydrogen peroxide (H₂O₂) generation, which is crucial for organic pollutant degradation [28]. In electrocoagulation, iron (Fe) or aluminum (Al) anodes produce coagulants (Fe/Al hydroxides) that effectively remove suspended particles from wastewater, with cathodes typically made from the same material to simplify operation. Meanwhile, in EAOPs, BDD anodes are widely used for their high oxidation potential, and MOFs have emerged as a promising alternative due to their high surface area, structural diversity, and catalytic activity, particularly in treating stubborn pollutants [50]. Carbon-based cathodes are commonly used in EAOPs for their high conductivity and adaptability to various reactor configurations [51].

In recent years, significant advancements have been made in electrode materials for EC wastewater treatment targeting the degradation of persistent organic pollutants and nutrients. Notably, SS/TiO₂/PbO₂-10%B, Ti/IrO₂, and Ti/SnO₂–Sb electrodes have demonstrated remarkable performance [52]. The SS/TiO₂/PbO₂-10%B electrode, in particular, has shown high efficiency and cost-effectiveness in the EC degradation of ampicillin, a commonly found antibiotic in wastewater. This modified electrode, supported on SS with a titanium oxide interlayer and boron-doped lead dioxide, exhibits a rougher active surface and a larger specific surface area, enhancing its ability to generate powerful oxidizing agents, which leads to significant improvements in degradation efficiency. For instance, in an electrochemical cell with a current density of 50 mA/cm² and an initial ampicillin concentration of 105 mg/L, the SS/TiO₂/PbO₂-10%B electrode achieved a 69.23% reduction in COD and a 60.30% average current efficiency (ACE), highlighting its potential for effective antibiotic removal from aqueous solutions [53]. The Ti/IrO₂ electrode has been identified as highly effective for the EC removal of norfloxacin, a widely used antibiotic that poses environmental risks due to its persistence and potential for promoting antibiotic resistance. The high catalytic activity and stability of this electrode in various electrolytic conditions contribute to its superior performance in treating pharmaceutical contaminants in wastewater. Ganzoury et al. [54] investigated the EC oxidation-in-situ coagulation (ECO–IC) process for the efficient treatment of mixed industrial wastewater. This process degrades organic pollutants via anodic EC oxidation and precipitates heavy metals through coagulants formed by cathode-generated hydroxyl ions reacting with dissolved iron. IrO₂–RuO₂ mixed metal oxide anodes proved highly effective, achieving 97% degradation of methyl orange within 15 min. The process reduced Fe by 96% and total organic carbon by up to 13% in industrial wastewater. Another study employed Ti/RuO₂–IrO₂–TiO₂ electrodes to electrochemically remove ammonia from wastewater by adjusting operating parameters, such as current density, initial pH, electrode spacing, and NaCl concentration, to achieve high removal efficiency. These electrodes are particularly effective for the EC oxidation of industrial wastewaters, such as high-sulfur concentration wastewaters, and are suitable for various industrial applications [55]. This electrode material, doped with antimony, improves EC oxidation, resulting in high pollutant removal efficiency. Cheng et al. highlighted the ability of the Ti/SnO₂–Sb electrode to handle challenging wastewaters, proving its robustness and efficiency in various industrial applications [56].

These recent developments in electrode materials for EC wastewater treatment signify a substantial leap forward in addressing persistent organic pollutants and nutrient contaminants. The SS/TiO₂/PbO₂-10%B, Ti/IrO₂, and Ti/SnO₂–Sb electrodes each offer unique advantages, making them suitable for different types of wastewater and specific contaminants. Continued research and optimization of these materials will further enhance their performance, offering more sustainable and efficient solutions for wastewater treatment. In EC wastewater treatment, electrode materials are continuously being developed to enhance performance and efficiency.

Table 2. Anode materials in electrochemical processes.

Electrode Material	Key Properties and Advantages	Drawbacks and Issues	Efficiency /Applications	Ref.
Boron-Doped Diamond (BDD)	- High durability - High reactivity for organics oxidation - Complete mineralization of organics	- High manufacturing cost	96% COD removal for methyl orange; effective for refractory pollutants.	[57,58,59]
Tin dioxide (SnO2)	- High oxidation power - Cost-effective - Doping with various metals possible	- Potential deactivation over time due to fouling. - Lower durability in highly corrosive environments.	85–90% COD removal; common in industrial wastewater treatment.	[60,61]
Lead dioxide (PbO2)	- High chemical stability - High current efficiency	- Generation of toxic Pb2+ causing secondary pollution - High manufacturing cost	79% TOC removal for dyes; used in chemical industry effluents.	[62,63]
Ti/IrO2–Ta2O5	- High catalytic activity - Favorable for oxygen evolution reaction (OER)	- Expensive - Limited complete mineralization of organics	79% COD removal in petrochemical wastewater.	[64,65]
Dimensionally Stable Anodes (DSA)	- Ti substrate coated with metal oxides like RuO2, TiO2 - High durability and efficiency	- Performance may - vary with specific applications	Used in industrial wastewater with complex organics.	[66,67]
Pt/Ti (Platinized Titanium)	- High catalytic activity - Corrosion-resistant in moderate environments	- Degrades in high chloride or harsh chemicals	- Organic oxidation, wastewater treatment	[2,18]
Pt/Nb (Platinum on Niobium)	- Superior chemical resistance - Long-term stability in extreme conditions	- Expensive - Slightly lower conductivity	- Aggressive wastewater, industrial use, fuel cells	[2,18]

summarizes the latest anode and

Table 3. Cathode materials in electrochemical processes.

Electrode Material	Key Properties and Advantage	Drawbacks and Issues	Ref.
Gas Diffusion Electrode (GDE)	- High activity for oxygen reduction reaction - High surface area	- High manufacturing cost - Potential durability issues	[68]
Carbon Nanotube (CNT)	- High conductivity - Large surface area - Excellent mechanical strength	- High cost - Difficult to produce in large quantities	[69]
Activated Carbon (AC)	- Low cost - Large surface area - Excellent adsorption properties	- Durability issues - Costs associated with regeneration	[59,70]
Reduced Graphene Oxide (rGO)	- High conductivity - Excellent electrochemical performance - Various surface functionalizations possible	- Complex manufacturing process - High cost	[71]
Metal–Organic Frameworks (MOFs)	- High surface area - Structural diversity - High catalytic activity	- Stability and durability issues - High cost	[50]

the latest cathode materials, along with their characteristics, advantages, disadvantages, and application examples.

In conclusion, electrodes such as Pt, DSA, BDD, graphite, and MOFs each possess unique advantages and disadvantages, allowing them to be selectively used in EC wastewater treatment under specific conditions. By leveraging the characteristics of these materials, the efficiency and application range of EC wastewater treatment can be significantly improved. Understanding and applying the optimal conditions for each electrode material will enable the implementation of more effective and sustainable wastewater treatment solutions. The selection of electrode materials is crucial for optimizing the performance of EC wastewater treatment systems. Although an ideal anode has not been clearly established, significant progress has been made. Continued research and development are necessary to overcome existing limitations and enhance the applicability of this technology. Focus areas should include improving cost efficiency, durability, and catalytic efficiency, which are essential to meet the demand for sustainable wastewater treatment solutions.

3. Mechanisms of Nutrient Removal

3.1. Key Principles and Characteristics of Electrochemical Technology

EC technology operates like chemical coagulation by generating cationic species in situ from sacrificial anodes (typically Fe or Al), which neutralize charges and precipitate pollutants (Equation (1)). Unlike chemical coagulation, EC effectively reduces pollutant concentrations, often eliminating the need for expensive coagulants. During the EC process, Fe and Al electrodes dissolve under electrical current, producing metal coagulants that aggregate colloids and form insoluble hydroxides, aiding in pollutant adsorption and coprecipitation (Equations (2) and (3)). Essential reactions include metal dissolution at the anode (Equation (1)) and hydrogen and oxygen gas generation at the cathode (Equation (3)) [29,72].

At the anode:

$${\mathrm{M}}_{\left(\mathrm{s}\right)}\to {\mathrm{M}}^{\mathrm{n}+}\left(\mathrm{a}\mathrm{q}\right)+{\mathrm{n}\mathrm{e}}^{-}$$

(1)

$$2{\mathrm{H}}_2\mathrm{O}\to 4{\mathrm{H}}^{+}\left(\mathrm{a}\mathrm{q}\right)+{\mathrm{O}}_{\mathrm{s}}\left(\mathrm{g}\right)+4{\mathrm{e}}^{-}$$

(2)

At the cathode:

$$\mathrm{n}{\mathrm{H}}_2\mathrm{O}+{\mathrm{n}\mathrm{e}}^{-}\to ({\displaystyle \frac{\mathrm{n}}{2}}){\mathrm{H}}^2(\mathrm{g})+\mathrm{n}\mathrm{O}{\mathrm{H}}^{-}(\mathrm{a}\mathrm{q})$$

(3)

Hydrogen gas facilitates electroflotation by lifting microflocs to the surface for removal. The applied current density significantly influences EC efficiency [73], affecting bubble size and formation rate and thus enhancing flotation. Faraday’s law determines the mass of the released metal ions (Equation (4)).

$$m=ItM/\left(FZ\right)$$

(4)

where m is the mass of released metal (g); I is the applied current (A); t is the electrolysis time (s); M denotes the molar mass of metal, for Fe, 56 g/mol, for Al, 27 g/mol; F is the Faraday constant (96,485 C/mol); and Z is the number of electrons involved in the reaction [29].

In chloride-rich environments, reactive chlorine species (RCS), such as Cl₂ and HOCl/ClO⁻, are generated, aiding in the degradation of organic contaminants (Equations (5)–(7)). Typically, RCS can help break down organic compounds and modify the structure of the original organic molecules [74,75]. Please check that intended meaning has been retained.

$$2{\mathrm{C}\mathrm{l}}^{-}\left(\mathrm{a}\mathrm{q}\right)\to {\mathrm{C}\mathrm{l}}_2\left(\mathrm{g}\right)+{2\mathrm{e}}^{-}$$

(5)

$$\mathrm{C}{\mathrm{l}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{a}\mathrm{q}\right)\to \mathrm{H}\mathrm{C}\mathrm{l}\mathrm{O}+\mathrm{C}{\mathrm{l}}^{-}\left(\mathrm{a}\mathrm{q}\right)+{\mathrm{H}}^{+}\left(\mathrm{a}\mathrm{q}\right)$$

(6)

$$\mathrm{H}\mathrm{C}\mathrm{l}\mathrm{O}\leftrightarrow \mathrm{C}\mathrm{l}{\mathrm{O}}^{-}+{\mathrm{H}}^{+}(\mathrm{p}{\mathrm{K}}_{\mathrm{a}}=7.56)$$

(7)

The process also produces reactive oxygen species (ROS) like hydroxyl radicals [76], which further oxidize pollutants (Equations (8)–(11)). The oxygen produced at the anode also plays a crucial role in forming hydrogen peroxide, which serves as an intermediate that aids in oxidizing toxic species into nontoxic forms. For instance, recent studies reported that in situ iron oxides produced by EC accelerate the oxidation of Fe²⁺ and the generation of hydroxyl radicals (•OH) by catalyzing O₂ (Equations (8)–(10)) [77,78].

$$\mathrm{F}{\mathrm{e}}^{2+}+{\mathrm{O}}_2\to \mathrm{F}{\mathrm{e}}^{3+}+{\mathrm{O}}_2{•}^{-}$$

(8)

$$\mathrm{F}{\mathrm{e}}^{2+}+{\mathrm{O}}_2{•}^{-}+2{\mathrm{H}}^{+}\to \mathrm{F}{\mathrm{e}}^{3+}+{\mathrm{H}}_2{\mathrm{O}}_2$$

(9)

$$\mathrm{F}{\mathrm{e}}^{2+}+{\mathrm{H}}_2{\mathrm{O}}_2\to \mathrm{F}{\mathrm{e}}^{3+}+•\mathrm{O}\mathrm{H}+\mathrm{O}{\mathrm{H}}^{-}$$

(10)

Other ROS, such as the superoxide anion (O₂•⁻) and ferryl ion (Fe(IV)) (Equation (11)) [79] may also be generated during the process. The standard reduction potentials for O₂•⁻/H₂O₂ are approximately 0.9 V/SHE (standard hydrogen electrode) [78]. Furthermore, ROS, such as singlet oxygen (¹O₂) and peroxyl radicals (ROO•), can be formed under certain conditions [80] (Equation (11)), enhancing the oxidative degradation of organic pollutants. These species significantly contribute to breaking down complex organic molecules, including pharmaceuticals and endocrine-disrupting compounds, into simpler, less harmful substances [81].

$$\mathrm{R}+{\mathrm{O}}_2\to \mathrm{R}{\mathrm{O}}_2$$

(11)

The combination of various ROS generated in the EC process ensures a comprehensive approach to pollutant degradation, making EC a robust and versatile method for wastewater treatment. EC generally results in less sludge production compared to chemical coagulation and offers higher pollutant removal efficiency. It incurs costs, however, related to electrode consumption, electricity, and the requirement for high conductivity [82]. Additionally, toxic by-products like the carcinogenic pollutant trihalomethanes can form in the presence of organic matter.

3.2. Advanced Electrochemical Approaches for Nitrogenous and Phosphorus Compounds Removal

EC processes have recently gained attention for the removal of nitrogen and phosphorus from wastewater. Nitrogen is typically present as ammonia (NH₄⁺) and nitrate (NO³⁻) [83], while phosphorus is primarily present as orthophosphate (PO₄³⁻). As they are major contributors to water quality degradation and eutrophication are, fortunately, both readily detected by commercial and low-cost open source devices [84]. EO can convert ammonia to nitrate or nitrogen gas (N₂), while electrodialysis selectively removes ammonium ions from wastewater [83]. Electrocoagulation facilitates the conversion of orthophosphate to insoluble precipitates, and EAOPs use reactive oxygen species to mineralize organic nitrogen and phosphorus compounds [85]. These EC processes offer high removal efficiencies, making them viable alternatives to conventional physical and chemical treatment methods. Recent research has focused on optimizing electrode materials and reaction conditions, which is expected to improve the practicality and sustainability of EC wastewater treatment technologies.

To optimize performance for organics removal, researchers have focused on finding the right electrode materials and operating conditions. Transition metal oxides, such as TiO₂ and ruthenium dioxide (RuO₂), offer an effective balance between high catalytic activity and lower cost, making them suitable for the EC removal of nutrient pollutants like nitrogen and phosphorus. Additionally, BDD electrodes have gained attention for oxygen evolution, which minimizes side reactions and enhances the efficiency of ammonia oxidation. Recent literature reviews have highlighted applications of these materials and their catalytic properties and cost-effectiveness in various EC processes [86]. EC processes using these advanced materials can achieve significant removal of nutrients from wastewater. Specifically, lead dioxide and boron-doped diamond electrodes have been shown to effectively oxidize ammonia and nitrate, converting them into less harmful nitrogen gases and thus reducing the nutrient load in treated effluent [40]. This is crucial for maintaining water quality and preventing nutrient pollution in aquatic environments. Numerous studies, as summarized in

Table 4. Selected examples of the electrochemical treatment of nutrient pollutants.

Pollutant	Anode Material	Electrolyte	Operating Conditions	Results	Ref.
Ammonia	BDD	0.1 M Na2SO4	Electrodes: BDD (7 cm2), Pt (7 cm2), and GC. pH: 6. Temperature: 25 °C Methods: Cyclic voltammetry and galvanostatic mode	Pt (100) showed faster ammonia oxidation due to the lower barrier of N2H4 formation via NH2 dimerization, compared to Pt (111).	[87]
		1100 mg/L Na2SO4	Batch electrochemical reactor with BDD anode, graphite cathode, 100 mg/L phenol, 30 mA/cm2 current density, pH 4.8, 1100 mg/L Na2SO4, 210 min at 23 °C.	Maximum 100% TOC removal for single phenol, decreased to 90.8%, 87.49%, 82.35% in binary matrices. Presence of S2−, CN−, and NH4+ lowered TOC removal efficiency.	[88]
Phosphate	Aluminum baffle plates with perforations.	150 mg/L K2HPO4	Initial pH: 6 Interelectrode distance: 0.5 cm Current density: 6 mA/cm2 Electrolysis time: 60 min Temperature: 20 ± 1 °C	Phosphate removal efficiency > 99% at pH 4–8 for Al and Fe electrodes. Al electrodes showed higher efficiency and lower energy consumption compared to Fe.	[89]
	Platinum-coated titanium	anaerobic digestion effluent	Batch electrolysis with Pt-coated Ti electrodes, 5L reactor, 4.0 A current (317 A/m2), 10, 5, and 1 mm electrode distance, 2 h electrolysis time, stirring.	P removal efficiency reduced with time. Initial precipitation as amorphous calcium phosphate (ACP), transforming to hydroxyapatite (HAP) over time.	[90]
	Aluminum (Al) and Iron (Fe)	Synthetic domestic wastewater	Initial pH: 4–7 Current density: 10–40 A/m2 EC time: 0–100 min Initial phosphorus concentration: 5.01–52.13 mg/L	Al electrodes more effective than Fe, achieving 99.9% removal at lower EC times and energy consumption. High P removal efficiency (>99%) at lower initial concentrations.	[91]

, confirm that materials like PbO₂ and BDD stand out for their high efficiency and stability, making them ideal choices for advanced wastewater treatment applications aimed at the removal of nitrogen, phosphorus, and other organic pollutants.

3.3. Electrochemical Ammonia Oxidation

Electrochemical ammonia oxidation (EAO) is an innovative technique for the removal of ammonia from wastewater. This process operates in an electrochemical (EC) cell where ammonium (NH₄⁺) undergoes oxidation at the anode. The appeal of EAO lies in its high efficiency, scalability, and ability to function under ambient conditions without chemical additives. This section explores the mechanisms underlying EAO while also highlighting recent advancements and research developments in this field [92]. The fundamental principle of EAO involves the direct oxidation of ammonium to nitrogen gas (N₂) or other nitrogen compounds at the anode. The overall reaction is typically represented by Equation (12).

$$2\mathrm{N}{\mathrm{H}}_4^{+}\to {\mathrm{N}}_2+8{\mathrm{H}}^{+}+6{\mathrm{e}}^{-}$$

(12)

The anodic oxidation of ammonia can proceed through various pathways, leading to different products, such as nitrogen gas (N₂), nitrite (NO₂⁻), and nitrate (NO₃⁻). The specific pathway taken depends on the electrode material and the operating conditions [92]. At the cathode, water is reduced, producing hydrogen gas (H₂) and hydroxide ions (OH⁻) through the following reaction (Equation (13)):

$$6{\mathrm{H}}_2\mathrm{O}+6{\mathrm{e}}^{-}\to 3{\mathrm{H}}_2+6\mathrm{O}{\mathrm{H}}^{-}$$

(13)

Additionally, under certain conditions, ammonium can be oxidized to nitrate through the following reaction (Equation (14)):

$$\mathrm{N}{\mathrm{H}}_4^{+}+3{\mathrm{H}}_2\mathrm{O}\to {\mathrm{N}{\mathrm{O}}_3}^{-}+8{\mathrm{H}}^{+}+8{\mathrm{e}}^{-}$$

(14)

Current density directly affects the oxidation rate, with higher densities increasing the rate but also raising energy consumption and encouraging side reactions. Optimizing current density depends on several factors. The pH of the electrolyte plays a role, with neutral to slightly alkaline conditions being ideal. Chloride ions (Cl⁻) enhance ammonia oxidation by forming active chlorine species, which are effective oxidants [93,94]. The choice of anode material is key to the efficiency of the chlorine evolution reaction (CER) and minimizing unwanted side reactions like hydroxyl radical formation. Nonactive anodes, such as SnO₂, PbO₂, and BDD, are efficient at generating hydroxyl radicals but suffer from poor conductivity and stability. Noble metal oxides like RuO₂ and IrO₂, used in DSAs, are highly effective for chlorine evolution but are expensive and less stable over time [95,96]. Recent research has focused on creating multilayered composite electrodes by incorporating metallic mixed oxides like TiO₂, Bi₂O₃, and SnO₂ into RuO₂ or IrO₂ [97,98,99]. These advanced DSAs, along with innovations like titania nanotube arrays, offer similar performance to commercial DSAs and BDD electrodes at a lower cost, making them viable for treating ammonia-rich wastewater in municipal and industrial settings [100].

Case studies have demonstrated the feasibility of EAO, as summarized in

Table 5. EAO techniques and recent research trends.

Approaches	Methodology Summary	Key Results	Ref.
Pt (100) facets for ammonia electrooxidation	DFT calculations on Pt (100) promote N-N bond formation, accelerating ammonia oxidation.	Demonstrated a lower energy barrier for NH4⁺ dimerization.	[87]
Electrochemical setup with platinum, palladium, or nickel electrodes	Setup in KOH/NaOH with controlled pH and temperature, using cyclic voltammetry and CA/CP analysis.	Identified key oxidation peaks and measured ammonia removal efficiency.	[101]
Electrolysis of liquid ammonia with platinum electrodes	Electrolysis in N,N-dimethylformamide with platinum electrodes under varying concentrations.	Observed electrode poisoning and hydrogen generation at the cathode.	[102]

. In municipal wastewater treatment, EAO has shown high removal efficiencies. It has also been applied to industrial wastewater in industries with high ammonia concentrations, such as fertilizers and petrochemicals, showcasing its robustness and versatility.

Despite these advancements, challenges remain in the long-term stability and fouling of electrodes. The development of fouling-resistant materials and effective cleaning protocols is essential for practical applications. Enhancing the energy efficiency of EAO is also critical for its economic viability. Thus, research is focused on optimizing electrode materials and operational parameters to reduce energy consumption. Additionally, integrating EAO with other treatment technologies, such as biological treatment or advanced oxidation processes, could provide synergistic benefits, improving overall treatment efficiency and cost-effectiveness [103].

In summary, EC ammonia oxidation is a promising technology for ammonia removal from wastewater. Advances in electrode materials and a deeper understanding of mechanistic pathways have improved its efficiency and applicability [83]. Continued research and development are necessary to address remaining challenges to fully harness the potential of EAO in wastewater treatment.

3.4. Electrocoagulation for Phosphate Removal

Phosphorus (P) is a vital nutrient for many organisms, and in recent years, phosphate has seen extensive use in agricultural fertilizers and animal feed. When total phosphorus (TP) levels in water bodies exceed 0.03 mg/L, however, it can lead to harmful events like algae blooms or red tides [104]. This underscores the importance of further reducing TP levels following biological treatment in municipal wastewater treatment plants. To achieve this, efficient, cost-effective, and sustainable treatment methods are crucial, integrating various physical, EC, and chemical post-treatment processes. These can include techniques like chemical coagulation-flocculation, advanced oxidation processes, and membrane bioreactor systems [105].

Electrocoagulation has emerged as a particularly effective method for treating a wide range of wastewaters, including municipal sewage, industrial effluents, and polluted natural water sources. Over the past 20 years, numerous studies have validated its efficacy in removing contaminants, such as heavy metals, oil droplets, dyes, suspended solids, natural organic matter (NOM), and phosphate. For instance, Mao et al. (2023) demonstrated electrocoagulation’s effectiveness in reducing phosphate concentrations, making it a valuable tool for nutrient pollution management [106,107,108,109,110,111,112,113,114].

This process involves the use of aluminum or iron electrodes, which dissolve into the wastewater under the influence of an electric current. The resultant metal ions form metal hydroxides that react with phosphate ions to create insoluble complexes that can be easily removed by sedimentation or filtration [115,116]. Electrocoagulation frequently achieves phosphate removal rates exceeding 90%, depending on variables such as current density, pH, and electrode material [113].

While the process offers several advantages, such as compatibility with diverse wastewater compositions and a reduced need for chemical additives, it also faces challenges. These include high energy consumption, potential electrode passivation, and sludge production, which necessitate regular maintenance and optimization of operational parameters like current density and pH. Nonetheless, electrocoagulation is particularly well suited for municipal and industrial wastewater treatment applications where high phosphate levels are present and chemical usage needs to be minimized [106,107,115]. Reactions involving iron electrodes are represented by Equations (15)–(17)

Iron electrodes reactions

Anode reaction:

$${\mathrm{F}\mathrm{e}\to \mathrm{F}\mathrm{e}}^{2+}+2{\mathrm{e}}^{-}$$

(15)

Iron(II) hydroxide formation:

$${\mathrm{F}\mathrm{e}}^{2+}+2{\mathrm{H}}_2\mathrm{O}\to \mathrm{F}\mathrm{e}{\left(\mathrm{O}\mathrm{H}\right)}_2{+2\mathrm{H}}^{+}$$

(16)

Further oxidation to Iron(III) hydroxide:

$$4\mathrm{F}\mathrm{e}(\mathrm{O}{\mathrm{H})}_2+{\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}\to 4\mathrm{F}\mathrm{e}{\left(\mathrm{O}\mathrm{H}\right)}_3$$

(17)

Optimization of electrocoagulation parameters, such as current density, electrode material and configuration, pH, reaction time, and mixing, is important for maximizing treatment efficiency. A notable advancement in electrocoagulation is the modification of electrodes with materials such as graphene oxide. Ghaffarian Khorram and Fallah [117] explored graphene oxide-modified electrodes for EC removal of inorganic contaminants from water. Their research demonstrated that the modified electrodes could significantly enhance pollutant removal through improved EC properties. The study suggested that incorporating graphene oxide into electrodes can expand the applicability and effectiveness of electrocoagulation in water treatment, particularly for inorganic pollutants. Hashim et al. [89] studied phosphate removal using a new baffle plate aluminum-based electrochemical cell (PBPR), which uses perforated baffle plates instead of magnetic stirrers. The study found that at an initial pH of 6, an interelectrode distance of 0.5 cm, a current density of 6 mA/cm², and an initial phosphate concentration of 100 mg/L, 99% of the phosphate was removed after 60 min. The operating cost was $0.503/m³, and the cell produced enough H₂ gas to generate 4.34 kWh/m³ of power. This method is promising for cost-effective phosphate removal.

In summary, electrocoagulation offers high pollutant removal efficiency, ease of operation, and a reduced need for chemical additives. However, challenges such as electrode passivation, sludge production, and energy consumption must be addressed through regular maintenance, proper sludge management, and the optimization of operational parameters. Recent research is needed to enhance electrocoagulation efficiency and broaden its application scope. For example, nanostructured electrodes and hybrid treatment systems combining electrocoagulation with biological, or membrane filtration techniques are promising areas of development.

4. Practical Application Studies

Scale-up is an essential step in developing full-scale EC systems. This analysis highlights key factors for scale-up, including plant size, efficiency, and economic feasibility. Pilot tests for commercialization are actively underway for industrial processes relying on generating •OH and various oxidants, such as chlorine, (per)bromate, persulfate, ozone, hydrogen peroxide, percarbonate, and others, directly at the site, using only water, salt, and energy. The benefit of employing these EAOPs lies in their ability to reduce COD/total organic carbon (TOC) from several hundred grams of oxygen demand per liter to just a few milligrams or even micrograms per liter, achieving up to a 99% reduction in organic constituents [118]. These processes offer the advantage of being easily integrated with conventional wastewater treatment for modular adaptation and scale-up. To accurately assess the economic feasibility of EAOPs during scale-up, calculating energy consumption is essential. Energy consumption (E) can be calculated using the following formula (Equation (18)):

$$E={\displaystyle \frac{V\times I\times t}{V_{treated}}}$$

(18)

where $V$ is the cell voltage (V), $I$ is the current (A), $t$ is the treatment time (h), and $V_{treated}$ is the volume of wastewater treated (m³). This formula provides a measure of the total energy required to treat a specific volume of wastewater. Energy consumption can also be expressed per unit of COD removed using the following formula (Equation (19)):

$$E_{cod}={\displaystyle \frac{V\times I\times t}{{∆COD\times V}_{treated}}}$$

(19)

In this equation, $E_{cod}$ represents the energy consumption per kilogram of COD removed (kWh/kg COD), and $∆COD$ is the change in COD concentration (kg/m³) before and after treatment. This metric is useful when comparing the efficiency of different EAOPs.

To contextualize the energy efficiency of EAOPs, it would be beneficial to compare them with traditional wastewater treatment methods. For instance, while EAOPs may consume 0.5–2.5 kWh/m³ for COD removal [119], activated sludge systems typically consume around 0.3–1.0 kWh/m³ [120]. Similarly, membrane bioreactors (MBRs) require 1.0–2.5 kWh/m³ [121], and AOPs like ozonation and UV/H₂O₂ can range from 0.5–2.5 kWh/m³ [51]. This comparison elucidates the relative energy efficiency of these technologies, aiding in the assessment of their scalability and economic viability.

Table 6. Comparative analysis of electrochemical methods vs. traditional nutrient removal technologies [119,120,121].

Technology	Cost	Scalability	Nutrient Removal Efficiency	Energy Consumption (kWh/m3)
Electrochemical Advanced Oxidation (EAOPs)	Moderate to High	High (with optimization)	>90% COD removal, effective for diverse pollutants	0.5–2.5
Activated Sludge	Low	High	Moderate for nutrient removal	0.3–1.0
Membrane Bioreactors (MBRs)	High (Membrane costs)	Medium to High	High, >90% for organic removal	1.0–2.5
Ozone/UV/H2O2	High (Chemical costs)	Medium	High (effective for organics)	0.5–2.5
Chemical Coagulation	Low	High	Moderate (limited to certain pollutants)	0.2–0.8
Anaerobic Digestion	Low	High	Effective for organic matter	0.1–0.3

provides a broader comparison of electrochemical methods against other traditional nutrient removal technologies, not only in terms of energy efficiency, but also with respect to cost, scalability, and nutrient removal efficiency. Specifically, for the cost parameter, ‘low’ is defined as less than $1/m³, ‘moderate’ ranges from $1 to $5/m³, and ‘high’ exceeds $5/m³ [119,120,121].

As there are still few studies on the large-scale application of EC processes for nutrient removal, this review presents performance data collected from various pilot projects and studies to evaluate the feasibility of EC nutrient removal technologies (

Table 7. Electrocoagulation techniques and recent research trends.

Study	Year	Anode Material	Target Contaminants	Key Findings	Energy Consumption	Ref.
Anglada et al.	2009	BDD	Landfill leachates	Almost complete removal of organic matter and ammonium nitrogen	35 kWh/m3 (120 kWh/kg COD)	[123]
Duran et al.	2019	Ti/Pt and BDD	Washing machine effluent	BDD showed >90% TOC removal; effective micropollutant remediation with low energy requirements	Not specified	[124]
Tawabini et al.	2020	BDD	BTEX, phenol in high salinity waters	Effective BTEX removal under optimal conditions	5.92 kWh/m3	[125]
Bugueño-Carrasco	2020	DSA	Antibiotics and NSAIDs	99.2% TOC removal after 100 min; effective solar photoelectro-Fenton process	7.15 kWh/m3	[126]
Brillas Working Group	Multiple	RuO2-based, air-diffusion cathode, BDD	Urban wastewater with carbofuran	PEF more effective than EF or EO-H2O2; superior organic removal and mineralization	Not specified	[127,128]
Malato et al.	Multiple	GDE (cathode) and BDD (anode)	Model pesticides	Over 50% pesticide removal in 5 min under optimal conditions	Not specified	[129,130]
Villaseñor-Basulto et al.	2020	BDD and EF	Black NT2 dye	Paired BDD–electro-Fenton showed higher degradation rates; optimal conditions identified for EF process	10.88 kWh/m3	[131]

) [122]. The results of pilot tests demonstrate that EC methods show high efficiency and maintain stable performance under various environmental conditions.

These studies illustrate the diverse applications and effectiveness of various electrode materials in the EC treatment of wastewater, demonstrating the potential for industrial use as well as the challenges to scale-up. These case studies prove the potential for commercializing EC wastewater treatment and provide foundational data for the development of large-scale systems. Despite promising results obtained from laboratory-scale tests, the industrial application of anodic oxidation for organic pollutant treatment remains limited. Example process flow diagrams (PFDs) illustrate how EC methods could be incorporated to achieve multiple treatment objectives, including pollutant removal, nutrient removal, and water reuse. Meng et al. investigated electrochemical oxidation for removing COD and ammonia nitrogen from high salinity tungsten smelting wastewater [132]. They presented results for the removal of COD and ammonia nitrogen (NH₃–N) from high salinity tungsten smelting wastewater (TSW) using one-step EO technology. The research progressed from bench-scale tests through pilot-scale tests, and, finally, to industrial-scale tests with the objective of identifying optimal conditions and assessing scalability to industrial applications. Initially, bench-scale tests were conducted to determine the effects of variables such as current density, anode material, and pH. The findings were then validated through pilot-scale tests, which operated under more realistic conditions with a treatment capacity of 200–500 L/h. The final stage involved large-scale industrial tests with a capacity of 100 m³/h, designed to assess the practical applicability and economic viability of the EO process.

Industrial tests demonstrated that EO technology was effective for consistently removing COD and NH₃–N to regulatory standards. The study also reported that the EO process was economically advantageous, reducing treatment costs by 73% compared to the traditional two-step process, which involves breakpoint chlorination and the addition of oxidants. This made the EO process more cost-effective and simplified operations, offering a sustainable solution for high salinity industrial wastewater. In summary, the study successfully showed that EO technology can be scaled up and applied industrially for the treatment of TSW. Further, the results suggest that this technology holds potential for broader applications in high salinity wastewaters containing COD and NH₃–N, offering a promising alternative for efficient and economical wastewater treatment. Figure 2 illustrates a structural schematic of the electrolytic cells used in these EC processes. Each power supply was connected to an electrolytic cell, and the electrolytic cells were connected in series. The electrodes were distinguished by different colors.

Ongoing advancements in electrocoagulation research reinforce its potential in wastewater treatment. Electrocoagulation stands out among EC processes due to its ability to treat wastewater without chemical additives. Additionally, its process versatility supports the treatment of a diverse array of wastewater types from various industries and domestic sources, addressing a broad spectrum of pollutants. Mishima et al. [133] conducted a study on the long-term removal of phosphorus using an iron-based electrocoagulation process in small-scale wastewater treatment plants. The study demonstrated that high phosphorus removal efficiency could be maintained under various operational conditions, highlighting the practical applicability of the process for sustained performance. They analyzed the characteristics of the flocs formed, noting that different iron oxides and hydroxides were produced depending on dissolved oxygen levels and water quality parameters. This work established iron electrocoagulation as an effective method for phosphorus removal in small-scale wastewater treatment settings. Devlin et al. [134] conducted a pilot study using iron and aluminum electrodes for electrocoagulation to remove phosphorus from wastewater, demonstrating its effectiveness in large-scale wastewater treatment plants. They found that aluminum electrodes were generally more efficient and cost-effective than iron, achieving a 98% removal rate with lower energy consumption and operating costs. Optimal operating conditions, including current density and pH, were identified as factors important to maximizing phosphorus removal. Additionally, the research highlighted the importance of floc formation, with aluminum electrodes producing effective amorphous alum hydroxide flocs, while iron electrodes generated iron oxide/hydroxide flocs, both crucial for successful phosphorus removal.

The application of EC processes at an industrial scale remains limited, particularly for the treatment of organic pollutants. The scale-up of EC processes must overcome these challenges. In full-scale applications, electrode fouling and material degradation may occur more rapidly than in bench-scale operations, leading to increased maintenance and reduced efficiency. The initial investment in large-scale EC systems can be prohibitively high, and operational costs may outweigh the benefits if the process is not optimized for scale. To address these challenges, research should focus on more durable and efficient electrode materials. Optimizing operational parameters like current density, flow rates, and electrolyte composition could minimize energy consumption while maximizing pollutant removal efficiency. Exploring hybrid systems that combine EC processes with other technologies could enhance overall efficiency. Additionally, advancements in automation and real-time monitoring could help maintain optimal conditions and prevent fouling. By overcoming these barriers, EC wastewater treatment can become more effective and feasible at an industrial scale.

5. Conclusions

This review emphasizes the role of EC methods in addressing nutrient pollution in wastewater, with a focus on the removal of nitrogen and phosphorus, which are key contributors to eutrophication. These nutrients, commonly introduced through agricultural runoff and industrial discharges, pose challenges to water quality and aquatic ecosystems. EC technologies, particularly those employing advanced electrode materials, such as boron-doped diamond and lead dioxide, have shown remarkable efficiency in both laboratory- and pilot-scale studies for removing these pollutants.

EC methods offer several advantages over traditional treatment approaches. They provide higher nutrient removal rates, reduce chemical consumption, and can be integrated with renewable energy sources, making them environmentally sustainable and economically viable. For instance, electrocoagulation removes phosphorus by generating coagulants in situ, while EO and electrodialysis are efficient for nitrogen removal, converting ammonia to nitrogen gas or selectively removing ammonium ions.

Widespread adoption of these technologies, however, is hampered by high operational costs, significant energy demands, and issues such as electrode fouling and by-product formation. Ensuring the long-term stability and efficiency of these methods will require further optimization of operational parameters, the development of cost-effective and durable electrode materials, and improvements in the overall energy efficiency of these processes.

Moreover, exploring hybrid systems that combine EC processes with other complementary technologies could significantly improve overall efficiency and broaden the application range. For example, combining electrocoagulation with biological treatments, such as activated sludge or anaerobic digestion, could enhance the breakdown of complex organic pollutants while reducing energy consumption. Similarly, integrating EC with membrane filtration systems could improve the removal efficiency of suspended solids and smaller organic compounds. These hybrid approaches not only leverage the strengths of each individual technology, but also address the limitations of standalone EC systems, offering a more robust and versatile solution for wastewater treatment. By carefully integrating these processes, it is possible to optimize performance in terms of both efficiency and cost-effectiveness, making EC technologies more attractive for large-scale industrial use. Additionally, advancements in automation and real-time monitoring could help maintain optimal conditions and prevent fouling, reducing downtime and operational costs. By overcoming these barriers, EC wastewater treatment can become more effective and feasible at an industrial scale. Future research in this area will be critical for improving the cost-effectiveness, energy efficiency, and scalability of EC processes, enabling them to play a larger role in industrial wastewater treatment and environmental sustainability.