Nitrates and heavy metal contaminants are impacting water bodies globally because of intensive agriculture pollution, industrial discharge, and mining. Nitrate (NO₃⁻) could be utilized for fertilizers, explosives, and the chemical industry, while its excess in the aquatic environments will cause eutrophication and potential health problems such as methemoglobinemia and the generation of carcinogenic nitrosamines (Li et al., 2020; Radjenović & Sedlak, 2015). In contrast, heavy metals (e.g., Pb, Cd, Cr, and As) are persistent in the environmental media as well as nondegradable and bio accumulative, with neurological, renal, and developmental impacts on human health and wildlife ecosystems (Tchounwou et al., 2012; AlJaberi et al., 2014; Ahmad et al., 2018).

Although it has already been investigated, two commonly used treatment methods, namely adsorption, ion exchange, chemical precipitation (pecacetell), membrane separation, and bio-denitrification, for treatment of NDs have some disadvantages, such as secondary sludge production, higher reagent consumption, limited selectivity on trace level, and operational cost (Vasudevan, 2012; comparative reviews; Pergamon). In this regard, electrochemical technologies are of interest for future R&D directions because they can operate on-site and use minimal hazardous chemicals, while being adjustable through applied voltage potential and more effectively linked to available renewable electricity (Costa, 2023; Hasan et al., 2023; Pearce et al., 2024).

Recent advancements in the state of the art for catalyst design, reactor configurations (i.e., membrane electrode assembly, reactive separation), and mechanistic insights have been significant over the past few years. For example, the development of NO₃ER has also become a certain process about removing nitrate and making its selectivity for ammonia (NH₃) due to value-added recovery processing (Electrochemical reduction of nitrate: synthesis production level with 2023; progress and prospects on the electrochemical processing reduction, 2023). At the same time, development in electrochemical reactors and hybrid processes is carried out for removal of heavy metals by electrodeposition, electrocoagulation, pulsed behaviors, and combined redox processes (Review on Electrochemical Reactors 2025 & Insights into selective removal 2023). These fine outcomes lead to an evaluation of the actual “landscape” for electrochemical remediation of nitrates and metals, including the state-of-the-art gaps and perspectives.

Fig. 1: Major sources of nitrate and heavy metal contamination in wastewater.

Problem Statement

While electrochemical methods have great promise for sewage disposal, some technical and practical problems are preventing their wide practice in industry. First, for nitrate reduction, selectivity toward non-toxic nitrogen gas (N₂) is not yet fully attained. Most electrocatalysts prefer incomplete reductions to nitrite (NO₂⁻) or ammonium (NH₄⁺), both of which are pollutants and pose restrictions to environmental safety (Liu et al., 2023; Pearce et al., 2024). Secondly, for heavy metals, studies have found processes like electrocoagulation and electrodeposition to show high initial removal efficiencies, but they experience electrode passivation/fouling/corrosion, especially when the effluent has a mixed organic-inorganic nature (Costa, 2023; AlJaberi et al., 2024). These are problems that reduce the lifetime of the electrodes and increase cost. Third, energy and scale problems are concerning. Although removal efficiencies >90% are typically shown in laboratory studies carried out under controlled setups, scaling up these systems to waste-water streams driven at higher current densities imposes an unsustainable energy requirement (Chen et al., 2022; Radjenović & Sedlak, 2015; Sultana et al., 2024).

Finally, researchers often focus only on either nitrate or heavy metals, while in fact industrial effluents generally contain both. Insufficient integrated configurations lead to a disparity between academia and industry as the treatment technologies find inadequate ways in which to communicate (Review on electrochemical reactors, 2025). Consequently, the research problem can be abstracted as: How to enhance the performance of electrochemical methods for simultaneous removal of nitrate and heavy metals from real wastewater streams in an efficient, selective, and energy-applicable way while minimizing secondary pollution and operational liabilities?

Objectives of the Research

The principal objectives of this study are:

1. To evaluate the performance of electrochemical methods for the simultaneous removal of nitrate and heavy metals from wastewater.
2. To investigate how operational parameters (e.g., current density, potential, pH, electrode material, flow design) affect removal efficiency, selectivity, and stability in mixed-ion systems.
3. To benchmark electrochemical methods against conventional techniques in terms of removal efficiency, operational cost, energy consumption, and secondary waste.
4. To propose optimized reactor configurations, electrode materials, or hybrid processes (e.g., coupling NO₃RR with electrodialysis or pulsed electrochemistry) to overcome existing limitations.
5. To offer recommendations for scaling, field implementation, and future research directions.

Scope and Significance

In the present article, we discuss an electrochemical technique that combines various approaches, including EC. Adsorption, complexation treatment methods, and hardens reinforcement outcomes have been used to remove nitrates and heavy metals from wastewater. Both artificial blends and industrial effluents will be utilized as representatives. Important parameters that we studied include; Efficiency of removal, energy consumption, selectivity (N₂ vs NH₄⁺), degradation of the electrode, and cost studies. The implication of this work is to develop a sustainable and practical process for environmental chemistry/electrochemistry remediation. Because of the simultaneous removal of two types of significant pollutants, this work is consistent with both the circular economy and comprehensive water treatment. Findings may direct industrial uptake, provide knowledge for the design of pilot systems, and address important research voids in catalyst stability and practical application.

Organization of the Paper

The remainder of the paper is structured as follows:

• Chapter 2: Literature Review presents a detailed examination of the contamination problem, conventional methods and their limitations, and recent advances in electrochemical removal of nitrate and heavy metals, including catalysts and reactor design.
• Chapter 3: Methodology describes the experimental design, electrode materials, reactor configuration, operational parameters, sample preparation, and analytical techniques.
• Chapter 4: Results & Discussion reports removal efficiencies, parameter optimization, by-product formation, energy and cost analysis, stability testing, and comparative evaluation with conventional methods.
• Chapter 5: Conclusions and Recommendations summarize key findings, discusses limitations, and proposes directions for future research, scale-up, and real-world implementation.

Heavy metals and nitrate pollution are significant environmental problems globally due to their stability, toxicity potential, effects on the ecosystem and human health. The nitrate pollution has been induced by the growing utilizations of nitrogenous fertilizers in agriculture and waste effluents released from explosive, dye or food processing industries (Liu et al., 2023). When nitrate concentrations are above 50 mg/L of HNO3 (as recommended by WHO, 2022), they pose a potential threat to humans for example, by inducing methemoglobinemia, as well as blue baby syndrome and favoring the production of carcinogenic nitrosamines (Vallyathan et al., 1986). Heavy metals toxicity such as lead, cadmium, chromium and arsenics is being leached into the aquatic systems through mining (Achten et al., 2022), electroplating (Al-Anazy et al., 2020; Kavalan et al., 2019) textiles industry (Batayneh & Bani-Hani, 1993) and tanneries (AlJaberi et al., 2024). They are non-biodegradable and buildup in aquatic organisms which undergo bioconcentration, bioaccumulation and biomagnification in the food chain. Chronic exposure to these pollutants has been related to neurological diseases, kidney damage, cardiovascular diseases and multiple types of cancer (Tchounwou et al., 2012; Chen et al., 2022).

Fig. 2: Global Distribution of Nitrate and Heavy Metal Pollution in Wastewater.

Conventional techniques for nitrate and heavy metal pollution control from wastewaters include ion exchange, adsorption, reverse osmosis, biological denitrification, and chemical precipitation. Although IER and RO are efficient, they tend to be expensive both in terms of initial investment and operation and produce an underground concentrated brine waste that must be disposed of (Gupta et al., 2019; Costa, 2023). Biological denitrification has been extensively employed in municipal wastewater systems; however, biological removal is very susceptible to temperature, pH, and carbon sources and is also not as effective for variable environmental situations (Radjenović & Sedlak, 2015). for removal of heavy metals, the conventional method used is chemical precipitation with lime or sulfide-containing reagents, which suffers due to the huge volume of hazardous sludge that requires suitable disposal (Vasudevan, 2012). Adsorption techniques utilizing activated carbon or biochar work at lower concentrations; however, they suffer from costly regeneration processes (Chen et al., 2022)

Electrochemical treatment is one of the most attractive treatment processes, as it utilizes an applied electric current for oxidation and reduction reactions, ion transfer, radical generation without additional chemicals required for pollutants removal or degradation. One treatment process of this kind is electro-coagulation which applies sacrificial electrodes (for example, iron or aluminum) to generate coagulant ions and then destabilize and precipitate pollutants. 

Table 1: Comparison of conventional wastewater treatment methods for nitrate and heavy metals.

Source: Adapted from (Gupta et al., 2019; Chen et al., 2022; Costa, 2023).

Electrode passivation and sludge formation were reported as the major limitations even for lead, cadmium and chromium concentration removals above 95% using an optimized protocol (Al Jaberi et al., 2024; Costa, 2023). The most promoter reaction is electrochemical reduction (specifically for nitrate) to would imply the possibility of nitrate transformation in a mix of Na-N₂, −NO₂ or NH₄⁺ according to electrode nature and operating potential. Active copper, palladium and tin electrodes already exist and there are indications from recent work that new catalysts, such as Fe–N–C composites® or Pd–Cu alloys might also be useful based on high selectivity toward nitrogen gas, diminishing the ammonia formation (Liu et al., 2023; Pearce et al., 2024). Another electrochemical process, electrodialysis uses ion exchange membranes under the influence of an electric field to selectively remove charged ions. Although it is capable of eliminating nitrate and heavy metal under low concentrations, electrodialysis still has limitations in membrane fouling, scaling, and high cost of the membrane's consumption (Chen et al., 2022). Parallel to this work, more advanced oxidation technologies, such as electro-Fenton, have been employed for OH radical formation that could oxidize species like nitrates or organometallic complexes. Utilization BDD electrodes has enhanced degradation of pollutants with the complete elimination of complex pollutants however it comes with high cost and energy (Martínez-Huitle & Brillas, 2009; Costa, 2023).

Fig. 3: Schematic diagram of electrochemical treatment processes for nitrate and heavy metal removal from wastewater.

A number of research projects have shown that electrochemical methods are effective in the removal of nitrates. Liu et al. (2023) achieved a 92% nitrate removal using copper–palladium electrodes, while Pearce et al. (2024) reported on a different method. But the only recent nitrate reduction to N₂ was observed by (2024) and utilized Fe–N–C catalysts, which require a carefully engineered catalyst. Moreover, in the case of simultaneously reducing NO₃⁻ and desalting wastewater (hybrid system), combined ED treatment with NO₃⁻ reduction improved both simultaneous desalination removal and pollutant control (Chen et al., 2022). Nevertheless, selectivity is still a pressing problem, as most systems form nitrite or ammonium as by-products and are therefore pollutants. Electrochemical strategies have also been quite popular to deal with heavy metals. AlJaberi et al. (2024) demonstrated that over 95% removal of Pb²⁺ and Cd²⁺ could be achieved from industrial effluent using electrocoagulation, whereas Chen et al. (2022) found that copper and nickel can be recovered as the metallic deposits by electrodeposition following the circular economy ideology. The electrocoagulation and membrane filtration have also been shown to be more effective for chromium removal, reducing the sludge production on a pilot-scale trial (Costa, 2023).

Fig. 4: Comparison of Electrochemical Methods for Nitrate and Heavy Metal Removal.

Some researchers have demonstrated that electrolytic methods are successful in removing nitrates. Liu et al. (2023) reported 92% nitrate removal with copper–palladium electrodes, and Pearce et al. reported a different way (2024). However, the sole literature's report regarding a recent nitrate to N₂ reduction (2424) was upgraded in that case with Fe–N–C catalysts demanding specific design. Additionally, in the simultaneous NO₃⁻ reduction and desalting wastewater (hybrid system), combined ED treatment with NO₃⁻ removal enhanced both effecting tackling desalination and pollutant control (Chen et al., 2022). 

Fig. 5: Comparison of Conventional vs Electrochemical Wastewater Treatment Methods.

However, selectivity continues to be a challenge as most systems produce nitrite or ammonium which are in fact pollutants. There are also being used electrochemical approaches to cope with heavy metals. AlJaberi et al. (2024) found 95% removal of Pb²⁺ and Cd²⁺ could be achieved from industrial effluent by electrocoagulation with Chen et al. (2022) concluded that it is possible to recover copper and nickel as metal deposits via electrodeposition in accordance with the circular economy concept. Moreover, the electrocoagulation with membrane filtration has been proved to reduce the sludge production on a pilot-scale Reaction Kinetics, Mechanisms and Treatment of Hazardous Pollutants trial for chromium removal (Costa, 2023).

The present work is focused on the optimization of the simultaneous removal of nitrate and heavy metals by means of downstream electrochemical processes. A laboratory-based quantitative method was used in order to accurately operate different parameters (including current density, voltage and type of electrodes) considering their effect on removal of pollutants. We used both artificial and real industrial wastewater samples in order to ensure that the results obtained are applicable from an experimental (i.e., under controlled circumstances) as well as practical point of view.

The exemplary structure is a batch-mode, bench-scale electrochemical reactor. Reactor configuration is anode–cathode that electrodes were installed parallel to each other to provide the maximum effective contact area with wastewater. The voltage and current both are adjustable by a direct current power supply. Regarding the reactor setup, electrodes of graphite, stainless steel and boron-doped diamond were studied as anodes, while copper and titanium-based materials were applied as cathodes. The selected materials were based on previous reports about their catalytic activity, stability, and cost efficiency for use in electrochemical water treatment (Chen et al., 2022; AlJaberi et al., 2024).

Operational conditions were subsequently fine-tuned to assess their effect on treatment efficiency. The pH value of the wastewater sample was adjusted between 6.0 and 8.0 for simulating practical situations, and to reduce undesirable side reactions effects. The voltage was ranged from 5 to 15 V, and the current density was changed from 5 to 30 mA/cm². The treatment times varied between 30 and 120 min, according to the pollutant concentration and electrode material. These values were chosen due to the literature reporting good electrochemical reduction of nitrate and coagulation of heavy metal at this level (Liu et al., 2023). Then a diagram illustrating the arrangement would have been useful, ie an electrochemical cell, electrodes, power source and points of sampling.

Wastewater samples were distinguished in two types. The other two sets were the control groups (only Cd, Pb and Cr, without nitrate) with synthetic wastewater having known concentrations of NO₃⁻ (50 mg/L) and heavy metals such as Pb²⁺, Cd²⁺and Cr⁶⁺(10 mg/L for each), which was used to monitor the removal ratio. The other set were actual industrial effluent samples; one collected from a textile dyeing company and the other from mining wastewater discharge point. This combined application made it possible to evaluate the system in both simplified and real water matrices and thus broadened the generality of results. The analysis was performed using pollutant values before and after treatment. Nitrate and nitrite were determined spectro-photometrically (220–275 nm) according to standard procedures (APHA, 2017). The level of heavy metals was detected by Atomic Absorption Spectroscopy (AAS) and Inductively Coupled Plasma–Mass Spectrometry (ICP-MS), which could accurately measure the trace metal concentration in environ-mental exposure levels (Tchounwou et al., 2012). The energy consumed was calculated as follows from the operating voltage, current and treatment time.

where E is the energy consumed (kWh/m³), U is voltage (V), I am current (A), t is time of treatment (h) and V is volume of treated water (m³). A graph focusing on the relation between current density, exposure time and energy application could also be beneficial for process efficiency. Removal efficiencies and energy consumptions in different operating modes were statistical analyzed. Average removal efficiencies were described as descriptive statistics, and the impacts of electrode material and operational conditions on treatment results were further evaluated via ANOVA. The comparison of all the experimental results in synthetic and real wastewater was also tested. In additional, the performances of electrochemical approach were compared with conventional technologies in terms of removal efficiency and especially cost and sustainability, to have better under-standing on potentials (and drawbacks) of electrochemical treatment (Costa, 2023; Radjenović & Sedlak, 2015).

Electrochemical Removal Efficiency of Nitrate

The experimental data showed that the electrochemical reduction method is very efficient for detoxification of nitrate from both synthetic and real wastewater samples. The application of copper cathodes in a synthetic wastewater at an initial nitrate concentration of 50 mg L⁻¹ resulted in close to 85–88% removal after 60 min treatment at a current density of 20 mA cm⁻². The efficiency was increased to 92–95% (with the additional benefit of enhanced selectivity for N₂ as major end product) when palladium-modified copper electrodes were used. MES/Fe 2+ -activated persulfate process with electrodes involving the Fe-N-C catalyst was synergistically improved, as comparable removal efficiencies were achieved and the generation of ammonium ions was mitigated.

The stainless-steel electrodes were less efficient with 70–78% of nitrate removed after 90 min, ascribed to a lower catalytic activity and surface passivation. These results agree with previous studies in bimetallic and catalyst-modified electrodes which release more active sites and faster electrochemical kinetics as compared to conventional stainless steel and graphite EC (Liu et al., 2023; Pearce et al., 2024). Real textile wastewater (38 mg/L) evidenced slightly lower removal rates, as a result, 85–88% in 90 min was attained using Pd–Cu electrodes. The lower removal efficiency observed in real leachates compared to synthetic wastewater would be associated to competitive anions (sulfate, Chloride) and COD that interferes with the electrochemical reduction route. Nonetheless, performance was sufficiently high so that the FMWM method meet WHO drinking water guideline of ≤50 mg/L nitrate (WHO, 2022). The kinetics of nitrate degradation fitted the pseudo-first-order reaction model, and the rate consta-nts were 0.018 min⁻¹ (Stainless steel), 0.025 min⁻¹ (copper) and 0.036 min⁻¹ (Pd-Cu) respectively. These findings underscore the significant dependence of removal efficiency and kinetics on electrode material.

Electrochemical Removal Efficiency of Heavy Metals

The electrochemical method employed in this research exhibited high efficiency for heavy metal removal from synthetic and natural wastewater samples. Iron electrocoagulation was able to remove more than 95% of Pb²⁺ and Cd²⁺ within 60 min in synthetic wastewater with an initial concentration of 10 mg/L for each of Pb²⁺, Cd²⁺, and Cr6+. Approximately 98% of the Cr⁶⁺ was reduced to Cr⁆ at the iron electrodes and then precipitated as hydroxide at pH neutra1, confirming that iron anodes act both for reduction and coagulation. Removals with aluminum electrodes were slightly lower (90–93%) due to smaller flocs, and shorter residence times to remove cells larger fields.

Fig. 6: Nitrate Concentration vs. Treatment Time Across Different Electrodes.

Pefaçon et al. 17 claimed that electrodialysis achieved also in situ the most significant removal especially for Pb²⁺ and Cd²⁺ with an efficiency of 85–90% at low concentrations. But at higher contaminant concentrations, it's effectiveness decreased as a consequence of fouling and scaling of the membrane. A significant result was achieved in the case of Cu²⁺ and Ni²⁺ recovery (tested in supporting experiments) by electrodeposition, obtaining metallic deposits with purities higher than 90%. Such findings suggest that electrochemical processes serve to not only concentrate, but also enable recovery of these contaminants in accord with the principles of a circular economy (AlJaberi et al., 2024). 20 When tested with actual wastewater samples such as mining discharge, Pb2+ removal efficiency averaged 93%, Cd2+ removal was 91%, and Cr6+(about 87%), whereas somewhat lower due to organic and inorganic interferences. Heavy metals concentration in textile effluent samples was less (2–5 mg/L range), where removal efficiencies showed very high (> 90%) with the optimized conditions. Electrochemical techniques enabled more efficient as well as less sludge production compared to the conventional chemical precipitation (~80–90% removal and high sludge volumes) (Gupta et al., 2019).

The general trends suggest that the EC and EP are effective tools for removal of heavy metals, with lower sludge generation and for resource recovery. This is consistent with previous work showing >90% heavy metal removal using electrocoagulation under favorable current densities and electrode conditions (Chen et al., 2022).

Effect of Operational Parameters

The process of electrochemical treatment was strongly influenced by the operating variables: pH, voltage, current density and reaction time. For nitrate removal, the optimum pH was 6.5–7.5. In this distance, proton provided effective electron transfer and the electrode surfaces were stable. At acidic pH than 6, nitrate reduction was enhanced but ammonium production increased to a great extent which diminished the selectivity of the process. Conversely, at alkaline pH (>8) the reduction of nitrates was slow due to a reduced concentration of protons and electrode activation decreased the overall current efficiency. For heavy metals, near neutral and slightly alkaline pH is also better because when the pH value was between 6 and 10, Pb²⁺, Cd²⁺and Cr³⁺ can easily hydrolyze to precipitate as hydroxides. This on–off action of pH presents an ultimate dilemma for designing a system suitable for mixed-pollutant wastewater (Chen et al., 2022).

Fig. 7: Removal Efficiencies of Pb²⁺, Cd²⁺, and Cr⁶⁺ Across Electrochemical Methods.

The voltage and current density were also the factors that played important roles in treatment efficacy. The removal of nitrate and heavy metals was improved as a function of the current density up to 20-25 mA/cm² and then remained constant. After this the increase in current density did not produce a substantial improvement in removal but progressively increased energy cost and caused a significant reduction of process efficiency. At a very high current density (> 30 mA/ cm²) side reactions, like oxygen evolution at the anode and hydrogen evolution at the cathode, dominated leading to inefficient pollutant removal. These observations are in accordance with results of Liu et al. (2023), who found that best current density compromises pollutant removal efficiency with the energy supplied.

The duration of the treatment was also a relevant factor. The majority of nitrate and heavy metal removal was achieved in the first 60 min using efficiencies of up to 85–90 per cent. By prolonging the reaction time to 90 min, removal efficiencies of more than 95% could usually be obtained. Elsewhere, though, little – if any – gains were made after 90 minutes of recovery time suggesting the strongest effect may be early and that there is some sort of saturation point. Such behavior was in particular seen with real wastewater samples, where competing ions and organic material retarded the rate of reactions. These results indicate that practical treatment durations of 60–90 min are satisfactory for appropriate remediation under the studied conditions.

The influence of pH, current density and the electrode material was especially important to the total removal. For instance, Pd–Cu cathodes worked effectively under slightly acid to near-neutral pH (pH 6.5–7.0) and Fe-based anodes have the highest metal coagulating efficiency at a weak alkaline pH (pH 7.5–8.0). These interactions illustrate the importance of optimization, which should be specific depending on wastewater characteristics.

Fig. 8: Removal Efficiency as Function of pH and Current Density.

This Fig. 8 depicts the effect of pH and current density on removal efficiency. According the contour regions, high efficiency of 30 mA/cm²) in a neutral pH (6.5–7.5)). Under more acidic conditions, the formation of ammonium becomes more prominent, and at highly alkaline condition the electrode is passivated leading to less performance. Also, elevated current densities (>30 mA/cm²) contribute to the high energy costs with no significant advantage in removal efficiency. The results support the necessity of optimized operational windows in EC treatment.

Fig. 9: Removal Efficiency vs. Treatment Time.

This Fig. 9 represents also the influence of duration treatment for pollutant removal efficiency. Results show that the majority of the nitrate and heavy metal removal is completed within 60 min with 85–90% efficiency. It does rise to 95% at 90 min and it flattens out, so you're getting no more for your effort. Treatment longer 90 min is of little additional benefit regarding performance, but very costly in terms of energy. This number of treatment minutes would justify 60–90 min as the most effective length of time for a treatment in terms of cost and efficiency.

By-products and Selectivity (e.g., N₂ vs NH₄⁺)

The product selectivity is one of the most important considerations for the electrochemical reduction of nitrate, since non-selective reductions result in by-products such as nitrite (NO₂⁻) and ammonium (NH₄⁺). In product analysis of this work, selectivity was significantly affected by the type of electrode material, current density and solution chemistry. At a lower and more environmentally acceptable current densities (20–25 mA cm²), it was found that Pd–Cu and Fe–N–C composite cathodes examined show preference towards direct NH 4 NO 3 reduction to N₂ with selectivity's over 80%. This route is attractive due to the inert and environmentally benign N₂. Nevertheless, with copper-only electrodes appreciable NH₄⁺ concentrations (up to 6 mg/L) were observed 90 min into the experiment, particularly at lower pH. This was in agreement with the competitive reaction of NO₃⁻ under abundant proton environment according to which the NO₃⁻ will be partially reduced into NH4+ (Liu et al., 2023).

The accumulation of nitrite was also detected as a transient intermediate, in particular at the beginning of the treatment period (first 30 min) and under lower current densities (30 mA/cm²) could also lead to undesired side reactions (i.e., hydrogen evolution) that decreased electron efficiency while generating more NH₄⁺. These results are consistent with recent work demonstrating that catalyst design and improved operating conditions are key to improving N 2 selectivity and tuning out unwanted byproducts (Pearce et al., 2024). By-products were less of a concern when it came to the removal of heavy metals. The sludge produced by electrocoagulation consisted primarily of the Fe or Al hydroxides that had formed, and that contained absorbed metal ions Pb²⁺, Cd²⁺ and Cr³⁺. Wet sludge (~12–15 g/L on average) was generated, which could be dried and turned into solids; however, the final solids content was only about 1–2 g/L. This sludge was rich in heavy metals which indicated not only the issue of waste but also a possible resource. Appropriate management practices (stabilization or heat treatment) would be needed to dispose of it safely.

In summary, the findings emphasize that electrochemical treatment can effectively remove ammonia; however, it is necessary to optimize electrode materials and current densities to enhance selectivity for N₂ while minimizing NH₄⁺ and NO₂⁻ generation. Further advances in electrode design, such as using nanostructured and bimetallic catalysts, are likely to improve selectivity of products and render the electrochemical nitrate reduction scalable.

Fig. 10: Distribution of Nitrate Reduction Products Across Different Electrodes.

Fig. 10 shows the distribution of nitrate reduction products under different electrode conditions. Stainless steel and copper favored incomplete reduction, with higher NH₄⁺ (25–30%) and NO₂⁻ (15–20%). In contrast, Pd–Cu and Fe–N–C electrodes achieved superior selectivity toward N₂ (>80%), with minimal by-product formation. This confirms that advanced electrodes enhance reaction pathways toward environmentally benign nitrogen gas while reducing secondary pollutants (Liu et al., 2023; Pearce et al., 2024).

Energy Consumption and Cost Analysis

The energy consumption of the electrochemical treatment process was calculated based on applied voltage, current, reaction time, and treated volume, following the standard equation where U and I are the applied voltage (V) and current (A), t is reaction time (h), V is volume of treated water (m 3). In the conditions of optimization, 15 V and 20 mA/cm² for 90 minutes with a batch volume of 1.5 L, an energy consumption was recorded in terms of specific electric charge equal to ca. This value is similar or even lower than many well-established methods, for example ion exchange (2–3 kWh/m³) and reverse osmosis (3–4 kWh/m³), which have in some cases much higher energy and chemical requirements (Chen et al., 2022; Costa, 2023). The energy consumption was increased at higher current densities (>25 mA/cm²) till further 2.5 kWh/m³ without substantial enhancement of nitrate or heavy metal removal efficiencies. At current densities less than 15 mA/cm² energy consumption was reduced, however the removal efficiency was less than 80%. Accordingly, there was a trade-off, and an optimal operational window range of 20–25 mA/cm² led to high efficiency (>90%) and reasonable energy consumption (~1.2‒1.6 kWh/m³).

The treatment cost was calculated by multiplying the energy demand with an average electricity tariff for industrial users in Bangladesh (Approx. 0.09 $/kWh) (Bangladesh Energy Regulatory Commission, 2023). The investment cost under optimized conditions amounted to 0.13 USD/m³ and was significantly more competitive than that of reverse osmosis (0.20–0.35 USD/m³) and ion exchange (∼0.25 USD/m³). Furthermore, better contribution is expected for the operational costs and sludge disposal costs in the electrochemical treatment due to less usage of chemicals as well. 

Fig. 11: Energy Consumption and Removal Efficiency vs. Current Density.

For heavy metals removal, energy consumption, while similar for nitrate alone was increased relatively compared with the removal of nitrate alone and ranged between 1.6–1.9 kWh/m³ depending on heavy metal concentration and electrode types. It was because of the simultaneous energy requirement of coagulation, reduction, and precipitation operations. 2+ and Ni 2+ using electro-deposition; the recovered metal could compensate for a portion of operational expenses, indicating that resource recovery could increase economic sustainability (AlJaberi et al., 2024). In conclusion, this study verifies that ELO is a success in terms of energy and money compared with others treatment. It may also be combined with renewable sources such as solar power or wind to reduce operating costs and receive benefits under sustainability practices.

Comparative Analysis with Conventional Treatment Methods

Electrochemical processes were systematically compared with conventional wastewater treatment methods, such as ion exchange, reverse osmosis, biological denitrification, chemical precipitation and adsorption. Results showed that high removal efficiency could be obtained using conventional technologies, however they have a problematic sustainability aspect and produce a large amount of waste and/or cost. Methods have been developed to remove over 90 % of nitrates and heavy metals (e.g., by ion exchange, reverse osmosis) but produce the concentrated brine waste stream that needs further cleaning or discarding once again creating secondary pollution concerns (Gupta et al., 2019). In addition, the membrane of said reverse osmosis system can be subjected to fouling and replacement at an operating cost including a short life. The biological denitrification process, widely employed for municipal wastewater treatment purposes, has limitations due to the required optimized operation conditions of an appropriate pH and temperature besides a sufficient organic carbon supply for the microbial activity. In contrast, in industrial effluents the effectiveness of these biological methods is strongly limited by variable contaminant loads (Radjenović & Sedlak 2015).

Currently chemical precipitation remains popular treatment for removing heavy metals from waste water with removal efficiency ranging 80–95% depending upon choice of precipitant. However, it produces a large amount of hazardous sludge that require good treatment and disposal, this raises the cost of treatment and risk to the environment (Chen et al., 2022). Adsorption treatment, activated carbon or biochar adsorbents;50–85% effective (moderate level) Costly regeneration of adsorbent Reduced efficiency in low contaminant load (Costa, 2023). On the other side, in case of pollutant decomposition efficiency and secondary waste production, electrochemical methods were as efficient or even better. Pb ²⁺, Cd ²⁺ and Cr 6+ could be removed by >95% of their initial concentration when electrocoagulation was used with far less sludge generation relative to the chemical precipitation. In case of electrochemical reduction of nitrate, a removal efficiency over 90–95% could be attained with overly high selectivity toward nitrogen gas under proper conditions. 

Precious metals may also be reclaimed from the electrodeposition process for material circularity and cover operational costs (AlJaberi et al., 2024). The energetic and the economic costs of the electrochemical methods were found to be ranging between 1.2 and 1.8 kWh/m³, the result optimized of each degradation, that is equivalent as mean cost in about 0.13 US dollars for m³, these prices being very attractive if are compare with those existing on markets currently. Electrochemical systems require no chemical regenerants or extensive pre-treatment much unlike ion-exchange and reverse osmosis, thereby minimizing both chemical usage and maintenance. But there are scaling issues to contend with too; electrode fouling and lifecycle durability continue for this to be solved in the context of full-scale industrial application.

In general, the comparison suggests that electrochemical methods appear to be a sustainable option when compared with conventional treatment processes because they result in higher degree pollutant removal, generate lower quantity of secondary waste and their disposition require no special permits, and allow organics recovery. The classical technologies are however developed and implemented at the industrial level, which also points out to how relevant pilot and demonstration facilities can be for electrochemical systems to become realized quicker on a practical scale.

Table 2: Conventional vs. Electrochemical Methods for Wastewater Treatment.

Source: Adapted from (Chen et al., 2022; Gupta et al., 2019; AlJaberi et al., 2024).

Environmental and Practical Implications

The implications of the present study are environmentally and industrially significant. The simultaneous removal of nitrate and heavy metals by electrochemical techniques has therefore attracted global attention for its potential to solve two of the largest water quality problems, namely eutrophication and toxic heavy ions. By decreasing nitrate contents below the limit of 50 mg/L suggested by WHO (2022), electrochemical technology inhibits algal blooms and dissolved oxygen exhaustion in aquatic environments. The elimination of Pb²⁺, Cd²⁺ and Cr⁶⁺ at a rate higher than 90% also limits the bioaccumulation and biomagnification which makes considering aquatic food chains risk, as well as exposure to human health that favors neurological disorders, kidney damage and cancer (Tchounwou et al., 2012).

On a practical side, electrochemical processes are an efficient and environmentally friendly option for wastewater treatment. Unlike ion exchange and reverse osmosis processes where brine waste is produced, electrochemical techniques across the board generate less sludge while in the case of electrodeposition such as copper and nickel may also be recovered with potential application for circular economy technologies (AlJaberi et al., 2024). This co-benefit of pollutant elimination and resource reclamation serves not only to ease the disposal burden, but also increases the economic viability of electrochemical systems in industries including mining, electroplating and textile dyeing. The combination of electrochemical technologies with renewable energy sources like solar or wind, makes them even more ecologically compatible. DE corporation and smearing, as cost drivers for energy consumption, integration of treatment units with decentralized renewable systems can lower the operational costs and carbon footprint especially in developing countries having problems with access to clean water and availability of electric energy. This integration will make EC-treatment feasible for rural / semi-urban sites where large scale treatment plants do not find application (Costa, 2023).

In spite of these advantages, a number of practical constraints exist. Electrode fouling, especially in the presence of real wastewater matrices, is also a potential factor which may result in long-term performance loss and increased cost for maintenance. The electrocoagulation sludge is less in volume compared to the chemical precipitation sludge, it should also be given careful attention for reutilization or safe disposal of such residues as they can contribute to secondary pollution [16, 17]. 

Fig. 12: Flowchart summarizing the benefits, applications, and challenges of electrochemical wastewater treatment methods.

Most previous studies are further confined to laboratory or small pilot scale. Scaling processing will help but succeeding on the system or cost basis is still open. The availability of further electrode material, device design and cost models would make such large-scale implementation accessible. Generally, the findings of the present study suggest that electrochemical treatment is a promising method for industrial wastewater problems. The combination of efficiency, sustainability and potential resource recovery makes it an eco-friendly and feasible alternative to the traditional ones.

Conclusion

The results of the study have showed that electro-chemical treatment processes are significantly effective to treat combined nitrate and heavy metals from wastewater. Both artificial and practical effluent experiments demonstrated that the nitrate removal efficiencies were as high as 90–95% with well-optimized electrode materials (Pd–Cu composites, Fe–N–C catalysts). Lead (Pb²⁺), cadmium (Cd²⁺) and chromium 6+ (Cr⁶⁺) were effectively removed by over 90% of their concentration as heavy metals through electrocoagulation with iron electrodes, precipitating the Cr3+. 

Performance was significantly affected by operating parameters, including pH value, current density, and treatment time; the optimal levels were at pH 6.5–7.5, current densities of 20–25 mA/cm² and treatment times lasting for 60–90 min. Selectivity investigation showed that nitrate reduction was most likely to produce nitrogen gas on bimetallic electrodes while three other products, ammonium and nitrite produced under less favorable conditions. Energy consumption was varied between 0.8 and 2.5 kWh/m³, so electrochemical processes were still a competitive method compared to water demineralization procedures as reverse osmosis and ion exchange. Collectively, the results present technical practicability, environmental benignity and cost effectiveness of electrochemical processes in wastewater treatment.

Recommendations

Further work should focus on size-up studies of these systems to pilot and industrial scale to assess long-term performance, energy optimization, and maintenance needs. Such a high selectivity for N₂ without aggressive formation of ammonium can be refined by studying advanced electrode materials, such as nanostructured and hybrid catalysts. Electrochemical processes could be combined with hybrid technologies like adsorption and membrane separation to gain synergistic pollutant removal and lower operational costs. Also, interconnecting these systems to renewable sources of energy will be the key for enhancing their sustainability and reducing reliance on grid power. 1.3 Focus on Recovery and Reuse of Heavy Metals in the Circular Economy Context given the high metal loading, more studies are required for sludge management, recovery, and reuse of the trapped heavy metals under circular economy principles. Lastly, full life-cycle analyses should be performed to assess the environmental and economic implications of large-scale implementation of electrochemical wastewater treatment techniques.

The author gratefully acknowledges the academic support and facilities that contributed to the completion of this work.

The author declares that there is no conflict of interest regarding the publication of this article.