Challenges in Designing Electrochemical Disinfection Systems for Reducing Microbial Contamination in Drinking Water Distribution Networks

Abstract

Electrochemical disinfection systems are gaining attention as potential solutions for reducing microbial contamination in drinking water distribution networks. While numerous recent studies suggest that these systems are easy to implement, real-world application reveals significant challenges. Many published works suffer from fundamental flaws, including inappropriate material selection, unrealistic operating conditions, and non-compliance with regulatory standards. This review critically examines studies published over the past 24 months, highlighting key issues that limit practical applicability. It discusses common pitfalls, such as the use of unstable or toxic electrode materials and the failure to provide residual disinfectant effects. Additionally, the review outlines essential characteristics for effective electrochemical disinfection systems, emphasizing compliance with health regulations, scalability to real-world conditions, and long-term operational stability. By identifying these gaps, this review article aims to guide future research toward more viable, safe, and sustainable electrochemical disinfection solutions for drinking water treatment.

1. Introduction

Drinking water disinfection is generally carried out at the water treatment plant, downstream of other physicochemical treatment stages which have the main objective of removing suspended solids, dissolved substances, and, ultimately, the microbial load [1].

An initial disinfection phase, typically using ozone or chlorine dioxide, serves to prevent the proliferation of algae and microorganisms harmful to subsequent treatments. It also oxidises some inorganic compound, such as iron, manganese, and ammonia. A second disinfection phase, known as post-chlorination or final disinfection, aims to destroy any residual microorganisms and provide a residual effect (“persistence”). This ensures the drinkability of the water up to the tap of the individual user [1]. Ozonation or UV irradiation followed by the addition of gaseous chlorine (to form hypochlorous acid) for persistence is commonly used with dosages that depend on the length of the path that the water must take to reach the user.

In most cases, the responsibility of the water supplier ends at the water meter. However, the presence of a disinfectant capable of ensuring a residual effect is far from certain. It is also common for the system downstream of the water meter to include several hundred meters of piping before reaching the water outlets. This is often the case in hotels, apartment buildings, hospitals, and elderly care facilities. The problem of the possible lack of a residual disinfection effect, with the consequent possibility of microbial proliferation in the water, becomes more critical where the vulnerability of the end user increases. Diseases caused by Legionella spp. or Pseudomonas aeruginosa are on the rise due to demographic aging, climate change, and the increased propensity to travel [2]. These diseases can have extremely serious consequences for vulnerable people, such as immunosuppressed people, the elderly, and newborns [3].

Hospitals and nursing homes are the facilities that most commonly implement drinking water disinfection systems. The goal is to restore a residual effect in their systems and minimise the proliferation of microorganisms and biofilms [4]. Several approaches to disinfection exist, each with its own advantages and disadvantages. These range from thermal or UV radiation treatments to the addition of chemicals such as hypochlorite, chlorine gas, chlorine dioxide, chloramines, hydrogen peroxide, ozone, and copper/silver ions [5].

In addition to these methods, electrochemical disinfection is a relatively new approach that has attracted some interest. It has the potential to solve problems related to the supply and storage of hazardous substances, especially in rural areas. However, researchers who have discussed this approach, even when reporting laboratory test results, have often approached the issue from a largely academic perspective. This shows a worrying ignorance of the difficulties associated with real-world application.

This contribution aims to shed light on these issues, educating and informing readers about the problems that need to be solved. To do so, works published in the last 24 months have been taken into consideration, highlighting their questionable aspects. However, it should be emphasised that any criticism is not directed at the researchers themselves but at the results obtained or the conclusions that could be drawn from them.

2. Publications of the Last Calendar Year

As reported in

Table 1. List of articles on electrochemical disinfection of drinking water, published since October 2023.

Title	Publication Date	Main Disinfection Approach	Ref.
Efficient electrocatalytic H2O2 activation over nitrogen-doped carbon encapsulated Co3O4 for drinking water disinfection	24 October 2023	Electrochemical synthesis of hydrogen peroxide	[6]
Decoupling locally enhanced electric field treatment (LEEFT) intensity and copper release by applying asymmetric electric pulses for water disinfection	10 November 2023	Electroporation/copper ions	[7]
Advances on electrochemical disinfection research: Mechanisms, influencing factors and applications	7 December 2023	(review article)	[8]
Approaching easy water disinfection for all: Can in situ electrochlorination outperform conventional chlorination under realistic conditions?	12 December 2023	Electrochemical synthesis of active chlorine	[9]
Nitrate electro-bioremediation and water disinfection for rural areas	2 February 2024	Electro-bioremediation	[10]
Drinking water electrochlorination in a single-pass biomimetic flow cell with zero salt dosing	14 February 2024	Electrochemical synthesis of active chlorine	[11]
Dielectric barrier discharge plasma promotes disinfection-residual-bacteria inactivation via electric field and reactive species	1 March 2024	Electroporation/electrochemical synthesis of ROS	[12]
Green and sustainable in situ water treatment: A review of noble-free catalysts for electrochemical oxygen reduction to hydrogen peroxide	1 April 2024	Electrochemical synthesis of hydrogen peroxide (review)	[13]
Electrochemical disinfection boosting by a pulsed-assisted MXene-based cathode	8 April 2024	Electrochemical synthesis of hydrogen peroxide	[14]
Enhancement of chlorine-resistant bacteria inactivation via coupling Magnéli phase Ti4O7-based electrochemical oxidation and chlorination	28 June 2024	Electrochemical oxidation/electrochemical synthesis of active chlorine	[15]
Magnéli Ti4O7 nanowire induces locally enhanced electric field and electrocatalytic activity for rapid and efficient water disinfection via synergistic electroporation and electrochlorination	23 July 2024	Electroporation/electrochemical synthesis of active chlorine	[16]
Emerging investigator series: Mitigation of harmful algal blooms by electrochemical ozonation: From bench-scale studies to field applications	26 July 2024	Electrochemical synthesis of ozone	[17]
Feasibility assessment of electrochemical chlorination for direct potable reuse	31 July 2024	Electrochemical synthesis of active chlorine	[18]
Tuning the locally enhanced electric field treatment (LEEFT) between electrophysical and electrochemical mechanisms for bacteria inactivation	6 August 2024	Electroporation/electrochemical synthesis of active chlorine	[19]
Engineering decentralized electrodisinfection to sustain consistent chlorine generation under varying drinking water chloride content	19 September 2024	Electrochemical synthesis of active chlorine	[20]

, fifteen papers on the topic of electrochemical disinfection of drinking water have been published in the last calendar year (since October 2023).

The review article by Li et al. [8] provides general insights into the mechanisms and applications of electrochemical disinfection as well as the factors influencing its effectiveness. However, it does not include any realistic case studies on drinking water treatment. Readers interested in practical applications should instead refer to Kraft’s 2008 publication [21].

Both Wen et al. [6] and Wang et al. [14] studied water disinfection processes based on hydrogen peroxide. Wen et al. [6] investigated a specially formulated electrocatalyst designed to efficiently activate H₂O₂ and generate hydroxyl radicals capable of reducing microbial loads in contaminated water. While the results appear promising, the approach requires an H₂O₂ electrosynthesis device installed upstream of the electrocatalytic device, making it difficult to implement in real-world application. Additionally, the authors did not examine the electrocatalyst’s stability or the potential impact of ions and other species on cathode performance. Given the short lifetime of hydroxyl radicals, all water to be treated would need to pass through the device, presenting significant scalability challenges. The current setup has a limited active surface area (0.78 cm²) and has only been tested with a flow rate of 1 mL/min. Furthermore, when treating natural waters with some degree of hardness, scales formation on the cathode could become a significant issue, but this was not addressed in the study. Wang et al. [14] explored a metal carbide electrocatalyst for the cathodic synthesis of H₂O₂. Under pulsed potential conditions, they achieved H₂O₂ production of up to 16.87 mg/L, which enabled a 4-Log reduction in Escherichia coli within 60 min of contact time. However, no real-world applicability was discussed, and the research appears to be of purely academic interest.

For more information on the use of noble metal-free catalysts for the electrochemical reduction of oxygen to H₂O₂ in in situ water treatment, readers can refer to the critical review by Liu et al. [13]; however, the potentially relevant studies cited in Section 4.2 in [13] (Disinfection) were all published between 2008 and 2023, placing them outside the time frame considered for this review article. The article by Shi et al. [22], published in 2023, will be discussed in a later section.

Mo et al. [7] explored a disinfection approach based on copper ions. To achieve effective disinfection while maintaining metal ion concentrations at safe levels (<0.5 mg/L), the system employs asymmetric electrical pulses to generate high electric fields and induce electroporation, making microorganisms more susceptible to the biocide. While this is an interesting approach, it does not appear to provide a lasting residual effect downstream. If the goal is to use minimal biocide concentrations, the biocide itself can only be effective when supported by electroporation—meaning disinfection occurs solely within the electrochemical device. In large hydraulic networks, multiple devices would likely be required. However, if copper ion levels remain stable after the initial production, it may be sufficient to replicate only the component responsible for generating asymmetric electrical pulses, allowing for additional electroporation treatments along the network.

Electroporation is also exploited in the studies by Deng et al. [12] and Wang and Xie [19]. Deng et al. [12] combined electroporation with the production of reactive oxygen species generated by plasma discharge in air. In this approach, bacterial inactivation resulted from both electric field-induced electroporation and oxidation by reactive oxygen (ROS) and nitrogen species. Their tests using Bacillus subtilis and Pseudomonas fluorescens achieved over 7-Log inactivation within 6 and 8 min, respectively. However, the authors did not discuss the potential application of their system for drinking water treatment. Even if feasible, it is unlikely that the treated water would retain residual disinfecting properties downstream of the device. Wang and Xie [19] explored a method that modulates the process from an electrophysical (electroporation) to an electrochemical (oxidation) mechanism by adjusting parameters such as electric field strength (1–12 kV/cm), pulse width (0.002 μs–0.2 s), frequency (0.05 Hz–5 MHz), and pulse width-to-period ratio (0.0001–100%). While the authors acknowledge the need for further optimisation, their approach is promising. If they can identify conditions that enable both electroporation (to minimise microbial load) and oxidation (to generate biocidal components with a residual effect downstream), their method could represent an ideal disinfection solution.

The study by Ceballos-Escalera et al. [10] is largely outside the scope of this review, as it focuses on groundwater treatment using an electro-bioremediation approach. Their system consists of a tubular reactor with a cylindrical titanium mesh coated with mixed metal oxide (Ti/MMO), a granular graphite cathode inoculated with a denitrifying community, and a tubular cation exchange membrane separating the two electrode compartments. The system operates under potentiostatic conditions, with the cathode (working electrode) maintained at −0.32 V versus a silver/silver chloride reference electrode to facilitate the complete reduction of nitrate to nitrogen gas. Various hydraulic retention times, ranging from 2.1 to 7.0 h, were tested using water recirculation. Given the extended treatment times required, this approach does not seem viable for improving drinking water quality in real-world applications. However, it is important to note that this was never the intended purpose of their study.

I previously provided comments on the work by Atrashkevich et al. [9] a few months ago (see [23]). I was particularly disappointed that the authors conducted tests using a “Micro Flow Cell” from ElectroCell (www.electrocell.com), which was equipped with a Ti/Pt cathode and a Ti/RuO₂ anode, operating at a flow rate of only 0.3 L/min. I criticised their choice of water flow rate, as it has no practical relevance for real-world applications. Additionally, the electrode materials used are unsuitable for the proposed application. As a result, both the experimental findings and the technical-economic analysis presented in their paper appear unreliable.

García-López et al. [11] also conducted experiments under conditions far from real-world applicability, using a water flow rate of ≤0.4 L/min. However, unlike Atrashkevich et al. [9], they did not claim immediate applicability, merely stating: “These results open up the possibility of scaling-up this electrochemical cell design to treat a higher water flow rate in a single-pass”. Despite this, their study suffers from the same fundamental issue—the use of unsuitable electrode materials (a graphite anode and a 304 stainless steel cathode, each with a surface area of 616 mm²). My criticisms of the previous paper apply to this one as well.

Li et al. [15] studied a flow-through electrochemical device featuring a Magnéli phase anode (Ti₄O₇ coating on graphite felt) and a graphite felt cathode. Graphite felts were 5 mm thick, had a 25 mm diameter, and their porosity allowed for a flow rate of approximately 4.1 mL/min, which translates to 500 L/h per square meter of electrode. While this flow rate may seem reasonable, it corresponds to only 8.3 L/min per 1 m² of electrode surface, which is quite low for practical applications. Additionally, in tests conducted with demineralised water supplemented with bacterial cultures, pure electrodisinfection proved largely ineffective, achieving only a ~1-Log reduction, even at voltages up to 4 V.

Li et al. [16] studied a similar flow-through electrochemical system but used graphite felts with slightly higher porosity (or a pump capable of exerting higher pressure). As a result, their system achieved a higher flow rate of 8.2 mL/min, equivalent to 1000 L/h per square meter of electrode surface. When operated with a 2 mM NaCl solution (70 mg/L of chloride), the device generated up to 2 mg/L of free chlorine, along with trace amounts of chlorate and perchlorate. This setup achieved bacterial inactivation of up to 6 Logs, primarily attributed to electroporation and electrochlorination. A seven-day test showed negligible damage to the anode structure, but natural water was not tested, leaving the impact of other ionic species unknown. For real-world application, periodic polarity reversal would likely be necessary to prevent scale buildup on the cathode, which could otherwise reduce porosity and impair system performance.

Yang et al. [17] investigated an electrochemical ozonation process using titanium mesh anodes coated with nickel-doped antimony tin oxide (Ti/Ni–Sb–SnO₂) and perforated stainless steel sheet cathodes to generate ozone and hydroxyl radicals. The study used a boat-mounted polycarbonate reactor with 10 m² of anode surface (comprising 20 anodes sandwiched between 21 cathodes) and an operating volume of 190 L. The system treated 378 L/min of lake water, applying up to 1000 A of current (at a current density of 10 mA/cm²) and a cell voltage of up to 20 V, achieving 62% removal of chlorophyll-a/cyanobacteria. Two one-day field tests were conducted, and the authors estimated an anode lifetime of 9800 h at the optimal current density of 7 mA/cm². However, since these tests were performed on lake water for a limited time, concerns remain regarding: efficiency and reliability in the presence of water containing ions that may cause cathodes deposits; inability to reverse polarity, which likely limits the system’s applicability for drinking water treatment; and the potential release of metal ions (antimony) into treated water, which could pose health risks.

Yang et al. [18] investigated electrochlorination for disinfecting domestic wastewater treated via reverse osmosis (RO) and non-RO processes, with the goal of making it suitable for reuse as drinking water. The study utilised multiple electrochemical cells, each with a working volume of just 10 mL, equipped with a Ti/IrO₂-RuO₂ anode and a Ti cathode. Continuous operation tests were conducted with a synthetic water flow rate of only 0.2 L/min. In a batch process, non-RO-treated water produced up to ~15 mg/L of chlorine after 60 s, whereas RO-treated water produced less than 0.14 mg/L. This difference was clearly linked to the chloride content: non-RO-treated water contained ~200 mg/L of chloride, while RO-treated water contained only ~3 mg/L of chloride. In a 30 min experiment using non-RO-treated water, a consistent 2.1 mg/L chlorine concentration was achieved with a 100 mA current. However, several concerns arise, namely: the electrode dimensions were not reported, making it difficult to assess scalability, and the study duration (30 min) was too short to properly evaluate scale formation. The authors reported no scale formation, but their analysis was limited to measuring calcium and magnesium concentration changes. Even assuming a minimal 0.02 mg/L decrease in both ions (within the variability of their measurements), estimated scale deposition during the 30 min test are as follows: 0.12 mg of calcium (~0.3 g of CaCO₃) and 0.12 mg of magnesium (~0.29 g of Mg(OH)₂). In a real-world application, periodic polarity reversal would be essential to clean the cathode(s), which the chosen electrode materials do not support.

The final study listed in Table 1 is another contribution by Atrashkevich and Garcia-Segura [20], which can be considered a follow-up to their previous work [9]. Unfortunately, this new study was conducted without addressing any of my prior criticisms [23]. Once again, the authors used the ElectroCell’s “Micro Flow Cell”, equipped with a Ti/Pt cathode. They tested three anode materials: Ti/RuO₂, Ti/IrO₂, and boron-doped diamond. Their experiments covered a current density range of 5–15 mA/cm², with water flow rates varying between 0.1 and 0.9 L/min. Based on their results, they concluded that “the Ti/RuO₂ anode” is “the most suitable for effective chlorine generation while minimizing the formation of ClO₃⁻ and ClO₄⁻”. However, this conclusion is problematic. In [23], I already explained why Ti/RuO₂ electrodes should not be used for drinking water treatment: the material is not stable under oxygen-evolving conditions. As established in the literature [24,25,26], ruthenium(IV) ions are easily oxidised to higher valence states, which are soluble, volatile, and toxic. This instability raises two major concerns: the anode’s service life cannot be guaranteed; more worryingly, ruthenium-based species may be released into the treated water, posing potential health risks.

3. Publications of the Previous Calendar Year

In the previous calendar year (October 2022 to September 2023—

Table 2. List of articles on electrochemical disinfection of drinking water, published in the period from October 2022 to September 2023.

Title	Publication Date	Main Disinfection Approach	Ref.
Lightning-rod effect on nanowire tips reinforces electro-poration and electrochemical oxidation: An efficient strategy for eliminating intracellular antibiotic resistance genes	30 January 2023	Electroporation/electrochemical synthesis of active chlorine	[27]
Water disinfection using durable ceramic filter coated with silver nanoparticles synthesized using actinomycetes	27 May 2023	Filtration/silver ions	[28]
A novel approach for water disinfection by enhanced photoanode oxidation using in-situ generated hydrogen peroxide	4 July 2023	Photoelectrochemical synthesis of hydrogen peroxide	[22]
Electrochemical filtration for drinking water purification: A review on membrane materials, mechanisms and roles	4 July 2023	Filtration/electrochemical synthesis of ROS and hydrogen peroxide (review)	[29]
Manganese oxide-functionalized graphene sponge electrodes for electrochemical chlorine-free disinfection of tap water	27 July 2023	Electro-oxidation	[30]
Technoeconomic assessment of electrochemical hydrogen peroxide production with gas diffusion electrodes under scenarios relevant to practical water treatment	23 August 2023	Electrochemical synthesis of hydrogen peroxide	[31]
Removal of disinfection byproducts through integrated adsorption and reductive degradation in a membrane-less electrochemical system	23 August 2023	Adsorption and reductive degradation	[32]
Decentralized approach toward organic pollutants removal using UV radiation in combination with H2O2-based electrochemical water technologies	4 September 2023	UV/photoelectrochemical Fenton approach	[33]

), eight more scientific works on electrochemical disinfection of drinking water were published.

Liu et al. [27] combined electroporation and electrochemical oxidation in a graphite felt-based flow-through system. The anode was modified with Co₃O₄ nanowires (~4 wires/μm², ~4 μm in length, and ~25 nm in diameter). To illustrate the so-called “lightning-rod effect”, they compared the performance of this nanowire-modified anode with that of a graphite felt anode coated with a Co₃O₄ thin film. The electric field and charge density were locally enhanced at the nanowire tips, which facilitated electroporation of microbial cells and acceleration of electrochemical reactions responsible for generating reactive species. A 5 mM NaCl electrolyte was used, allowing for the production of reactive oxygen species, reactive chlorine species, and active chlorine. By coupling electroporation with electrochemical oxidation, the system achieved a 1–1.5-Log reduction in intracellular antibiotic resistance genes at voltages above 4.0 V. Notably, this was accomplished with ~6–9 times lower energy consumption compared to electrochemical oxidation alone. The authors proposed that this combined approach could be integrated with conventional chemical disinfection methods to enhance the removal of antibiotic resistance genes from drinking water. However, in my opinion, further research is needed to confirm the compatibility of the materials with the proposed application, particularly considering that the release of cobalt ions would be unsuitable for drinking water treatment. Additionally, it is important to investigate whether possible scale deposition on the cathodes could pose operational challenges over time.

Codina et al. [30] investigated the disinfection of tap water spiked with 10⁷ CFU/mL of E. coli using a cylindrical continuous flow reactor. The reactor operated at a flow rate of 5 mL/min and was equipped with a manganese oxide-functionalised graphene sponge anode and an N-doped graphene sponge cathode, separated by a thin polypropylene mesh to prevent short circuits. The graphene sponge electrodes were 1 cm thick with a projected surface area of 17.3 cm². Applying a current density of 29 A/m² resulted in a 2.7-Log reduction in E. coli. The authors reported no residual free chlorine in the treated water, despite a chloride concentration of ~36 mg/L, and thus claimed that sanitisation occurred without the formation of active chlorine species. However, this conclusion appears questionable. Activated carbon beds are commonly used to remove active chlorine, and a similar effect might be expected with graphene. Additionally, the potential release of manganese ions into the treated water raises concerns, along with the risk of cathode clogging due to the precipitation of insoluble carbonates and hydroxides. For real-world applications, scaling-up the system based on the provided experimental data suggests that electrodes 4000 times larger would be required to treat a flow of at least 20 L/min—the equivalent of a single household tap. Clearly, such large electrode dimensions, while still insufficient for many practical applications, pose significant challenges to the feasibility and implementation of this approach.

A somewhat similar approach, albeit of primarily academic interest, is presented by Yang et al. [32]. The authors examined the removal of disinfection by-products through adsorption and reductive degradation using an electrochemical system. This system featured a cathode made of 1 g of granular activated carbon (GAC) wrapped in a 2 cm × 5 cm carbon cloth, paired with a second piece of carbon cloth serving as the anode. The electrodes were placed inside a 100 mL cell with a flow rate of 25 mL/h. The authors suggested that scaling up their system would be relatively straightforward due to the absence of a separating membrane. However, considering that 1 g of GAC is needed to treat a flow rate of 25 mL/h (0.417 mL/min), approximately 48 kg of GAC would be necessary to handle a flow rate of just 20 L/min. This requirement highlights the impracticality of scaling up the system for real-world applications.

The papers by Barazorda-Ccahuana et al. [33], Shi et al. [22], and Zhao et al. [31] present proposals for water treatment using hydrogen peroxide. Barazorda-Ccahuana et al. [33] aimed to remove methylparaben as a model pollutant in drinking water, proposing a Fenton photoelectrochemical approach combined with UV-A or UV-C radiation. However, real-world application seems unlikely given their methodology: they added 50 mmol/L of Na₂SO₄ (7.1 g/L) for electrochemical testing, adjusted the pH to 3 with sulfuric acid, and added 0.5 mmol/L of Fe²⁺ (28 mg/L). Their setup also included a boron-doped diamond thin-film anode, and a gas diffusion electrode supplied with pure oxygen at 300 mL/min. These conditions are impractical for drinking water treatment. Shi et al. [22] used a 5 mM Na₂SO₄ electrolyte which, although 10 times lower than Barazorda-Ccahuana et al.’s concentration, still amounts to 0.7 g/L, posing similar challenges for drinking water applications. Their system featured a 250 mL batch reactor with a 20 cm² photoanode (MoS₂-BiOI-modified reticulated vitreous carbon, RVC) and a 20 cm² RVC cathode fed with oxygen at 200 mL/min, illuminated by a 500 W xenon lamp. The complexity and resource intensity of this setup further hinder its practicality. Zhao et al. [31] acknowledged the practical difficulties of producing hydrogen peroxide with gas diffusion electrodes directly in the water to be treated, due to the rapid cathode degradation from strong oxidants and scale deposits. They explored on-site electrosynthesis of H₂O₂ in 1 M Na₂SO₄ using a split cell, achieving a concentrated H₂O₂ solution (>30,000 mg/L) with a current efficiency of 60%. However, the estimated cathode lifetime of ~1000 h remains insufficient for practical applications. They projected H₂O₂ production cost between $1.62 and $1.94 per kg, exceeding the market price of industrial-grade H₂O₂ (~0.7–1.2 $/kg). Although the simultaneous production of sodium hypochlorite at the anode could offset some costs, addressing the limited cathode lifetime is crucial for practical viability.

The remaining two papers from Table 2 focus on filtration systems. Wafy et al. [28] studied ceramic filters impregnated with silver nanoparticles (AgNPs) synthesised through the reaction of silver nitrate with actinomycetes. The adhesion of AgNPs to the filters was facilitated by terminal amino groups of a linker (3-aminopropyl triethoxysilane), which binds to the ceramic surface. Although this approach is not electrochemical and does not ensure residual effects downstream of the filter, it appears more practical than many previously discussed methods. Qi et al. [29] reviewed potential substrates and electrocatalysts to enhance the performances of electrochemical membranes, integrating both contaminant separation and degradation. These systems can theoretically synthesise reactive oxygen species and hydrogen peroxide at the anodes and cathodes, respectively. The review covered studies between 2015 and 2020, focusing on microorganism removal (disinfection), heavy metal removal, and micropollutant removal in drinking water. However, further research is needed to address safety concerns related to the leaching of nanomaterials or metals.

4. General Discussion

While scientific publications are not necessarily expected to provide ready-to-use solutions, researchers have a responsibility to ensure their studies produce accurate and applicable results. Misleading or impractical findings not only waste resources but may also pose risks to society. In the context of drinking water treatment, particular attention should be given to compliance with existing regulations, even if these are not widely recognised in academic circles.

Over the past two years, twenty-three scientific articles have been published on topics related to electrochemical disinfection of drinking water. However, none of these studies appear to offer practical or reproducible solutions without potential risks to end users. The primary issue lies in the choice of materials used in contact with the water being treated—most notably, the electrodes. In many cases, the selected materials are unsuitable for the intended application, raising concerns about the researchers’ expertise, particularly given the critical role of electrode safety in electrochemical disinfection.

The effectiveness of electrochemical disinfection depends on the method used. Approaches relying on hydrogen peroxide or electroporation do not provide a lasting disinfectant effect, allowing microorganisms to regrow in the distribution network and rendering the process ineffective. Similarly, filtration-based methods, even when enhanced by short-lived reactive oxygen species (ROS) or bacteriostatic ions like silver, fail to maintain long-term disinfection. As a result, the most viable approach appears to be the generation of active chlorine.

Unless used in chemotherapy as a substitute for platinum compounds, ruthenium compounds should be considered highly toxic and carcinogenic. The NSF/ANSI/CAN 61 standard [34], which addresses drinking water system components covering health effects, references NSF/ANSI/CAN 600 [35], which outlines “toxicological review and evaluation procedures for the evaluation of substances imparted to drinking water through contact with drinking water system components (and drinking water additives)”. Regulatory limits for both regulated and unregulated contaminants, as established by the US EPA and Health Canada, are summarised in Table 4.1 in [35]. For ruthenium, the maximum concentration that a single product can contribute (SPAC) is set at 0.0003 mg/L (i.e., 0.3 μg/L). Slightly higher limits apply to antimony (0.0006 mg/L) and cobalt (0.0007 mg/L).

According to Cherevko et al. [24], when RuO₂ electrodes were used to record current-potential curves starting from 1.2 V_RHE and scanned anodically at 10 mV/s up to a current density of 5 mA/cm², dissolved ruthenium levels of approximately 2 and 5 ng/cm² were detected in 0.1 M H₂SO₄ and in 0.05 M NaOH, respectively. Appreciable currents (≥0.5 mA/cm²) were observed only at potentials exceeding ~1.57 V_RHE, with the target current density reached at ~1.63 V_RHE in 0.1 M H₂SO₄, and ~1.66 V_RHE in 0.05 M NaOH. The relevant portion of each scan lasted approximately 6 s in 0.1 M H₂SO₄ and 9 s in 0.05 M NaOH. While it is reasonable to assume that RuO₂ dissolution increases with applied current density, the average dissolution rate can be estimated at 0.333 ng cm⁻² s⁻¹ in 0.1 M H₂SO₄, and 0.556 ng cm⁻² s⁻¹ in 0.05 M NaOH.

In the paper by Atrashkevich and Garcia-Segura [20], the applied current density ranged from 5 to 15 mA/cm², with electrodes having a geometric area of 10 cm² and a studied water flow rate between 0.1 and 0.9 L/min. Even considering ruthenium release in an acidic environment (which is lower than in an alkaline environment), the amount of ruthenium leached into the treated water from a 10 cm² electrode surface is at least 3.33 ng/s. This corresponds to a concentration of 2 μg/L when using the lowest water flow rate and current density reported in the study. Notably, this value exceeds the SPAC limit set in NSF/ANSI/CAN 600 [35] by approximately 6 times and is expected to increase with higher current densities.

In Atrashkevich et al. [9], the authors applied a higher current density of 20 mA/cm² and conducted tests at a flow rate of 0.3 L/min. Even using the previously estimated ruthenium release rate of 3.33 ng/s (based on current densities up to 5 mA/cm²), the resulting concentration in the treated water is approximately 0.67 μg/L—more than twice the SPAC limit.

Yang et al. [18] did not specify the dimensions of their electrodes; however, they used a Ti/IrO₂-RuO₂ anode, which is expected to offer significantly greater stability. According to Cherevko et al. [24], IrO₂ dissolution is two orders of magnitude lower than that of RuO₂.

Based on the above, while the Ti/RuO₂ anode may have appeared to be the most suitable among the three materials studied by Atrashkevich and Garcia-Segura [20]—whose investigation focused only on the potential formation of toxic oxychlorinated species—its use should have been ruled out a priori, as it does not meet the requirements for drinking water system components.

Furthermore, many experiments are conducted at flow rates far below those encountered in real-world applications. For instance, a typical water-efficient showerhead uses around 9 L/min and an older style showerhead up to 20 L/min, whereas many studies test systems at flow rates below 1 L/min. This discrepancy raises questions about the scalability and practicality of the proposed approaches.

Conducting laboratory investigations using devices and experimental setups that do not fully replicate real-world conditions is entirely valid. However, it is essential to clearly acknowledge these limitations. Researchers should be cautious about proposing scale-ups without thoroughly considering—or worse, downplaying—the potential challenges that may arise.

A well-designed drinking water disinfection device must, above all, be safe for contact with water intended for human consumption. This imposes strict limitations on the materials used, which must not leach any substances into the treated water, especially under operating conditions. Additionally, the device must meet the requirements for integration into a drinking water distribution system. For example, in Australia, WaterMark certification is mandatory, meaning the device must withstand a hydrostatic pressure of 20 bar (even though operating pressures rarely exceed 16 bar).

Electrodes must not only be stable and ideally catalytic, but also capable of withstanding periodic polarity reversals. This ensures their long-term usability in water containing reasonable amounts of calcium and magnesium ions. As a result, viable disinfection solutions are largely limited to systems that generate active chlorine, since it appears highly unlikely that a single electrode material could both synthesise hydrogen peroxide and function effectively as an anode.

Since the operating conditions of a real application fluctuate over time (the water flow rate varies according to the user’s demands), it is essential to adjust the current accordingly. Conventional chlorination systems allow for chemical dosing based on water flow rate, and an electrochlorination system must be designed with similar functionality. Therefore, the system should include a flow meter and/or a residual chlorine meter. If the water being treated contains insufficient chloride, small amounts of brine should be dosed where possible. Additionally, the electrochemical process generates gases—oxygen at the anode and hydrogen at the cathode. While these gases disperse safely in the water and do not pose a direct risk, gas accumulation in the pipes can cause hammering effects. To prevent this, an automatic gas release valve may be necessary in the hydraulic system.

Systems with these features are already available on the market, though they are not yet widely known. For example, the eBooster^TM technology developed by Ecas4 Australia (www.ebooster.com.au) utilises a patented reactor available in three different sizes, capable of handling flow rates of up to 800 L/min. For higher flow rates, multiple reactors can be installed in parallel. Installation examples and further details can be found on the company’s website under Resources > Installation.

5. Conclusions

Reviewing articles published in the last 24 months highlights both the potential and challenges of electrochemical disinfection for drinking water treatment. Several critical issues remain unsolved, limiting the practical applicability of many proposed systems.

Many studies focus on laboratory-scale experiments with flow rates and conditions that do not reflect real-world scenarios. This raises concerns about the scalability of these systems.

The use of unstable or toxic electrode materials, such as ruthenium dioxide (RuO₂) or cobalt oxide (Co₃O₄), is a recurring problem. These materials can release harmful substances into the water, violating regulatory limits.

Many electrochemical methods, such as those based on hydrogen peroxide or electroporation, are unable to provide a residual disinfectant effect. Without this, microorganisms can regrow in the distribution network, rendering the disinfection process ineffective.

A significant gap in many studies is the lack of attention to regulatory requirements. Drinking water treatment systems must comply with stringent health and safety standards, such as NSF/ANSI/CAN 61 and 600, which limit the concentration of harmful substances and require that the systems be durable and reliable.

To address these challenges, future research should focus on:

• systems that can handle realistic flow rates and variable water quality, ensuring that the proposed approaches can be integrated into existing infrastructure;
• stable and non-toxic materials;
• methods that provide a residual disinfectant effect to ensure long-lasting protection throughout the distribution network;
• systems that comply with drinking water regulations, including limits on harmful substances and durability requirements;
• long-term testing to evaluate electrode life, scaling potential, and overall system reliability under real-world conditions.