Electrochemical generation of sodium hypochlorite is conceptually straightforward. When a sodium chloride brine is electrolyzed, chloride ions are oxidized at the anode to produce chlorine gas, which hydrolyzes in water to form hypochlorous acid and, in the bulk solution, hypochlorite. Meanwhile, water is reduced at the cathode, generating hydrogen gas and hydroxide ions that combine with the hypochlorite to yield sodium hypochlorite. The overall reaction can be written in simplified form as NaCl plus H2O yielding NaOCl plus H2. In practice, however, the process is riddled with competing pathways. Oxygen evolution at the anode steals electrons that should go to chlorine production, hypochlorite decomposes chemically, chlorine can volatilize out of solution, and elevated voltages drive secondary oxidation to chlorate. The efficiency of the whole enterprise therefore hinges on the electrode material and the geometry of the cell.

The industrial gold standard is the dimensionally stable anode, or DSA: a titanium substrate coated with mixed metal oxides such as ruthenium and iridium dioxide. These anodes achieve current efficiencies above 90 percent and last for years, but they are expensive and often inaccessible in the decentralized, resource-limited settings where on-site generation would be most valuable. Recent research has pushed the frontier further with titanium suboxide architectures, cost-efficient Ti–V–Sn–Sb electrodes, and even high-entropy alloy nanowires capable of selective chlorine evolution from seawater. What has been missing, the Ghanaian team argues, is something more mundane but arguably more practical: a fair, side-by-side comparison of the cheap, widely available materials that a workshop in a rural clinic or a small water utility could actually obtain.

That gap matters because most published electrochlorination studies examine a single electrode material under its own idiosyncratic conditions: different reactor geometries, electrolyte concentrations, hydrodynamics, and voltages. Differences in reported performance may therefore reflect the operating conditions rather than the intrinsic properties of the material. To eliminate this confounding, Samuel Kofi Tulashie and colleagues evaluated five accessible non-DSA materials—aluminum, copper, graphite, stainless steel, and platinum—under strictly identical conditions. Each material served as both anode and cathode in a membrane-less, stirred 250-milliliter batch cell containing 20 grams per liter of sodium chloride at near-neutral pH of 7.02. The team systematically varied the electrode spacing from 4 to 10 centimeters and the applied voltage from 6 to 12 volts, running each electrolysis for 40 minutes and quantifying accumulated free chlorine by iodometric titration at 10-minute intervals.

The first finding concerns geometry. Reducing the electrode spacing from 10 to 8 centimeters increased free chlorine formation for every material tested, an effect the authors attribute to reduced ohmic resistance in the solution, which lowers the required cell potential and increases the effective current delivered at a fixed applied voltage. But the trend did not continue monotonically. Shrinking the gap further to 6 and then 4 centimeters actually reduced free chlorine output, even though output at those spacings still exceeded the 10-centimeter case. The maximum at 8 centimeters suggests a sweet spot where electrical, mass-transport, and hydrodynamic effects are favorably balanced. Below the optimum, the researchers propose, concentration polarization and non-uniform current distributions may intensify competing side reactions, while the chlorine and oxygen bubbles generated at the electrodes can crowd together, partially blocking active sites and disrupting electrolyte flow. The authors are careful to note that bubble dynamics were not directly measured, so these explanations remain plausible interpretations rather than demonstrated mechanisms.

When it came to the materials themselves, graphite emerged as the clear winner, accumulating approximately 189 milligrams per liter of free chlorine after 40 minutes—the highest of any electrode. Stainless steel followed at roughly 156 milligrams per liter, copper at about 89, aluminum at about 75, and platinum, remarkably, brought up the rear at around 71 milligrams per liter. The graphite result is consistent with a growing literature on carbon-based electrochlorination and makes physical sense: graphite surfaces are relatively inert toward active chlorine, limiting catalytic decomposition and allowing hypochlorite to accumulate. Stainless steel performed well because the mixed iron-chromium oxide layers that form during anodic polarization remain sufficiently stable under these conditions to sustain chlorine production before extensive passivation sets in.

The underperformance of aluminum and copper tells a cautionary tale about corrosion. Under anodic polarization in chloride-rich electrolyte, copper readily forms Cu+ and Cu2+ species, while aluminum undergoes localized pitting corrosion once its passive oxide layer breaks down. Dissolved metal ions are known catalysts for active chlorine decomposition through redox cycling, so these electrodes effectively destroy the very product they generate. The modest, near-linear rise in free chlorine over time for these materials suggests that generation and decomposition proceeded simultaneously throughout the electrolysis. Platinum’s poor showing is more subtle and, in its way, more instructive. The noble metal sustained the highest current densities across the entire voltage range, yet converted only a small fraction of that charge into measurable free chlorine. The likely culprit is the competing oxygen evolution reaction, which on platinum diverts electrons away from chloride oxidation. The lesson is blunt: pushing more current through a cell does not guarantee more disinfectant.

To quantify this, the team calculated absolute Faradaic efficiencies for free chlorine formation, relating the moles of product to the total charge passed. For all electrodes, efficiency decreased as applied voltage rose, indicating that progressively more of the electrical charge was lost to parasitic pathways—oxygen evolution, chlorine volatilization, hypochlorite decomposition, corrosion reactions, and chlorate formation. Graphite and stainless steel posted the highest efficiencies across the voltage range, confirming their superior charge utilization, while platinum, aluminum, and copper lagged substantially. For the corroding metals, anodic dissolution itself consumed charge that should have gone to chlorine production. The authors emphasize that these figures represent system-level charge utilization rather than intrinsic chlorine-evolution selectivity, since iodometric titration measures total free chlorine without distinguishing species or accounting for oxychlorine by-products.

The study is candid about its limitations, which is part of what makes it useful. The experiments captured only short-duration performance in an undivided batch cell; long-term electrode stability, chlorate and perchlorate formation, specific energy consumption, and lifecycle cost were all beyond scope. Electrode geometries differed—flat plates for the metals, cylindrical rods for graphite and platinum—and the constant-voltage operation without a reference electrode means the results should be read as comparative system benchmarks, not intrinsic electrocatalytic rankings. Minor chlorine loss to the headspace of the open, stirred reactor may also have introduced a small negative bias. The authors call for future work with geometrically identical electrodes under constant-current conditions, extended operation, cyclic voltammetry, impedance spectroscopy, and techno-economic assessment.

Even with those caveats, the practical message is striking. Two of the cheapest, most universally available materials on the planet—graphite and stainless steel—delivered the best combination of disinfectant output and charge efficiency, outperforming platinum under these conditions. For communities and small utilities considering decentralized electrochlorination, where titanium-based DSAs may be unavailable or economically prohibitive, that is genuinely good news. It suggests that the barrier to safe, locally produced disinfectant is not exotic materials science but careful engineering of the cells we can already build, with the right electrode gap, the right voltage, and the right pair of humble electrodes immersed in salt water.

Subject of Research: Benchmarking of low-cost electrode materials for electrochemical sodium hypochlorite generation

Article Title: Benchmarking accessible electrode materials for electrochemical sodium hypochlorite production

Article References: Tulashie, S. K., Atiiga, A.-W. I., Mensah, S., Teye, S. O., Arkorful, R., Iddrisu, M., Olorunyomi, M. O., Nsiah, F., Zugle, R., Alimoh, G., Adukpo, G., & Koomson, S. (2026). Benchmarking accessible electrode materials for electrochemical sodium hypochlorite production. Discover Electrochemistry, 3(1), Article 64. https://doi.org/10.1007/s44373-026-00152-z

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00152-z

Keywords: sodium hypochlorite, electrochlorination, graphite electrode, stainless steel, platinum, Faradaic efficiency, chlorine evolution, on-site disinfection, electrode spacing, water treatment, decentralized systems, electrochemistry

The team’s central concern was the formation of disinfection by-products. Chlorination remains the most common disinfection method worldwide because it is cheap, simple, and provides a lasting protective residual, but chlorine reacts vigorously with the dissolved organic matter that hospital effluents contain in abundance. These reactions generate organic acids, aldehydes, and trihalomethanes, compounds with documented risks to aquatic ecosystems and human health. Peracetic acid, by contrast, is a broad-spectrum antimicrobial oxidant that decomposes into water and acetic acid, by-products considered harmless to aquatic life. Its global market is projected to grow faster than any other water treatment disinfectant, and the study set out to test whether that enthusiasm is scientifically justified when pharmaceuticals such as antibiotics are present in the water.

To answer the question under controlled and reproducible conditions, the researchers prepared a synthetic hospital wastewater based on a published formulation containing carbohydrates, proteins, salts, and organic matter at concentrations resembling real hospital discharges. The mixture included glucose, sodium carbonate, ammonium sulfate, potassium phosphate, and trace metals, and yielded an average chemical oxygen demand of roughly 1044 milligrams per liter and a pH of about 9.38, values consistent with published characterizations of actual hospital effluents from Brazil, China, India, Iran, Turkey, Benin, and Vietnam. The team then inoculated the synthetic effluent with Escherichia coli at approximately 10^5 colony-forming units per milliliter, a level reported in real hospital wastewater, using the standard ATCC 25922 reference strain as an indicator organism.

The experimental design was deliberately rigorous. A full factorial experiment crossed two disinfectants, the presence or absence of the antibiotic amoxicillin, two disinfectant concentrations of 5 and 15 milligrams per liter, and two contact times of 5 and 15 minutes, producing sixteen treatments that were each run in triplicate for a total of 48 samples. Amoxicillin was selected because of its widespread clinical use and frequent detection in hospital effluents, and was added at 23.58 milligrams per liter to match concentrations measured in real wastewater by other researchers. Statistical analysis using one-way ANOVA followed by Tukey’s post hoc tests identified significant differences among treatments for chemical oxygen demand, pH, residual disinfectant concentrations, and bacterial removal efficiency.

The microbiological results were strikingly clear: both disinfectants substantially reduced E. coli across all conditions, and the highest doses delivered reductions exceeding four logarithmic units, equivalent to inactivating more than 99.99 percent of the bacteria. The single best performance came from sodium hypochlorite at 15 milligrams per liter over 15 minutes, which achieved a 5.28 log reduction with a calculated C·t value of 48.30 milligram-minutes per liter. Peracetic acid at the same dose achieved reductions of 5.15 and 4.73 logs. Even the weakest treatments, peracetic acid at 5 milligrams per liter, delivered reductions approaching three logs. These findings align with earlier work showing that peracetic acid can match or exceed chlorine in inactivating E. coli, coliphages, and Clostridium perfringens in water with high organic content, and even methicillin-resistant Staphylococcus aureus in hospital surface disinfection studies.

The chemistry told a more nuanced story. Every treatment produced a measurable rise in chemical oxygen demand relative to the raw effluent, because both oxidants convert recalcitrant organic compounds into more biodegradable forms that still register in the COD assay. Notably, samples containing amoxicillin consistently showed higher COD values than their drug-free counterparts, and the largest increase, reaching 1066.5 milligrams per liter, occurred when amoxicillin-laced effluent was treated with 15 milligrams per liter sodium hypochlorite for 15 minutes. This suggests that even a single antibiotic can measurably alter the behavior and by-product profile of disinfection, a factor that most treatment studies do not account for. All treatments also lowered the pH of the alkaline synthetic effluent, with the largest drops observed in the highest-dose chlorination runs, a pattern consistent with the known tendency of trihalomethane formation to increase at elevated pH.

Residual chemistry raised additional red flags for chlorine. Treatments using 15 milligrams per liter of sodium hypochlorite left total and free residual chlorine concentrations exceeding the 2 milligrams per liter discharge limit enforced by the local sanitation utility, and above the free chlorine range of 0.09 to 0.55 milligrams per liter measured in real hospital effluents by earlier investigators. Residual chlorine is toxic to aquatic organisms and can select for chlorine-resistant bacteria and propagate antibiotic resistance genes in downstream treatment plants. The researchers specifically tested for chloroform, the dominant trihalomethane typically produced during chlorination, in two high-dose samples, but concentrations fell below the analytical quantification limit of 0.005 milligrams per liter. The authors caution, however, that their synthetic matrix lacks the recalcitrant compounds found in real hospital effluent, where chlorination can generate haloacetic acids, haloacetonitriles, haloketones, trichloronitromethane, and chloral hydrate.

Peracetic acid residuals behaved predictably, with higher doses leaving higher residuals, and organic matter consuming much of the disinfectant within the first five minutes of contact, echoing prior observations that organic compounds demand peracetic acid rapidly while inorganic constituents such as iron consume it more slowly over about an hour. From an economic standpoint, the study notes that although peracetic acid has historically been more expensive than chlorine, its self-decomposing nature eliminates costly dechlorination steps, and its lower doses and shorter contact times can generate operational savings. The global peracetic acid market is projected to reach 1.3 billion dollars by 2026, with the wastewater segment growing at roughly eight percent annually, and combined peracetic acid followed by chlorine dosing has shown promise at full scale for facilities seeking better disinfection compliance.

The authors conclude that peracetic acid is a credible alternative to chlorination for hospital wastewater pre-treatment, offering comparable E. coli inactivation while producing by-products that do not harm the environment. They emphasize, however, that their work was conducted on synthetic effluent under controlled laboratory conditions, and that further studies using real hospital wastewater are needed to confirm the findings and fully characterize by-product formation. They also call for research into the toxic potential of hospital effluents, particularly in Brazil, where no specific legislation establishes discharge standards for hospital effluents entering public sanitary sewer systems. As concerns about antibiotic resistance and pharmaceutical pollution intensify worldwide, the humble choice of a disinfectant chemical may prove to be one of the most consequential decisions a hospital can make about its environmental footprint.

Subject of Research: Comparative evaluation of sodium hypochlorite and peracetic acid for disinfecting synthetic hospital wastewater and controlling disinfection by-products

Article Title: Evaluation of sodium hypochlorite and peracetic acid for disinfection of synthetic hospital wastewater

Article References: Koga, A., dos Santos, D. F., Martins, D. C. C., de Oliveira, L. T., de Abreu Filho, B. A., Benatti, C. T., & de Barros, M. A. S. D. (2026). Evaluation of sodium hypochlorite and peracetic acid for disinfection of synthetic hospital wastewater. Heliyon, 12(15), Article e45429. https://doi.org/10.1016/j.heliyon.2026.e45429

Image Credits: AI Generated

DOI: 10.1016/j.heliyon.2026.e45429

Keywords: hospital wastewater, disinfection, peracetic acid, sodium hypochlorite, E. coli, disinfection by-products, trihalomethanes, amoxicillin, chemical oxygen demand, antibiotic resistance, wastewater treatment, Heliyon

The wastewater at the heart of the study came straight from the dyeing process outlet of a textile factory in Isfahan, in central Iran, and it was as dirty as the researchers expected. Chemical oxygen demand, a measure of organic pollution, stood at 8100 milligrams per liter, roughly 135 times the permissible limit for discharge to surface water in Iran. Color intensity registered 23,480 platinum-cobalt units, turbidity 620 nephelometric turbidity units, and total suspended solids 3890 milligrams per liter. Elemental analysis added another layer of concern. The effluent carried 5500 micrograms per liter of aluminum, 5300 of iron, an extraordinary 4200 of the toxic metal thallium, along with antimony, manganese, zinc, copper and lead at levels far above natural background. In Iran only about 20 percent of industrial effluents receive proper treatment before discharge, so the stakes for finding an affordable, effective recipe are high.

Polyaluminum chloride, or PACl, has become a favored coagulant in water treatment because it works across a wide pH range, forms dense and fast-settling flocs and produces less sludge than traditional alum. It is sold in both powdered and liquid form, and the two differ in ways that matter to plant operators. The powdered grade used here contained 28.05 percent aluminum oxide, more than double the 10.48 percent of the liquid grade, but liquid PACl arrives ready to dose, skipping on-site dissolution. The researchers optimized each coagulant independently through standard jar tests on 1-liter samples, defining the optimum as the minimum dose that pushed residual turbidity to 20 NTU or below with the smallest settled sludge volume. Powdered PACl settled on 0.7 grams per liter while liquid PACl required 3.0 milliliters per liter. Every scenario also received sodium hypochlorite at 75 milliliters per liter, chosen because color removal plateaued beyond that dose, and calcium oxide at 1.0 gram per liter, enough to push pH above 10.5 so that dissolved metals could precipitate as hydroxides.

Five treatment configurations were tested in triplicate. The first used powdered PACl, the second liquid PACl, the third a blend of the two, and the fourth and fifth replaced commercial coagulant entirely, or nearly so, with clarifier sludge collected from a local drinking water plant that itself uses PACl. The idea behind the sludge experiments was elegantly circular: the sedimentation basin sludge contains residual polyaluminum chloride and amorphous aluminum hydroxides, so it might act as a free, waste-derived coagulant that simultaneously reduces chemical purchases and diverts waste from landfills. The sludge was mixed into wastewater at a ratio of one part sludge to five parts effluent, the ratio that preliminary trials showed produced maximum floc formation. For the fifth scenario, a modest half-milliliter dose of liquid PACl was added on top of the sludge to test whether virgin and recycled coagulants could work synergistically.

The results split the metals into two camps. Zinc and chromium were the consistent success stories, removed at better than 96 percent in every configuration, with residual zinc concentrations falling below 0.2 micrograms per liter in most scenarios. Thallium, iron, manganese and silicon also dropped by more than 98 percent in the liquid and mixed PACl scenarios. Barium and strontium, by contrast, proved stubbornly recalcitrant, with strontium removal never exceeding 33 percent anywhere in the study, marking these two elements as priority targets for future work. Most striking was the fate of aluminum itself. Clarifier sludge alone removed 99.8 percent of aluminum, the best figure of any scenario, and near-complete removal of lithium and barium besides. But in the fifth scenario, where a small PACl dose was layered onto the sludge, aluminum removal collapsed to zero, and the treated water actually carried more aluminum than the mixed inlet, 4800 micrograms per liter against 4567 going in.

That counterintuitive collapse points to a phenomenon known as overdosing or charge reversal. Coagulants work by neutralizing the negative charges that keep colloidal particles suspended, and beyond the optimum dose the excess positive charge can flip particle surfaces back to a stable, restabilized state, re-suspending material that had already clumped. The sludge, already laden with residual aluminum hydroxides, plus the added PACl apparently tipped the system past that threshold. The authors caution that they did not measure zeta potential, so the mechanism remains a hypothesis, but the practical lessons are unambiguous: more coagulant is not better, combining waste-derived and virgin coagulants without re-optimization can backfire, and fixed-dose recipes are inadequate for wastewater whose composition shifts from batch to batch.

On the conventional pollutants, the combined PACl scenario proved the most robust all-rounder, cutting chemical oxygen demand by 95 percent to a residual 380 milligrams per liter and turbidity by 95 percent, while removing nearly 97 percent of suspended solids. Clarifier sludge alone, despite its dazzling color removal of 99.6 percent, managed only 19.8 percent turbidity removal and 79.9 percent for chemical oxygen demand, confirming that recycled sludge cannot substitute for commercial coagulant on high-strength textile effluent. Electrical conductivity rose in every scenario because calcium oxide and PACl both add dissolved ions, and final pH ranged from 10.74 to 12.51, values that would require neutralization before any discharge or reuse.

The study’s most distinctive move was its scoring system. Rather than ranking treatments by individual removal percentages, the team calculated the grey water footprint, an indicator that translates each pollutant load into the volume of freshwater needed to dilute it to regulatory limits. The critical pollutant for the raw effluent was chemical oxygen demand, driving a footprint of 121,500 cubic meters per month at the facility’s assumed discharge of 750 cubic meters per month, meaning the factory’s pollution load would demand dilution water more than 160 times its own flow. Liquid PACl delivered the best outcome: a 92.96 percent reduction in the footprint, statistically the top performance by analysis of variance, with the combined PACl scenario statistically comparable at 90.85 percent and powdered PACl at 88.27 percent. The sludge-only scenario ranked last at 83.33 percent, despite its standout aluminum and color numbers, because its weak performance on organic matter and turbidity dominated the overall environmental burden.

The grey water footprint also exposed a hidden bottleneck that conventional single-parameter assessment would have missed. In the combined PACl scenario, chemical oxygen demand was cut so effectively that antimony, with only 49 percent removal, quietly became the limiting pollutant, its footprint climbing above the organic load’s. Optimizing one pollutant, in other words, can mask the factor that actually constrains environmental performance. The researchers argue that the metric offers an objective common currency for comparing heterogeneous treatment trains, and note that their chemically enhanced primary treatment approached the footprint reductions typically associated with secondary biological processes such as activated sludge.

For plant operators, the study lands on a concrete protocol: liquid PACl at 3.0 milliliters per liter, sodium hypochlorite at 3750 milligrams per liter of active chlorine, and calcium oxide at 1.0 gram per liter, a combination that cut the grey water footprint by 93 percent while stripping more than 99 percent of thallium and zinc. Clarifier sludge, meanwhile, earns a narrower but genuine role as a free, selective coagulant aid for specific targets such as aluminum and color, and as a landfill-diversion strategy, so long as its dose is optimized independently and its reactive aluminum content is properly characterized. The authors flag open questions, including chlorinated byproducts from hypochlorite oxidation, the economics of full-scale deployment, and the mechanistic differences between PACl formulations, but the headline conclusion stands: when environmental impact is tallied honestly across every pollutant, the liquid form of a familiar coagulant is the strongest tool yet tested for taming textile wastewater.

Subject of Research: Comparative evaluation of PACl coagulant variants and recycled clarifier sludge for treating real textile wastewater using the grey water footprint metric

Article Title: Comparative assessment of PACl variants and clarifier sludge for textile wastewater treatment: A grey water footprint approach

Article References: Tabandeh, L., Arastou, K., & Ebrahimi, A. (2026). Comparative assessment of PACl variants and clarifier sludge for textile wastewater treatment: A grey water footprint approach. Cleaner Engineering and Technology, 34, Article 101319. https://doi.org/10.1016/j.clet.2026.101319

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101319

Keywords: textile wastewater, polyaluminum chloride, grey water footprint, coagulation-flocculation, clarifier sludge, heavy metal removal, chemical oxygen demand, sodium hypochlorite, calcium oxide, circular economy, water treatment, industrial effluent