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

The research, conducted by Kudzai Mutisi, Baraka Celestin Sempuga and Mabatho Moreroa and published in Case Studies in Chemical and Environmental Engineering, systematically tested how biochar dosage shapes biogas production during the 40-day anaerobic digestion of abattoir effluent. Biochar, produced by heating biomass in the absence of oxygen, is alkaline, porous, and rich in carbon, and it has attracted growing attention as an additive that can stabilise anaerobic digesters. But the literature reveals a puzzling inconsistency: optimal doses reported for other substrates span four orders of magnitude, from fractions of a gram per litre for food waste to more than ten grams per litre for thermophilic co-digestion systems. Whether a dose that works for olive mill wastewater or piggery effluent translates to protein- and fat-laden slaughterhouse wastewater was unknown.

To answer that question, the team collected effluent from a red meat abattoir in Roodeplaat, east of Pretoria, a facility slaughtering roughly twenty cattle and ten sheep daily and discharging its wastewater into an underground concrete reservoir. They characterised a commercial biochar using an arsenal of analytical techniques. Fourier-transform infrared spectroscopy revealed a surface dominated by aromatic carbon structures studded with hydroxyl, carbonyl and ether functional groups, the chemical handles that allow biochar to adsorb inhibitory compounds and exchange cations. Energy-dispersive X-ray spectroscopy showed the material was roughly ninety percent carbon by weight, with smaller amounts of oxygen, calcium, potassium, magnesium and sodium, ash-derived base cations capable of buffering acidity. Scanning electron microscopy exposed brittle, plate-like lamellar particles whose surfaces and inter-particle voids can host microbial biofilms, while X-ray diffraction confirmed a largely amorphous, poorly graphitised carbon structure. The biochar’s pH measured a strongly alkaline 9.51.

The batch digestion experiments were run in an Automated Methane Potential Test System with nine parallel reactors held at a mesophilic 35 degrees Celsius, each fed abattoir effluent inoculated with cow dung and amended with biochar at 0, 2, 4, 8, 30 or 70 grams per litre, all in triplicate. Carbon dioxide was scrubbed chemically so that methane volumes could be measured directly and continuously. The results painted a striking picture of a non-linear dose response. At two grams per litre, the lowest dose tested, cumulative methane reached 2371.9 millilitres, a 30.5 percent increase over the unamended control, while cumulative biogas climbed to 3864.9 millilitres, 43.1 percent above the control. At the opposite extreme, 30 grams per litre delivered essentially the same methane as the control, and 70 grams per litre actually reduced methane output by 3.5 percent. More charcoal, in other words, was emphatically not better.

The chemistry of the digestate helps explain why. Biochar addition lifted the initial substrate pH from an acidic 6.74 into the neutral range favourable for methanogenesis, and it kept digestate pH within a narrow, stable band of roughly 7.3 to 7.5, compared with a drift of more than a full pH unit in the control. Soluble chemical oxygen demand removal, a measure of how much dissolved organic matter the microbes consumed, peaked at 73.14 percent at two grams per litre, well above the control’s 45.32 percent, and fell below the control at the two highest doses. Residual ammonia dropped to its lowest measured level, 21.23 milligrams per litre, at the same optimal dose, and hexane-extractable fats, oils and grease were reduced by 94.4 percent, the best performance of any treatment. Nitrate was undetectable throughout, consistent with the reduced, oxygen-poor chemistry of slaughterhouse wastewater.

Kinetic modelling added a further layer of insight. The researchers fitted first-order, second-order and modified Gompertz models to the cumulative gas curves and found that the modified Gompertz model, which explicitly captures the lag phase before methanogenesis accelerates and the maximum production rate, described the data best, with coefficients of determination approaching 0.999. Biochar shortened the lag phase from 5.17 days in the control to under 3.2 days at two to eight grams per litre, and it raised the apparent first-order rate constant more than fourfold. The time needed to reach half of total methane production fell from about twenty days in the control to fourteen to sixteen days at moderate doses. Interestingly, the fastest kinetics occurred at four grams per litre, while eight grams per litre produced the richest gas, a methane fraction of about 69 percent, even though two grams per litre yielded the greatest total volume.

The authors attribute the benefits at low to moderate doses to a combination of mechanisms that biochar researchers have been assembling over the past decade. Its alkaline ash buffers the pH swings that accompany acid accumulation. Its adsorptive surfaces sequester ammonium, hydrogen sulfide, volatile fatty acids and long-chain fatty acids, the principal inhibitors in protein- and lipid-rich feedstocks. Its lamellar plates provide attachment sites where fermentative bacteria, syntrophic acetogens and methanogenic archaea can cluster in close proximity, potentially enabling direct interspecies electron transfer, a shortcut through which microbes exchange electrons via conductive surfaces rather than diffusing hydrogen. But at 30 to 70 grams per litre these advantages reverse: excessive solids displace active reactor volume, non-selective sorption strips nutrients and soluble substrates away from the microbes, and mass transfer deteriorates under high solids loading.

The practical implications cut in two directions. On one hand, the study positions biochar as a powerful enhancer of the primary anaerobic treatment step, cutting organic load substantially before any polishing stage and reducing the energy and chemical demands of downstream processes. On the other hand, even at the optimum dose the digestate still carried more than one gram per litre of soluble chemical oxygen demand, far above the roughly 75 to 125 milligrams per litre that many jurisdictions permit for direct discharge of industrial effluents. Biochar-amended digestion, the authors caution, is not a complete compliance solution; aerobic polishing, dissolved air flotation, constructed wetlands or membrane bioreactors would still be required to meet discharge standards.

The researchers also acknowledge the limits of their batch-scale evidence. The experiments used a single inoculum, a single commercial biochar and a closed 40-day batch configuration, whereas full-scale digesters operate continuously with mixing, fluctuating loading and long-term biochar ageing that could shift the optimal dose. They recommend follow-up work in continuous reactors, mechanistic monitoring of volatile fatty acids, long-chain fatty acids and microbial community structure to disentangle adsorption and buffering from electron-transfer effects, and integrated treatment trains that pair biochar-enhanced digestion with polishing steps. They further suggest that dosing should be normalised not only per litre of reactor volume but per unit of volatile solids or chemical oxygen demand, and that biochar reuse, sourcing and cost-benefit trade-offs deserve attention before the technology scales.

Even with those caveats, the central message is compelling and likely to resonate well beyond the abattoir sector. In an era when wastewater treatment is increasingly framed as resource recovery rather than disposal, the finding that two grams of biochar per litre, a modest spoonful in reactor terms, can lift methane output by nearly a third while accelerating digestion and stripping inhibitors offers a low-cost, circular-economy-friendly lever. Because biochar can be produced from agricultural residues, and because the amended digestate retains agronomic value, the approach closes loops rather than opening new material streams. For slaughterhouses, food processors and municipal utilities wrestling with fat- and protein-rich effluents, the study suggests that the future of biogas may depend less on adding more of a good thing than on finding, precisely, the smallest dose that does the most.

Subject of Research: Effect of biochar dosage on biogas production during anaerobic digestion of abattoir effluent

Article Title: Evaluating the effect of biochar dosage on biogas production during the anaerobic digestion of biochar-infused abattoir effluent

Article References: Evaluating the effect of biochar dosage on biogas production during the anaerobic digestion of biochar-infused abattoir effluent. (n.d.). https://doi.org/10.1016/j.cscee.2026.101479

Image Credits: AI Generated

DOI: 10.1016/j.cscee.2026.101479

Keywords: biochar, anaerobic digestion, biogas, abattoir effluent, methane, wastewater treatment, chemical oxygen demand, ammonia inhibition, modified Gompertz model, renewable energy, circular economy, long-chain fatty acids

The research, published in Cleaner Engineering and Technology by a team from the Tecnológico Nacional de México led by Bethsabet Jaramillo-Sierra, tackles a contamination problem that spans the globe. Acetaminophen has been detected in wastewater and surface waters on nearly every continent, at concentrations ranging from tens of nanograms per liter in France and Canada to hundreds of micrograms per liter in Colombia and northern Mexico. Although each individual measurement may seem small, the compound’s sheer consumption volume, its availability over the counter, and its resistance to biological degradation mean it accumulates persistently in rivers, drinking water sources, and even treated effluents.

The concern is not merely the presence of the parent molecule. Acetaminophen is poorly biodegradable, so it passes through conventional treatment largely intact, and it has been linked in laboratory studies to genetic damage, oxidative lipid degradation, and liver injury in living organisms. Worse still, during some tertiary treatment steps the compound can transform into by-products that are more dangerous than the original drug, including 1,4-benzoquinone and N-acetyl-p-benzoquinone imine, a hepatotoxic metabolite capable of causing hepatic failure and necrosis. Any credible remediation strategy must therefore do more than hide the molecule; it must destroy it or convert it into harmless end products.

The Mexican team turned to advanced oxidation processes, or AOPs, a family of water treatment methods that operate at ambient temperature and pressure and rely on the generation of highly reactive chemical species, most notably the hydroxyl radical. This radical carries a higher oxidation potential than chlorine and reacts non-selectively with a broad range of organic pollutants, which makes it attractive for treating trace contaminants of many kinds. AOPs also avoid sludge production, do not require adsorbents that need controlled disposal, and can be driven by easily handled reagents such as ozone and hydrogen peroxide, with ozone generated on site from atmospheric air to reduce storage and transport costs.

The experimental apparatus was deliberately simple: a cylindrical stainless-steel reactor with an 11-watt ultraviolet lamp emitting at 200 to 280 nanometers, housed in a quartz tube, coupled to a 12-watt ozone generator and a recirculating reservoir. Synthetic solutions of acetaminophen at 100 milligrams per liter were treated for 60 minutes in 500-milliliter batches, with hydrogen peroxide added at doses of 5, 10, and 15 milligrams per liter. Degradation was tracked by ultraviolet-visible spectrophotometry, chemical oxygen demand was measured colorimetrically, and oxidation by-products were identified using gas chromatography-mass spectrometry following solid-phase extraction.

The results revealed a clear hierarchy of effectiveness. Ultraviolet light alone managed only about 11 percent degradation in an hour, primarily by photolyzing water molecules into hydroxyl radicals and hydrogen atoms, a process that accelerates around the 254-nanometer wavelength. Hydrogen peroxide alone reached roughly 27 percent at the highest dose. Ozone alone, attacking through both direct molecular oxidation and indirect decomposition into hydroxyl radicals, achieved 73 percent. Pairing ozone with ultraviolet light pushed the figure to 84 percent, because photolysis of dissolved ozone generates additional atomic oxygen, hydroxyl radicals, and even hydrogen peroxide in solution, creating multiple parallel destruction pathways.

The real breakthrough came when all three agents were applied simultaneously. The ozone-hydrogen peroxide combination, known as peroxone, promotes hydroxyl radical formation through the mutual reaction of the two oxidants, and adding ultraviolet irradiation on top of this triggered photolysis of both peroxide and dissolved ozone. Under these conditions, with an initial hydrogen peroxide concentration of just 5 milligrams per liter, the team achieved 99 percent acetaminophen degradation in 60 minutes. Notably, the study found an optimal peroxide dose: higher concentrations of 10 and 15 milligrams per liter actually performed worse over time, because excess peroxide and the hydroperoxyl radical it forms act as scavengers, consuming the very hydroxyl radicals that destroy the pollutant.

Chemical analysis confirmed that the combined treatment went beyond mere transformation. Carbon dioxide production rose steadily across the treatment combinations, peaking at 37 milligrams per liter for the triple system, evidence of genuine mineralization rather than simple conversion to other organics. Chemical oxygen demand removal reached 74 percent in the same configuration, compared with just 9 percent for ultraviolet light alone. Color measurements told a parallel story: untreated solutions stayed clear, ultraviolet treatment alone produced a pale carmine tint at 150 platinum-cobalt units as aromatic ring breakdown products accumulated, while the triple system yielded only a faint yellow at 5 units, indicating that even the colored intermediates were being further oxidized. Gas chromatography-mass spectrometry identified by-products dominated by carboxylic acid, ester, and alcohol structures arising from aromatic ring cleavage and recombination, and crucially, the team did not detect hydroquinone or 1,4-benzoquinone, suggesting these hazardous intermediates were themselves degraded during the process.

Energetically, the triple treatment also proved competitive. The researchers calculated the electrical energy per order, a standard metric describing the kilowatt-hours needed to reduce pollutant concentration by one order of magnitude per cubic meter, and obtained 23.00 kilowatt-hours per cubic meter for the peroxide-ozone-UV system, well below the 537 kilowatt-hours per cubic meter required for ultraviolet treatment alone and below several values reported in comparable literature. The estimated operating cost of the best configuration came to 5.04 US dollars per cubic meter, with ultraviolet irradiation dominating the energy bill, ozone generation second, and hydrogen peroxide contributing least. The degradation kinetics followed a pseudo first-order model, with rate constants rising as processes were combined, consistent with the theory that degradation depends primarily on pollutant concentration while oxidant doses remain effectively constant.

Finally, the team assessed whether the treated water was actually safer, using the germination of lettuce seeds as a biological toxicity screen. Untreated and lightly treated samples showed moderate toxicity, with ozone alone inhibiting germination by 40 percent, a sign that oxidative intermediates can be more harmful than the parent drug. But the full triple treatment reduced inhibition to 15 percent, close to the control level, demonstrating that synergistic oxidation both destroys the pollutant and neutralizes its residual toxic footprint. Taken together, the findings position the combined peroxide-ozone-UV process as an operationally simple, reproducible, and relatively inexpensive route to eliminating one of the world’s most ubiquitous pharmaceutical pollutants, though the authors note that complete mineralization would likely require longer treatment times or more intensified oxidative conditions to drive the remaining low-complexity organic by-products all the way to inorganic carbon.

Subject of Research: Degradation of the pharmaceutical pollutant acetaminophen in water using combined advanced oxidation processes involving ozone, hydrogen peroxide, and ultraviolet radiation.

Article Title: Acetaminophen degradation process applying a combination of oxidizing agents and ultraviolet radiation

Article References: Jaramillo-Sierra, B., Mercado-Cabrera, A., Ibañez-Olvera, M., Peña-Eguíluz, R., Rodríguez-Méndez, B. G., & López-Callejas, R. (2026). Acetaminophen degradation process applying a combination of oxidizing agents and ultraviolet radiation. Cleaner Engineering and Technology, 34, Article 101301. https://doi.org/10.1016/j.clet.2026.101301

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101301

Keywords: acetaminophen, paracetamol, advanced oxidation processes, ozone, hydrogen peroxide, ultraviolet radiation, hydroxyl radicals, wastewater treatment, pharmaceutical pollution, water purification, mineralization, chemical oxygen demand