Peracetic Acid Emerges as a Safer Rival to Chlorine for Hospital Wastewater

Hospitals are among the most chemically and microbiologically complex sources of wastewater in the modern world. Their effluents carry antibiotic-resistant bacteria, pathogenic microorganisms, pharmaceutical residues, and in some cases radioactive and infectious materials, making them far more hazardous than ordinary domestic sewage. Researchers estimate that hospital wastewater can be five to 150 times more toxic than typical municipal wastewater, yet in many countries there is no specific legislation requiring pre-treatment before these discharges enter public sewer systems. A new study published in the journal Heliyon by Arisa Koga and colleagues at the State University of Maringá in Brazil now provides some of the most detailed evidence yet on how two of the most widely considered disinfectants, sodium hypochlorite and peracetic acid, perform when applied to hospital effluent, and the results point toward a gradual shift in the chemistry of wastewater treatment.

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