Antibiotics that save lives can also become hidden environmental threats once they leave hospitals and households. A new study reports an innovative solution that transforms sewage waste into a low cost, eco friendly sensor capable of detecting trace levels of the widely used antibiotic trimethoprim in water, urine, and pharmaceutical samples.
Researchers developed a disposable electrochemical device made from biochar produced from sewage treatment plant sludge. The sensor offers a sustainable way to monitor antibiotic pollution while giving new value to a difficult waste material. The study was published in the journal Biochar.
Trimethoprim is commonly prescribed to treat urinary, intestinal, and respiratory infections. After use, the drug can enter wastewater systems and eventually reach rivers, lakes, and soils. Even at very low concentrations, antibiotics in the environment can promote antibiotic resistance and harm aquatic organisms.
"Monitoring these compounds is essential, but many current methods are expensive, slow, and require complex laboratory infrastructure," said lead author Julia Oliveira Fernandes. "Our goal was to create a sensor that is simple, fast, and environmentally responsible."
The key to the device is biochar, a carbon rich material produced by heating organic waste in the absence of oxygen. In this case, the team used sludge collected from a sewage treatment plant in Rio de Janeiro, Brazil. After controlled pyrolysis, the resulting biochar was applied as a nanomaterial coating on screen printed carbon electrodes.
The biochar's porous structure and surface chemistry significantly enhanced the sensor's performance. Laboratory tests showed that the device could detect trimethoprim at concentrations as low as 71 nanomoles per liter, with a wide and reliable measurement range. The sensor also demonstrated high selectivity, meaning it could accurately detect trimethoprim even in the presence of other common compounds such as urea, sulfamethoxazole, and ascorbic acid.
"Our results show a clear synergistic effect between the biochar and the electrochemical electrode," said co corresponding author Fernando Henrique Cincotto. "The biochar improves electron transfer and increases the active surface area, which directly boosts sensitivity."
To demonstrate real world usefulness, the researchers tested the sensor on tap water, synthetic urine, and commercial pharmaceutical tablets. No sample pretreatment was required, and recovery rates ranged from 92 to 99 percent, indicating strong accuracy across different sample types.
Because the electrodes are screen printed, the devices are inexpensive to produce and designed for single use. This reduces contamination risks and eliminates the need for cleaning or recalibration, making the technology suitable for on site monitoring.
Beyond antibiotic detection, the study highlights a broader sustainability benefit. Sewage sludge is produced in large quantities worldwide and is often landfilled or incinerated, practices that can be costly and environmentally harmful. Converting this waste into biochar for high value sensing applications supports circular economy principles and waste reuse.
"This work shows that sewage sludge is not just a problem to be managed, but a resource that can be transformed into advanced functional materials," Fernandes said. "By linking waste management with environmental monitoring, we can address multiple challenges at once."
The researchers believe the platform could be adapted to detect other emerging pollutants, including pharmaceuticals and personal care products. With further development, biochar based sensors could become a practical tool for protecting water quality and public health while reducing environmental waste.
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Journal Reference: Fernandes, J.O., Bernardino, C.A.R., Silva, F.W.L. et al. Disposable eco-friendly electrochemical device for trimethoprim antibiotic determination using biochar from sewage treatment plant sludge. Biochar 8, 7 (2026).
https://doi.org/10.1007/s42773-025-00504-9
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
