Sewage sludge is typically viewed as a costly by-product of wastewater treatment. New research led by Shenyang Agricultural University, in collaboration with Brazilian scientists working with sewage treatment facilities in Rio de Janeiro, suggests it could become a frontline tool in antibiotic monitoring.
Published in Biochar, the study details the development of a disposable electrochemical sensor made from biochar derived from sewage treatment plant sludge collected in Rio de Janeiro. The device is designed to detect trimethoprim, a commonly prescribed antibiotic increasingly detected in environmental waters.
For utilities managing both biosolids and emerging contaminant risk, the work connects sludge valorisation with water quality surveillance.
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Why trimethoprim detection matters for utilities
Trimethoprim is widely used to treat urinary, intestinal and respiratory infections. After human use, residues can pass through sewer networks and wastewater treatment processes, entering rivers, lakes and soils.
Even trace concentrations can contribute to antimicrobial resistance and pose risks to aquatic ecosystems. Monitoring these compounds remains technically demanding, often requiring laboratory-based analytical methods.
Julia Oliveira Fernandes, lead author of the study, said the research team set out to address this barrier.
“Our goal was to create a sensor that is simple, fast, and environmentally responsible.”
Wastewater samples were not the only matrices tested. The sensor was validated using tap water, synthetic urine, and pharmaceutical tablets, achieving recovery rates of 92-99 per cent without sample pretreatment.
Turning sewage sludge into a functional carbon material
The biochar used in the sensor was produced through controlled pyrolysis of sewage sludge from a sewage treatment plant in Rio de Janeiro. Heating at 400°C preserved oxygen-containing surface groups that enhance adsorption and electrochemical activity.
Material characterisation confirmed a mesoporous structure with increased electroactive surface area. Electrochemical testing showed that the biochar-modified electrode significantly reduced charge transfer resistance compared with an unmodified carbon electrode, resulting in stronger and more stable analytical signals.
Fernando Henrique Cincotto, a co-corresponding author and collaborator in Brazil, said the interaction between sludge-derived carbon and the electrode surface drove the performance gain.
“The biochar improves electron transfer and increases the active surface area, which directly boosts sensitivity.”
The device achieved detection limits as low as 71 nanomoles per litre across a broad linear measurement range, with strong selectivity even in the presence of other common compounds such as urea and sulfamethoxazole.
Circular economy potential in wastewater operations
Globally, sewage sludge management remains an operational and regulatory challenge. Landfilling and incineration carry financial and environmental costs, while pressure grows to recover value from biosolids streams.
The researchers argue that converting sludge into functional carbon materials supports circular economy objectives while strengthening environmental monitoring capacity.
“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.
The screen-printed electrodes are inexpensive and designed for single use, reducing the risk of contamination and eliminating the need for recalibration. This makes the platform suitable for decentralised or on-site monitoring.
Although the current study focused on trimethoprim, the research team indicates that the biochar platform could be adapted for other pharmaceuticals and emerging contaminants.
For wastewater utilities, the study demonstrates how biosolids management, materials science, and electrochemical sensing can intersect, offering a pathway in which waste streams directly contribute to improved water quality oversight.