Paracetamol in wastewater: sources, effects, and ozone-based removal strategies

Author: The Conversation

Paracetamol from medicines makes its way into wastewater after human use, with up to around 95% of a dose eventually excreted and degraded through the liver before entering the water cycle. This has led to detectable paracetamol in rivers and lakes worldwide, including the River Thames and various estuaries, often at microgram-per-litre levels. Even though 81% of EU wastewater is collected and treated, current municipal plants are not designed to remove micropollutants like paracetamol. Hospitals also contribute, sometimes disproportionately, to wastewater streams. The EU is moving toward on-site hospital pre-treatment or separate facilities and upgrading large treatment works to use ozonation. However, ozonation has limits: the process is not equally effective for all micropollutants, can increase toxicity in some cases, and may require combining with other treatments. Upgrades are slated for completion by 2045.

Introduction

The article examines how a common analgesic, paracetamol, ends up in water supplies and the implications for aquatic environments. It highlights that only a portion of a drug crosses into the bloodstream after ingestion, while the remainder is excreted in urine. Over roughly a day, most of a paracetamol dose is expelled, with the drug then entering wastewater during routine toilet use. This physical excretion pathway helps explain why paracetamol is increasingly detected in rivers and estuaries around the world, as well as in some lakes in Europe and Asia. The piece situates these findings within a broader concern: wastewater treatment plants, including municipal facilities, are not fully equipped to handle micropollutants at trace levels.

Paracetamol in the environment and sources of input

Paracetamol is released into wastewater from households and hospitals alike. While households are a major source, hospitals contribute volumes of medications that can significantly influence local wastewater composition. In Oslo, hospital wastewater accounted for about 12% of the input to a local wastewater treatment plant—the highest share among tested pharmaceuticals. The article also notes that while urban wastewater treatment helps reduce pollution, the remaining micropollutants still pose ecological risks, particularly to aquatic organisms. In Nairobi river and other Asian waters, paracetamol concentrations have been reported at levels high enough to cause cellular damage in certain organisms such as clams. The broader pattern shows rising concentrations in some regions, driven by increasing pharmaceutical consumption, urbanization, and wastewater flow.

“Paracetamol concentrations in rivers can reach levels that are biologically active for aquatic life,” - Researchers

Wastewater treatment and the challenge of micropollutants

The article explains that although a large fraction of wastewater is collected and treated in the EU, many micropollutants—including paracetamol—still pass through treatment plants and enter natural waters. The term micropollutants refers to trace-level chemicals, often present in concentrations that are nonetheless ecologically relevant. Treatment plants are not yet optimized for such compounds, and the chemical complexity of wastewater makes remediation more difficult than for pure water. The piece emphasizes that concentrations in surface waters have declined since the late 1990s due to improvements in wastewater treatment, but ongoing growth in pharmaceutical consumption could offset those gains if upgrades do not keep pace.

“Ozonation can tackle some micropollutants effectively, but it does not uniformly remove everything in wastewater,” - Researchers

Ozonation as a potential solution and its caveats

Ozonation is presented as a promising technique to address paracetamol and several other micropollutants in wastewater. Ozone reacts with contaminants to degrade them, and paracetamol is among substances that are comparatively easy to remove with this method. However, the technology has limitations. Higher ozone doses are needed in wastewater than in pure water because natural organic matter and other constituents in wastewater scavenge ozone, reducing its availability for target pollutants. This phenomenon, known as ozone-scavenging, increases operational costs. Moreover, some micropollutants respond poorly to ozone and may require additional or alternative treatment steps to achieve complete degradation. The article notes that while ozonation can be effective for paracetamol, other substances—such as certain antihypertensives—may require substantial ozone to degrade fully, and some pollutants (like PFAS) may be resistant to ozonation altogether.

“Ozonation can sometimes even increase toxicity in the wastewater,” - Researchers

The piece also underscores that degradation products formed during ozonation can, in some cases, be more toxic than the original compound, though ozonation can be combined with other processes to mitigate this risk. The overall takeaway is that ozonation is part of a toolkit rather than a stand-alone fix, and its effectiveness depends on the pollutant mix and the configuration of subsequent treatment steps.

Implications for policy, infrastructure, and future directions

The article highlights policy trajectories within the European Union aimed at reducing micropollutant inputs into drinking water. The EU is moving toward upgrading large treatment works and introducing treatment at wastewater plants to tackle paracetamol and other medicines in the water supply, with a goal that these facilities be upgraded by 2045. It also suggests hospital wastewater could be treated on-site or at dedicated facilities to prevent high concentrations from entering municipal sewers. While ozonation offers a path forward for some substances, it is not a universal solution; the cost implications of higher ozone doses and the need for complementary methods require careful planning and investment. The piece concludes that, given rising pharmaceutical consumption, upgrading wastewater treatment infrastructure is essential to maintain clean drinking water and healthy aquatic ecosystems.

“The EU is now working on introducing treatment at wastewater plants to tackle levels of paracetamol and other medicines in the water supply. Large treatment works will need to upgrade their facilities by 2045,” - Researchers