Researchers led by Neele Puhlmann and Oliver Olsson of the Institute of Sustainable Chemistry at Leuphana University of Lüneburg, together with colleagues from the Ecologic Institute in Berlin, the Dutch National Institute for Public Health and the Environment (RIVM), and the University of Helsinki, set out to gauge how prepared Europe’s healthcare sector is to embrace so-called “greener” active pharmaceutical ingredients, or APIs. These are drug molecules deliberately designed at the molecular level to combine therapeutic efficacy with inherently lower environmental risk — for instance, by degrading more readily after excretion or by binding less persistently in sediments. The work, published in BMC Health Services Research, forms part of the wider PREMIER initiative, a public-private project funded through the Innovative Medicines Initiative that examines the environmental and health impacts of medicines across their life cycle.

The team conducted semi-structured interviews with 16 healthcare professionals working across Europe between February and April 2024. The deliberately diverse group included three doctors, three pharmacists, three procurement experts, and specialists in reimbursement, market authorisation, healthcare provision and industry sustainability reporting, as well as one professional from an environmental non-governmental organisation. This breadth was central to the study’s design: pharmaceuticals pass through many hands before reaching a patient, and each actor along that chain — from the regulator who approves a drug to the hospital manager who signs a purchasing contract — holds some influence over which molecules ultimately enter the environment. The researchers analysed the transcripts using qualitative content analysis, a systematic method for identifying recurring themes, opportunities and obstacles within unstructured interview data.

The central message emerging from the interviews was one of cautious but genuine enthusiasm. According to the study, there is clear interest among healthcare professionals in minimising the environmental impacts of the medicines they prescribe and purchase. Crucially, this is not merely an abstract sentiment. Some practical strategies already exist, the interviewees noted, such as incorporating environmental criteria into the public tenders issued by procurement agencies. In several European healthcare systems, hospitals and regional authorities purchase medicines through competitive tendering, and adding environmental specifications to those tenders is one of the few immediate levers available without new legislation. The participants expected that environmental properties of APIs will play a more significant role in healthcare decision-making in the future, moving from a niche concern to a standard consideration alongside efficacy, safety and cost.

Yet the study also makes clear that good intentions collide with hard practical constraints. The most frequently voiced obstacle was a lack of reliable scientific data. Healthcare professionals cannot weigh the environmental footprint of one drug against another if manufacturers do not disclose ecotoxicity profiles, persistence and bioaccumulation data in a comparable, accessible form. The interviewees said that access to robust evidence on the environmental impacts of APIs is a prerequisite for any systematic consideration of greenness in prescribing or purchasing decisions. Without such data, environmental criteria risk remaining vague aspirations rather than measurable benchmarks.

A second, equally fundamental barrier is conceptual: how does one balance a molecule’s benefits and risks for patients against its properties in the environment? The researchers found that interviewees considered this balancing act inherently product-specific. A life-saving cancer therapy with few alternatives may justify a heavier environmental burden than, say, a widely prescribed medicine for which greener substitutes exist. This means that a simple “green score” for all pharmaceuticals is unlikely to be appropriate. Instead, the weighing of patient benefit against environmental risk must be embedded in structured, centralised frameworks — something individual prescribers and pharmacists cannot and should not do alone at the bedside or in the pharmacy.

That observation points to the study’s most consequential finding: the marketing authorisation process is viewed as the main intervention point in the pharmaceutical life cycle for strengthening environmental risk considerations. Every medicine sold in Europe must pass through regulatory assessment before it reaches the market, making this the single checkpoint where all stakeholders converge. The interviewees called for legislative and regulatory frameworks, and practical guidance documents, to ensure that environmental properties are assessed and weighed in a centralised and harmonised manner across Europe. A patchwork of national rules, they suggested, would fragment the market and dilute incentives for manufacturers to invest in greener molecular design. The timing is notable, as the European Union’s pharmaceutical legislation is currently undergoing its most substantial revision in two decades, and environmental considerations have featured prominently in the debate.

The authors also identified a plausible pathway from awareness to action. The evident interest among healthcare professionals, they conclude, may stimulate data sharing by pharmaceutical companies in the short term. If procurement agencies, hospital pharmacies and prescribers begin explicitly requesting environmental information, manufacturers will face commercial pressure to publish it. In the long term, this demand signal could cascade upstream into research and development, encouraging medicinal chemists to design APIs that retain their clinical potency while breaking down more readily in wastewater treatment plants or natural waters. This is the essence of sustainable chemistry thinking, championed in the study by co-author Klaus Kümmerer: environmental benignity should be an intrinsic design property of a molecule, not an afterthought remediated at the end of the pipe.

The technical challenges involved should not be understated. Designing a greener API requires balancing multiple molecular properties that often pull in opposite directions. A compound must be stable enough to survive storage, gastric acid and plasma circulation, yet labile enough to degrade once excreted. It must be potent at low doses, which reduces the mass released into the environment, but selective enough to avoid harming non-target organisms. Degradation products themselves must be benign, since transformation in the environment does not guarantee detoxification. Quantitative frameworks for evaluating such trade-offs — combining predictive toxicology, biodegradability screening and environmental fate modelling with traditional pharmacological assessment — are still maturing, which is precisely why the study’s participants emphasised the need for shared evidence and harmonised guidance.

The study’s methodology has clear boundaries that the authors themselves acknowledge. Sixteen interviews cannot capture the full diversity of European healthcare systems, and qualitative content analysis identifies themes rather than measuring their statistical prevalence. The participants were also, by definition, professionals interested enough in the topic to discuss it, which may inflate the apparent enthusiasm. Nevertheless, the qualitative approach is well suited to mapping the decision landscape: it reveals how actors reason, where they feel empowered or blocked, and which interventions they consider legitimate. The authors explicitly conclude that future research should target the barriers identified and their potential solutions, translating the expressed willingness into concrete instruments — validated environmental criteria for tenders, standardised data formats from industry, and regulatory guidance for market authorisation.

What makes the study resonate beyond academic circles is its reframing of responsibility. Pharmaceutical pollution has often been portrayed as a problem of individual behaviour — patients flushing unused medicines — or of inadequate wastewater technology. This research shifts the focus to the professionals and institutions that decide which medicines enter the market and the clinic. Doctors, pharmacists, procurement officers and regulators collectively wield enormous leverage, and the study suggests they are prepared to use it. The transition to greener APIs will ultimately be won or lost in the chemistry itself, but the demand side, this research shows, is no longer waiting passively. If Europe’s regulatory reform aligns with the appetite its healthcare professionals have expressed, the next generation of medicines may be designed not only to heal patients, but to spare the environment that receives them.

The comprehensive study, recently published in the prestigious journal Nature Water, estimates that U.S. wastewater treatment plants alone are responsible for emitting the equivalent of approximately 47 million metric tons of CO2 annually. Crucially, the research highlights that methane (CH4) and nitrous oxide (N2O)—two greenhouse gases far more potent than CO2 in terms of global warming potential—account for a disproportionately large share of these emissions. Methane and nitrous oxide contributions exceed current governmental estimates by about 41%, reshaping our understanding of the sector’s true environmental footprint.

Jennifer Dunn, a professor of chemical and biological engineering at Northwestern University’s McCormick School of Engineering and the study’s senior author, remarked on the significance of these emissions. She noted that detecting methane and nitrous oxide as dominant factors was both surprising and critical, given that previous assessments underestimated their prevalence. These potent greenhouse gases derive largely from the biological and chemical processes that wastewater treatment plants use to purify water, revealing emission sources that were insufficiently accounted for in traditional carbon-centric climate models.

This reassessment of wastewater treatment’s environmental impact opens a new window into climate mitigation potential. Rather than being solely a constraint, the study suggests the sector contains “low-hanging-fruit” opportunities to reduce emissions. Some emissions result from relatively addressable issues like leaks in anaerobic digesters, while others require innovative technology development to fundamentally transform nitrogen treatment and energy harvesting approaches within plants. Dunn emphasized that identifying these leverage points is crucial for aligning wastewater treatment with broader decarbonization goals.

Wastewater treatment involves multiple stages, within which wastewater’s solids, or sewage sludge, are broken down using various biological processes. A common method involves anaerobic digestion, where microorganisms metabolize organic material without oxygen and produce biogas dominated by methane. However, the process carries a significant drawback: methane leakage. Despite biogas’s potential as a renewable energy source, unintended emissions from leaks can negate the environmental benefits of onsite energy recovery systems.

The study brings to light the troubling reality that many anaerobic digesters leak significant amounts of methane into the atmosphere. Dunn explained that while these leaks can be severe, they are fundamentally fixable through improved monitoring, maintenance, and design enhancements. Such mitigation strategies represent immediate and cost-effective emissions reduction options that wastewater treatment operators can implement without requiring major infrastructure overhauls.

Another critical but often overlooked greenhouse gas associated with wastewater treatment is nitrous oxide. This gas primarily arises from the processes used to remove nitrogen from wastewater, especially nitrification-denitrification. Nitrogen removal is crucial to prevent eutrophication—a phenomenon where excess nutrients cause harmful algal blooms and oxygen depletion in freshwater ecosystems. However, conventional nitrogen removal technologies inadvertently release nitrous oxide, a greenhouse gas with nearly 300 times the global warming potential of CO2.

While nitrification-denitrification remains the dominant method for nitrogen removal, it is energy-intensive and presents climate trade-offs due to its nitrous oxide emissions. Alternative technologies that aim to recover nitrogen before it escapes into the atmosphere offer promise. For example, methods that can capture nitrogen directly from wastewater and convert it into valuable products such as fertilizer or animal feed could simultaneously reduce greenhouse gas emissions and support circular economic models. Such innovations would close the nitrogen cycle, turning wastewater treatment plants from emission sources into carbon and nutrient resource hubs.

To achieve these advances, the research team is collaborating extensively with wastewater treatment facilities to gather high-resolution, plant-specific emissions data. They are also refining an open-source modeling tool designed to help operators quantify and manage their greenhouse gas emissions across the entire wastewater treatment lifecycle. This tool integrates emissions from onsite biological processes, energy and chemical input production, and waste disposal stages, providing a holistic evaluation framework that can guide decarbonization strategies tailored to individual plants.

The team’s approach not only aids municipalities with climate action plans looking to reduce their carbon footprints but also establishes a scalable methodology adaptable to treatment plants worldwide. Despite the study’s focus on U.S. facilities, its underlying principles and modeling tools can be applied globally, aiding regions with growing populations and expanding sanitation infrastructure. As cities and countries strive to meet ambitious climate targets, addressing emissions from wastewater systems emerges as a vital yet often neglected sector in the decarbonization landscape.

Given the expanding scale of wastewater treatment services—with public sanitary coverage reaching billions of people globally—the environmental impact and mitigation potential of the sector cannot be ignored. Dunn underscored the urgency, stating that wastewater treatment is a substantial sector “that needs attention.” She highlighted the pressing need for continued research, innovation, and policy support focused on reducing methane leaks, minimizing nitrous oxide emissions, and developing sustainable nutrient recovery technologies.

Ultimately, this landmark study reshapes the conversation about wastewater treatment’s role in climate change. It moves beyond simplistic CO2 metrics to account for potent methane and nitrous oxide emissions, directly linking operational processes to climate outcomes. The integration of new data, innovative modeling, and practical mitigation strategies provides a pathway toward a more sustainable and resilient future for water infrastructure worldwide.

As wastewater treatment plants pivot toward cleaner, more efficient operations, their evolution could serve as a blueprint for industrial sectors tackling indirect emissions and resource circularity. Investing in targeted research, adopting best practices, and deploying cutting-edge technologies will be instrumental in minimizing the concealed climate costs of one of society’s essential public services. With coordinated global efforts, the environmental legacy of wastewater treatment can shift from a climate liability to a model of sustainable environmental stewardship.

Subject of Research: Greenhouse gas emissions from wastewater treatment plants and their implications for climate change mitigation

Article Title: Benchmarking greenhouse gas emissions from US wastewater treatment for targeted reduction

News Publication Date: 8-Oct-2025

Web References:

• Original article: https://www.nature.com/articles/s44221-025-00485-w
• Northwestern Center for Engineering Sustainability and Resilience: https://www.engineeringsustainability.northwestern.edu/
• QSDSAN open-source tool: https://qsdsan.com/
• Northwestern fertilizer research: https://news.northwestern.edu/stories/2023/09/hybrid-catalyst-produces-critical-fertilizer-and-cleans-wastewater/

Keywords: Wastewater, Water, Climate change, Greenhouse gases