Article Masthead

  • Category: Market Intelligence
  • Topic: Microplastics Monitoring and Source Control
  • Region: Europe
  • Signal Type: Scientific Monitoring Trend
  • Published Date: 2026-09-10
  • Original Source Date: 2026-09-10

01 What Happened

Swiss researchers from Eawag, Empa and Agroscope published the country’s first robust nationwide estimate of microplastic emissions from wastewater treatment plants on September 10. Measurements at 51 WWTPs, serving about 44% of the Swiss population, were extrapolated to estimate that approximately 4.7 tonnes of microplastics larger than 20 µm leave Swiss treatment plants and enter the environment each year.

The study’s most important contribution is methodological. Measuring very low concentrations of free microplastic particles directly in treated effluent is difficult and can produce large uncertainty. The researchers instead analysed activated sludge, where almost all of the measured microplastics larger than 20 µm were attached to sludge flocs. Because WWTPs already quantify the amount of sludge flocs escaping with treated effluent, the team could combine floc discharge with microplastic concentration per floc to estimate total particle loads. Verification tests supported the approach.

The study covered both municipal and industrial WWTPs and found no systematic difference between the two groups, although individual outliers were observed. At one plant, unusually high polypropylene concentrations were linked by the researchers to a PP carrier material used within the treatment process itself.

The nationwide WWTP estimate also changes perspective when compared with another pathway. Parallel work by Empa estimates that around 10 tonnes of microplastics enter Swiss waters each year through atmospheric deposition, roughly twice the load attributed to wastewater treatment plants.

The researchers therefore argue that wastewater treatment can remove a large share of microplastics, but treatment upgrades alone cannot address the full environmental load. Switzerland is adding advanced treatment stages at many WWTPs for pharmaceuticals and pesticides, and the researchers expect these stages to capture additional microplastic particles. Even so, a substantial fraction of emissions occurs upstream of any wastewater plant.

02 Key Takeaways

01 Measurements at 51 WWTPs covering about 44% of the Swiss population produced an estimated national WWTP discharge of 4.7 tonnes of microplastics per year.

02 The researchers used sludge-floc-associated microplastics rather than relying only on direct effluent measurements, improving the robustness of the national estimate.

03 Atmospheric deposition is estimated to deliver about 10 tonnes of microplastics to Swiss waters annually, showing that wastewater treatment is only one pathway.

03 Why It Matters

The significance is not that Swiss WWTPs are ineffective. Most microplastics entering wastewater are retained during treatment and ultimately leave with sewage sludge, which in Switzerland is incinerated. Only a relatively small fraction escapes to receiving waters.

The more important policy question is where intervention produces the largest reduction in environmental load. If atmospheric deposition contributes approximately twice the microplastic load of WWTP effluent, increasingly sophisticated polishing at every plant may produce diminishing returns unless emissions from products, transport, textiles, litter and other diffuse sources are also reduced.

The sampling method is equally important. Microplastics regulation has been hindered by inconsistent methods, particle-size cutoffs and analytical recovery. By linking microplastic concentration to routinely measured sludge-floc loss, the Swiss work offers a more scalable monitoring approach for particles above the study’s 20 µm threshold.

04 ATLAS Engineering View

From an ATLAS engineering perspective, treatment priorities should follow mass pathways rather than public visibility.

Microplastics are easy to associate with wastewater because fibres and fragments visibly enter sewers. But once WWTPs already retain most particles, the largest additional improvement may shift toward source control.

The study also cautions against treating “microplastics” as one engineering contaminant. Particle size, polymer type, density, surface chemistry and attachment to biological flocs all influence removal. The 4.7 tonnes/year estimate applies to the analytical scope of this study, particularly particles above 20 µm; it is not a complete mass balance for nanoplastics or smaller particles.

For plant design, a layered approach is more defensible: optimize solids capture first, evaluate tertiary polishing where receiving-water risk justifies it, and avoid assuming that expensive end-of-pipe treatment can compensate for uncontrolled upstream emissions. The broader trend mirrors PFAS: better monitoring eventually shifts the question from “can treatment remove it?” to “where in the system should control occur?”

05 Sources