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Published: 2023-06-22

PFAS found in waste incineration residues

NEWS Per- and polyfluoroalkyl substances, PFAS, are not completely degraded in waste incineration and can be found in ashes, process water and flue gases. This is shown in a new study by researchers at the Department of Chemistry, Umeå University. The project is carried out within the Industrial Doctoral School, in collaboration with Umeå Energi.

Text: Sara-Lena Brännström

Per- and polyfluoroalkyl substances, known as PFAS, are a family of thousands of chemicals found in a variety of products such as detergents, cosmetics, cookware with non-stick coating, ski wax, and dirt- and water-repellent textiles and leisurewear. PFAS, sometimes referred to as “forever chemicals”, are very stable and, unlike many other environmental pollutants, also have the ability to disperse with water.

Some PFAS have been linked to reduced birth weight in children, adverse effects on the immune system and elevated cholesterol levels. However, for most of the thousands of PFAS on the market, the effects are unknown.

PFAS in ash, water and flue gases

Products containing PFAS will naturally end up in our waste sooner or later. A previous study from Umeå University has shown that PFAS can leach from waste stockpiles awaiting incineration. Now the same research group has investigated the presence of PFAS in a range of waste incineration residues, such as ash, process water and flue gases. The results, recently published in the journal Environmental Science & Technology, show that PFAS could be found in all the residues analysed.

“The aim of the study was to take a snapshot of how PFAS are distributed in a waste incineration plant,” says Sofie Björklund, a doctoral student at the Department of Chemistry and one of the researchers behind the study, who carried out most of the sampling and analyses. She continues:

“What we found was mostly short PFAS, and they were present in all the residual fractions we examined. What we don't yet know is to what extent these are the result of degradation of other, longer PFAS, or whether it is simply these shorter PFAS that can withstand the high temperatures of waste incineration.

Completely new results

The study, which is the first of its kind, was able to measure and identify PFAS in waste incineration flue gases for the first time.

“Previously, there were no methods for sampling PFAS in flue gases, but as our research group has extensive experience in measuring dioxins in flue gases, we were able to modify our methods to also capture PFAS. Further tests are required to fully adapt the method, but we have been able to establish that PFAS can occur in flue gases from waste incineration, which is completely new,” says Stina Jansson, associate professor at the Department of Chemistry and head of the project.

The researchers also examined the difference between incinerating regular waste and mixing sewage sludge with the waste that was incinerated. They found that the total levels of PFAS leaving the incineration plant per year are 3-4 times higher with the addition of sewage sludge, compared to the incineration of regular waste alone.

“These results are not surprising given that PFAS are well known to be present in sewage sludge. Although there is probably some degradation during incineration, we cannot currently say how much,” says Sofie Björklund.

More research needed

The conditions under which degradation of PFAS can occur and the degradation products that can be formed are currently unknown, but are the subject of future studies. During the year, the research group will hire another doctoral student to investigate in more detail how PFAS are degraded at high temperatures. This project will also be carried out in collaboration with Umeå Energi within the framework of the Industrial Doctoral School at Umeå University.

“With the results obtained so far, we can conclude that PFAS in consumer products do not disappear just because we throw them away. Fortunately, in the not too distant future, the EU may severely restrict the use of PFAS, which will at least limit the inflow. A further investment in research is the way to both knowledge about what actually happens in an incineration plant and how we can reduce the spread of these harmful substances," says Åsa Benckert, senior environmental engineer at Umeå Energi.

Sofie Björklund is conducting her doctoral studies within a collaborative project between Umeå University and Umeå Energi.

About the scientific study

Sofie Björklund, Eva Weidemann, Stina Jansson. Emission of Per- and Polyfluoroalkyl Substances from a Waste-to-Energy Plant─Occurrence in Ashes, Treated Process Water, and First Observation in Flue Gas. Environmental Science & Technology, 2023, DOI: 10.1021/acs.est.2c08960

Read the full article

About the Industrial Doctoral School

The Industrial Doctoral School is an inter-faculty research school that is based on collaboration between Umeå University and an organisation or a company. IDS aims to promote collaboration in order to strengthen research and development, increase the doctoral students’ employability, independence and innovative capacity, and increase knowledge and innovation in society.

Read more about the Industrial Doctoral School

For more information, please contact:

Stina Jansson
Associate professor