Forever chemicals persist through waste incineration, researcher finds

PFAS, often called “forever chemicals,” present in municipal solid waste can survive the high temperatures of waste incineration and continue to spread into the environment via residues from waste-to-energy plants.

A new doctoral thesis from Sofie Björklund, a student at Umeå University’s Industrial Doctoral School, reveals that the most common type of PFAS found in ash, condensate, and flue gases is also the most challenging to capture once they have entered the environment.

The research, initiated by the collaboration partner Umeå Energi, aimed to uncover the fate of PFAS during the handling and incineration of municipal solid waste.

“When we began this project a few years ago, there was very little research on PFAS behavior in large-scale waste-to-energy facilities. Now, an increasing number of studies, including those from our research group, confirm that PFAS are not completely destroyed during incineration and can be found in the byproducts of the process,” says Björklund.

Short-chain PFAS are the most common

The research found that short-chain PFAS were the most common compounds identified, both in the leachate from unburned waste and in the ash, condensate, and flue gases produced during incineration.

“This is concerning because short-chain PFAS are highly mobile in water and difficult to capture once they have entered the environment. What we need to determine next is whether these shorter PFAS are breakdown products of longer-chain PFAS,” says Björklund.

One of the studies in the thesis examined the efficiency of flue gas cleaning in reducing PFAS levels. The results showed that wet flue gas treatment removed an average of 35% of total PFAS, though the effectiveness varied significantly depending on the specific PFAS compounds.

The thesis also highlights that adding 5% of sewage sludge from wastewater treatment plants to regular waste fuel could increase the annual emissions of PFAS from the incineration plant by three to four times compared to burning regular waste alone.

“It’s likely possible to optimize flue gas cleaning to capture even more PFAS. A hazardous waste incineration plant in Belgium has already had success in this area,” says Björklund.

Despite these findings, she notes that waste-to-energy plants are not the sole source of PFAS emissions.

“There are several other major sources, such as firefighting training sites and wastewater treatment plants, which likely contribute significantly more PFAS to the environment. That said, minimizing PFAS emissions wherever possible is critical, as these chemicals persist in the environment indefinitely.”

Exploring breakdown products

Åsa Benckert, senior environmental engineer at Umeå Energi, emphasizes the need for better end-of-life planning for products containing PFAS. When products are brought to market, there’s often no plan for how they will be handled once they become waste. There is still the lack of a full understanding of what happens to different substances in the collection and treatment chain.

“It’s clear that PFAS from consumer products aren’t fully destroyed by current waste management practices. More research is needed to understand exactly what happens during incineration and how we can reduce the spread of these harmful substances,” she says.

The research team plans to expand their studies, focusing on the conditions under which PFAS breakdown might occur and identifying the resulting breakdown products. To support this work, a new doctoral student has joined the group.