Forever Chemicals and WtE : “PFAS are present in waste because of their extensive use in our societies”

Could you summarize the main findings of your study on PFAS in WtE facilities?

In brief, we found PFAS (Σ18) in some of the residue streams (bottom ash, treated process water, and flue gas) during incineration of “normal” municipal solid waste (MSW). When a PFAS‐laden fuel (municipal wastewater treatment sludge) was co‐incinerated with the MSW, the concentration increased, and we found PFAS in all the residue streams that we analyzed.

 We also found that the wet flue gas cleaning seemed to transfer PFAS from the flue gas stream into the in‐house process water treatment, at least when the condensate scrubber was in use. The summarized amounts of PFAS found in the residues were less than those found in the runoff waters from the fuel storage, and in relation to the amount of incinerated waste, we made an estimation that less PFAS remain after incineration than prior to incineration.

It must be emphasized that our study reports on the findings of 18 individual PFAS, which is a small subset of the huge family of PFAS which exceeds 10,000 individual substances (or up to 7 million, if you use the OECD definition). There are many unanswered questions regarding PFAS in waste and in the environment, and the current knowledge within the scientific community on what degradation products can be expected from PFAS in incineration processes, or the environmental burden they carry, is very limited. We are only in the very beginning of exploring the research field of the fate of PFAS in waste incineration, and it is a bit like looking into a large room with a weak flashlight, finding a spider in the corner but not seeing the wolf behind us. Are we even analyzing for and assessing the most relevant PFAS substances from an environmental and/or human health perspective? To be frank, the only fact regarding PFAS degradation that holds general consensus is that degrading PFAS seems to end up as trifluoroacetic acid (TFA). TFA is extremely hard to remediate due to its small molecular size and high water solubility and degrades very slowly.

What we also know is that PFAS are present in waste because of their extensive use in our societies, and their presence in waste means that they will end up in waste management processes such as WtE. This is an inevitable effect of our production and consumption habits.

MSW is not a product of a waste handling process, it is a product (and a mirror) of the society that generates the waste. Unlike dioxins, for example, PFAS do not originate from the waste-handling process (as dioxins do in incineration or composting); they enter the WtE plant as a contaminant in the waste. Therefore, regardless of the chosen waste management methodology, removing PFAS from products and materials that end up as waste is undoubtedly the most beneficial approach for the environment and human health.

Related article: PFAS in Waste-to-Energy facilities: A burning question

How should WtE facilities manage these PFAS‐laden residues to prevent environmental contamination?

In our investigation, the PFAS ended up in bottom ash, flue gas, and treated water. It is very difficult to say how the residual streams should be treated because there are virtually no studies performed on these residual streams with regard to PFAS. There is simply not sufficient scientific basis for making recommendations of that type at this time.

Are there any existing technologies or future innovations that you think could improve the capture or degradation of PFAS in WtE facilities?

For the treated water, it is likely that introducing an additional cleaning step using an active carbon adsorbent or degradation through oxidative or electrochemical treatments could be beneficial. However, since the treated process water is extremely salty (<20 % NaCl and KCl) and can contain other trace contaminants than PFAS, it´s hard to predict the performance and efficiency those types of treatment would have. Naturally, this type of targeted separation/degradation approach is something that we intend to examine in upcoming studies, but before those are conducted and we have data to base conclusions on it is too early to say more about the potential of such treatments in in‐house process water treatment.

You found PFAS in almost all sample types except boiler ash. What might explain the absence of PFAS in boiler ash in particular?

Based on the available data, we cannot say with certainty why this was so. One possible explanation is that within the set of individual PFAS that we analyzed, the PFAS that may have survived the incineration process intact were more prone to leaving the plant via the water vapor in the flue gas stream, and less prone to interacting with ash surfaces at those temperatures. PFAS, in contrast to other types of persistent organic pollutants (POPs) commonly associated with WtE (primarily dioxins and PCB), are less prone to adhering to surfaces than dioxins and PCBs. PFAS are often at least partially water‐soluble. A reason we find them in the filter ash could be a result of a phase shift, from gas to droplets, as the temperature decreases. It must be noted that before the filters, active carbon is injected into the flue gas stream to capture dioxins, and it is possible that the active carbon captures PFAS as well.

Related article: Water Treatment: Perfectly filtered

Your study found that flue gas treatment can remove PFAS. What are the mechanisms behind this removal and are these rates sufficient to protect the environment?

The mechanisms behind the removal are yet unknown, and to understand these substantial studies on a more fundamental, mechanistic level are required. As discussed in our 2024 ES&T paper, this could be related to the addition of another washing step, at a temperature where it is more efficient.

The question of whether or not these rates are sufficient is quite complex, both because there is currently no legislation regulating emissions of PFAS, but also because of the severely understudied state of this scientific field. Much more research is required on the fate of PFAS in incineration processes, to build a better understanding of how efficient WtE facilities are in capturing and/or degrading PFAS, and to what extent removal can, and should, be improved.

Based on your findings, what are the main challenges to the complete capture or destruction of PFAS in WtE plants?

Some PFAS and PFAS degradation products are small and volatile molecules, which are difficult to capture regardless of treatment technique. Since we at this time have such limited understanding of what happens with PFAS during incineration, we cannot draw any general conclusions about WtE as a source or sink of PFAS. We have analyzed some of our water samples for TFA, finding levels similar to natural waters, which could indicate that WtE is not an alarming source of TFA to the environment. Again, with scientific studies on this being scarce, there is not enough data on this to support conclusions of this kind.

How do the PFAS levels you have measured in WtE facilities compare to those found in other types of waste treatment facilities, such as landfills or incinerators?

The answer to this question depends entirely on what is placed on the landfill, and the type of incineration process. The scientific literature reports PFAS concentrations in landfill leachate ranging from below those we found, to emissions several orders of magnitudes higher. When compared to the leachates from MSW storage sites, the PFAS concentrations in the WtE residues were found to be lower.

How do you see the role of WtE facilities in managing PFAS‐contaminated waste streams? Are they an effective part of the solution or do they present new challenges?

Our findings indicate that it is likely that some PFAS degrade during incineration in a WtE plant, at least partially. However, an elevated PFAS load into the incineration process seems to yield a higher concentration of PFAS in the solid and aqueous residue streams, which naturally indicates that a waste fuel with lower concentrations of PFAS would be preferable from a PFAS emission perspective. Of course, it would be ideal if there were no PFAS emissions from WtE, but then we are back to the general issue of waste handling. Regardless of waste type, treatment methodology, and available infrastructure, the waste that is generated in our societies must be dealt with, one way or the other. And regardless of how the waste is managed and processed, PFAS needs to be taken into consideration due to their extensive use in products and materials that surround us in our daily lives. I would like to emphasize that this holds true for ALL waste-handling processes, including recycling.

Therefore, the only long‐term solution, regardless of waste management technique, is to limit non‐essential use of PFAS in products and materials. What role WtE will or will not play in the PFAS detoxification of our societies is not a question that can be answered based on the available scientific knowledge.

Related article: PFAS: New bill wants to protect waste and compost industry from liability claims

PFAS are known to persist in the environment. What does your study suggest about the long‐term fate of PFAS after they have passed through WtE plants?

This is not within the expertise of me and my research group. The molecular stability of a PFAS substance will, however, be the same regardless of whether it is released from a WtE facility or from some other emission source. PFAS are inherently highly persistent, i.e., they are chemically stable, which makes them challenging to degrade, and when they do eventually degrade, they are most likely to rupture into smaller, and potentially even more persistent PFAS species.

What are the wider public health and policy implications of your findings, particularly with regard to the regulation of PFAS emissions from industrial sources?

This is very difficult to say at this point. Our studies are pioneering, and the field of PFAS degradation in incineration is so scarcely investigated that the wider implications are almost impossible to foresee. The human health implications of PFAS are quite well investigated though and are the same regardless of the source of the PFAS released into the environment. The type of exposure can, however, be different, depending on the source.

Do you think that current regulations on PFAS emissions and waste management are sufficient, or do you think that stricter guidelines are needed?

Before stricter guidelines are implemented, it´s important that we make sure that we are regulating the most relevant and critical emissions. This connects back to the analogy in the first question – what do we gain from banning the spider just because that is what we can observe, if the wolf is the most severe problem? As stated earlier, a blanket ban on PFAS (like the one suggested within the EU) is most likely the most efficient way to reduce PFAS emissions, regardless of source.

How can the results of your study be used to better inform the design or improvement of WtE facilities to minimize the release of PFAS to the environment?

The studies we have conducted thus far cannot be used by themselves as a basis for an extensive transformation of WtE facilities; much more research is needed for that. We still have quite a long way to go before we understand what happens with PFAS in WtE and how factors like fuel composition and operational parameters influence the fate of this huge family of chemicals. So far, the reports of PFAS in waste incineration have been somewhat conflicting, where some studies have made an observation that another study cannot verify, or observe something completely different. That is not uncommon in research and particularly in a new field where very few studies exist. When we have more studies available in scientific literature, I expect us to be able to say more about what potential process alterations could be relevant for minimizing PFAS emissions. There are, however, some improvements of a quite general character that could be implemented, such as active carbon filtration of water streams, but the reported efficiency on PFAS specifically is varying.

Related article: "PFAS contamination presents both opportunities and challenges for the waste management industry"

What are the next steps in your research? Are there other aspects of PFAS behavior in WtE facilities that need further investigation?

Yes, all of them require more research, and not only by us. We will continue looking into the fate of PFAS in WtE, applying a wider analytical scope and conducting more extensive sampling campaigns to try to elucidate the fate and the degradation mechanisms of PFAS. At this time, we have only just scratched the surface of understanding the fate of PFAS in waste streams, or in the WtE process.

Are there any existing technologies or future innovations that you think could improve the management of PFAS?

I am certain that there will be. There are existing technologies capable of degrading PFAS, but they are costly and technically demanding. There is also the challenge of collecting and concentrating the PFAS, since they are so prone to spreading out.

Are there other emerging contaminants that you are concerned about in addition to PFAS that may be present in waste streams going to WtE facilities?

Absolutely. There are many contaminants that enter WtE plants together with the waste, but most of them are not as stable as the PFAS and can therefore readily be degraded in the incineration process. The persistence of PFAS is linked to the exceptional strength of the CF bond, and the challenge for the WtE is to efficiently degrade them. One example of less stable contaminants is pharmaceuticals, which are of high environmental concern but when introduced into a WtE facility they cannot pass undegraded. Flame retardants are a bit more challenging, but the fact that they have chemical properties more similar to classic POPs (i.e., the tendency to stick to particle surfaces) enables their removal. In fact, the entire flue gas cleaning system in WtE facilities is designed to remove harmful metals, organic contaminants, and acidifying gases from the residual streams. This, however, assumes that they are well‐maintained, modern plants with the required flue gas cleaning.

How does your work fit into global efforts to manage and reduce PFAS contamination in the environment?

Our work contributes critical pieces of knowledge on what happens to PFAS in waste management and WtE, which is of key importance for minimizing or even eliminating emissions of PFAS from these societal cornerstone functions.

Stina Jansson is an Associate professor at the  Department of Chemistry at Umea University, Sweden. Her research is mainly focused on the thermal treatment of biomass and other organic materials and waste fractions from an environmental chemistry perspective.