Sciencemadness Discussion Board - PFAS Degredation

PFAS Degredation

thrax - 10-2-2025 at 12:24

There is a lot of research into how PFAS could be scalably removed from municipal water supplies, but the rejected PFAS will still need to be destroyed.

I am not a fluoride chemist, so I’m not up to date with the most cutting-edge research in the area. Still, to me, it seems that the degradation processes for PFAS are bespoke for each compound.

I’ve heard about pyrolysis, but that still doesn’t degrade them to elemental fluorine/HF. Is there a reason the breakdown products aren’t electrochemically destroyed in an arc furnace, as demonstrated in this paper:
https://www.aappsdpp.org/DPP2021/A/5090.pdf?

Is recovering fluorine compounds so profitable that it makes more sense to attempt bespoke recovery methods instead of just converting them to HF and mineralizing them with metals?

Sulaiman - 11-2-2025 at 04:43

I can not at the moment think of any environmentally friendly route that would not require lots of very short wavelength u.v. light.

In my last place of employment we repaired the electronics for uv water treatment plants.
Just to kill bacteria on a municipal water scale requires a lot of large uv units per installation,,
to cleave PFAS at this scale would, I imagine, require large capital and running costs,
are we willing to pay for this service?

_____________________
Maybe because I am not educated enough in this topic but
clearly we need to minimise production of PFAS
but I am wondering what is the biological threat from inert/forever molecules?

Keras - 11-2-2025 at 06:18

Not so inert, unfortunately. TFA, trifluoroacetic acid, which seems to be the endpoint of biological ‘degradation’ is extremely acidic and has been classified as potential endocrine disruptor and/or carcinogenic. What I’m wondering is why it can’t be neutralised with a proper base, and after that eliminated as a salt.

[Edited on 11-2-2025 by Keras]

chempyre235 - 11-2-2025 at 06:45

Can PFAS be cleaved with ozone or hydroxyl radicals (i.e. Fenton's reagent or analogues)? I know perchlorinated compounds are eliminated from affluent mixtures in this manner, but PFAS compounds have higher stability than these.

thrax - 11-2-2025 at 06:50

Quote: Originally posted by Sulaiman

I can not at the moment think of any environmentally friendly route that would not require lots of very short wavelength u.v. light.

In my last place of employment we repaired the electronics for uv water treatment plants.
Just to kill bacteria on a municipal water scale requires a lot of large uv units per installation,,
to cleave PFAS at this scale would, I imagine, require large capital and running costs,
are we willing to pay for this service?

_____________________
Maybe because I am not educated enough in this topic but
clearly we need to minimise production of PFAS
but I am wondering what is the biological threat from inert/forever molecules?

I agree it might be cost-prohibitive, but I was mostly thinking about why we are focusing on highly specialized methods instead of "dumb" methods like UVing the crap out of it or zapping it with plasma from a high current DC ARC welder. I can't imagine a steel vat with a UV lamp or graphite anode would be more expensive than complicated reactors with specialized chemicals.

As for the biological threats from PFASs, I mentioned I'm not a fluoride chemist, but as a biochemist, I can speak about the biological effects a bit.

PFASs tend to bio-accumulate since they are generally more soluble in nonpolar environments than aqueous ones, and no biological processes selectively remove PFASs [1]. To reduce tissue PFAS concentration, you kinda just need to dilute it out of an organism by feeding it a noncontaminated diet for an extended period.
PFAS are also hard to detect in an organism because they are unreactive and usually in extremely low concentration, so unless someone is using specialized tests, it's hard to measure how contaminated your diet is.
As for the direct biological effects, we don't know the whole scope of problems they cause. Still, there is strong evidence that PFASs interfere with fatty acid metabolic pathways [3,4] and disrupt cell membrane homeostasis [2].

Both fatty acid metabolism and cell membrane homeostasis are highly regulated processes that are done in every cell, so you can probably guess that broad disruptions to them can cause many unknown downstream effects.

1. Brunn H, Arnold G, Körner W, Rippen G, Steinhäuser KG, Valentin I. PFAS: forever chemicals—persistent, bioaccumulative and mobile. Reviewing the status and the need for their phase out and remediation of contaminated sites. Environmental Sciences Europe. 2023;35(1):20. doi:10.1186/s12302-023-00721-8
2. Hu W yue, Jones PD, DeCoen W, et al. Alterations in cell membrane properties caused by perfluorinated compounds. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology. 2003;135(1):77-88. doi:10.1016/S1532-0456(03)00043-7
3. Hyötyläinen T, Bodin J, Duberg D, Dirven H, Nygaard UC, Orešič M. Lipidomic Analyses Reveal Modulation of Lipid Metabolism by the PFAS Perfluoroundecanoic Acid (PFUnDA) in Non-Obese Diabetic Mice. Front Genet. 2021;12. doi:10.3389/fgene.2021.721507
4. Rotander A, Ramos MJG, Mueller JF, Toms LM, Hyötyläinen T. Metabolic changes associated with PFAS exposure in firefighters: A pilot study. Science of The Total Environment. 2024;953:176004. doi:10.1016/j.scitotenv.2024.176004

thrax - 11-2-2025 at 06:56

Quote: Originally posted by Keras

Not so inert, unfortunately. TFA, trifluoroacetic acid, which seems to be the endpoint of biological ‘degradation’ is extremely acidic and has been classified as potential endocrine disruptor and/or carcinogenic. What I’m wondering is why it can’t be neutralised with a proper base, and after that eliminated as a salt.

[Edited on 11-2-2025 by Keras]

Ya, all those highly halogenated carboxylic or sulfonic acids are always highly reactive. I'm pretty sure the reason you can't just base neutralize them to deal with them is because the salts of the PFAS are still liquids, and their solubility doesn't change much.

DraconicAcid - 11-2-2025 at 06:57

Quote: Originally posted by Keras

I'm pretty sure its carcinogenic and disruptive properties won't be changed upon neutralization.

Keras - 11-2-2025 at 08:05

Quote: Originally posted by DraconicAcid

I'm pretty sure its carcinogenic and disruptive properties won't be changed upon neutralization.

Possible, but maybe it is easier to filter it out using activated carbon when it is present as a salt than as the vanilla acid form???

chempyre235 - 11-2-2025 at 08:12

It seems that PFAS compounds can be heat treated with lime at about 800°C.
https://www.sciencedirect.com/science/article/pii/S004565352...

This should give mostly CaF₂ and a mixture of CO and CO₂ with some water.

[Edited on 2/11/2025 by chempyre235]

metalresearcher - 11-2-2025 at 08:31

PFASes are indeed very bad in the environment. Maybe the CaO process might help, but the most rigorous way to get rid of really dangerous chemicals is indeed the electric arc. The temperature is so high dat even simple and stable molecules like CF4 or even HF and H2O are dissociated.

DuPont manufactured Teflon and was using PFOA (C7F16COOH) which is very toxic and carcinogen. Read this article about a corporate lawyer who finally worked against DuPont.
https://www.nytimes.com/2016/01/10/magazine/the-lawyer-who-b...

[Edited on 2025-2-11 by metalresearcher]

Sulaiman - 11-2-2025 at 16:59

an electric arc would consume electrodes quickly due to the products of decomposition
so
we need electrodes that are consumed by the 'neutralisation' of the products
eg consuming carbon could be a first step before further 'neutralisiation (eg CxHyFz)
there must be 'cleverer' compositions for consumable electrodes...