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Comment by momoschili | Hacker News Reader

3. Do #2 without platinum, palladium, rhodium, ruthenium to make it economically viable

Is that much of a problem for a catalyst? Presumably you do not need many of these: at water treatment plants and at the waste-stream for manufacturing processes which emit PFAS. You might not be able to justify the expense inside your home water purification system, but it could still be cost effective for large scale installations.

You would need a lot of catalyst because the water infrastructure to supply several hundred million people in the US is massive, let alone the rest of the world.

The problem with those catalysts is that the latter two are minor components of platinum and copper/nickel ores and despite how expensive they are, the extraction is only economically viable as part of other mining. Their supply can only grow as much as platinum extraction allows and demand is already pretty significant with environmental regulations often necessitating their use. Any more demand for them will cause their prices to rise dramatically and its a long way before they become profitable enough to mine on their own (flooding the platinum market in the process which has much higher yields from the ores).

it depends on the scale and the required amounts. If having a limited amount of catalyst wasn't such a big problem I suspect hydrogen power would have been much more economically viable.

I thought the point of catalysts was that they don't get used up in the reaction they promote.

The real world is messy - catalysts gradually need replacement over time in non lab conditions

https://en.m.wikipedia.org/wiki/Catalyst_poisoning

The issue with hydrogen is the source of hydrogen.

Activated carbon filtering removes up to about 75% of PFAS. Reverse-osmosis removes almost all.

Doesn't get rid of them, to be clear. It would still be better if a way could be found to chemically (and cheaply) convert them to something less harmful.

> Activated carbon filtering removes up to about 75% of PFAS

Common inexpensive non-RO filter systems come with independent test results showing 99% removal of PFOA/PFOS (see e.g https://www.brondell.com/content/UC300_Coral_PDS.pdf). Do we have reason to believe that other PFAS don't filter as easily?

AIHI the shorter PFAS molecules are not captured as effectively by activated carbon.

> Activated carbon filtering removes up to about 75%

Seems like the limitation must be more than reducing concentrations in fluid? Otherwise you'd just do multiple passes?

Yes, the key here is the degradation of the forever chemical, not the removal. Removal itself doesn't really change the environmental scale of it

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