this post was submitted on 01 May 2025
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Our waterways are becoming more and more polluted due to PFAS, plastics, medicines, drugs, and new chemicals made by companies that just hand over the responsibility of cleaning to plants paid for by public moneys. Detecting the different chemicals and filtering them out if getting harder and harder. Could the simple solution of heating up past a point where even PFAS/forever chemicals decomposes (400C for PFAS, 500C to be more sure about other stuff) be alright?

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[–] Brainsploosh@lemmy.world 61 points 1 day ago* (last edited 1 day ago) (7 children)

Raising water temperature from 10 to 500 degrees requires about 500 calories/mm3. That's 2 MJ/litre, meaning if you want to heat 1 liter/second you need 2 MW with perfect insulation, so a power plant of say 10 MW.

A post industrial world citizen could probably get by on 200 l/day (US averages about 300/day). That needs 2 kW/person/day.

Total global energy production is about 630 EJ which averages out at about 12 TW.

Meaning if the whole global energy production went to treat water in that way, we have enough clean water for about 6 million people.

[–] Redex68@lemmy.world 6 points 1 day ago (2 children)

How the hell do people use that much water? Are they including water consumption needed for the products we use or? Let's say a flush is 8L and the average person flushes 5 times a day, that's 40L. The average person needs about 2L of water a day. Let's say an average shower is 100L. Cleaning dishes at worst is probably like 20L per person without a dishwasher. That's like 160L of water per day and I feel like most of those were over-estimates. How did they get to that number?

[–] Initiateofthevoid@lemmy.dbzer0.com 4 points 21 hours ago (1 children)

Dishwashing is a significant underestimate here, and don't forget hand-washing (before/after bathroom, food, cleaning...).

Plus you missed outdoor and gardening, which would help explain why the Land of the ~~Free~~ Lawns uses more than anybody else.

[–] Redex68@lemmy.world 1 points 16 hours ago

Ok yeah the second part makes sense, but for the first part I was calculating it based on hand washing, dishwashers would be way less since you have to split the usage per person in the household, which holds for hand washing as well. Idk for other people but when I'm alone I use the dishwasher probably every 3-4th day and for handwashing I'd say 20L is realistic, double it maybe but still isn't that much.

[–] jerkface@lemmy.ca 11 points 1 day ago (4 children)
[–] atro_city@fedia.io 6 points 1 day ago (1 children)
[–] jerkface@lemmy.ca 7 points 1 day ago* (last edited 1 day ago) (7 children)

How much water do you believe AI consumes? The 31 billion land animals we keep in captivity and the crops we grow to feed them dwarf most human water consumption.

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[–] pineapplelover@lemm.ee 8 points 1 day ago (1 children)

This would be carcinogenic beyond imagination

[–] atro_city@fedia.io 3 points 1 day ago (1 children)
[–] Alloi@lemmy.world 3 points 18 hours ago (2 children)

Because you're essentially cooking a cocktail of complex chemicals, many of which were never designed to be heated, and the result is often airborne toxins and volatile organic compounds (VOCs) that are far worse than drinking trace amounts of the original chemicals.the chemicals dont vanish or turn into pure air when vaporized. they degrade into other more harmful chemicals. which are carcinogenic and more toxic.

[–] pineapplelover@lemm.ee 2 points 15 hours ago

My guy you're burning plastic

[–] atro_city@fedia.io 1 points 18 hours ago (1 children)

Can the degraded chemicals withstand sustained exposure to 500C?

[–] AwesomeLowlander@sh.itjust.works 1 points 7 hours ago (1 children)

The chemicals don't just disappear, whatever they've degraded into will still remain.

[–] atro_city@fedia.io 1 points 2 hours ago (1 children)

Yes, but will they all be harmful?

At this point I think we've figured out that all chemicals should be considered harmful unless we have specifically tested and concluded otherwise.

[–] ptc075@lemmy.zip 28 points 1 day ago (16 children)

At the risk of sounding silly - Instead of focusing on burning the solids, boil the water. Water boils at 100C, at which point the water vapor should separate and leave all the solids behind. Then capture the vapors and condense it back down into clean water. Now, if you later want to incinerate the leftover solids, sure, go for it, fire's always cool in my book.

I'll add, simply boiling water is energy intensive. What you are proposing probably won't work at any scale.

[–] MajorMajormajormajor@lemmy.ca 11 points 1 day ago

fire's always cool in my book.

I think you're doing fire wrong, friendo.

[–] I_Has_A_Hat@lemmy.world 8 points 1 day ago (1 children)

Golly gee, if only there were some form of energy generation that required boiling vast amounts of water to turn into steam. But no, that would be silly.

[–] neukenindekeuken@sh.itjust.works 7 points 1 day ago (1 children)

You definitely wouldn't want to drink the water from any of those systems you're describing though :)

[–] Rakonat@lemmy.world 2 points 15 hours ago

The steam you see coming off a cooling tower is not the water than went through the reactor or turbine, a secondary cooling loop is used specifically cause the plants are not allowed to release radioactive material in any form, including the cooling processes.

The real reason this idea would not work is the same problem desalination has, making clean and safe drinking water is the easy part, it's what are you doing with all the contaminants and water products left behind that quickly becoming a concentrated pool of filth and toxins at the bottom of your heat exchanger.

[–] x00z@lemmy.world 8 points 1 day ago

I thought about this too for a while but I learned that even rain contains microplastics.

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[–] LostXOR@fedia.io 94 points 2 days ago (12 children)

Yes; this is something that has been studied. However as other commenters have said it requires a lot of energy, and is better suited for processing smaller quantities of water with a high level of PFAS contamination than massive quantities of water with an extremely low level of PFAS. It's also not a standalone solution, as plenty of harmful chemicals survive heating past 400/500C (heavy metals like cadmium, lead, and mercury do not break down at any temperature).

[–] atro_city@fedia.io 19 points 2 days ago (2 children)

Thank you for the only response that actually answers the main question and linking to a scientific paper. Much appreciated.

Regarding harmful chemicals that do not decompose beyond 500C, could it be more likely that the number of such chemicals/materials (known and unknown) is much lower than the number of chemicals/materials at the temperatures used for current clarification processes?

[–] FeelzGoodMan420@eviltoast.org 3 points 1 day ago (2 children)

As you can see, these communities are an absolute fucking joke, and only like 15% tops of the comments are actually helpful or backed up by reputable sources.

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[–] LostXOR@fedia.io 7 points 1 day ago

Always good to do a quick search of the literature to make sure your intuition about something is actually correct; I too thought "no way" when I first saw your question.

I don't think only heating water to 500C would remove more harmful chemicals than a typical full treatment process, as they have a lot of steps to filter various things out, but I don't have a source for that.

Even if it did, there's still the issue of heating up the water taking an enormous amount of energy, which is probably a dealbreaker. My local wastewater plant treats 40 million gallons a day, which by a quick calculation would take 150 GWh to heat, 83% the daily energy consumption of the whole of Minnesota. That can be reduced significantly with heat exchangers but even 1% of that would be far too expensive.

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[–] robato@lemmy.world 5 points 1 day ago (6 children)

Molten Salt Nuclear Reactors (like the one China's making with thorium) operate at something like 700* C to generate electricity. With the waste heat, we could desalinate water. Instead of Yucca Mountain as a nuclear waste repository, it becomes Yucca Mountain Molten Salt Nuclear Reactor and brackish groundwater distillation for Las Vegas.

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[–] TerranFenrir@lemmy.ca 54 points 2 days ago (33 children)

Let's assume that heating water to 500C does what you want it to do. Even then, the sheer amount of energy required to do this would be massive. It would just be incredibly uneconomical to do this, when other cheaper solutions (like not polluting in the first place) exist.

[–] dual_sport_dork@lemmy.world 49 points 2 days ago (1 children)

Not only that, but given that heating up volumes of water is basically the metric around which energy units and calculations are all derived, it's easy to determine just how much energy.

Assuming an inlet temperature of a fairly optimistic 60°F or 15.56°C, it takes 12,934,470.48 joules to heat one US gallon of water to 500°C. Or if you prefer, possibly because you're an American used to reading your electricity bill, 3.59 kWh to heat that gallon. Just one.

The EPA estimates that just in the US alone, wastewater plants treat 34 billion, with a B, gallons of water per day. No need to get out your calculator, that's 122,060,000,000 kWh or if you prefer, just under 11.5 times the existing average daily power production of the entire country (10,640,243 MWh, if you're wondering).

So, uh. Yeah. Probably not feasible.

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[–] specialseaweed@sh.itjust.works 23 points 2 days ago* (last edited 2 days ago) (6 children)

No. The far more likely way to handle it is with flocculation/coagulation since plants are already set up to support this.

Edit: the quick and dirty overview: shit water comes in. Chlorine and other chemicals are added to the water which kills the bad stuff. Polymers are added to the water which binds to the chlorine, causing chunks. Chunks removed. Water discharged. You can change the polymers used to bind specifically to which pollutant is coming in.

That part of the process is called flocculation. Using it to add polymers that have additional capability (like removing microplastic) is where you’d want to do it. The cost is the polymer which would be some sort of reasonable, not rebuilding every plant that exists to boil water.

Check out the video on the flocculation page. Does a great job of showing how floc works.

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

https://en.m.wikipedia.org/w/index.php?title=Wastewater_treatment&wprov=rarw1

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[–] zxqwas@lemmy.world 9 points 2 days ago (1 children)

That sounds expensive.

And the chemicals decompose into what? How do you get whatever they decompose into out of the water?

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