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?
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.
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.
You definitely wouldn’t want to drink the water from any of those systems you’re describing though :)
I thought about this too for a while but I learned that even rain contains microplastics.
fire’s always cool in my book.
I think you’re doing fire wrong, friendo.
Yeah, turning wastewater plants into sewage distilleries doesn’t seem like a public health win.
What exactly do you think evaporation ponds are doing, then?
Evaporation is a component of distilling, but if you don’t capture the vapor and condense it it’s just evaporation.
Why would you capture it? It’s waste water, evaporation into the atmosphere should be fine.
That might be possible but there are particles that also will be present in vapor which might be toxic. Simply sending the out into the atmosphere would probably not be a good idea. PFAS for example do not break down under ~400C and just creating a fine PFAS mist is probably not what we want.
But yes, of course while heating up the water there will be residue. How to dispose of that will probably also have to be thought of. Maybe 500C is also the answer, but I don’t know.
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.
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?
They eat meat.
Yeah but it says “at home” and gives recommendations how you personally can reduce water consumption (like more efficient taps or showerheads), which makes me believe that it’s not your entire direct and indirect water consumption (which realistically isn’t even relevant for the argument since the water used for crops isn’t gonna be getting treated anyway)
The estimations for water required to make meat even include rainwater. As if cows are out standing in the field collecting water through their hooves or something.
They use AI.
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.
The global AI demand may even require 4.2 – 6.6 billion cubic meters of water withdrawal in 2027, which is more than the total annual water withdrawal of 4 – 6 Denmark or half of the United Kingdom
https://oecd.ai/en/wonk/how-much-water-does-ai-consume
AI’s projected water usage could hit 6.6 billion m³ by 2027
Yes, with our current energy output it would not be possible, but I’m asking about whether even theoretically it could be an easier way to clean water. Maybe in 10, 20, 50 or 100 years it’s a method worth pursuing.
This is simple math. We would need to increase our energy production by 1000 times to just treat water, maybe only 250 times if we used more efficient systems than simply heating it and letting the heat dissipate. If we doubled our energy production every year, it would still take a decade to do it (8 years if we were aiming at 250 times). That isn’t a realistic amount for a civilization at our tech level.
You say 1000, another poster says 11, and yet another gives another number I can’t remember.
If I’m reading the graph right on page 20 of Homo Sapiens’ Energy Dependence and Use Throughout Human History and Evolution, in 1820 we needed about 20 EJ. That’s a 31 fold increase to ~530 EJ in 2010 (190 years). Looking at the chart, you can see that the rate of increase has sped up, not slowed down. In 1960 it was ~120 EJ making it a 4x increase in years.
It might take time, but it’s not impossible. And unless a great calamity happens upon us, we will not stay at our current tech level for another 200 years.
I understand the pessimism, but my question wasn’t about “is this possible within our lifetimes” or “how much energy would this need” but “Could wastewater plants simply heat up water past 500C to decompose all chemicals and output clean water?”. I just want to know if with our understanding the water will be clean after going through a procedure where it’s heated past 500C. That could be once or multiple times, it could involve adding a filter, removing deposited waste material, etc.
That sounds expensive.
And the chemicals decompose into what? How do you get whatever they decompose into out of the water?
At 500C there’s not much water to speak of… And if they decompose enough it would be a bunch of carbon a hydrogen mainly, so a bit of CO2 and more water.
The temperature will be impossible to maintain at any scale. Why do you think our high end computers use “water cooling”?
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).
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?
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.
In a practical sense, making lead hot won’t break it down. But I wonder if there is any temperature where lead would stop being lead and continue to not be lead after the results cool down again?
Well… The Large Hadron Collider can smash lead nuclei together at nearly the speed of light, which turns them into something that is definitely no longer lead.
Alchemy! Now this is the out-of-the-box thinking that I like!
In all seriousness, lead is lead because it’s made of lead atoms. It can’t not be lead. (The reference to alchemy was because before we knew about atoms, many alchemists tried their hand at turning low-value metals like lead into high-value metals like gold).
To answer your question in a silly but scientifically accurate way, there is a temperature to which lead can be heated to become something else, but these are nuclear fusion temperatures, like you get in the Sun.
Much higher than the sun, unless you’re also adding the pressure of a star.
My mother is busy sitting on something else that afternoon
Magnetic fields should be able to extract lead.
How would that work? You gonna ionise the lead? 🤔
Why would that be necessary? Does led not react to magnetic fields?
Very few metals do!
Lead does not.
Edit. Here’s a list of things you can pickup with a magnet.
https://en.m.wikipedia.org/wiki/Category:Ferromagnetic_materials
Lead being an element means you would either need to make it radioactively decay somehow(which I’m not sure any form of lead is want to do) or perform some kind of alchemy.
Artificial elemental transmutation of lead into other elements is not just fantasy, it’s entirely possible and happens in particle accelerators and nuclear reactors. It’s just extremely impractical as it’s an extremely slow process at anywhere near the particle fluxes we can practically achieve. Plutonium is made through a similar process (though the exact mechanism used to produce plutonium is relatively more efficient) as well as small quantities of useful radioisotopes, but it is also possible with lead.
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.
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.
You’d have heat exchangers, like a desalination plant
https://en.m.wikipedia.org/wiki/Multi-stage_flash_distillation
Such plants can operate at 23–27 kWh/m3 (appr. 90 MJ/m3) of distilled water.[5]
So still impossible, but not unfathomable
edit:
122,060,000,000 kWh becomes
003,500,000,000 kWhAbout a third of the national capacity
when other cheaper solutions (like not polluting in the first place) exist
That involves convincing your polluting cousin, who doesn’t believes climate change doesn’t exist, not to buy non-stick pans or not to dump their pills into the toilet.
Edit:
Let’s assume that heating water to 500C does what you want it to do.
That’s the question I’m asking btw.
You could always regulate and ban toxics at the point of production or sale, before they get into the waste stream
Yeah, sure, but regulation needs enforcement and countries are pretty lax on that. Just look at England that was dumping toxins into rivers for decades and recently raised the allowed levels in order to continue doing so. If there were a way to go “whatever, all you need to do is install this and you can dump as much as you like because it won’t end up in the water anyway” wouldn’t that be preferable?
Barring the fact that most pollutants aren’t that easy to deal with, I don’t think so. I think you’d suffer from a kind of Jevon’s Paradox of toxicity, where people would just dump more in, until whatever “ok” threshold previously existed would be breached, and you’d be left in the same situation, just systematically worse.
You realise water boils at 100°C, right?
Edit: yes, I know it boils a different temperatures, but we’re talking about 500°C for a practical use case at scale here…
Bit pendantic but I think its interesting: no, water doesn’t always boil at 100 °C. It can boil anywhere between -50 °C and 317 °C, depending on pressure.
On top of Mt. Everest you cannot cook potatoes because the water boils at 71 °C. On the other hand, with enough pressure water does not boil at all, instead becoming a supercritical fluid - a different phase from gas or liquid.
I think at this point, it would be more economical to distill the water than to burn up contaminants.
You can still heat it up past 100 once it’s turned to vapor. However, it requires a ton of energy to convert it to vapor in the first place.
There’s no need to be condescending. You seem to have misunderstood the question. I’m not trying to keep water liquid at 500C and decompose other particles at that temperature. The state of the water isn’t mentioned anywhere in my post, just the temperature.
FYI, lava is 800-1000C and regularly comes in contact with water. The resulting vapor has a temperature way higher than 100C.
Fair enough, sorry. It’s just that your question (and some of your answers) don’t seem to be accounting for dealing with the volume change of steam, and how that would be managed.
Also the fact that if you’re evaporating the water off anyway, why not just let it escape and concentrate the chemicals, and then deal with them that way? I’d guess most of them would not be in the vapour anyway? (unless they’re volatile, in which case they’d probably boil off even earlier)
Re: Lava contact. I don’t think the resulting water vapour is much more than 100°C? The phase change takes a lot of energy to phase change, and is still at about 100°C after that, and then the steam would escape very quickly, and be displaced by more water, so it would not have much chance to heat up more. The lava-water interface would always be at about 100°C, give or take a few tens of degrees for the Leidenfrost effect, maybe? I might be wrong here, but I can’t see how it would get MUCH hotter than 100°C (assuming normal surface pressure).
At standard pressure. high pressures can make it liquid. I can’t find charts that go high enough with a simple search but it looks like you need to get to 4000-5000psi. industry does go that high for some operations. It needs special design to toeit safely though.
Right… Have you considered that a basic order-of-magnitude estimate of scale of water, energy, and pressure requirements make the idea wildly infeasible in practice?
A lot is all I need to know. Since others have allready pointed out we have ways that work that use much less energy I don’t feel a need to estimate deeper.
sorry, thought I was replying to OP
Unfortunately, even if we stopped using PFAS entirely it will remain a legacy problem in wastewater and landfills because so many consumer products contain PFAS. That said, some places are working towards banning PFAS in new products and some of the really nasty ones are already banned in many countries. Here is Canada’s plan to phase PFAS out of industrial and consumer goods:
Heat exchangers are extremely efficient. You use the 500C water to heat 400C water, then use your 400C water to heat 300C water etc etc. It still takes energy, but you recover over 90% of it.
Stopping pollution is difficult, and filtering water is expensive, but boilers are well established technology.
Now explain making steel.
There isn’t a steel supply tap to every house is it? I don’t think I’ve had to replace or buy any steel pieces over the last two months or so. Different story with water.
Why would you need to purify the water locally at everyone’s individual house? Your logic makes me chuckle. Just wait untill you find out about a steam engine.
Their point, which you quite clearly missed, is that people don’t need a steady, reliable, high volume flow of steel delivered to every single home and business.
And maybe you should look into steam engines a little more and check out things like how hot that water actually gets. You’re gonna discover that for all the prodigious fuel use, the temperature is far below the goal of 500C and the flow rate far below requirements. But keep up the sass.
The point you missed and everyone’s autism is preventing y’all from seeing that the fact that we have water and elecricity flowing to most houses in the USA. Things which were deemed impossible back in the day. Imagine the energy cost of conditioning the air individually at everyone’s house let alone their moving car too. It would be iMpOsSiBlE.
It’s not 100 perfect so let’s do nothing.- great idea enjoy your day.
An idea that requires 11.5 times more energy production on a daily basis than the entire country’s output is a lot more than “Not perfect.” So maybe you pipe down before you go calling everyone who disagrees with you autistic, m’kay?
You’re right technology never improves. I loved you in that movie “Idiocracy” Red_october he’s got what plants crave! Enjoy your job at Costco.
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
For simplicity, this process is called clarification.
Unfortunately, coagulants are not effective at removing PFAS. The only effective methods for PFAS removal are adsorption (using granular activated carbon or ion exchange resins) or reverse osmosis filtration. These approaches are not used in traditional wastewater treatment because they are very expensive and are not required to meet registrations. However, potable reuse facilities will use these approaches to further treat wastewater effluent to drinking water standards. This is the future of water supply for arid areas like the southwest USA.
Also PS, the most commonly used coagulants are aluminum sulphate (alum) and ferric sulphate, which are not polymers. Polymers definitely are used (especially where I live) but they are more expensive and thus avoided when not needed.
Yes, that’s why I said my explanation was quick and dirty. Regular people don’t know what a plant does.
The difficulty is that you need to target all the pollutants and you can’t know of all the pollutants. There are new ones constantly entering the market and being discovered years, maybe even decades later.
Correct. Samples are taken regularly in order to determine if there’s something in there that’s not in the models or polymer table.
I can’t name names but there was a plant in Houston, TX that would have incoming water that would glow when a local very large company would illegally dump. I witnessed it personally after I overheard plant operators talking about it and I asked them to show me. Samples of the water would be taken and passed up to state authorities.
That was back when Texas had state authorities that sort of gave a shit about pollution.
They’re all gone now.
You COULD name names… Perhaps via Tor to a journalist
bruh it’s houston literally everyone is polluting on the east side of the city. the only people that don’t know are the people that don’t wanna know. honestly the fact that their plant never exploded killing people and belching nightmarish shit into the air made them good guys
Where does the energy to do that come from.
Same place as nearly everything else, the Sun.
I’m not a scientist but wouldn’t the atmospheric pressure need to be insane to bring the boiling point of water to 500°C? Is that even possible?
500C is above the critical temperature for water. So it would probably be a supercritical fluid. Unless the pressure was above 10 GPa or so in which case it would be solid.
Its above the critical point, so water will be a supercritical fluid. 370 C already requires 217 atm of pressure.
Lava is 800 to 1200C and regularly comes in contact with water, which turns into vapor in our atmosphere.
It’s not about bringing the boiling point to 500C, but getting the water (vapor at that point) to 500C.
