371–380 of 644 posts
Ocean waves can be used to create electricity and it is also possible to create a dam that uses an artificial river sourced by the ocean and make hydroelectric plants to use that energy. Is it a cost issue in both cases that prevents using electricity generated that way to desalinate?
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The brine waste from RO is still mostly water. In order to extract the salt you'd need to evaporate the water which still takes a lot more energy. You could use evaporative ponds to let the Sun do the work but that takes a lot of space. In either case you're spending a lot more money per pound than just digging the salt out of a mine.
> https://www.bbc.com/news/business-61483491 Nuclear desalination like on naval ships is the answer. US and Russian ships already have the technology, it just needs to be scaled for use on land.
It's not difficult. It's just energetically uphill. Undoing entropy costs energy. Second Law of Thermodynamics.
It's not tricky , but it's a lot of work, which is a kind of difficulty.
Most raw material processing involves some separation process which requires energy. First, there's gathering something that contains some of what you want. Then there's a phase that often involves breaking big stuff into little stuff and some mechanical separation of easily removed crud. Then there's some chemical step, such as smelting, leaching or distillation, which takes energy and feedstocks to pull the good stuff out of the bad stuff. Then there's getting rid of the bad stuff, which is the source of most industrial pollution. Now you finally have something that's mostly what you want, and go on from there. From desalinization to iron making to fertilizer to oil production, the front end looks like that.
All of those processes are energetically uphill, and all are routinely done on huge scales.
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In 2022, 85% of the country's drinkable water was produced through desalination of saltwater and brackish water. If there is a real need, and a will to address it, we have everything we need to to it. https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in...
>85% of the country's drinkable water "the country" in this context is Israel, since HN truncates the wiki link right before that.
Maybe it's time to understand that it's not a long term strategy ? That may be they should move to another place where water is naturally more abundant ?
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Freshwater withdrawals per capita in the US (which includes agricultural exports and animal feed such as alfalfa sent to Saudi Arabia) are around 1550 cubic meters per year. https://ourworldindata.org/grapher/water-withdrawals-per-cap... So that is around $775 per person per year assuming no net change in water use. In contrast, Germany uses around 410 m^3, France around 475 m^3, and Australia around 724 m^3, so the…
> 1550 cubic meters per year This is an interesting number. Recently, I saw complaints that green hydrogen is impractical because it would use too much water. But if all the per capita energy use in the US went to electrolysis, it would use about 1% of this water per capita (and, of course, green hydrogen would be only a fraction of total energy use, due to all the preferred direct uses of electrical energy.)
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You've pretty much nailed it except for one minor nit: > It takes less energy but produces a concentrated liquid waste stream that must be disposed of. This implies that creating a concentrated waste stream is a problem unique to reverse osmosis. It isn't. No matter what you do you're going to end up with a bunch of salt that you have to get rid of somehow.
The Israelis ran into this problem with their mineral extraction in the Dead Sea, so they're bulldozing the dry salt waste to build a physical wall for border security (more than 10 meters high) that's apparently hard to climb: https://www.youtube.com/watch?v=tgTheUjeDlg
I just remember thinking to myself "Bear Grylls drinking his own pee is such a philistine, here is an actual pro using science to remove all the water from that pee instead first." Genuine moment of awe personally.
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> the water in the tank was so pure it had dissolved a spanner/wrench that was left in the bottom "Apparently somebody had left a wrench there when they filled it in 1995," he said. "When they drained it in 2000 the wrench had dissolved." I dunno, I think if you left a wrench soaking in regular water for five years there wouldn't be much left of it after that either.
What's the process, though? The "dissolving" is presumably rusting and then motion of water washing away the rust, but rust requires an oxygen source for the chemical reaction, and apparently Super Kamiokande has dissolved oxygen specifically removed using a vacuum degasifier to prevent interference and growth of bacteria. I'm not feeling particularly convinced by this anecdote. It sounds a bit urban legendy. Still,…
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You've pretty much nailed it except for one minor nit: > It takes less energy but produces a concentrated liquid waste stream that must be disposed of. This implies that creating a concentrated waste stream is a problem unique to reverse osmosis. It isn't. No matter what you do you're going to end up with a bunch of salt that you have to get rid of somehow.
The Israelis ran into this problem with their mineral extraction in the Dead Sea, so they're bulldozing the dry salt waste to build a physical wall for border security (more than 10 meters high) that's apparently hard to climb: https://www.youtube.com/watch?v=tgTheUjeDlg
Put the steam turbines inside the steam room to recover some of the heat as power and you are good to go