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Comment by zb1plus | Hacker News Reader

I don't understand why we aren't building nuclear-powered desalinization plants? I am sure the upfront investment is costly, but they seem like an ideal solution if you can get over the "Nuclear scary" aspect for the general public.

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Because this isn't cost-competitive on a per-gallon basis versus continuing to do business as usual, and the environmental impact of any kind of desalinization can be shockingly negative depending on how the waste output is managed. The process produces a hyper-concentrated sludge of minerals/metals/whatever else was in the water that's toxic to basically anything living. You don't want to just drop it in landfills to leach into ground water / spread on the surface, and piping it out to sea ends up creating a massive dead zone around the outlet.

So is the recommended solution a giant concrete vat that costs a fortune and that's the downside?

The ideal solution is to separate and capture useful minerals and metals from the waste, but the current (lack of) cost effectiveness is presently a steep barrier to adoption.

A big problem for desalination is the brine, the highly saline solution left over after the fresh water is removed. You can't just dump it in the sea again, because its high salt content will kill all of the fish, coral, kelp, etc. So you end up with a large retention pond full of dangerous water until it dries up, then the salt is put in a landfill. It's pretty far from sustainable.

Brine is just concentrated lithium for batteries:

https://www.csis.org/analysis/south-americas-lithium-triangl...

If we are smart about it it’s a win win win. Unfortunately we don’t have the workforce to accelerate nuclear development as Greenpeace etc. scared away investment over many decades.

Brine is just water plus the salt that was in the seawater before. You have to dilute it and spread it.

But, sufficiently diluted, it’s just seawater.

In a sense, it’s the same effect as water evaporating over the ocean: Water goes out and salt remains.

It's not as easy as 'dilute and spread' -- highly concentrated brine doesn't really mix readily (halocline effect) when released back into the sea.

Couldn’t there be some kind of dilution step in the plant, using pumps to mix it 1:10 with seawater?

After that, it’s just slightly more salty seawater.

Relatively small differences in dissolved salts are enough to cause halocline barriers that don't really mix well and still pose a hazard to local flora/fauna.

Technically uranium is in all kinds of soil in small amounts... turns out the poison is the dose.

It starts getting really expensive moving a lot of heavy brine and attempting to dilute it, especially when the amounts of water you'll need will create mountains of salt.

Is there a good way to dilute it without using water?

As long as you can dilute it with salt water (until it's not deadly) that shouldn't be a problem.

The US consumes about 322 billion gallons of water per day. There are about 66.5 cubic centimeters of salt in a gallon of water. If we bury the salt in 200-foot deep landfills, that's a total of roughly 32k acres per year, less than 2% of the total landfill capacity in the US (which is roughly 1.8M acres, less than 0.1% of the total land area, so there's plenty of room for more landfills if necessary).

And of course that's assuming we use desalination for 100% of water use in the entire US.

Why is it unsustainable to put the salt in a landfill? There's a lot of land.

I mean, sure, technically it could run out over millenia or something?

The concentrated minerals and metals in the waste, as well as the chemical additives used during the desalination process, are incredibly difficult to contain given their solubility in water.

There is a lot of desert where desalination is typically used. Seems like putting problematic water soluble in places where the main problem is lack of water would work out ok. Unless they are also blown around by wind in some problematic way.

Is this more of an issue for evaporated brine than for regular landfills? I thought that modern landfills had pretty advanced systems for preventing groundwater contamination, but it does seem possible that the problem is harder for water soluble brine.

We don't build nuclear because it's expensive because we don't build nuclear.

If we hadn't made the terrible decision of halting construction for decades and miring the process in an impossible tangle of red tape, nuclear power would be much cheaper today. The only way forward is to build and build so we get the unit economics down and our energy production way up.

Mining and disposing of fissile material is carbon intense, even if the recycling reactors can scale. Construction and maintenance of plants too is carbon intense.

The full lifecycle cost of nuclear may still be worth it. Though I don't think that's guaranteed and risks are greater than wind, solar, and batteries.

Because it's ludicrously expensive and only economically viable for cities. Also, there's enough water to supply cities, just not enough to supply cities and agriculture. Given that, if cities need more water, it's cheaper to buy out some farms and take their water rights than it is to build a nuclear + desalination plant for a few billion dollars.

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