Hacker News Reader

Comment by yabones | Hacker News Reader

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.

View on HN

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.

Reply on news.ycombinator.com