3 ms·

> I've heard that this brine is toxic. Does this make disposal an issue? Is the toxicity true or hyperbole? I mean, do we know how bad it is, and if we can do a

by tivert 3y ago

> I've heard that this brine is toxic. Does this make disposal an issue? Is the toxicity true or hyperbole? I mean, do we know how bad it is, and if we can do anything safely with it? It seems like "salt" is useful in a lot of contexts, including industrial, so can we do something with the brine besides disposing it somewhere? Too much salt can kill stuff (e.g. people, plants), so I suppose that makes it "toxic." Maybe there's a tiny amount old industrial pollution from anywhere an everywhere that concentrated in there, too. However, if you're desalinating seawater, what's the problem with just dumping the brine back in the sea? Unless you introduced new stuff into it during the desalination process, you wouldn't be making anything worse.

grogenaut 3y ago
Because the brine is hyper-salty compared to ocean water and takes a while to mix back in, essentially creating a new ecosystem, brackish, where the outlets are. What's wrong with pumping 10% CO2 into your office constantly from a compressed gas plant extracting oxygen and argon next door?
- tivert 3y ago
  > Because the brine is hyper-salty compared to ocean water and takes a while to mix back in, essentially creating a new ecosystem, brackish, where the outlets are. How large would those brackish areas near the outlets be? It seems to be that would be a big problem in an enclosed bay, but much less so on a shore facing open ocean. Could they run pipes out a few kilometers with small, regular holes (maybe some modification of oil pipeline technology) to spread the discharge out and mitigate the concentration problem? Could they make the waste output less concentrated? Maybe by either running the desalination process less (would that also increase energy efficiency?) or by pre-mixing the waste with some un-desalinated intake water?
  - rtkwe 3y ago
    The pipe with many holes is one of the solutions used today it's just imperfect and requires a lot of pipe to make sure the waste output isn't too concentrated in a single area.
jerf 3y ago
There are several practical problems dumping the brine back in the sea. If you dump it on a living ecosystem you tend to kill it. Living ecosystems are, unfortunately, concentrated right where we are desalinating and is cheap to dump. Compounding this problem is that water mixes much more slowly than your intuition suggests. It can stay a coherent mass of high-salt water way longer than you'd think, killing as it goes. This is one of the more surprising things I've learned in the past few years, honestly. Your kitchen-scale-based intuition of how long it takes for liquids of different characteristics to blend together turns out to be way off. Trying to pipe it away to somewhere where it is less of a problem is expensive. In the long term just dropping it back into the ocean is not a big deal, but that short term is surprisingly destructive. You'd think you could just drop it in and maybe a few hundred feet from the outlet it would be all dissipated and harmless, but unfortunately the physics don't work out that way.
- scythe 3y ago
  The "clever" version I've seen in some papers is to use reverse electrodialysis to recover energy as you dilute the waste brine with seawater. AFAIK, this has not been incorporated into any existing installations.
- margalabargala 3y ago
  > water mixes much more slowly than your intuition suggests As a visceral example of this in the other direction, the freshwater plume of the Amazon River extends more than 60km into the ocean. [0] I would love to see these plants placed in areas where there's a nearby dry below-sea-level basin, into which the brine may be discharged. The Salton Sea in CA is one example, there's another similar location in Egypt I'm aware of. The advantage of such locations is they are usually extremely hot and arid, which means there's generally not much of a local ecosystem or human population, and there is ample solar power availability. [0] https://eos.org/science-updates/the-amazon-rivers-ecosystem-where-land-meets-the-sea https://eos.org/science-updates/the-amazon-rivers-ecosystem-...
  - AnimalMuppet 3y ago
    The Salton Sea is over a hundred miles from the ocean, though, with at least one mountain range in the way. It might be a good dumping ground (or maybe not - there at least were fish in it, if there still are, this would almost certainly kill them). But it would definitely take a lot of energy to pump the water there.

by tivert 3y ago

grogenaut 3y ago

Because the brine is hyper-salty compared to ocean water and takes a while to mix back in, essentially creating a new ecosystem, brackish, where the outlets are. What's wrong with pumping 10% CO2 into your office constantly from a compressed gas plant extracting oxygen and argon next door?

tivert 3y ago
> Because the brine is hyper-salty compared to ocean water and takes a while to mix back in, essentially creating a new ecosystem, brackish, where the outlets are. How large would those brackish areas near the outlets be? It seems to be that would be a big problem in an enclosed bay, but much less so on a shore facing open ocean. Could they run pipes out a few kilometers with small, regular holes (maybe some modification of oil pipeline technology) to spread the discharge out and mitigate the concentration problem? Could they make the waste output less concentrated? Maybe by either running the desalination process less (would that also increase energy efficiency?) or by pre-mixing the waste with some un-desalinated intake water?
- rtkwe 3y ago
  The pipe with many holes is one of the solutions used today it's just imperfect and requires a lot of pipe to make sure the waste output isn't too concentrated in a single area.

jerf 3y ago

There are several practical problems dumping the brine back in the sea. If you dump it on a living ecosystem you tend to kill it. Living ecosystems are, unfortunately, concentrated right where we are desalinating and is cheap to dump. Compounding this problem is that water mixes much more slowly than your intuition suggests. It can stay a coherent mass of high-salt water way longer than you'd think, killing as it goes. This is one of the more surprising things I've learned in the past few years, honestly. Your kitchen-scale-based intuition of how long it takes for liquids of different characteristics to blend together turns out to be way off. Trying to pipe it away to somewhere where it is less of a problem is expensive. In the long term just dropping it back into the ocean is not a big deal, but that short term is surprisingly destructive. You'd think you could just drop it in and maybe a few hundred feet from the outlet it would be all dissipated and harmless, but unfortunately the physics don't work out that way.

scythe 3y ago
The "clever" version I've seen in some papers is to use reverse electrodialysis to recover energy as you dilute the waste brine with seawater. AFAIK, this has not been incorporated into any existing installations.
margalabargala 3y ago
> water mixes much more slowly than your intuition suggests As a visceral example of this in the other direction, the freshwater plume of the Amazon River extends more than 60km into the ocean. [0] I would love to see these plants placed in areas where there's a nearby dry below-sea-level basin, into which the brine may be discharged. The Salton Sea in CA is one example, there's another similar location in Egypt I'm aware of. The advantage of such locations is they are usually extremely hot and arid, which means there's generally not much of a local ecosystem or human population, and there is ample solar power availability. [0] https://eos.org/science-updates/the-amazon-rivers-ecosystem-where-land-meets-the-sea https://eos.org/science-updates/the-amazon-rivers-ecosystem-...
- AnimalMuppet 3y ago
  The Salton Sea is over a hundred miles from the ocean, though, with at least one mountain range in the way. It might be a good dumping ground (or maybe not - there at least were fish in it, if there still are, this would almost certainly kill them). But it would definitely take a lot of energy to pump the water there.