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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, unfort

by 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.
  - cyanydeez 3y ago
    Great movie: Salton Sea
  - margalabargala 3y ago
    It would take one mildly expensive tunnel. As a bonus, you might be able to put hydro turbines on it, if they can handle the salt. The Salton Sea's salinity is already well over that of the ocean (44g per liter compared to 35), and is getting saltier. Considering that the very existence of the Salton Sea is already an ecological disaster, I don't really see dumping salt into it to be another one. The Salton Sea is 70 miles from the Pacific Ocean. If this were built, it would be only the third longest water tunnel in the world, and second in the US.
- avar 3y ago
  > the freshwater plume of the Amazon River extends more than 60km into the ocean. It really doesn't, or perhaps only in the most pedantic sense. That "ocean" is still the mouth of the Amazon itself, and most of it's less than 10 meters deep. It's really the estuary of the river itself. See: https://www.frontiersin.org/articles/10.3389/fmars.2017.00026/full https://www.frontiersin.org/articles/10.3389/fmars.2017.0002...
bjelkeman-again 3y ago
The extreme volumes produced in the Arabian Gulf is subject to a lot of studies (some plants produce one million m2 per day). This does cause issues. An in-depth look at possible futures can be found here. http://essay.utwente.nl/79579/1/Dols%2C%20F.J.%201862227%20_openbaar.pdf http://essay.utwente.nl/79579/1/Dols%2C%20F.J.%201862227%20_...
Robotbeat 3y ago
> If you dump it on a living ecosystem you tend to kill it. This is false and somewhat dishonest. This is simply a choice of not diluting it enough. There is nothing about the discharge from reverse osmosis that is any more fundamentally toxic than the natural process of evaporation. Proper dilution is essential, and treating the discharge as fundamentally toxic actually undermines the engineering to do this proper dilution because people will figure “oh well, I guess there’s nothing we can do as it’s going to tend to kill no matter what.” People need to stop misleading about discharge toxicity.
- schiffern 3y ago
  >This is simply a choice of not diluting it enough. If that choice were up to engineers, it's fine. In practice the choice is actually made by MBA types, a field where harmful short-termism is almost a religion.
  - cyanydeez 3y ago
    It's made by practical money and people who don't want to consume local resources.
- cyanydeez 3y ago
  This is dishonest: toxicity, dosage are fundamental properties. You can't just wave a word at it like dilution and think you're solving an engineering problem. If you got 1 gallon out of sea water, what do you think you need to dilute it to be safe? Typically, it's 99%∆.
  - xyzzyz 3y ago
    You don’t need to dilute a gallon of sea water at all, it is perfectly safe to dump it back into sea as is.
    - cyanydeez 3y ago
      For you, locally, sure. It'll kill however, plenty of things.

by jerf 3y ago

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.
- cyanydeez 3y ago
  Great movie: Salton Sea
- margalabargala 3y ago
  It would take one mildly expensive tunnel. As a bonus, you might be able to put hydro turbines on it, if they can handle the salt. The Salton Sea's salinity is already well over that of the ocean (44g per liter compared to 35), and is getting saltier. Considering that the very existence of the Salton Sea is already an ecological disaster, I don't really see dumping salt into it to be another one. The Salton Sea is 70 miles from the Pacific Ocean. If this were built, it would be only the third longest water tunnel in the world, and second in the US.
avar 3y ago
> the freshwater plume of the Amazon River extends more than 60km into the ocean. It really doesn't, or perhaps only in the most pedantic sense. That "ocean" is still the mouth of the Amazon itself, and most of it's less than 10 meters deep. It's really the estuary of the river itself. See: https://www.frontiersin.org/articles/10.3389/fmars.2017.00026/full https://www.frontiersin.org/articles/10.3389/fmars.2017.0002...

bjelkeman-again 3y ago

The extreme volumes produced in the Arabian Gulf is subject to a lot of studies (some plants produce one million m2 per day). This does cause issues. An in-depth look at possible futures can be found here. http://essay.utwente.nl/79579/1/Dols%2C%20F.J.%201862227%20_openbaar.pdf http://essay.utwente.nl/79579/1/Dols%2C%20F.J.%201862227%20_...

Robotbeat 3y ago

> If you dump it on a living ecosystem you tend to kill it. This is false and somewhat dishonest. This is simply a choice of not diluting it enough. There is nothing about the discharge from reverse osmosis that is any more fundamentally toxic than the natural process of evaporation. Proper dilution is essential, and treating the discharge as fundamentally toxic actually undermines the engineering to do this proper dilution because people will figure “oh well, I guess there’s nothing we can do as it’s going to tend to kill no matter what.” People need to stop misleading about discharge toxicity.

schiffern 3y ago
>This is simply a choice of not diluting it enough. If that choice were up to engineers, it's fine. In practice the choice is actually made by MBA types, a field where harmful short-termism is almost a religion.
- cyanydeez 3y ago
  It's made by practical money and people who don't want to consume local resources.
cyanydeez 3y ago
This is dishonest: toxicity, dosage are fundamental properties. You can't just wave a word at it like dilution and think you're solving an engineering problem. If you got 1 gallon out of sea water, what do you think you need to dilute it to be safe? Typically, it's 99%∆.
- xyzzyz 3y ago
  You don’t need to dilute a gallon of sea water at all, it is perfectly safe to dump it back into sea as is.
  - cyanydeez 3y ago
    For you, locally, sure. It'll kill however, plenty of things.