4 ms·

FTA: "Unlike some desalination systems, there is no accumulation of salt or concentrated brines to be disposed of. In a free-floating configuration, any salt th

FTA: "Unlike some desalination systems, there is no accumulation of salt or concentrated brines to be disposed of. In a free-floating configuration, any salt that accumulates during the day would simply be carried back out at night through the wicking material and back into the seawater, according to the researchers." The capabilities are freaking interesting, but let's say someone builds a big enough settlement on a coastline or island in which every building has one or more of these devices on its rooftop. Would this release back enough salt so that the surrounding seawater becomes hostile to its previous lifeforms? Also, since then the water used in the process would contain more salt, how much would that render the device less efficient?

dystroy 5y ago
Salt release is already a huge environmental concern with exiting desalinization systems. Energy consumption and installation costs aren't the sole (and probably not the main) problems. Desalinization is inherently a pollution.
- Someone 5y ago
  A small part of it can be avoided by combining this with a salt evaporation pond (https://en.wikipedia.org/wiki/Salt_evaporation_pond https://en.wikipedia.org/wiki/Salt_evaporation_pond) Problem will be that we’ll get way too much salt (a few grams of salt per liter of water), so it won’t help much.
- throwaway894345 5y ago
  Why not release the salt back to the sea? Presumably it would not increase the salt content of the ocean very much considering the vastness of the ocean and the sheer quantity of fresh water that is being added to it by melting glaciers, etc? What am I missing?
  - dystroy 5y ago
    The salt you release isn't instantly diluted in the whole ocean and we're speaking, for a plant, of millions cubic meters of salt enriched water per day. The release area is just dying.
    - shellfishgene 5y ago
      Can you provide a source for that? I dove near a desalination plant exit pipe in Saudi, the impact on the marine live did not seem to big in the area. But it was a small plant for a few thousand people and we did not do a proper assessment. I don't doubt there is an effect, but am not convinced that the "release area just dying" is correct.
      - EricE 5y ago
        https://www.keiken-engineering.com/en/brine-disposal-how-efficient-desalination-plants-get-rid-of-toxic-remnant/ https://www.keiken-engineering.com/en/brine-disposal-how-eff... Brine disposal is indeed a complex issue. Should be noted the above URL is from a desalinization industry proponent so I would say it's probably a little more optimistically biased but it was one of the better summaries I found so it still has value from that perspective. If you do more digging around each of the solutions they discuss you can find more pro's/con's for each and you will quickly find out that it is a pretty significant issue.
        shellfishgene 5y ago
        The link does not really show any evidence that marine ecology at brine outlets is disturbed. It does however suggest that pouring the brine on land or roads (for de-icing) are alternative solutions, which I doubt ;). I was more thinking of proper studies, such as reviewed in [0], which says in the abstract: "Ecological monitoring studies have found variable effects ranging from no significant impacts to benthic communities, through to widespread alterations to community structure in seagrass, coral reef and soft-sediment ecosystems when discharges are released to poorly flushed environments. In most other cases environmental effects appear to be limited to within 10s of meters of outfalls." So, impact yes, but "release area is just dying", probably not. [0] https://www.sciencedirect.com/science/article/abs/pii/S0043135410002903 https://www.sciencedirect.com/science/article/abs/pii/S00431...
  - kevstev 5y ago
    Why not just collect the salt, and sell it as... salt? Even if its not ok for cooking, it should be fine for roads? I am sure there are other industrial uses for salt.
    - SV_BubbleTime 5y ago
      Actual salt is rarely used on the roads in the USA anymore. Majority use magnesium chloride now. Don’t know about the rest of the world. Lots of reasons, pros and cons. I work in automotive and hate it.
    - EricE 5y ago
      Salt from roads is seriously contaminating our environment and significantly impacting farming in more and more areas. Ever hear of the Romans salting the earth of people the conquered? It was so they couldn't grow crops - yet we routinely do this to ourselves - pretty daft.
      - throwaway894345 5y ago
        We also farm in a way that is almost optimized for erosion of topsoil. We’ve already lost a third of it and it only renews on geological timescales. Daft is too polite.
lucbocahut 5y ago
I wonder if the fresh water used in such a way wouldn’t eventually be released back into the ocean thus somewhat mitigating the effect.
EugeneOZ 5y ago
In large enough systems some kind of “salt removal” mechanism might be added - I think it wasn't added to a PoC just to make it as simple and cheap as possible.
dsr_ 5y ago
This chunk from the article is, unfortunately, an outright lie. By definition, removing salt from seawater leaves you with water and salt. The article handwaves the salt away by supposing that the desalinator will float on top of the ocean. In actual production configurations other than towing it behind your sailboat, you will end up with a brine pool that needs to be disposed of, or a concentration in the wicking material that prevents low-concentration seawater from entering, or a pumping system. This is not just a common negative externality, but a casual lie about it.
- KaiserPro 5y ago
  > supposing that the desalinator will float on top of the ocean. I think that as its solar, you only have 50% duty cycle (more or less) so the idea is that you "just" slow down the water supply to remove the salt over night.
- adrianmonk 5y ago
  I don't think they are talking about the impact on the environment. I think they are talking about the procedures for operating the equipment. The way I read it, they mean whoever operates this device does not have to periodically go empty some bin/tank of salt or brine. An analogy would be to a frost-free refrigerator. When you say the freezer compartment of your fridge is frost-free, you don't mean that it never generates frost. You mean it does generate frost, but it also automatically removes it. It's "free" of frost in the sense that you are free of doing a chore that you have to do with a freezer that lacks this feature.
  - dsr_ 5y ago
    If you operate it directly on the open ocean, towing it behind your sailboat, you don't have to do anything special. If you operate it in a commercial, protected context where you pump water through it, you will generate brine. If you operate it en-masse in the ocean, the things that are insignificant at the scale of 1 and 10 square meters may become significant at the scale of 1 and 10 square kilometers. All of these things are true for other desalinization systems, too. Claiming "you don't have to worry about brine" because it floats on the water surface is misleading at best. You can put any system you want on the water and make it float -- we have concrete and steel hulls, no problem -- but that doesn't solve the concentration problem.
amn79 5y ago
Why release the salt back into sea water? This is salt production alongside desalination.
- jedberg 5y ago
  We already have a massive oversupply of salt from existing desalination. The cost of table salt is basically all transportation at this point.
  - mixmastamyk 5y ago
    Can be buried also.
  - e12e 5y ago
    > The cost of table salt is basically all transportation at this point. Using the salt on site would save the transport, though?
bruce511 5y ago
There are two counterpoints to the issue of excess salt being an environmental hazard. A) brine can be introduced back into the ocean combined with waste water. In the Cape Town drought of 2017 some small desalination plants were brought into service very quickly, and the brine was expelled in the same pipe as the outflow from a (treated waste) sewerage plant. B) the ocean is big - very big - and at least by our coast seldom "calm". So outflow of anything would disperse very quickly. Hot-water outflow from a nuclear power station dissipates very quickly for example - typically within tens of metres of the outflow. C) the natural salinity of the ocean varies a fair bit at the very local level - think river mouths - storm water - evaporation etc. Outside of specifc closed bodies of water (Dead Sea etc) we'd need desalination on a massive scale to even measure the impact.

dystroy 5y ago

Salt release is already a huge environmental concern with exiting desalinization systems. Energy consumption and installation costs aren't the sole (and probably not the main) problems. Desalinization is inherently a pollution.

Someone 5y ago
A small part of it can be avoided by combining this with a salt evaporation pond (https://en.wikipedia.org/wiki/Salt_evaporation_pond https://en.wikipedia.org/wiki/Salt_evaporation_pond) Problem will be that we’ll get way too much salt (a few grams of salt per liter of water), so it won’t help much.
throwaway894345 5y ago
Why not release the salt back to the sea? Presumably it would not increase the salt content of the ocean very much considering the vastness of the ocean and the sheer quantity of fresh water that is being added to it by melting glaciers, etc? What am I missing?
- dystroy 5y ago
  The salt you release isn't instantly diluted in the whole ocean and we're speaking, for a plant, of millions cubic meters of salt enriched water per day. The release area is just dying.
  - shellfishgene 5y ago
    Can you provide a source for that? I dove near a desalination plant exit pipe in Saudi, the impact on the marine live did not seem to big in the area. But it was a small plant for a few thousand people and we did not do a proper assessment. I don't doubt there is an effect, but am not convinced that the "release area just dying" is correct.
    - EricE 5y ago
      https://www.keiken-engineering.com/en/brine-disposal-how-efficient-desalination-plants-get-rid-of-toxic-remnant/ https://www.keiken-engineering.com/en/brine-disposal-how-eff... Brine disposal is indeed a complex issue. Should be noted the above URL is from a desalinization industry proponent so I would say it's probably a little more optimistically biased but it was one of the better summaries I found so it still has value from that perspective. If you do more digging around each of the solutions they discuss you can find more pro's/con's for each and you will quickly find out that it is a pretty significant issue.
      - shellfishgene 5y ago
        The link does not really show any evidence that marine ecology at brine outlets is disturbed. It does however suggest that pouring the brine on land or roads (for de-icing) are alternative solutions, which I doubt ;). I was more thinking of proper studies, such as reviewed in [0], which says in the abstract: "Ecological monitoring studies have found variable effects ranging from no significant impacts to benthic communities, through to widespread alterations to community structure in seagrass, coral reef and soft-sediment ecosystems when discharges are released to poorly flushed environments. In most other cases environmental effects appear to be limited to within 10s of meters of outfalls." So, impact yes, but "release area is just dying", probably not. [0] https://www.sciencedirect.com/science/article/abs/pii/S0043135410002903 https://www.sciencedirect.com/science/article/abs/pii/S00431...
- kevstev 5y ago
  Why not just collect the salt, and sell it as... salt? Even if its not ok for cooking, it should be fine for roads? I am sure there are other industrial uses for salt.
  - SV_BubbleTime 5y ago
    Actual salt is rarely used on the roads in the USA anymore. Majority use magnesium chloride now. Don’t know about the rest of the world. Lots of reasons, pros and cons. I work in automotive and hate it.
  - EricE 5y ago
    Salt from roads is seriously contaminating our environment and significantly impacting farming in more and more areas. Ever hear of the Romans salting the earth of people the conquered? It was so they couldn't grow crops - yet we routinely do this to ourselves - pretty daft.
    - throwaway894345 5y ago
      We also farm in a way that is almost optimized for erosion of topsoil. We’ve already lost a third of it and it only renews on geological timescales. Daft is too polite.

lucbocahut 5y ago

I wonder if the fresh water used in such a way wouldn’t eventually be released back into the ocean thus somewhat mitigating the effect.

EugeneOZ 5y ago

In large enough systems some kind of “salt removal” mechanism might be added - I think it wasn't added to a PoC just to make it as simple and cheap as possible.

dsr_ 5y ago

This chunk from the article is, unfortunately, an outright lie. By definition, removing salt from seawater leaves you with water and salt. The article handwaves the salt away by supposing that the desalinator will float on top of the ocean. In actual production configurations other than towing it behind your sailboat, you will end up with a brine pool that needs to be disposed of, or a concentration in the wicking material that prevents low-concentration seawater from entering, or a pumping system. This is not just a common negative externality, but a casual lie about it.

KaiserPro 5y ago
> supposing that the desalinator will float on top of the ocean. I think that as its solar, you only have 50% duty cycle (more or less) so the idea is that you "just" slow down the water supply to remove the salt over night.
adrianmonk 5y ago
I don't think they are talking about the impact on the environment. I think they are talking about the procedures for operating the equipment. The way I read it, they mean whoever operates this device does not have to periodically go empty some bin/tank of salt or brine. An analogy would be to a frost-free refrigerator. When you say the freezer compartment of your fridge is frost-free, you don't mean that it never generates frost. You mean it does generate frost, but it also automatically removes it. It's "free" of frost in the sense that you are free of doing a chore that you have to do with a freezer that lacks this feature.
- dsr_ 5y ago
  If you operate it directly on the open ocean, towing it behind your sailboat, you don't have to do anything special. If you operate it in a commercial, protected context where you pump water through it, you will generate brine. If you operate it en-masse in the ocean, the things that are insignificant at the scale of 1 and 10 square meters may become significant at the scale of 1 and 10 square kilometers. All of these things are true for other desalinization systems, too. Claiming "you don't have to worry about brine" because it floats on the water surface is misleading at best. You can put any system you want on the water and make it float -- we have concrete and steel hulls, no problem -- but that doesn't solve the concentration problem.

amn79 5y ago

Why release the salt back into sea water? This is salt production alongside desalination.

jedberg 5y ago
We already have a massive oversupply of salt from existing desalination. The cost of table salt is basically all transportation at this point.
- mixmastamyk 5y ago
  Can be buried also.
- e12e 5y ago
  > The cost of table salt is basically all transportation at this point. Using the salt on site would save the transport, though?

bruce511 5y ago

There are two counterpoints to the issue of excess salt being an environmental hazard. A) brine can be introduced back into the ocean combined with waste water. In the Cape Town drought of 2017 some small desalination plants were brought into service very quickly, and the brine was expelled in the same pipe as the outflow from a (treated waste) sewerage plant. B) the ocean is big - very big - and at least by our coast seldom "calm". So outflow of anything would disperse very quickly. Hot-water outflow from a nuclear power station dissipates very quickly for example - typically within tens of metres of the outflow. C) the natural salinity of the ocean varies a fair bit at the very local level - think river mouths - storm water - evaporation etc. Outside of specifc closed bodies of water (Dead Sea etc) we'd need desalination on a massive scale to even measure the impact.