4 ms·

Where does the salt go when you desalinate? At a large enough scale, would we risk salting some area (or body of water) to death?

barbecue_sauce 7y ago
That's the major issue with desalination. Dumping the brine byproduct back into the ocean is roughly equivalent of dumping other chemicals into the ocean, if not worse.
- AnimalMuppet 7y ago
  Why worse? I'd argue that it's less bad, because the salt was already there. Now, it can still be just as toxic, and that has to be handled. But if properly diluted, then it should be equivalent to the ocean evaporating water, which happens constantly.
  - bryanlarsen 7y ago
    Also, the water created through desalination will end up back in the ocean eventually.
  - noodle 7y ago
    > But if properly diluted That's the key phrase here. Obviously, if you dump it back into the ocean such that it actually does not impact local salinity levels, its fine. But that's also true for essentially anything dumped into the ocean - if you can manage the dumping of a toxic chemical such that it has no impact, wouldn't it also be fine?
    - AnimalMuppet 7y ago
      No. If I take saltwater from the ocean, and desalinate it, and put the salt back in the ocean, the salt was already there before I started. If I dump a toxic chemical in the ocean, the toxic chemical was not there before I started. Those are not equivalent.
- bluGill 7y ago
  Since we are dumping sewage back into the ocean (after treatment), can't we dilute the salt back into what we are putting back? Of course if you go down that route much you realize that the output of sewage plants is safe for human consumption there is no technical reason not to put it back into the water supply and greatly reduce the need for makeup water.
- ClumsyPilot 7y ago
  This statement is so wrong, brine contains salt that was in the ocean to begin with. As long as it's spread/diluted well, it has no impact. Are you claiming this is comparable to an oil spill or eutherification?
ohiovr 7y ago
I think it is a problem: https://www.ncbi.nlm.nih.gov/pubmed/24241776 https://www.ncbi.nlm.nih.gov/pubmed/24241776 Maybe if the plant can spread the salt water further it could be less of an issue?
thinkcontext 7y ago
Typically the waste brine is pumped back out to sea. Its spread over a wide(ish) area to attempt to minimize the environmental impact. There are varying opinions about whether enough is done to avoid damaging the environment. https://en.wikipedia.org/wiki/Desalination#Environmental https://en.wikipedia.org/wiki/Desalination#Environmental
ars 7y ago
Back into the ocean. If you just dump the saline in one place it's bad, but good practice is to dilute the saline with sea water, after which it's perfectly safe. The ocean evaporates more fresh water from its surface than humans could ever possibly match by desalination, so that part is perfectly fine. Just avoid dumping the saline in high concentration (which is easy to do).
journalctl 7y ago
The oceans are big. Like... really really really big. According to [1], humanity uses about four trillion cubic meters of water per year. The oceans, per [2], contain about 321,003,271 cubic miles of water. Adjusting units and turning that into a percentage, we would use 4.154*10^-4 percent (0.0004154%) of the ocean’s water per year. My guess is we can just dump the salt back in. :) Edit: actually add sources. [1] https://ourworldindata.org/water-use-stress https://ourworldindata.org/water-use-stress [2] https://oceanservice.noaa.gov/facts/oceanwater.html https://oceanservice.noaa.gov/facts/oceanwater.html
- orf 7y ago
  That didn't work for sewage or plastic though. The ocean is huge, which is why if you look at the numbers then you can put all human garbage into it and it won't even take up 0.001% of it. In reality, the ocean is huge. So all that salt/garbage/whatever is increadibly uneavenly distributed and will naturally collect in certain areas. In the case of extra salt it could easily have an adverse effect on local ecosystems.
  - BubRoss 7y ago
    The ocean is made of saltwater already, it wasn't made of garbage or plastic. Also salt dissolves in water which is why desalination is needed in the first place. Really think for a moment about what are saying must be true.
    - orf 7y ago
      Ocean water has a specific level of salt. Increasing that in specific areas, by even a small amount, could have disastrous consequences. Life has evolved in the ocean at a particular saline level. The point is not that plastic dissolves I’m water, it’s that the saline concentration won’t be spread evenly throughout the entire expansive ocean without first increasing it locally.
      - BubRoss 7y ago
        That's not what you said originally, you said it would cluster together like garbage and plastic.
morei 7y ago
The energy cost of desalination is a function of the salt concentration (saltier water => more power per liter of fresh water). So when doing commercial desalination you don't want to produce very high salinity output (because it means that at some point in the process you were getting fresh water from very salty water ==> more power). Of course, this has to offset against the cost of pumping et al, so there's an optimal cost output salinity. The TL;DR for most modern desalination plants is that the output salinity is not that high. Typically under 7% dissolved solids (versus the ocean at about 3.5%). Meaning that pumping it back into the ocean is fine. To put it a different way: If the overall salinity of the body of water being desalinated rose appreciably, it would probably render the desalination plant uneconomic.

barbecue_sauce 7y ago

That's the major issue with desalination. Dumping the brine byproduct back into the ocean is roughly equivalent of dumping other chemicals into the ocean, if not worse.

AnimalMuppet 7y ago
Why worse? I'd argue that it's less bad, because the salt was already there. Now, it can still be just as toxic, and that has to be handled. But if properly diluted, then it should be equivalent to the ocean evaporating water, which happens constantly.
- bryanlarsen 7y ago
  Also, the water created through desalination will end up back in the ocean eventually.
- noodle 7y ago
  > But if properly diluted That's the key phrase here. Obviously, if you dump it back into the ocean such that it actually does not impact local salinity levels, its fine. But that's also true for essentially anything dumped into the ocean - if you can manage the dumping of a toxic chemical such that it has no impact, wouldn't it also be fine?
  - AnimalMuppet 7y ago
    No. If I take saltwater from the ocean, and desalinate it, and put the salt back in the ocean, the salt was already there before I started. If I dump a toxic chemical in the ocean, the toxic chemical was not there before I started. Those are not equivalent.
bluGill 7y ago
Since we are dumping sewage back into the ocean (after treatment), can't we dilute the salt back into what we are putting back? Of course if you go down that route much you realize that the output of sewage plants is safe for human consumption there is no technical reason not to put it back into the water supply and greatly reduce the need for makeup water.
ClumsyPilot 7y ago
This statement is so wrong, brine contains salt that was in the ocean to begin with. As long as it's spread/diluted well, it has no impact. Are you claiming this is comparable to an oil spill or eutherification?

ohiovr 7y ago

I think it is a problem: https://www.ncbi.nlm.nih.gov/pubmed/24241776 https://www.ncbi.nlm.nih.gov/pubmed/24241776 Maybe if the plant can spread the salt water further it could be less of an issue?

thinkcontext 7y ago

Typically the waste brine is pumped back out to sea. Its spread over a wide(ish) area to attempt to minimize the environmental impact. There are varying opinions about whether enough is done to avoid damaging the environment. https://en.wikipedia.org/wiki/Desalination#Environmental https://en.wikipedia.org/wiki/Desalination#Environmental

ars 7y ago

Back into the ocean. If you just dump the saline in one place it's bad, but good practice is to dilute the saline with sea water, after which it's perfectly safe. The ocean evaporates more fresh water from its surface than humans could ever possibly match by desalination, so that part is perfectly fine. Just avoid dumping the saline in high concentration (which is easy to do).

journalctl 7y ago

The oceans are big. Like... really really really big. According to [1], humanity uses about four trillion cubic meters of water per year. The oceans, per [2], contain about 321,003,271 cubic miles of water. Adjusting units and turning that into a percentage, we would use 4.154*10^-4 percent (0.0004154%) of the ocean’s water per year. My guess is we can just dump the salt back in. :) Edit: actually add sources. [1] https://ourworldindata.org/water-use-stress https://ourworldindata.org/water-use-stress [2] https://oceanservice.noaa.gov/facts/oceanwater.html https://oceanservice.noaa.gov/facts/oceanwater.html

orf 7y ago
That didn't work for sewage or plastic though. The ocean is huge, which is why if you look at the numbers then you can put all human garbage into it and it won't even take up 0.001% of it. In reality, the ocean is huge. So all that salt/garbage/whatever is increadibly uneavenly distributed and will naturally collect in certain areas. In the case of extra salt it could easily have an adverse effect on local ecosystems.
- BubRoss 7y ago
  The ocean is made of saltwater already, it wasn't made of garbage or plastic. Also salt dissolves in water which is why desalination is needed in the first place. Really think for a moment about what are saying must be true.
  - orf 7y ago
    Ocean water has a specific level of salt. Increasing that in specific areas, by even a small amount, could have disastrous consequences. Life has evolved in the ocean at a particular saline level. The point is not that plastic dissolves I’m water, it’s that the saline concentration won’t be spread evenly throughout the entire expansive ocean without first increasing it locally.
    - BubRoss 7y ago
      That's not what you said originally, you said it would cluster together like garbage and plastic.

morei 7y ago

The energy cost of desalination is a function of the salt concentration (saltier water => more power per liter of fresh water). So when doing commercial desalination you don't want to produce very high salinity output (because it means that at some point in the process you were getting fresh water from very salty water ==> more power). Of course, this has to offset against the cost of pumping et al, so there's an optimal cost output salinity. The TL;DR for most modern desalination plants is that the output salinity is not that high. Typically under 7% dissolved solids (versus the ocean at about 3.5%). Meaning that pumping it back into the ocean is fine. To put it a different way: If the overall salinity of the body of water being desalinated rose appreciably, it would probably render the desalination plant uneconomic.