4 ms·

No, fresh water just enters the water cycle. It will eventually evaporate or end up in a river and back into the ocean where it will be reunited with the salt.

No, fresh water just enters the water cycle. It will eventually evaporate or end up in a river and back into the ocean where it will be reunited with the salt. The overall salt concentration of the ocean would not be changed unless we sequestered the fresh water permanently. Even then it would take a tremendous effort to make even the tiniest difference in salinity.

rtkwe 3y ago
It will change the salinity on the short term though at the release location and the amount a large plant will be discharging is enough to alter the local salinity so long as the plant remains operational which will negatively affect sea life in that area.
- Robotbeat 3y ago
  Only if the discharge is not diluted sufficiently. There is nothing about reverse osmosis that is fundamentally more toxic or harmful than the typical evaporation that takes place naturally in the ocean. And it’s pretty dishonest to claim otherwise. If there’s a problem with too high salinity of discharge, that’s an engineering problem that should be fixed with greater dilution.
  - xenadu02 3y ago
    I almost addressed this point in my original post... you need a diffusion system that runs the brine out into the ocean and mixes it with seawater to a certain concentration... as long as it isn't super concentrated or at a very different temperature it won't create a brine pool and the salt will diffuse harmlessly.
  - strken 3y ago
    If you're drawing water from a bay and not putting all that water back in, then the salinity of the bay must depend on the rate it mixes with the outside ocean, since you're removing water from the system. I assume that in practice the amount of water taken by a desal plan is tiny and most bays have high tidal inflow and outflow, but it's obvious that more than just dilution should be considered.
  - 8n4vidtmkvmk 3y ago
    What would you dilute it with? Surely not the water we just extracted?
    - Robotbeat 3y ago
      You dilute it with more seawater. The salinity of the ocean changes significantly just due to evaporation. The band of variability is roughly 30 to 40 grams of salts per liter for sea surface salinity. So if your discharge is within that band, it's not going to be a significant ecological problem (especially if the discharge is at the right location). It's no more a "mass ecological problem" than surface evaporation of seawater is.
      - rtkwe 3y ago
        Mass dilution is going to be fairly expensive because you have to move a significant multiple of the water you actually process. The brine waste water is roughly double the salinity of normal sea water at 70 ppt so to get back to the 33-37 ppt that's the real average band you're looking at moving a lot of sea water to dilute the output. If you run the numbers you're looking at 15:1 of volume to get 70ppt to 37ppt using 35ppt water all while ensuring you're at a place with enough natural mixing that your inputs and outputs don't start feeding back into each other.
  - rtkwe 3y ago
    Of course but read the comment I was replying to, to my reading they're saying the regular water cycle would take care of the excess salinity which is drastically wrong in the human scale and a complete misread of the issue. The problem isn't that we'll over salinate the whole ocean but that locally the released brine will kill some, potentially large, area of underwater life before it diffuses back down to the rough background levels.

rtkwe 3y ago

It will change the salinity on the short term though at the release location and the amount a large plant will be discharging is enough to alter the local salinity so long as the plant remains operational which will negatively affect sea life in that area.

Robotbeat 3y ago
Only if the discharge is not diluted sufficiently. There is nothing about reverse osmosis that is fundamentally more toxic or harmful than the typical evaporation that takes place naturally in the ocean. And it’s pretty dishonest to claim otherwise. If there’s a problem with too high salinity of discharge, that’s an engineering problem that should be fixed with greater dilution.
- xenadu02 3y ago
  I almost addressed this point in my original post... you need a diffusion system that runs the brine out into the ocean and mixes it with seawater to a certain concentration... as long as it isn't super concentrated or at a very different temperature it won't create a brine pool and the salt will diffuse harmlessly.
- strken 3y ago
  If you're drawing water from a bay and not putting all that water back in, then the salinity of the bay must depend on the rate it mixes with the outside ocean, since you're removing water from the system. I assume that in practice the amount of water taken by a desal plan is tiny and most bays have high tidal inflow and outflow, but it's obvious that more than just dilution should be considered.
- 8n4vidtmkvmk 3y ago
  What would you dilute it with? Surely not the water we just extracted?
  - Robotbeat 3y ago
    You dilute it with more seawater. The salinity of the ocean changes significantly just due to evaporation. The band of variability is roughly 30 to 40 grams of salts per liter for sea surface salinity. So if your discharge is within that band, it's not going to be a significant ecological problem (especially if the discharge is at the right location). It's no more a "mass ecological problem" than surface evaporation of seawater is.
    - rtkwe 3y ago
      Mass dilution is going to be fairly expensive because you have to move a significant multiple of the water you actually process. The brine waste water is roughly double the salinity of normal sea water at 70 ppt so to get back to the 33-37 ppt that's the real average band you're looking at moving a lot of sea water to dilute the output. If you run the numbers you're looking at 15:1 of volume to get 70ppt to 37ppt using 35ppt water all while ensuring you're at a place with enough natural mixing that your inputs and outputs don't start feeding back into each other.
- rtkwe 3y ago
  Of course but read the comment I was replying to, to my reading they're saying the regular water cycle would take care of the excess salinity which is drastically wrong in the human scale and a complete misread of the issue. The problem isn't that we'll over salinate the whole ocean but that locally the released brine will kill some, potentially large, area of underwater life before it diffuses back down to the rough background levels.