5 ms·

Hypothetical (impossibly efficient) desalinator for consideration, turns 101L seawater into 100L potable water and 1L brine effluent. If you diluted the brine w

Hypothetical (impossibly efficient) desalinator for consideration, turns 101L seawater into 100L potable water and 1L brine effluent. If you diluted the brine with another 100L of seawater, the diluted effluent would have twice the salinity of natural seawater. Dilute that 1L of effluent with 1000L and it would still be 10% above background (3.8% salinity, rather than 3.5%), which I think would affect sea life in the discharge area. Would have to dilute it with 10,000 litres to get it back down to 1% of background level (3.53% instead of 3.5%). I'm sure some saltwater aquarium people would have comments here :) More mixing and dilution will happen after discharge, which would likely make it not a big deal for moving brine source. But a land based desalinator would need a very detailed impact assessment to prove it wouldn't have an impact on marine life at the discharge site

mcguire 7y ago
Back in the '80s, Grant Callin wrote a couple of pretty decent hard science fiction novels. In one, the aliens had a magic quantum mechanical technology that enabled flying cars and such, but generated very large amounts of heat as a side effect. (A Lion on Tharthee, https://archive.org/details/lionontharthee0000call https://archive.org/details/lionontharthee0000call) "What do you do with the heat?" "We store it temporarily on the vehicles and then radiate it into the ocean." "Doesn't that cause an ecological problem?" "Hah! That's the joke! We could do this for hundreds of thousands of years before we raised the ocean temperature 0.1 degree." My question: How do you distribute gigawatts of energy uniformly through the ocean? Or are you simply boiling a bay somewhere and calling it good?
- sjwright 7y ago
  If you disperse it into an ocean current, you’d have much of the mixing done for you. (How that would affect the ocean current, given that they’re thermally driven, is less clear and unlikely to be good.)
- SECProto 7y ago
  > My question: How do you distribute gigawatts of energy uniformly through the ocean? Or are you simply boiling a bay somewhere and calling it good? Assuming this is your question, and not a continuation of the quote: thermal energy is definitely a concern. It could be solved with dilution, like other pollutants. In the particular case we're discussing, of using heat from a nuclear power plant to desalinate water: Every thermal power plant already creates waste thermal heat. They exhaust this heat either through evaporation (the stereotypical hyperboloid cooling tower of a nuclear power plant) or discharge into a body of water (thermal plants around me do this). The latter is definitely a sticking point in gaining modern environmental approval.
ncmncm 7y ago
Why in the world would you concentrate seawater to 100:1, and then dilute it, instead of just reducing it to 2:1? If it is a matter of heat efficiency, surely a long heat exchanger can recover it all on the way back to the sea, absorbing it into the incoming water.
- SECProto 7y ago
  It was a hypothetical to illustrate how much dilution is needed to get effleunt close to background level salinity. It isn't even possible to extract that much fresh, since seawater is 3.5% salt. I was not talking about heat at all. To illustrate: the effluent dilution requirement in your case isn't actually much better. If you took in 100L of seawater, extracted 50L fresh, that leaves you with 50L brine at twice the background concentration. To get that effluent back to 1% above background, you have to dilute that 50L brine with 4950L of seawater.

mcguire 7y ago

Back in the '80s, Grant Callin wrote a couple of pretty decent hard science fiction novels. In one, the aliens had a magic quantum mechanical technology that enabled flying cars and such, but generated very large amounts of heat as a side effect. (A Lion on Tharthee, https://archive.org/details/lionontharthee0000call https://archive.org/details/lionontharthee0000call) "What do you do with the heat?" "We store it temporarily on the vehicles and then radiate it into the ocean." "Doesn't that cause an ecological problem?" "Hah! That's the joke! We could do this for hundreds of thousands of years before we raised the ocean temperature 0.1 degree." My question: How do you distribute gigawatts of energy uniformly through the ocean? Or are you simply boiling a bay somewhere and calling it good?

sjwright 7y ago
If you disperse it into an ocean current, you’d have much of the mixing done for you. (How that would affect the ocean current, given that they’re thermally driven, is less clear and unlikely to be good.)
SECProto 7y ago
> My question: How do you distribute gigawatts of energy uniformly through the ocean? Or are you simply boiling a bay somewhere and calling it good? Assuming this is your question, and not a continuation of the quote: thermal energy is definitely a concern. It could be solved with dilution, like other pollutants. In the particular case we're discussing, of using heat from a nuclear power plant to desalinate water: Every thermal power plant already creates waste thermal heat. They exhaust this heat either through evaporation (the stereotypical hyperboloid cooling tower of a nuclear power plant) or discharge into a body of water (thermal plants around me do this). The latter is definitely a sticking point in gaining modern environmental approval.

ncmncm 7y ago

Why in the world would you concentrate seawater to 100:1, and then dilute it, instead of just reducing it to 2:1? If it is a matter of heat efficiency, surely a long heat exchanger can recover it all on the way back to the sea, absorbing it into the incoming water.

SECProto 7y ago
It was a hypothetical to illustrate how much dilution is needed to get effleunt close to background level salinity. It isn't even possible to extract that much fresh, since seawater is 3.5% salt. I was not talking about heat at all. To illustrate: the effluent dilution requirement in your case isn't actually much better. If you took in 100L of seawater, extracted 50L fresh, that leaves you with 50L brine at twice the background concentration. To get that effluent back to 1% above background, you have to dilute that 50L brine with 4950L of seawater.