Japan has opened its first osmotic power plant
19 comments
·August 25, 2025elil17
rdtsc
> They really fail to explain a key point here. The reason you colocate this with a desalination plant is because you use the super-salty wastewater from desalination as the salty side of the osmosis power plant. Then you find some wastewater which is low in salt (such as semi-treated sewage), and use that as the fresh side of the osmosis power plant.
They do hint at it at end:
> “It is also noteworthy that the Japanese plant uses concentrated seawater, the brine left after removal of fresh water in a desalination plant, as the feed, which increases the difference in salt concentrations and thus the energy available.”
And the "fresh" water is also "treated wastewater". That could mean a bunch of things but in most cases it's water that's released into the environment by the water treatment plant. Its quality can be as good as clean water, but most municipalities wouldn't feed that right back to the consumer, they dump in a river or lake instead.
hinkley
Basically this is like the recouperator on early heat engines, but with a liquid gradient instead of a thermal one.
It's making desalination more efficient and the effluent a bit easier on the ecosystem.
throwmeaway222
explains your username, explain like im like 17
thanks
setgree
> While it is still an emerging technology being used only on a modest scale as yet, it does have an advantage over some other renewable energies in that it is available around the clock.
I notice the 'some' here, and the absence of the word 'nuclear' from the article, which of course is also available around the clock. Most readers will know something about Japan's troubled relationship with nuclear power and can fill in that context themselves, but to my eyes, it's a startling omission.
Arnavion
Some other *renewable* energies. Nuclear isn't generally considered renewable.
p1mrx
> it is expected to generate about 880,000 kilowatt hours of electricity each year
100 kW, in sensible units.
Etheryte
It is expected to have about 8760 hours each year.
throwawaysoxjje
*An average of 100kW assuming 100% duty cycle.
hinkley
Expecting it to operate most of the time is a safer bet than expecting it to have a peak output that’s substantially higher than the average. It’s be smart to try to align it with power usage, but in truth it’ll lag behind peak water usage by however long it takes to top off the tanks. I don’t know when that is but I would suspect before morning rush hour.
Probably this thing peaks at 120-150KW which isn’t going to fix the grid.
krunck
So let me get this straight:
1. I take a shower and produce non-salty waste water
2. That waste water and brine from a desalinization plant can be used in this plant.
3. The result is concentrated waste water and less salty brine and some power
4. The power can be used to (partially) power the desalinization plant produces fresh water from sea water and brine.
5. I get fresh water for my shower.
And the diluted brine from step 3 goes to the sea? Or can it be run through the desalinization plant again? Does concentrating the waste water in step 3 also help with the eventual treatment of it
Johnny555
Does it generate enough electricity from freshwater to offset the energy used to desalinate more water? Would it be more efficient to just treat the freshwater that would have been used to run the plant for drinking water and desalinate less water?
aidenn0
It seems like it would have to be more efficient to further treat the semi-treated wastewater. However there is often resistance to putting treated waste-water into reservoirs.
zahlman
Coverage readable (although most images are missing) without JavaScript: https://www.independent.co.uk/climate-change/news/japan-osmo...
skybrian
It sounds like this recovers some of the energy that the desalination plant used to create fresh water and brine from ocean water?
nisegami
As well as diluting the brine produced by desalination. Unclear if it's worthwhile though. As another commenter pointed out, you could treat the source of your low salinity water to produce fresh water instead and bypass a lot of this.
valorzard
Japan seems to really be into osmotic pressure for whatever reason. It reminds me how in Splatoon, the reason given for why the character die when they touch water is osmotic pressure and there's a whole scientific explanation about it.[1] However, that all got cut out in the international localization for some reason.
Maybe there's a cultural reason why Japan is more aware this is a thing that exists? Dunno
They really fail to explain a key point here. The reason you colocate this with a desalination plant is because you use the super-salty wastewater from desalination as the salty side of the osmosis power plant. Then you find some wastewater which is low in salt (such as semi-treated sewage), and use that as the fresh side of the osmosis power plant.
The end result is that the salty wastewater is partially diluted, which means it has a lower environmental impact when it is discharged to the ocean.