Submitted 3 weeks ago by kalkulat@lemmy.world to technology@lemmy.world
https://www.theguardian.com/world/2025/aug/25/japan-osmotic-power-plant-fukuoka
It’s not -a lot- of electricity … a couple of thousand kWh per day. It’s also used to de-salinate ocean water … of which there’s plenty.
So, they’re using brine from a reverse osmosis plant and wastewater to run this process, both waste products, and probably producing something roughly the same as seawater.
Sounds bizarre, but apparently it works.
The reason being that dumping the brine back into the ocean creates a dead zone wherever that dump point is, since the relative concentration of salts is higher compared to regular seawater.
They’re almost certainly recreating seawater just to help alleviate the dead zone effect and figured out how to get some free electricity out of it too
Right. It seems analogous to regenerative braking in a gas/electric hybrid car. The momentum is turned back into electricity to reclaim potential energy. Some of the energy was already spent in RO stage and this process gets some of it back.
I sounds more like it makes electricity out of fresh water, destroying it in the process (turning it into saltwater through osmosis/dilution). Sure… if there is some crazy salty water you have, and want to turn it into “still salty, but maybe less so”, you can indeed gather a tiny little fraction of the power.
But given that fresh water is also a precious resource in many places, this seems relatively niche.
From what the article says, it’s actually a pretty cool way of improving desalination plants. They use the left over brine, from desalination, that has a very high concentration of salt, and use it as the high salt concentration side, with regular seawater being used on the other side. This both gives them free energy and reduces the side effects of pumping that extremely salty water into the sea.
It can use treated waste water, so it’s not that specialized.
Right. So it’s 100kW output, which is almost enough to pull the skin off a rice pudding. It also uses the brine from a desalination plant, so it’s basically resalinating fresh water to get some of the power back that was taken to desalinate it.
As a means of power production, it seems a bit pointless.
It generates 880.000kWh/year, where I live that enough for 176 families (2 adults, 2 kids) with an average consumption in a house, and almost 350 in apartments. That’s not an insignificant amount IMO.
Doesn’t sound all that economical compared with other energy sources. It probably needs to be compared to longer-term energy storage solutions that don’t rely on geography like hot sand, the possibility to store the energy source (concentrated salt water) relatively cheaply is the most interesting part about it.
This plant is part of a bigger chain. So while yes, on its own it seems waste of effort, as part of the entire chain it’s a reasonable step to be more environmentally friendly and recover some energy in the process.
A local plant desalinates water, resulting in fresh water and a brine solution that has much higher concentration of salt in it than regular sea water.
Dumping the brine solution on its own would kill most plant and animal life around the dump site due to large saltwater concentration, so an alternative method must be found to dispose of the brine.
Waste water from other processes can be mixed with the brine to bring it more in line with seawater salinity, making it safe to reintroduce to the ocean without severe ecological impact. This waste water is deemed to difficult or intensive to purify and treat to bring it back up clean water standards, and I’m assuming tested or filtered so as not to introduce hazardous chemicals that could damage the reverse osmosis membranes as well as sea life.
Because there is way to mix the waste water and brine through membranes that can be used to generate electricity, this process is utilized to recover some of the energy expended in purifing the original batch of seawater resulting in the brine.
It’s not a perfect process but it is a means of getting some use out a waste product, similar to burning garbage or rotting food rather than just dumping it into a pit and letting it rot and release methane.
You should call up Japan and let them know how wrong they are.
Its miles better than traditional desalination - requiring so much energy that burning fossil fuels is unavoidable. And brine is chucked back in the ocean. Basically an environmental catastrophe.
If you think of it on the scale of one community - providing potable water, dealing with treated wastewater AND getting a surplus of energy while treating the brine it is actually pretty clever.
If it makes you feel better you could probably slap some solar panels on those flat roofs too.
I’m hoping soon that the salt is used to make batteries.
As desalination plant need a lot of power it is a plus. But there is always that question in background with this approach what are they gonna do with this salt ?
It’s pretty common to produce table salt by dehydrating sea water. This saltwater electricity plant doesn’t produce salt, though, since the basis of their electricity generation process is diluting concentrated salt water.
I swear, nobody in this comment section actually understood the article.
To my knowledge, desalination plants do not recover salt from brine. There is a European project that is studying this feasibility. Generally, brines are discharged into the sea, which is destructive for the environment due to their concentration.
Here before the idiots who comment misinformation about Japan show up
lemmylommy@lemmy.world 3 weeks ago
Combine salt and water to create electricity to power a desalination plant that removes salt from water. I am sure there is more to it, but the article sounds like it’s one of those mad perpetual free energy schemes that defy the laws of physics.
rumschlumpel@feddit.org 3 weeks ago
If they’re mostly using electricity or even combustion to evaporate the water (as opposed to sunlight), there’s no chance that the concentrated saltwater creates more electricity than it costs.
Ilovethebomb@sh.itjust.works 3 weeks ago
They’re using brine from a reverse osmosis plans and wastewater, so yes, that is indeed the case.
Jason2357@lemmy.ca 3 weeks ago
They are just re-capturing some of the energy the system spent turning salt water into fresh. Because that results in extremely salty brine water waste, you can get some energy as it gets diluted back down to sea water concentration.
There no “new” energy in the system, it’s just wasting less.
happydoors@lemmy.world 3 weeks ago
Isn’t efficiency just getting closer and closer to a perpetual machine? Using science and the physics to the absolute limit!