Submitted 3 weeks ago by floofloof@lemmy.ca to technology@lemmy.world
Technical explanation : with reverse osmosis you have :
(salty water + energy )
→ ( fresh water + highly salty water )
So, reverse this process (call it osmosis plant ?) and you get energy … e.i. :
( fresh water + highly salty water )
→ (salty water + energy )
I think it’s more like:
(salty water + unpotable fresh water) → (salty water + potable fresh water + energy)
…with a few steps in between. Even if most of the power is used in running the plant, you end up with potable fresh water and no brine being dumped into the ocean, which is a net win.
I think the article author is completely confused and doesn’t understand what’s happening. Their are hints of what’s happening in this paragraph.
Fresh water—or treated wastewater—is placed on one side of a membrane. On the other side is seawater, made even saltier by concentrating leftover brine from a desalination process. The difference in saltiness pulls the fresh water across the membrane, increasing the pressure on the saltwater side. That pressure is then used to drive a turbine, generating electricity.
I don’t think any fresh water is being used. I think what’s actually happening is…
Very salty wastewater (from the desalinization plant) is placed on one side of a membrane. On the other side is seawater. The difference in saltiness pulls the wastewater across the membrane, increasing the pressure on the saltwater side. That pressure is then used to drive a turbine, generating electricity. The waste then is just water that’s saltier than sea water, but less salty than what came from the desalinization plant.
According to Japanese sources Mainichi, it is indeed treated waste water one one side and desalination brine on the other. Both the waste water and brine are meant to be dumped anyway, and it’s also harmful to sea life to dump brine directly. Treated waste water isn’t saline, so is perfect for diluting the brine. Might as well get some free power out of it.
That makes a lot more sense than sea water and fresh water.
Yeah, it’s just recovering a little of the energy spent in desalination, making it slightly less energy consuming.
So it’s a turbo engine.
Why isn’t it fresh (non-salty) wastewater?
Lots of places treat their wastewater and then discharge it. For example, where I live, wastewater, that is to say, sewage which has had solids filtered out, is still rather pooey and pissy but not salty, gets treated (I don’t know how) and is then injected into natural underground aquifers where it eventually percolates out to bores or springs where it’s collected and used for irrigation, contributes to natural springs, or possibly even winds up in a drinking water catchment.
All wastewater, regardless what happens to it, has to be treated before release. If it’s still 99.9% fresh, then why not use it to create osmotic pressure before dumping it.
Aside from obvious confusion of running a water desalination plant by salinating water, there’s one more concern: don’t we have quite a limited supply of fresh water? Sure, saltwater is everywhere, but fresh water is relatively scarce.
The article refers to treated wastewater being used, not fresh water.
Another thought: what if we would instead use concentrated brine from desalination plant and seawater? Yes, power will be lower, but this way we don’t use fresh water that we, erm, try to produce.
Desalinating water gives you potable fresh water, whereas the fresh water being used might require treatment before being potable? Or it’s unreliable in quantity. IDK, few possible reasons, I’m just speculating
Based on the limited power generated I wonder if we can do something similar with cola and menthos.
Wow, I did not even think of that! This guy sciences!
Could this run with contaminated water as a source? For instance during fallout?
It really depends. Osmosis is a chemical process, so if the source of the radiation would be filtered, then it would remove the radioactive component. If the water is made with radioactive isotopes of hydrogen and oxygen, it would just flow through.
But the desalination process is powered by the energy manufacturing, the water is not shared between them. I was more thinking about the safety and capability of the energy manufacturing, as fallout makes other systems much more difficult.
sbv@sh.itjust.works 3 weeks ago
treadful@lemmy.zip 3 weeks ago
Using it to run desalination is confusing.
thann@lemmy.dbzer0.com 3 weeks ago
I created fresh water using nothing but sea water, a membrane, and fresh water.
AmidFuror@fedia.io 3 weeks ago
This seems like a terrible use, since these plants work by mixing fresh water with seawater (or in this case the brine leftover from desalination). I guess the catch is they can use treated wastewater instead of potable water.
This method gains very little net energy compared to other renewables.
underline960@sh.itjust.works 3 weeks ago
Why do it, then?
Is this a proof of concept/MVP build, so they can iterate more efficient versions? A vanity project? A mistake?
AmidFuror@fedia.io 2 weeks ago
Returning to this thread long after everyone has moved on.
How do you get enough net energy out of mixing brine from desalination with fresh water to use to separate saltwater into brine and fresh water? Especially when the energy producing method is already known to have poor efficiency?
This seems like this is just terrible at converting treated wastewater into drinking water. Must have something to do with government subsidies instead.
sexy_peach@feddit.org 3 weeks ago
Finally, power at night, when everyone’s asleep and we always have had excess.
Kolanaki@pawb.social 3 weeks ago
Me who is up all night using up the excess power
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frank@sopuli.xyz 3 weeks ago
This is a very old school and outdated mentality.
In my part of the EU this year, we had very very many days of negative sale prices and having to curtail wind parks because just solar and wind were making up more than demand during the day. Afaik we only curtailed at night one time.
Source: wrote curtailment algorithms for wind turbines
hark@lemmy.world 3 weeks ago
That’s when my electric car is plugged in and taking up quite a bit of power.
shplane@lemmy.world 3 weeks ago
The energy can be stored for use for later during the day