I think the article author is completely confused and doesn’t understand what’s happening. There 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 (or maybe the other way around). 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.
There*
Friggin hell. Thanks.
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.
Well, yes, dumping irradiated water into the ocean was always an option. So long as the power-generating components aren’t the same as the desalination components, you’re good as far as the potable water is concerned. This isn’t much of a solution for the irradiated water, though, any more than just dumping it into the ocean was in the first place.
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!
The plant will generate about 880,000 kilowatt hours of electricity per year—enough to help run a nearby desalination facility and supply around 220 homes. That equals the output of two soccer fields of solar panels, but osmotic power keeps running day and night, in any weather.
Using it to run desalination is confusing.
I created a bucket of fresh water using nothing but sea water, a membrane, and a bucket of fresh water.
Fresh water doesn’t mean drinkable water, it just means not salt water. The desalination plant produces drinkable water.
It sounds like they’re not quite using fresh water, but waste water. I presume it’s been treated, but even if it’s not 100% back to potable, if this also helps solve the problem of what to do with the brine after desalination, I think it’s a win all around.
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.
“While energy is released when the salt water is mixed with fresh water, a lot of energy is lost in pumping the two streams into the power plant and from the frictional loss across the membranes. This means that the net energy that can be gained is small,” said Kentish.
Why do it, then?
Is this a proof of concept/MVP build, so they can iterate more efficient versions? A vanity project? A mistake?
Turning unpotable water into potable water with little or no additional cost, while not harming the environment, isn’t exactly a loss.
Because osmotic power has enormous potential in the sense that millions of cubic meters of fresh water is running into oceans all over the world every minute. If we’re able to get even a low-efficiency method of using the salinity gradient to generate power working then every place a river meets the sea is essentially an unlimited (albeit low-yield) power source.
This is tech that doesn’t rely on elevation (like hydropower) or weather conditions (like wind/solar) it’s stable and in principle possible to set up at pretty much any river outlet, which is great!
Gotta be careful about ecosystems though. River deltas are incredibly important and fragile areas.
Oh absolutely. As with all other infrastructure, there is a cost to be paid. However, when you look at an average to small river, even routing 10 % of the water via an osmosis plant before passing it to the sea is an absolutely massive volume. There’s also the point that you don’t want to build these things in large, meandering, flat river deltas. You want a large salinity gradient, which means relatively small, fast-running fresh water meeting the ocean more “suddenly” than what you get in a classical river delta is the optimal source here.
Dams 2.0
Finally, power at night, when everyone’s asleep and we always have had excess.
Me who is up all night using up the excess power
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
Do you mean my mentality or the one of the new technology?
It’s not necessary to produce power 24/7 since demand isn’t 24/7 either. Strong peaks and valleys.
Your mentality is old school. We have often more need at night than during the day for non renewable electricity right now
I see. Do you know what’s using that power?
Do you go to bed at sunset?
Do you turn off your heat at sunset in the winter? Maybe you do, but most people don’t.Also, most people with an electric car and a garage to park it can just use a cheap Level 1 charger to trickle charge it whenever it’s in the garage and always have plenty of range for their commute and errands. This means all of those cars are charging. … at night while the owner sleeps.
At night?
We use less power at night. We generate a LOT less power at night. Because the sun is off for the most part.
That’s when my electric car is plugged in and taking up quite a bit of power.
That’s when it should be plugged in.
So, then why are you confused about what’s using power at night?
The energy can be stored for use for later during the day
Aside from obvious confusion of running a water desalination plant by salinating water, there’s one more concern: outside of such installations, 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.
Oh, missed that. But won’t wastewater clog the membrane?
“Treated” means the solids and goo that may have been a problem has been removed. It is mostly water, a lot a fecal bacteries, and diverse dissolved chemical that wasn’t removed.
Alrightie then!
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 supply. IDK, few possible reasons, I’m just speculating
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.
