> In the meantime, the leftover salt continues to circulate through and out of the device, rather than accumulating and clogging the system.
I don't want to detract from the innovation of this, however my understanding is that one of the largest unsolved problems with desalination is what to do with the waste product: usually incredibly salty brackish water. Dumping it back into the ocean can be disruptive to the local ecosystem.
The salinity is normally only increased by a factor of four (assuming a 25% reject ratio) so just be aware that brine discharge is a very highly localised environmental issue, it doesn't spread too far.
I wouldn't call it an unsolved problem necessarily. We probably disrupt the ecosystem more when we build a parking lot.
Just talking out my ass here, but can't it be combined with, say, treated wastewater?
We're taking the salt out of the water in order to "drink" it, but the reality is that most of it gets used for irrigation or toilets or whatever, and eventually returned either as groundwater or to the ocean.
The salty sea water could even become the water to flush your toilet with as one use for the waste?!
I agree with the above, the scale of the proposed system shouldn't lead to sealife issues.
I don't think running saltwater through a toilet is straightforward. You would need higher quality parts, more frequent valve maintenance, and downstream waste processing equipped to handle the salt.
Sailboats use sea water in their toilets all the time but using it would require two systems, one fresh and another brackish. Very doable but more expensive. I believe they've also use grey water for toilets and plants but again it requires splitting the systems and having storage.
Isn't the reject ratio typically closer to 75%? At least, my filter at home has a reject ratio of 75%, which means the wastewater is only ~33% more ppm than the starting water.
So, it's probably a good example then, since we currently accept the building of parking lots.
The point is, people are always writing letters to the editor and what-not when some green tech has some environmental impact, far more than they do over their city making another parking lot or any of a million other things. I assume it's because it triggers some notion of hypocrisy. c.f. wind turbines and dead birds.
How about we put our energy into fighting cars and parking lots first, before we worry about solar-powered desalination that could potentially save the Western states from the over-extraction of water that's turning them into dust bowls?
Carbon-based energy is socially acceptable, as are completely unsecured computing devices and mass corporate surveillance, but that isn't the standard of a good idea. If it was, we wouldn't want a forum like HN.
That's pretty cool. Personally, I'd prefer small roads and outdoor parking lots to be au naturel unpaved. Zero construction cost, and I imagine the maintenance cost is just trimming grass.
Only works if the natural soil is remarkably solid or the traffic negligible. Unpaved roads with more than very modest traffic generally need routine grading (repairing corrugations by scraping it over with a levelling blade) and re-graveling
Accurate. And, if there is significant rain and/or snowmelt, roads can quickly become impassable (see: "mud season" in New England, and surely many other places)
On a tangential note, I don't why paved outdoor parking lots are built[1]. It seems to be an entirely pointless exercise in aesthetics to me. I've parked on unpaved spots (in large parks near hiking trails, etc), and never had an issue.
We really should have more unpaved outdoor that is simply trimmed semi-regularly if or when the plant growth gets too big.
[1] Unless you're in a sandy or snowy area, where shoveling the sand or snow is difficult on an unpaved surface.
Pure soil wouldn't be a good option. Anything that's subject to high traffic, whether foot or vehicular, will also be subject to soil compaction which implies water pooling. That's a long way of saying those parking lots will turn into mud lots. At a minimum you could grade and gravel them, going the extra mile to crush the gravel so it stays in place longer. I do this with the driveway at my house because it rains a lot where I live. Paving would arguably last a lot longer and probably be more bang for my buck, but not having a place for water to go and having a basement is not a good combination.
On my driveway we only tend to get clovers and really resilient weeds. So, either really shallow rooted plants or weeds with absurdly strong roots. You're not likely to get native plans to grow unless you section off parts of the area for maintaining living soil.
Unpaved parking lots tend to lose their plant growth when frequently used, after which the parking lot turns to mud in wet weather, which then results in stuck cars and dirt getting into stores with the customers that walked through that mud.
To give a visceral example- There's an episode of Clarkson's Farm where the customers that parked in the grass at his farm shop need to get their cars pulled out of the mud by a tractor.
This plant helps Perth (a city of 2m people) get over half of its fresh water from desalination. We used to get most of our fresh water from the local aquifer and from dams, but this was totally unsustainable. The water table has been recovering over the past 10 years, and is on track to recover to pre-invasion levels in the next decade. By which time we should be at over 90% renewables for power too! Quite proud to be a West Australian really.
It's actually only a challenge in shallow water that doesn't move, which if you think about it isn't that surprising. If you pump it out a bit further, you quite literally have a whole ocean to dilute the salt in. Off the coast of California, for example, which is a state that should have no water shortage as it has abundant access to clean solar and wind energy and the entire pacific to desalinate, ocean depths drop quickly even just a few miles out. You would not be able to affect salinity levels of ocean waters there in any measurable way even if you wanted to.
So, the solution is pipes and pumps. Those add cost of course but it's a completely solvable problem otherwise. Exhausting natural sources of ground water and aquifers also has an impact. Desalination done right might give some of those stressed ecosystems a chance to recover.
> It's actually only a challenge in shallow water that doesn't move, which if you think about it isn't that surprising. If you pump it out a bit further, you quite literally have a whole ocean to dilute the salt in.
What do the studies say what the effects of stripping water from the oceans and increasig the concentration of salt and other things are?
Yea, but it's different. For example, we have harmed ecosystems by our flood, erosion, etc. control of rivers. They're supposed to move, but we don't let them, and that has detrimental downstream, figuratively and literally, effects. And it's because we view rivers as just a vessel or tract of water rather than as part of a system. Analogously, the ocean is not just a bucket of water.
Coastal ecosystems are particularly sensitive and are already at a tipping point. Are they meant to have bits of it pumped out, filtered, and everything but the water dumped back in?
I have been downvoted here, but is it really a bad thing to attempt to understand things a bit better? Before we solve one problem by creating another problem, something humans are really good at?
My controversial take is that the best solution will be to accept that solving the drinking water problem for people is worth worsening the environment for some local sea life.
A poorly implemented runoff would nuke a square km or five of ocean floor with high salinity waste. It would not impact food supply in any discernable way. The ocean is simply too big.
I don't think humanity is ever really considering environmental impact unless it impacts it somehow. We care about disappearing species which amuse us, which we can see at our scale level, not much below. Some rare lion? Tragedy! Thousands species of fungi living underground which don't impact us directly? Irrelevant. Same goes for climate change and others. We only care if it impacts us in any way, even if only our entertainment.
So long story short we probably care about sea life.
> Or just sell it as salt? We use, I don’t know, billions of pounds of salt per year in food production?
Are you sure the math even remotely checks out? Just looking up some numbers, even if we naively assume ocean "saltwater" is just H2O + NaCl (which it obviously isn't): the world consumes around 300 billion kg salt/year, whereas (say) Los Angeles alone uses 700 billion kg water/year. So even if a city like LA provides for the whole world's use of salt, what does everyone else do?
I'm sorry, perhaps my engineering education makes me handwave at problems -- but the water we're desalinating has to return to the ocean someway, it's not like we throw it into black holes, why can't we just dump the brine 20 miles into the ocean, the water we've desalinated will return by other means.
"Could have" is doing a lot of heavy lifting there. Assuming spherical cows, 12 is an upper limit, okay. What you could actually do is neither remotely close to that nor is that itself remotely close to what the world needs, was the point.
You’re assuming we need to get 100% of our water from desalination when it would only need to cover any shortfall from other methods. We’re currently getting 100% of the water we need from those other methods.
Really depends who "we" is. Israel gets 75% of its water from desalination already, and that's just right now. And a lot of the other water sources right now are nonrenewable (groundwater, etc.), hence a big part of the motivation to look for new ones in the first place. The current situation is not sustainable on its own in many parts of the world, let alone the effects of dramatically increasing population sizes and global warming.
Further concentrated salt solutions deposit in the device, clogging it causing it to not work. You could harvest the salt, but then it is no longer passive.
Everything we do affects the environment. Locally making the ocean a little bit saltier by removing water and not removing salt sounds like a very minor problem.
I haven't heard of any coral reefs at the Sea of Cortez, which is one place they're considering desalination, for Arizona (importing water from Mexico).
Edit: I checked and there are coral reefs along the Sea of Cortez. :) I don't know where would be safer to do it, but I'm sure it makes a difference where. And sadly it may not be as important at places where we've already destroyed the habitats.
Seems like we could also just add it to the other places where water is flowing into the ocean. Do we not disrupt the ocean ecosystem with our fresh water runoff?
If you had a lot of fresh water runoff, you might use that fresh water for drinking rather than desalinating seawater though.
But... If you are using this water for drinking, it's going to come back through the sewage system, and maybe you can dilute the brine with outflows from local sewage treatment plants.
Depending on details, the combined outflow could be more or less salty than the seawater input to the desal plant.
Only some of it comes back through the sewage system. A lot of it just ends up lost to evaporation, or being incorporated into products. Think about your typical use of water to irrigate farmland (which is the majority use of water in many places); you don't really get any of that back as freshwater discharge at all. If you did, that means they're irrigating too much to the point that they're flooding their fields and causing runoff.
Sure, but do people really pay desal prices to irrigate fields?
Also, a lot of places are using desal to augment other supplies. If you've got 15% of your municipal water supply coming from desal, sewage treatment outflows should be significant compared to brine.
Basically before releasing it back mix it with sea water at 1:10 or 1:100 ratio and it should not make that much of a difference. And make the outlet pipe quite far away from the inlet directly into a current if possible so it will mix with the rest of the sea.
You're using solar energy to separate the saltwater from freshwater. You're not going to gain any more energy than that from mixing them back again, so this idea is just solar with extra steps.
Looking at the comments, I'm baffled by the number of people that still think it's "minor issue" while doing absolutely no research.
It's not just a little bit of salt, it's enough to kill fishes and whole ecosystem at scale, and it's all in the quoted article that people have definitely not read.
Until you notice that in some indirect way your life livelihood (or that of others in your community or some other actor with influence) does depend on that sea life. People are really quick to argue for the seemingly simple fix when interacting with complex systems. It rarely works out in the long term.
Source: climate change. It was really nice to emit a lot of carbon for a few decades, now it begins to cause real problems, conflicts and costs. Technical innovations should not simply assume that negative externalities are „fine“. Innovators should have to assume the burden of identifying and resolving the externalities before widespread distribution of the innovation.
> Innovators should have to assume the burden of identifying and resolving the externalities before widespread distribution of the innovation.
Based on what timescale, though? We can only work with what we know about. E.g. until Radium was deemed highly unsafe, it was deemed safe. No one paints Radium onto watch hands any more because we discovered that that's a terrible idea.
Or, it might turn out in 30 years that CO2 has a large positive effect on re-greening the Earth, and all those low CO2 innovations were harmful.
In other words: I don't understand how your statement makes sense without hindsight, and I don't understand how any innovation can happen if hindsight (that is based on that innovation happening) is its prerequisite.
> until Radium was deemed highly unsafe, it was deemed safe
You countered your own argument: Radium was never safe, it was just deemed safe because FAAFO was in fashion. Lead, Australian frogs, cigarettes, DDT, thalidomide, deforestation, and asbestos among (many) others have had lasting negative effects simply because we pushed ahead without considering whole-system complexity.
> because we pushed ahead without considering whole-system complexity
No, because we didn't know better. My argument was: how long do we wait til we decide we know better? Do we stop everything? How long is long enough?
You're talking as though right now many things we think are the best thing to do won't turn out to be a terrible idea. They will be, because there is no way to consider "whole-system complexity" on a long enough time period to do things completely safely, or even to do anything at all, as anything might turn out to be a bad idea on a long enough timescale.
> how long do we wait til we decide we know better? Do we stop everything? How long is long enough?
I agree with your premise and not with the threshold.
To make an analogy: you give a kid a bike and only teach them balance as they ride it.
Someone who has a “nothing can hurt me” mentality will jump on, go down hills, jump through bushes, etc. It’s most likely that they would break bones and possible that they die before learning what they need to know to be safe (enough).
Someone who has an overcautious mentality may try to fully understand the physics of bike riding before venturing past the lawn. It’s likely they won’t get hurt at all and it’s possible that they simply never ride outside the yard.
In my opinion, both are negative outcomes.
However: if someone is of the right mentality they will experiment safely, seek to understand enough of the physics to know the dangers, and take on challenges that are appropriate for their level. They will probably get hurt and might even break a bone but they will be able to recover and keep riding.
In my opinion, if we put genuine care and attention in to thinking about system complexity before/as we progress we can avoid many of the “obvious” problems without having to stop everything. I agree that there’s no way to avoid all potential fallout, but I think we can stay with consequences we can recover from if we accept that it means seeing ourselves as a part of a much bigger picture.
This device is small-scale for individual families and small off-grid communities.
It's solar powered and passive. There's limitation on the salinity of the brine because you don't want to accumulate in the device. My impression is that this is not going to be a very big problem.
One possibility I have been thinking about is to locate desalination in an area with extreme tidal variation, particularly the northern Gulf of California (which coincidentally happens to be in a very thirsty region), where natural flows might be sufficient to disperse the brine. I have seen various studies talking about tidal currents dispersing brine but I haven't heard of any evidence that you can take advantage of highly tidal bays.
Is turning it into a solid too energy consuming? The main problem seems to have been it clogging up the multi stage system. If you can dump it you should be able to turn it into a solid in a separate setup.
Salt is very hydrophilic, I believe this means that it's very difficult to get the last bit of water out. Further, if you leave dry salt out in a humid environment and it naturally pulls humidity out of the air.
It collects on top though. Fleur de sel is made that way i believe. You arguably dont need to get all the water out of there as long as you have a steady stream of water with high salt content coming in.
Much of the price of that is coming from not breaking the formed patterns during harvest.
The desert is far away. The ocean is much closer. Issues with increasing salinity go down drastically if you pump just a bit further into the ocean, where it is rapidly spread by currents. If that's considered too difficult/costly/energy demanding then pumping to a desert would be that much worse.
Most deserts are inhabited by endangered or threatened species. There aren't actually a lot of deserts so lifeless that you could avoid environmental activists getting in the way, at least not in the US.
US deserts are full of life; they're very far from lifeless. They're nothing like the endless sand dunes we envision when we think of the Sahara desert, Saudi Arabia, or the planet Arrakis.
The flush tank of my toilet was leaking. I called a plumber, and the first thing he did was to scoop up more than 2 handful of salt solids from the flush tank and clean it well - I wasn't aware that our community uses untreated hard water for toilets. And I was shocked, as I wasn't aware this happened, at the amount of left over salt that had accumulated!
Salt is a by-product of desalination and, as I understand, not easy to dispose without affecting the ecology of the area where it is disposed (let's not forget that salting of fields was done as an act of warfare against the enemy to make their lands barren, and then there's the natural Dead Sea - https://en.wikipedia.org/wiki/Dead_Sea - that exists and highlights what happens to marine life when water has too much salt content in it). Unless salt waste disposal is solved, desalination isn't going to become popular.
The brine more often than not contains traces of pretreatment chemicals, heavy metals, and other byproducts. It's frequently treated before being disposed of. Methods include pumping it down to the ocean floor or mixing with a source of less salty (wastewater/hydro) runoff. Removing the trace chemicals to make salt out of the brine would be prohibitively expensive.
I grew up in a city that was once an important part of the salt trade routes to Bohemia. These routes were called "Goldener Steig" (golden path), and salt was considered "white gold". Entire wars were fought for salt. And now it's so abundant, that we're sitting on mountains of it, not knowing what to do with it. Thinking about that feels kinda unreal.
So could it be behind this dead zone? ''The largest such dead zone in the world is in the Gulf of Oman, a strait bordered by Iran, Pakistan, Oman, and the UAE. It occupies a whopping 165,000 square kilometres of the water body, an area bigger than even the state of Tamil Nadu (130,060 square kilometres). https://nyuad.nyu.edu/en/news/latest-news/science-and-techno...
Sorry for the extremely ignorant comment: but can't salt be solidified and stored somewhere as waste? and then maybe sold as food or for industrial uses?
Surely it would be more efficient than salt pans or mining salt as we do today...
My understanding is that this system is meant to be used at a small and distributed scale, not at an industrial scale like city-level desalination plants. In that case, it shouldn't be a big issue.
Yeah this is one of my concerns, too: what impact on on the oceans will this have? Maybe the salt can be used in electric car batteries somehow? What impact if any would desalination have on oncean water levels? If the process makes for water cheaper than at the tap what’s to stop industrial users?
There is a plan made by Israel and Jordan to bring water from the red sea to a desalination plant, and dump the leftover in the dead sea, it's like the perfect solution
Wouldn’t the rising sea levels more than counter any salt being returned to the sea, as long as it’s dumped far out enough? Won’t climate change cause the concentration of salt in seawater to go down?
For the same reason we can't drink seawater: there is too much salt in it. The recommended water intake for a human is ~2kg, the recommended salt intake is ~2g. That's 0.2%, seawater has 1.5%. After you'd have eaten your share of salt, there is some leftover. You can't have someone else eat it, because then you'd also need more water. You could try to export it, but that requires quite a bit of extra processing, and the global demand for salt isn't high enough to pay for the transport costs.
I don't know anything but how about putting it in a hole ?
What would be the consequences of that ? (Sure there are plenty but I am too dumb to think of any)
After lithium extraction, there's still a brine with roughly the same salt concentration, but likely with more other pollutants. You'd just be kicking the problem down the road.
But the issue is dumping the brine into the ocean as the only economical way to deal with it. If someone can make a significant profit off the brine, it may be feasible to truck it to a lithium facility then deal with disposal in a way that isn't just "dump it in the ocean and pretend it's not a problem".
> Dumping it back into the ocean can be disruptive to the local ecosystem.
I question this as being a problem. The ocean is saturated with the salts that are exposed on the sea floor. When there is too much salt in a solution, the excess will precipitate as solids. As the ocean is already exposed to more salt than it can put into solution, I don't think this would cause a serious issue.
I don't want to detract from the innovation of this, however my understanding is that one of the largest unsolved problems with desalination is what to do with the waste product: usually incredibly salty brackish water. Dumping it back into the ocean can be disruptive to the local ecosystem.
A quick search turned up this Scientific American article about the issue: https://www.scientificamerican.com/article/slaking-the-world...
"The excess salt decreases dissolved oxygen in the water, suffocating animals on the seafloor"
"In addition to harming sea life, extreme salinity also makes desalinating the water more difficult and expensive."