Why don't we get our drinking water by taking salt out seawater? (2008)

https://www.scientificamerican.com/article/why-dont-we-get-our-drinking-water-from-the-ocean/

by Bender • 3 years ago

125 356 3 years ago

scientificamerican.com

jacooper• 3 years ago

TLDR too expensive.

It depends on the country though, countries like Saudi Arabia get most of their water though desalination.

_0ffh• 3 years ago

IIRC Israel even produces enough fresh water to establish a flourishing export business.

nir• 3 years ago

I don't know about exports but for certain there's quite a lot of water Israel transfers to Jordan as part of the 90s peace accords. That's a huge deal in the Mid East.

For decades, the weather report in Israel would include the water level of the Sea of Galilee, the only real lake in the country and the source of most of the nation's drinkable water. It would be a major concern during droughts. Now there's so much desalinated water that some are actually being pumped into the lake, for environmental reasons.

mhb• 3 years ago

Also big cruise ships.

reaperman• 3 years ago

Qatar has no groundwater or surface water anymore AIUI. But they have an incredible oversupply of natural gas that they can’t build enough export capacity for. So it mashes sense to use the gas they can’t export to desalinate water, and they do.

politelemon2• 3 years ago

It would be ironic if they become a supplier of water to other countries too.

Xeoncross2• 3 years ago

Why don't we...

money.

Think of everything good in the world we could have but don't because we and everyone else want to keep as much money as possible.

the_snooze• 3 years ago

It's not a matter of greed as you seem to be implying. In this case, the money is really just a proxy for how practically difficult desalinazation is vs. the alternatives. It's the same reason why we don't ship parcels via ICBM; the alternatives are way easier on multiple dimensions. The juice isn't worth the squeeze.

xcv1232• 3 years ago

That's not how money works.

Otherwise you could solve these problem by printing money.

Xeoncross2• 3 years ago

That's exactly how money works. People want it, so they cut corners and/or hoard it instead of being generous with it. Printing money would just mean someone would hoard the printed money (which, as you can see, already happens).

Collecting money is just a side-effect of people being selfish.

kelnos7• 3 years ago

In this case, that's not really the issue. Yes, the issue is money, but it's not as nefarious and cynical as you make it sound. People don't want desalination, they want fresh water. If there are cheaper ways to meet water demand than desalination -- which is currently the case for most (but not all) places in the world -- then there's no need for desalination. Certainly as water scarcity becomes more of a problem, we'll have to re-evaluate this situation, and at some point desalination may end up being competitive with the alternatives.

We also might find more efficient (cheaper) ways to do desalination, which could tip the scales toward it earlier.

Arnt3• 3 years ago

The article sidesteps something that seems important to my naïve eye: Water is easy to store if you don't have very much of it, so this is the kind of thing you can do when the sun is shining and store for nights and rainy days. Storing water for a year or two would be hard, of course.

slv77• 3 years ago

Return on capital and deprecation tend to exceed energy input costs for most plants so it makes sense to run them 24x7x365 rather than over-size them and run them when energy costs are lower.

Arnt3• 3 years ago

They tend to exceed energry costs because energy costs are dominated by the cost of purchasing oil, which is as easy to store as water. We're moving away from that now, towards a world where solar power plants produce power at stunningly low prices some of the time (like €0.01114/kWh on the top google hit just now) and those who need a lot of power and can adapt their usage to match solar power plants can make use of those prices.

sidewndr46• 3 years ago

Most of Texas consists of "build a dam at this convenient chokepoint and create a huge reservoir" for its freshwater. So I disagree. We don't do anything special. The biggest issue is invasive species taking up residence in the newly formed reservoirs.

flangola7• 3 years ago

Like birds? Or fish?

ianburrell• 3 years ago

Places with intermittent water have lots of water storage in reservoirs. The problem is that reservoirs are up in the hills away from the coast so it would cost a lot to pump it up.

But running the desalination when energy is cheap makes a lot of sense. Especially when not providing all the water but topping up when supply is low. The only problem is the capital costs of desalination plant that isn't used all the time.

klaustopher• 3 years ago

Great video explaining this in some more detail: https://youtu.be/mxqOPdEUNTs

JumpCrisscross• 3 years ago

Is there a video of a physicist answering this question? Why is this problem so difficult?

Metacelsus2• 3 years ago

See also: a way to potentially do this with no energy input (exploiting density differences): https://www.science.org/doi/10.1126/science.183.4121.157

Basically you put a reverse-osmosis membrane at least 231 meters deep in the ocean. If you put it deeper, you could potentially extract both freshwater and energy.

MarkMarine6• 3 years ago

That is amazing! I’d never thought of leveraging the pressure of ocean depth for this, it’s a great idea. For anyone reading, the energy that OP is talking about would actually force the fresh water above the surface of the ocean without pumps.

I didn’t get to the whole paper, but I imagine the challenges of keeping that membrane clean are remarkable.

Metacelsus2• 3 years ago

Yeah, I thought of it a few years ago, then realized I'd been scooped by ~40 years. But given the advances in technology maybe it's possible today?

IshKebab6• 3 years ago

It's not amazing, it's obviously delusional.

Think about it - if it really worked you have invented a perpetual motion machine, since you could just feed the fresh water through a little water wheel back into the ocean.

You don't need to do any maths at all to know that his maths has gone drastically wrong somewhere.

bell-cot• 3 years ago

That article's subtitle: "In principal, but probably not in practice, fresh water can be extracted from our oceans for no expenditure of energy" [Italics mine]

Also - 231 meters deep is where, in theory, you'll just start getting fresh water coming through your membrane. Which is 231m deep. Fresh water that you'll spend plenty of $energy to pump up to the ocean surface.

(For reference - Hoover Dam, when brim-full, has a slightly lesser drop from the water surface in the reservoir to the output of the hydroelectric turbines. You'll be pumping $energy in, to lift each ounce of your "free" fresh water up to where it is useful.)

[Edit - from some quick calculations, and the density of sea water relative to fresh water...it looks like the "don't need to pay to pump the fresh water back up" version of this scheme will need to run its osmotic membranes at the bottom of the Challenger Deep (~11,000m), or something pretty close to that.]

basseed• 3 years ago

*principle

eslaught• 3 years ago

If I built an ocean base 231 meters below the surface, does that mean I'd get free fresh water by sticking a membrane on the outside of my base? (Ignoring the impracticality of building an underwater base, of course.)

Sounds like a cool sci-fi premise.

geysersam• 3 years ago

Still, pumping water from 230 m is not that expensive energy wise compared to other approaches.

Best case scenario, pumping 1 kg of water 230 meters costs 2.3kJ.

Elsewhere in this thread it was mentioned that typical desalination approaches need 10-15kJ/kg.

iancmceachern2• 3 years ago

It seems there is one use case that would be viable.

If we use the water at depth. I think the way to go is underwater living pods.

If we go this route, I propose we also kickoff a solid Merpeople program (Mermaids, Merman, etc). The goal woukd be to gradually move the human race to be Merpeople. One day we will be viewed as the Neanderthals and Merpeople the people. As everyone knows, the hallmark of any reputable Merpeople program I'd breathing underwater, indefinitely, in Salt water. If we've been able to achieve that it's reasonable to assume we'd also be able to engineer the ability to "drink" seawater directly.

All this to say, I guess there isn't really an application for this.

irrational3• 3 years ago

Haven’t there been experiments with using wave motion to generate electricity? If practical, maybe wave motion at the top could be used to generate electricity for pumps at the bottom.

golergka• 3 years ago

If you would just build a pipe that goes up to the sea level, wouldn't the fresh water naturally go up it because of pressure enacted at it at 231 meters? You would only need to pump it up from the sea level.

cma• 3 years ago

How much energy does it take to pump it back up from 231 meters, compared to traditional methods? That would be 2.25kJ of energy per liter. Normal desalination I believe is 3kJ per thousand liters.

paulcole2• 3 years ago

My idea is to not pump it back up but to let it drain down to Australia.

greesil• 3 years ago

You can power it by pumping down an equal amount of surface water

Natsu• 3 years ago

Just dig a ditch from California to Arizona, then use the sunlight to evaporate the water. Easy, right? :)

jrockway4• 3 years ago

That's the most common way of collecting drinking water, right? Sun evaporates water from the ocean, then it condenses in clouds, and the clouds rain into a river which we suck the water out of. Boom! Plus you can get electricity out of it.

blurker• 3 years ago

It's surprisingly difficult to separate salt from water to the point that it's drinkable. That difficulty translates to it being very costly and that cost is so prohibitive that most places will choose another option. Like even building massive pipelines to transport water across 1000's of kilometers is probably going to be a better option. It's pretty much always going to be more economical to use the water that the earth is naturally desalinating for us.

Obscurity4340• 3 years ago

Doesn't Israel (have the tech to) do it for like nothing or extremely nominal cost?

josh_fyi3• 3 years ago

Not nothing or nominal, but cheap enough that it is feasible, and about the same as other options. We also recycle 80% of the water, first in the world. The second-place country does 15%,

slashdev2• 3 years ago

Actually it's quite cheap, and Israel does it at scale, among other places.

It's just still much more expensive that just pumping free fresh water from rivers, lakes, and ground water. So you'd only do it if water were actually scarce.

I think this is why the scare-mongering over fresh water availability (agriculture excluded) is mostly just hot air. Fresh water is only scarce at ridiculously low prices. Raise the price and the market will solve the problem quickly. That matters for agriculture, but not for human consumption.

Even many dry regions that are far from the ocean, like the southwest US, only have water problems because most of it is used for agriculture at ridiculously low prices. Price it appropriately and that will end very quickly and there won't be any shortage.

zbrozek2• 3 years ago

Though the southwest is a great place to farm if you have the water to leverage the sun and the relative dearth of pests. Given the economic potential of a huge fraction of the country, I'd wager that getting water there will be worthwhile within my lifetime.

I'd love to see an aqueduct covered in solar panels roughly along I-40. Drain the too-wet southeast to irrigate the too-dry southwest.

kelnos7• 3 years ago

That's exactly the problem, though, no? If you keep raising the prices, then at some point desalination will be an attractive option.

Agree that the current system in the southwest/western US around agricultural water rights is just stupid, though. Agriculture uses water in some disgustingly inefficient and wasteful ways, because they're incentivized to do so.

AshamedCaptain• 3 years ago

In addition, voters complain about the taste.

josh_fyi3• 3 years ago

In Israel they add minerals back in because the desalinated water is too pure.

politelemon2• 3 years ago

I've vaguely known that what the taste is related to minerals. Does anyone know what kind of minerals they're adding back in?

seu• 3 years ago

Indirectly related: https://seawatergreenhouse.com/

"The idea behind the process is simple. It combines two unlimited resources - sunlight and seawater - to provide ideal growing conditions for crops in hot, arid environments.

The innovation utilises the cooling and humidifying power of water vapour produced from evaporating salt water. Using modeling and simulation techniques developed in collaboration with our partners at Aston University, we are able to process local climate data to predict greenhouse performance and inform the design. The combined effect of reducing temperature and increasing humidity, together with providing a protected environment for crops, results in up to 90% reduction in evapotranspiration. This greatly reduces irrigation requirements, which can be provided by desalination, and improved growing conditions.

As a result operating costs are lower, yields increase, and farmers can benefit from year-round production of high-value horticultural produce. "

ChrisArchitect• 3 years ago

So many newer attempts since then it feels like, different approaches

Like this Creating Drinking Water Using Ocean Wave Power (https://news.ycombinator.com/item?id=10522700)

But what happens to them? Initiatives never seem to go anywhere far....... energy requirements.... no financial incentive/interest? Same sort of tepid interest as general climate change initiatives?

admax88qqq• 3 years ago

Lack of drinking water is sadly mostly an issue in poor countries, so there's little money to invest/spend on new ways of creating it.

quertered5• 3 years ago

Question: why is desalinated water costs calculated based on as if the water was immediately thrown back into the ocean? Wouldn't it rather be recycled after once desalinated?

IshKebab6• 3 years ago

Because it's easier to desalinate salt water than sewage?

quertered5• 3 years ago

How would salt end up back in sewage?

e_y_• 3 years ago

Recycled water is usually considered non-potable, so while it can be reused it's usually not available for drinking water and needs separate pipes.

quertered5• 3 years ago

Though there are processes that turn it back into potable water, just reusing it even once in agriculture would bring huge cost savings compared to having to desalinate it again, which is why I wonder why there doesen't seem to be any studies of the realistic likely costs of desalinated water when accounting for reasonable reuse

freitzkriesler22• 3 years ago

We do in some places. But in other places like California NIMBYs and greens decided putting extra salty brine back into the ocean was worse than taking fresh water run off from the inland, worsening desertification

Really mostly nimbys. Greens have relented.

Nuclear desalination would solve a lot of the fresh water problems but we can't have solutions now can we?

Gibbon1• 3 years ago

Really mostly nimbys. Greens have relented.

Head in the Sandies is probably even more encompassing. From people that tink the solution is drilling for oil in national parks to people thinking suing developers and separating their trash is all you need to do. They're stupid people. Neither should be influencing policy.

Seems to me that the usual historical options aren't acceptable. Business as usual looks bad. The traditional solution, genocidal warfare seems like a really bad idea for someone living in an industrial civilization. We could degrowth. But the Khmer Rouge tried that in the 1970's and back to the rice fields didn't work very well for most people.

So seems like technological mitigation is all we can hope for.

kelnos7• 3 years ago

Greens have relented probably because there are safer ways to put the brine back into the ocean that don't disturb ecosystems all that much.

freitzkriesler22• 3 years ago

From a cursory search, the greens have lost their bite simply because there isn't an alternative. Water supplies are drying up and the alternatives would end up being losing political power.

The state approved 3 new plants this year alone and more are coming.

konschubert2• 3 years ago

Isreal does. California also has desalination, no?

If power costs are the driver then solar will be the answer

retrocryptid• 3 years ago

Because it's expensive. There, saved you a click.

motohagiography• 3 years ago

If you want anything to be economical or "worth it," you create the conditions where you are providing something to external parties, and the money will come in to sustain it. The economics of desalination are trivially viable if you can set up a stable financial regulatory environment in the region that has competitive taxation internationally.

Desalination is economical in the middle east because they export oil. In Israel it's economical because they export tech knowhow, and have foreign income sources from their diaspora networks. Some people will moan about "tax havens! for the filthy rich!" But really it's just viable habitation for locations without a lot of resources to export. Favourable capital rules are a valuable export. We do this in customs-free zones around the world today. If you have those rules in an area that needs a desalination plant to survive, I guarantee you it's going to work really, really well.

dukeyukey2• 3 years ago

Same in Australia - you've got a very wealthy population, living on the coastal outskirts of a wind/solar/coal heavy desert. Basically the perfect combo for desalination.

AnotherGoodName5• 3 years ago

The coastal areas of Australia have literally some of the highest rainfall anywhere in the world. Sydney has more annual rainfall than 'rainy' Seattle or London.

For Australia the correct thing is to store the damn (or should I say dam) water that falls where people live.

koyote• 3 years ago

Which is why the Sydney desalination plant is entirely (I believe) powered by renewables.

parentheses• 3 years ago

Knowing that the vast majority of water use is not the water flowing to homes for drinking, plants and washing, the government (local or federal) could subsidize it for individuals while taxing industrial water consumers.

As mentioned in another post. Basic utilities can easily become affordable with proper regulation.

shaunxcode• 3 years ago

Yet. Why don’t we yet.

superb-owl• 3 years ago

It'd be helpful to know the minimal energy requirement to desalinate a gallon of water. With perfect technology, how expensive (in terms of energy) would it be? What's our current level of efficiency?

Enginerrrd2• 3 years ago

Depends a lot on what you start with and on some of the other assumptions you make, but for seawater, the theoretical limit is probably ~3 kJ/kg, and the absolute state of the art full scale desalination is probably 11-14 kJ/kg

nsenifty• 3 years ago

Or about $0.20 per US person per day.

Given average water use per person in US is 310 liters/day (82 gallons) [1] and average electricity cost/kwh is $0.17 [2], and assuming 14 kJ/kg. 310 * (14 / 3600) * $0.17 = $0.20.

[1] https://www.epa.gov/watersense/statistics-and-facts

[2] https://www.bls.gov/regions/midwest/data/averageenergyprices...

hamandcheese• 3 years ago

Theoretically, about 0.86 kWh of energy is needed to desalinate 1 m3 of salt water (34 500 ppm). This is equivalent to 3 kJ kg-1. The present day desalination plants use 5 to 26 times as much as this theoretical minimum depending on the type of process used.

That translates to about 3.25 watt-hours/gallon as the theoretical limit, if my math is correct.

Source: https://www.desware.net/Energy-Requirements-Desalination-Pro....

YesThatTom2• 3 years ago

We need to figure out how to make cell phones out of the refuse salt / salty sludge.

We’d find new ways to desalinate in a week!

fullspectrumdev• 3 years ago

I mean, we probably could extract industrially useful chlorine and sodium from it, if sodium batteries ever actually take off as a lithium replacement that could be extremely viable.

wheelerof4te• 3 years ago

Where's that guy advocating for the desalination plants in Phoenix now?

thunkshift1• 3 years ago

All comments seem to focus on the cost/energy requirements of the filtration process.. but the elephant in the room is the waste. How to safely dispose off the waste water after filtration completes? That water is virtually useless

samtho• 3 years ago

Run long tubes (1-3mi) out into then ocean with perforations so you can diffuse the highly salty water back into the ocean without disrupting local ecosystems.

lovemenot• 3 years ago

Ocean-going vessels could be fitted to take on brine as ballast in port and gradually replace it with sea-water during their voyage.

toomuchtodo3• 3 years ago

This has the useful side effect that it should prevent the transfer of invasive species in ballast tanks, as most cannot survive high salinity conditions.

niemandhier• 3 years ago

Are state of the art systems more efficient than the ion-pumps in cell membranes?

I remember reading about light driven sodium and chloride pumps, if we could make these transport ions across some biomembrane we could desalinate water.

jokoon• 3 years ago

What about that small cheap device invention thing that can be used by people who live on the coast to produce enough drinking water?

whatshisface• 3 years ago

A kettle.

drbojingle• 3 years ago

Same reason as always: cost. If it was easy we'd be doing it long ago kn every boat and every coastal city.

runjake• 3 years ago

Spoiler: desalination requires a lot of energy.

konschubert2• 3 years ago

Solar is cheap

grej2• 3 years ago

Solar is cheap when active, and the good news this is one of the cases where intermittency doesn't really matter. We should really explore more use of intermittent power for cases like this where the limited reliability of wind and solar is less significant.

Groxx• 3 years ago

If solar was cheap enough, it would be used.

In a handful of places, it is. In the rest, it's so much more expensive than alternatives that it's borderline insanity to use it.

Like ice: ice is cheap in Antarctica! But importing Antarctic ice to a desert would be absurd.

AnotherGoodName5• 3 years ago

Although it shouldn't. Adding salt to water is endothermic, it absorbs energy to add salt and releases it to separate them. The article talks about the trouble of breaking the bonds but this is wrong. It's harder to break the na-cl bond to make salt water in the first place.

We just haven't found a good process. That's it. Cheap desalination is not physically impossible. The deep ocean separation that someone here mentioned seems quite promising and gives off energy which is expected. Salt has weak bonds in water and when they reform the na-cl bond there's a lot of energy to be had.

bagels3• 3 years ago

Article puts the cost to produce a cubic meter of water at $1-$2

In the bay area, I'm paying ~$2.80 per cubic meter.

I don't see why it's not feasible.

Yes, there are transmission/pumping costs. Assuming the water we're getting now is free, that's still only ~50-75% increase in cost over current costs.

labster• 3 years ago

Article is 15 years old, energy and labor prices have increased a lot. We need a new cost estimate.

pstuart2• 3 years ago

Solar prices have plummeted, and that use case can skip storage issues (just run when there's power available). Obviously land, labor, and infra cost are not so simple.

scythe2• 3 years ago

Desalination seems to be well-positioned to take advantage of variable energy prices, particularly in dry-summer climates where demand for water increases at the same time as solar energy availability. If you run the desalination system when energy is cheapest, your energy storage problem becomes a water storage problem, but a simpler one than with pumped-hydroelectric storage.

I haven't seen a detailed analysis, but this could look good for California, notwithstanding the other problems with desalination (ecological).

pstuart2• 3 years ago

Another thing I'm curious about -- Dean Kamen's "Slingshot". Seems like we'd be well served if his vision was realized: https://www.slingshotdoc.com/the-film

tuatoru• 3 years ago

Desal costs seem to have decreased a lot since 2008. Now maybe one-third as much, based on a quick image search for charts of the price trend of desalination.

wdr1• 3 years ago

Additionally, if there was a nationwide push to nuclear power, we'd have cheap, clean energy -- putting a sizable dent in both clean drinking water & climate change at the same time.

adamrezich• 3 years ago

that would fuck up too many monopolies and political narratives though

myspy• 3 years ago

I'd like to ask this here again because I haven't got a clear answer yet. What about building a plant, getting the fuel, storing the fuel, and decommissioning the plant, how is that affecting the cheap and the clean energy in total greenhouse gas emissions? Is it worthwhile compared to wind farms and solar power? And where is the fuel stored in the States, because here in Germany it's hard to find a place to store it for 10 millennia.

Kon5ole2• 3 years ago

Additionally, if there was a nationwide push to nuclear power, we'd have cheap, clean energy -- putting a sizable dent in both clean drinking water & climate change at the same time.

Nuclear power is prohibitively expensive even in a best-case scenario. All estimates that have indicated otherwise simply ignore most of the costs. Political decisions socialize the costs to the state and future generations. Even in the US.

Read up on the current costs of closed plants like Rancho Seco in the US, recent developments around EDF in France, and the statements from Sweden's riksgalden for more info about this. TLDR, you are paying for closed nuclear plants already, and so will your great great great grandchildren. They will pay all their lives for plants that won't give them a single watthour of power. This is a monumentally bad idea IMO.

How about we instead make a nationwide push on things like hydrogen gas from seawater and solar?

When the hydrogen gas is burnt, it creates salt-free H2O as a byproduct, and in the meantime it's a good energy storage solution to solve the intermittence of renewables.

Your grandchildren will praise you instead of curse you.

gruez3• 3 years ago

I don't see why it's not feasible.

Realistically speaking, because buying water rights from existing farmers is probably even cheaper.

LoganDark6• 3 years ago

See, "Why is Soda Cheaper Than Water?"

https://www.youtube.com/watch?v=9nlkW16t5lM

It's probable the reason water costs that much for you is because people are still willing to pay that price for it.

Capitalism truly sucks.

gruez3• 3 years ago

See, "Why is Soda Cheaper Than Water?"

Except the core premise is not true, so far as I can tell. To confirm this I went on Uber Eats, looked for chain restaurants near Salesforce Tower, and surveyed their beverage menus. At initial glance, most restaurants charged more for "water" than for soda. However, on further inspection this is because in those cases, the soda was dispensed from a fountain and the water was bottled. The latter obviously would cost more than the former, because of the cost of having to transport individual bottles. This can hardly be attributed to "Capitalism truly sucks". Furthermore, in cases where a soda fountain is available, the restaurant is legally mandated to provide the water to you for free[1], which makes the cost of water in those places $0. Of the places that only sell bottled beverages (there's surprisingly few):

* California Pizza Kitchen charges the same for water as for canned soda, and gives you more water[2]

* Chipotle Mexican Grill's cheapest beverage is bottled water[3]. The second cheapest option? San Pellegrino sparkling water, shipped all the way to California from Italy.

That said, the economic principle of "thing x costs more because people are willing to pay for it" is probably true (see for instance, airfare that's bought late), but this isn't one of those cases.

[1] All restaurants are technically supposed to, but having a soda fountain virtually guarantees that they can't weasel out of it by saying that they only serve bottled beverages and don't have cups for serving tap water

[2] https://www.ubereats.com/store/california-pizza-kitchen-53-t...

[3] https://www.ubereats.com/store/chipotle-mexican-grill-211-su...

ChuckMcM11• 3 years ago

As a person who has run through this particular loop once with local politics (Sunnyvale's northern border is the SF Bay which has former Morton Salt ponds in it) what I ran into was two things, one that there wasn't a cost effective power solution for just desalination, and two, the players don't care about water to individuals (drinking water and what not) because there is absolutely no risk whatsoever in the bay area of not having "enough" of it. The political block that kills it is a combination of local pop saying "we don't want nuclear/cheap power in our back yard" and the folks farming the desert in the central valley saying "If you can't supply farms, why would you do it?"

My hope is that one day, small scale nuclear power (sometimes called "modular nuclear power") will make this a reality.

BurningFrog6• 3 years ago

Desalination seems ideal for cheap but unreliable energy like solar or wind. You just need a water reservoir to act as "battery".

jojobas3• 3 years ago

The smaller the reactor, the worse neutron efficiency gets, good old cubes and squares. Good practices also require as many hands/eyes for normal operation a GW class reactor as a 50MW one.

ChuckMcM11• 3 years ago

FWIW there is a really fun "disruptive" desalination option that could work in places like Monterey Bay which is just dropping a really really long pipe down into the ocean that has the desalination membrane at the bottom of it. Top of the pipe is above the surface. Water pressure at depth drives water through the membrane and up the pipe. At the surface you just pump fresh water out of the pipe like an ordinary fresh water well.

Maintenance is basically pulling the pipe up every couple of years and replacing the membrane which will become fouled over time, but generally it would be deep enough that it would not get barnacles and other mollusks on it.

abhibeckert• 3 years ago

there wasn't a cost effective power solution for just desalination

There absolutely is.

All you need is a bunch of mirrors to direct the sun at a chamber filled with water. The water will evaporate, the expansion into steam creates significant pressure so you can run it through a turbine, and then once the steam cools down and liquifies again, it won't have any salt in it.

It's not even remotely expensive. Mirrors are cheap. The turbines/etc are basically the same as a coal or gas power plant and mirrors are a hell of a lot cheaper than mining coal or gas. Also if you're boiling a usable quantity of water you'll be generating a lot of power, which is a handy byproduct (more valuable than the water to be honest).

"Not in our back yard" is the real issue. The chamber is generally at the top of a tower, and even painted black all that sunlight focused onto it is very bright. People generally don't want a really bright object on top of a tower anywhere near them. I guess you could build a wall around it or something, but you'll still get complaints from aircraft/etc.

Driving into the sunset or sunrise is annoying. Imagine if that was all day every day instead of just for 20 minutes or so.

Having said that, if you're in a remote area to counter the NIMBY issue, and clean water is hard to find, then the system I've described is very effective and they are being used for cost competitive farming of cheap crops.

Anyone who actually wants to desalinate seawater can do it. It's just that almost nobody wants to right now.

neodypsis3• 3 years ago

You have cheaper water in the Bay Area than in San Jose, Costa Rica.

bagels3• 3 years ago

This page disagrees: https://www.costarica.com/business/water-rates

thomasahle• 3 years ago

Is it possible that desalination at large scale would push the energy demand and price up enough that it would stop being feasible?

galleywest200• 3 years ago

Sure, but could we just build nuclear reactors that power just these intense machines?

tguvot3• 3 years ago

In Israel, where everything is more expensive, desalination costs are ~$0.4 per cubic meter of water

andbberger2• 3 years ago

that's money we could spend on building infrastructure to divert peak flows on wet years to recharging the central valley aquifer, which is several orders of magnitudes larger than all other reservoirs in the state combined

cratermoon3• 3 years ago

This came up on HN recently. tl;dr: it's harder than it looks https://practical.engineering/blog/2023/6/28/why-is-desalina...

ainiriand2• 3 years ago

Well this it's done in some parts of the world, I am not sure why they claim is not. My brother lives in Lanzarote an the water is extracted from the sea just like this. The energy comes from 2 huge wind turbines in the plant.

taneq• 3 years ago

Might be the (2008) bit? I remember there was a bit of political hoo-hah here in Perth about a big desalination plant back then. Now most of our drinking water is from either desalination or waste water reprocessing.

RagnarD• 3 years ago

New technology is making it easier and cheaper. There's also the fact that environmentalist suppression of nuclear power has made electricity much costlier, intermittent, and much less reliable.

https://scitechdaily.com/new-device-purifies-saltwater-over-...

graeme• 3 years ago

There’s an enormous amount of lithium in desalinated water iirc

userbinator• 3 years ago

We actually do --- we just let the sun do it for us. ;-)

labrador• 3 years ago

I wonder how much it would cost in electricity to run a current through salt water to produce hydrogen and oxygen, then run the hydrogen through a hydrogen powered generator to recover most of the electricity and the fresh water byproduct?

cwillu2• 3 years ago

My understanding is that at the salinity levels involved, this gives you hydrogen and bleach as outputs.

Maxion4• 3 years ago

At least our toilets will be clean when this thread starts producing fresh water.

eterevsky• 3 years ago

Also Scientific American, 8 years later (2016): Israel Proves the Desalination Era Is Here (https://www.scientificamerican.com/article/israel-proves-the...)

karteum• 3 years ago

I found this a few years ago (uses only a simple low-tech design, simple materials, and heat from the sun. I don't know how efficient it really is)

http://www.gabrielediamanti.com/projects/eliodomestico/

eftychis• 3 years ago

Fun fact: A good number of Greek islands end up using desalination.

E.g. https://www.nationalgeographic.com/science/article/partner-c....

And this is not by choice: Greece has to deal with extreme volatility in resource consumption throughout the year. Add to that it has ~6000 islands (around 200 being inhabited year round -- 227 as I google). And the tourist island/islet focus changes throughout the years. With this context, there can be no "I will create a pipeline of fresh water" or any other project like that really.

yodelshady3• 3 years ago

Right, islands (and Israel) normally do because there's not the space for a large enough reservoir.

We're playing silly buggers with economics again here; when it's rainy, "DeSaL iS uNcOmPeTiTiVe", because the "market rate" for water is pennies per meter cubed. Except, oh wait; suddenly it's dry, the "market rate" skyrockets" and large parts of your economy collapse. The "market rate" was always giving a massive* surplus to consumers, and now it's gone.

This is A Bad Thing.

Turns out it would have been better to have a slightly more expensive water source that was reliable. This fact is somehow obvious to everyone except economists, who should (at least in Europe) be called out as frauds for universally advocating along such idiotic lines.

danbr• 3 years ago

Practical Engineering just did a great video on Desalination.

Why Is Desalination So Difficult? - https://www.youtube.com/watch?v=mxqOPdEUNTs

afinlayson• 3 years ago

I've read that we are starting up use other sources of heat to do desalination projects. There's so many sources of heat that we are just dissipating into the atmosphere. Nuclear or other power plants is an obvious choice.

drawkbox• 3 years ago

Concentrated solar stills is one way [1][2]

A great thing about desalination with stills is it uses the natural water cycle, the water that comes out is cleaner than any other as it uses that.

A concentrated solar still is a system that uses the same quantity of solar heat input (same solar collection area) as a simple solar still but can produce a volume of freshwater that is many times greater. While a simple solar still is a way of distilling water by using the heat of the sun to drive evaporation from a water source and ambient air to cool a condenser film, a concentrated solar still uses a concentrated solar thermal collector to concentrate solar heat and deliver it to a multi-effect evaporation process for distillation, thus increasing the natural rate of evaporation. The concentrated solar still is capable of large-scale water production in areas with plentiful solar energy.

[1] https://en.wikipedia.org/wiki/Solar_still

[2] https://en.wikipedia.org/wiki/Concentrated_solar_still

jaimex2• 3 years ago

Can desalination and electrolysis be combined so we have two useful bi-products?

Clean drinking water. Hydrogen for for fuel.

clement_b• 3 years ago

Feels like a problem that will be solved as soon as incentives will be here, and cost of fresh water from other sources depleted or protected. The costs mentioned in this 15 years old article aren't that high in a world where we have to be careful with water.

I wonder what is the reality now.

squarefoot• 3 years ago

Why not using the sun to evaporate it, then collect the salt? Temperature have risen in the last 15 years, unless one wants to extract water only by desalination, it should be feasible, and could at least help less densely populated areas near the sea. Maintenance aside, energy costs would be negligible.

Why don't we get our drinking water by taking salt out seawater? (2008)

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