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The Dirty Truth About Turning Seawater into Drinking Water (gizmodo.com)
98 points by aceperry 30 days ago | hide | past | web | favorite | 127 comments

> In fact, the study concluded that for every liter of freshwater a plant produces, 0.4 gallons (1.5 liters) of brine are produced on average.

I hate that they mix the units here. Why not "for every liter of freshwater a plant produces, 1.5 liters of brine are produced" or "for every gallon of freshwater a plant produces, 1.5 gallon of brine are produced" or even "for every unit of freshwater a plant produces, 1.5 units of brine are produced"

Also, producing more brine would make the brine less concentrated and less harmful - it would be better not worse.

> Also, producing more brine would make the brine less concentrated and less harmful - it would be better not worse.

Producing more brine, by diluting it, still would require something to dilute it with.

The most obvious, non toxic, choice would probably be water, but the whole exercise is about getting water in the first place.

You could produce a larger volume of more dilute brine by extracting less water per unit of input seawater.

You would need to spend more energy on pumping seawater and brine, but less energy on moving water up a concentration gradient. I have no idea which cost would dominate.

There is also the concentrate it less option - don't wring out all of the water just what is easy and move onto the next batch vs "supersaturated brine".

No water added just less removed from input - which means more but less potent.

You can just dilute with seawater, as discussed elsewhere in this thread.

Does diluting it with seawater (after which I assume it is returned to the sea?) result in an endlessly increasing salt level in the seawater, over a long period of time, that will reach a dangerous level at some point?

Edit: I realize my naivety now. Other comments mentioned the desalinated water (at least some of it) will end up back in the sea eventually, so that would maybe counterbalance such a concern.

The short term effects are increased salinity and reduced oxygenation for water in the immediate vicinity of the desalination plant, which is enough to drastically alter the biome (aka “kill all the sea life”).

I believe at least some desalination plants add copper and or chlorine to the input water to prevent biofouling. In that case running more water through the plant to produce less concentrated brine would require more chemicals

Just to be clear, "brine" isn't "salty water."

> This untreated salt water can’t just hang around in ponds—or, in worst-case scenarios, go into oceans or sewers. Disposal depends on geography, but typically the waste does go into oceans or sewers, if not injected into wells or kept in evaporation ponds. The high concentrations of salt, as well as chemicals like copper and chlorine, can make it toxic to marine life.

> “Brine underflows deplete dissolved oxygen in the receiving waters,” said lead author Edward Jones, who worked at the institute and is now at Wageningen University in the Netherlands, in a press release. “High salinity and reduced dissolved oxygen levels can have profound impacts on benthic organisms, which can translate into ecological effects observable throughout the food chain.”

It's an actual waste product that has to actually be responsibly handled. It's not "just the salty water from the ocean that we can dump back in however we want."

Just to be clear, "brine" isn't "salty water."

It mostly is, and the additional chemicals they mention are already in the sea water, not that were added somehow in the process. It's just concentrated.

That it's concentrated is a problem, obviously -- very high-saline water (e.g. brine) and concentrated toxins are a problem, and would cause environmental problems if just dumped. The most common way to deal with brine is simply diluting it before discharge, ensuring that the salt content isn't high enough that it sinks and forms a brine pool.

True. Basically, the brine is just sea water with some of the water removed. Based on the numbers in TFA, 2.5L of sea water becomes 1.0L of fresh water and 1.5L of brine. And so the brine is just 67% more salty than the sea water was.

And it doesn't seem like diluting the brine with sea water before discharge would increase cost very much. From a 2010 presentation by Carlos Campos ("The Economics of Desalination for Various Uses") I get that seawater pumping and screening accounts for just 2-6% of the energy used in reverse osmosis.[0]

0) http://www.rac.es/ficheros/doc/00731.pdf at p 24

Diluting it with ... fresh water?

You churn it with a large volume of sea water and then discharge it when the salinity is only acceptably above the natural amount. I believe France limits it to 10% above the natural salinity.

e.g. take 3 gallons of sea water and extract 1 gallon of fresh water. You have 2 gallons of +50% salinity brine. Churn it with 8 gallons of seawater and you're back to +10% salinity. Wash it out into the ocean.

> the additional chemicals they mention are already in the sea water, not that were added somehow in the process.

Are you sure? The article made it sound like they were added. If they're natural to sea water, simply diluting it with more sea water or possibly sewage that's headed for the ocean anyway, sounds like the obvious solution.

Yup, desalination doesn't require adding "chemicals" to the water. It works using heat, electricity, and osmosis membranes[1]. I'm not sure why the article took the tone that it did.

[1] http://large.stanford.edu/courses/2011/ph240/parise2/

Don't they add copper and other chemicals to prevent fouling of the pipes? Not strictly required for desalination, but required to keep the desalination plant running with minimum manual cleaning.

Yes, just like exhaled breath is a waste product full of C02 and containing very little oxygen. If other people had to breath that they would become very sick or even die.

Exhaled air consists of 78 percent nitrogen, 16 percent oxygen, 4 percent carbon dioxide.


The minimum oxygen concentration in the air required for human breathing is 19.5 percent. ... hen oxygen concentrations drop from 19.5 to 16 percent, and you engage in physical activity, your cells fail to receive the oxygen needed to function correctly. Mental functions become impaired and respiration intermittent at oxygen concentrations that drop from 10 to 14 percent; at these levels with any amount of physical activity, the body becomes exhausted. Humans won't survive with levels at 6 percent or lower. https://sciencing.com/minimum-oxygen-concentration-human-bre...

You're not going to thrive or compete athletically on second-hand air.

But if you're not breathing on your own, it can save your life. That's what rescue breathing (what used to be called "artificial respiration") is.

There is more than enough oxygen in exhaled air to support life. At least until medical care arrives.

Actual question, how many time can air be breathed? I think you can live on second-hand breath.

I'd be quite dangerous and very uncomfortable: exhaled air contains ~4% CO₂, 16% O₂ and is at roughly 100% humidity.

* at 4% CO₂ you'll be suffering from moderate CO₂ toxicity (narcosis, dizzy spells, increased heart rate & blood pressure, mild shortness of breath, exaggerated response to effort)

* at only 16% O₂ (but assuming atmospheric pressure), you're well into chronic hypoxia land, not quite sure lethal but not far, the hyperventilation from CO₂ poisoning will make this slightly better but nowhere near good

* the combination of hypoxia and CO₂ poisoning will make effort (let alone exercise) possibly to probably lethal

* the extreme levels of humidity will make the entire thing even worse as you'll have a hard time cooling down

You can probably live in this situation for a few days, but the CO₂ levels alone would make it lethal past a few weeks, the combination of all factors means likely no more than a pair thereof, at best.

Can you please provide sources? I am very interested

Well that's how CPR works ... I can't remember the details ... it's many many years ago I studied first aid but I think it's something like 1/3 of the Oxegen gets used, so when you're giving the kiss of life you're imparting the remaining 2/3

I thought that CPR was largely about getting CO2 into the lungs to trigger a breath reflex.

It could well be. I’m just recalling something an instructor taught me about 25 years ago ...

Can't answer the question, but I can say that when I did HUET we'd breathe into a bag in the suit and back again. This worked surprisingly well for the time we needed to stay underwater before we could escape. I'd still warn against implementing ones own version of this without studying the topic well, there's a number of pitfalls that one might not be obvious of up front.

I've briefly considered if there might be something to remove CO2 inside the bag, but decided against it since this was training equipment so not sealed and probably reused multiple times.

Chemically scrubbing the CO2 from exhaled air so it can be breathed again is the principle rebreathers work on.

CO2 concentrations above 7% are enough to suffocate you even if there is otherwise ample oxygen.

Yet somehow, we don't typically do Sylvester Brosch or Holger Nielsen any more. Instead, we favour the direct transmission of exhaled air as a method of artificial respiration.

The dictionary definition of brine is "water strongly impregnated with salt." ie salty water.

When in technical contexts, the technical definition matters more than the dictionary definition. Clearly the plant isn’t discharging the stuff I season my chicken with!

No. You can’t take the dictionary definition, ignore the important word, then claim two things are equal.

Salty water is not water strongly impregnated with salt.

To simplify, the difference between salty water and brine is that brine is very salty water. The concentration of salt completely changes the environmental impact. Dumping post-desalination brine back into the ocean is an environmental disaster.

Is there any use for it at all?

It's possible to use salt water and limestone to capture CO2; I wonder whether brine could be used for this purpose.

That would be really interesting. Two birds with one stone: clean water and capture CO2.

Though I assume you then still have a waste product you need to do something with, and how fast are we going to run out of limestone if we start doing this on a large scale?

I guess you could use it to extract salt - one could place evaporation pools next to the water extraction plant. It would evaporate faster than regular seawater.

I’m surprised this article mentions nothing about energy. Practically all desalination in existence is powered by fossil fuels, with Israel and Saudi Arabia being the worst offenders. The only reason it’s even economically viable is the externalized cost of carbon emission. It’s simply not a long term tenable solution until this is addressed.

Carbon emissions is a grave problem with existing desalination infrastructure, but this seems something that can be solved. I'd expect desalination to be well suited for opportunistic use of solar or wind power. Build up reserves of clean water when it's sunny or windy, then deplete those reserves when cheap spare energy isn't available.

Of course this goes for new desalination plants. Whether there's political will to convert existing plants to non-fossil fuel sources is another matter. But at least from an engineering perspective there is a way forward.

What I get out of the article is that disposing of brine is an ecological hazard. This shouldn't really be a surprise since any engineering effort at large scale is going to have some kind of environmental impact, but this is a new consideration for those of us who don't work in the industry and hadn't thought too deeply about the process.

Most desalination plants around the world are operating at 100% capacity all of the time, because that's what needed to avoid depletion of the reservoirs.

To be able to "build up reserves" means that you have to build much higher capacity, but only use as much of it as clean energy allows - in today's world, this is highly uneconomical.

If anything, the reserves to be built are energy reserves that allow water to be desalinated continuously -- and that's something which makes sense in general, possibly grid scale as storage technology improves, regardless of the specifics of water desalination.

I’ve heard on the grapevine that facilities are now being designed which work at under 100% capacity in order to soak up excess/cheap power.

I believe this is coming about because: 1) the high cost of power and presence of sporadically cheap power makes it economically viable, and 2) designing equipment with lower duty cycles can actually provide substantial cost savings. Ie a facility which only runs 50% of the time is much cheaper to build & run than once which runs 100% of the time.

Sorry I cannot cite sources right now.

I believe the reason for that is the expense. They prefer to delay and trying to cut back drastically even when the situation is obviously unsustainable. Thus it gets run at 100% capacity when they finally build it and need three more.

To take truly economically fantastic extremes for current technology if desalination was fiscally cheaper than drilling wells we would see them doing that far more.

In Western Australia, a desal plant was built a few years ago [0]. At the same time, a wind farm [1] that offset the power use of the desal plant was built.

[0] https://www.watercorporation.com.au/water-supply/our-water-s...

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

> Practically all desalination in existence is powered by fossil fuels, with Israel and Saudi Arabia being the worst offenders.

Sound like really obvious places to use solar.

Perhaps the issue is that solar farms are more susceptible to sabotage, simply by taking up a much larger area?

Well the US is currently a net producer of oil and gas. The fracking boom is huge- America has more fossil fuels they know what to do with.

Desalination is good for drinking water but its not going to save California's farming though.

This is not a show stopper. If you discharge brine into the sea, you should have to have a plan to dilute and mix brine.

High concentration brine does not automatically mix into the sea water. The underflow goes into the bottom of the sea and forms a separate layer. But you can use nozzle diffusers, mixer etc. and discharge into high currents.

In Southern California I think the plans are to mix the brine discharge with the treated sewage outflow.

Sure, the high salt concentration kills sea life for a couple hundred meters around where the waste comes out, but compared to the total size of the ocean, I'd imagine the affected area would be TINY. Once you get to a larger area it'd be totally diluted by the normal salinity seawater.

Why don't you just build a pipeline to put the dead spot a couple miles away from shore, far away from economically important beaches, fisheries and reefs?

Maybe have an additional pump to send fresh seawater into the areas of highest concentration, basically set up a countercurrent exchange gradient.

I'm sure there are trivial, low-cost engineering solutions to this problem.

That is what I intuitively thought, until I learnt that salinity in the Persian Gulf (a huge body of water connected to the ocean) is up significantly due to desalination. Salinity has risen 50% over the last two decades. See e.g. https://financialtribune.com/articles/people-environment/434...

Simple math will tell you that this increase cannot be due to desalination. Look:

Volume of the Persian Gulf = Area (251,000 sq km) * average depth (50 m) = 12,000 cubic km approx.

Total amount of desalinated water produced in the world, per annum = 86 million cu. m = 0.086 cu. km,

So if all of the world's desalinated water was taken from the Persian Gulf, for 150 years, the salinity would only increase by 0.08*150/12000 = 0.1%, roughly.

Edit: the entire article is bad, and the headline is sensationalist bullsh#t.

Always good to do some math. I double checked your input figure, and that should be per day, not per year. So 365 times as high. Other assumptions being the same that would give 0.2% rise per year, or 4% in twenty years. Not 50%, but not insignificant.

You are right, thanks for pointing this out. I hate making mistakes like that.

It doesn't need to be responsible for all of the change, it might only be one among many contributing factors like climate change.

In that context, it would be shortsighted and naive to pretend it couldn't have any impact at all even on bigger and longer scales.

Except that the article you link to explicitly states two opposing theories as to why the salinity is so high, and has risen so much.

The two competing theories seem to be 1. desalination and 2. climate change causing excessive evaporation.

Or just mix it with more sea water before releasing it.

> At the very least, we should be treating the brine so it’s safe to discharge into the ocean.

This amused me as I pictured people mixing newly produced fresh water with the brine and releasing this "new" seawater back.

Seriously though, I guess I assumed people were at least turning this stuff into salt. I watched a documentary on salt production (Italy I think) and they just got sea water and evaporated it in huge salt beds.

I kind of assumed the sea salt (Malden) I buy has been created using the same process.

Sea salt has it's own problems due to it's microplastics content. Around 90% of domestic sea salt contains microplastics and the average adult consumes around 2,000 microplastic particles as a result every year. People who go out of their way to buy sea salt presumably ingest significantly more on average.

My mother used to love sea salt, but recently switched to rock salt.

The estuary from which Maldon sea salt is harvested was also used for cooling nuclear reactors from the '60s until 2002 [1], so microplastics probably aren't even its most interesting feature.

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

I will be dissapointed if I don't get some sort of salty superpowers then.

I don't think microplastic particles in the human digestive system are that big of a problem; most of it is fairly inert and will just pass through, the other stuff is in low enough quantities that our stomach should be able to deal with it.

> I don't think microplastic particles in the human digestive system are that big of a problem; most of it is fairly inert and will just pass through, the other stuff is in low enough quantities that our stomach should be able to deal with it.

"The primary concern with human health in regards to microplastics is more directed towards the different toxic and carcinogenic chemicals used to make these plastics and what they carry. It has also been thought that microplastics can act as a vector for pathogens as well as heavy metals. More specifically, pregnant women in particular are in danger of causing birth defects to male infants such as anogenital distance, penile width, and testicular descent. This comes from phthalate exposure and DEHP metabolites that interfere with the development of the male reproductive tract."

"Another dangerous ingredient is called Tetrabromobisphenol A (TBBPA) which is a flame retardant in many different types of plastics such as those used in microcircuits. This chemical has been linked to disruptions in thyroid hormones balance, pituitary function, and infertility. The endocrine system is affected by TBBPA through disruption of the natural T3 functions with the nuclear suspension in pituitary and thyroid."

"Many people can expect to come in contact with various types of microplastics on a daily basis in the aforementioned sources (see sources). However, the average citizen is exposed to microplastics through their various types of food included in a normal diet. For instance: Salt. Researchers in China tested three types of table salt samples available in supermarkets and found the presence of microplastics in all of them. Sea salt has the highest amounts of microplastics compared to lake salt and rock/well salt."

Even if we ignore the environmental impact, there's ample evidence to indicate we should not dismiss the dangers of microplastics to human health without further research.

[0] https://en.wikipedia.org/wiki/Microplastics

Still we are talking about ingesting few microscopic particles per day. If they were cyanide it might have been harmful but they are mostly inert undigestible polymer with possibly traces of some additive if they surivived all previous stages of plastics life. Like floating in saltwater for few years or perhaps even already being in digestive systems of some aninals.

I wouldn't bother with microplastics in salt. Not when I'm exposing my blood directly to mixture of hydrocarbons and soot with every breath I take.

>Still we are talking about ingesting few microscopic particles per day.

Which is going to increase. Plastic plumbing, plastic containers, plastic clothes, plastic cooking surfaces, plastic in the water, plastic in the salt, plastic in the air, plastic toothbrush bristles, plastic microbeads in body scrubs etc.

Most plastics are effectively forever, they break down into smaller and smaller pieces creating the microplastics. A recent (very small) study found every single person out of the group of 8 had microplastics in their stool, on average about 20 particles for every 3.5 ounces of stool. The study had one test subject per country from Finland, the Netherlands, Poland, Austria, Italy, the United Kingdom, Russia and Japan.

I'm just saying there are bigger concerns right now. Such as air quality.

Another point to consider, a recent study [1] found that comparable amounts of microplastics are deposited on your food from dust falling on it while you eat. So unless you either ban all synthetic textiles from your house/workplace/favourite restaurants, or make sure to always eat underneath a huge laminar flow air extractor, you're gonna ingest some microplastics.

[1] https://www.sciencedirect.com/science/article/pii/S026974911...

Things can get weird at very small sizes because of the huge ratio of surface area to mass. An amount of plastic that is safe to place against your skin as one object, might have more significant chemical interactions as a collection of particles in your digestive system--which specializes in leaching complex chemicals out the materials that pass through it.

There can also be strange physical issues at small scales. A block of plastic cannot get lodged between cells or poke through into the bloodstream.

On some level I find it totally fair that we're at least swallowing some of that microplastic. A little solidarity with the fishes for the problem we created.

Well you could probably run an osmosis power station off it. I'm not sure about the efficiency, but it's a viable way to store energy.


> how about generating electricity with hydropower

I am intrigued to hear how the author plans to take water from sea level then use it to generate hydroelectric energy.

A while back in the Netherlands, there was a plan to use the saline gradient between salt and fresh water as a battery. It was briefly in the news, and then I never heard anything, but perhaps that is the idea?

The energy from desalination goes into creating a fresh-salt gradient. It stands to reason that some of that energy could be recovered from the gradient between the brine and the sea water.

> this salty-ass junk

Do you mean sea water? The amount of fresh water the human race will extract from the oceans will be what fraction of a percentage point of the total? Not accounting for, of course, the fact that most of it will make its way back to the oceans.

If pumping it back in has a local effect, then by all means try to mitigate that. But the idea that we're producing 'toxic waste' by creating saltier sea water is absurd.

What is with journalism today?

I know it's not generally accepted on HN to say "please read the article before commenting on the article." But it's worth noting that the contents and effect of the "brine" as distinct from "sea water" get two full paragraphs devoted to them in the article.

Maybe let's not attack the journalist.

He should not call something "salty-ass junk" if he wants his "work" to be respected.

"While most studies focus on salinity as the primary cause of biological effects, many chemicals are used in the desalination process (e.g. antiscalants, biocides, etc.), some of which can be toxic."[1]

[1] https://www.waterboards.ca.gov/water_issues/programs/ocean/d...

This isn't absurd at all. Sea water contains lots of components, not just salt. Many are non-toxic at their current concentration; if you remove the water and pump in the rest into the ocean, you're potentially increasing the concentration enough to make it toxic. It is quite literally toxic waste. And the journalist did you the favor of linking to scientific research that says the same thing.

"at their current concentration"

So the solution is obvious. Mix 1 part brine with X parts seawater before releasing. Oceans are big, so X can be a very large number, if that is necessary.

I wonder why that never occurred to the researchers who spend their professional lives studying how to safely dispose of brine?

As the article points out, desalinization produces "37.5 billion gallons (142 billion liters) of this salty-ass junk every day." What's your plan for pumping in X times that from the oceans, diluting it, and then pumping it out?

I'm fairly confident that the plant designers and researchers know this and that journalists have messed it up.

They're already pumping in 37.5B + 37.5*2.5/1.5B gallons of it, so pumping in a multiple of that is just a problem requiring money.

But getting the money to do so requires scaring the public into giving it to them, thus the scare articles like this one in the press.

> is just a problem requiring money

Any problem of providing fresh water for human civilization is "just a problem requiring money." It's not like there is a lack of water on the Earth. So it's kind of silly to pick one single particular aspect (diluting brine) to try to hand-wave away as just a money problem.

In general, money is a significant constraint on engineering and can't be hand-waved away.

Interesting. Why do you think this article will help scare the public into giving "them" the money? According to the paper linked in the article (Jones et al. 2019), many of these desalinization plants are in the Middle East and North Africa: "Brine production in Saudi Arabia, UAE, Kuwait and Qatar accounts for 55% of the total global share." Do you think that the general public in those countries reads Gizmodo and also has voting power to adjust the budgets for desalinization plants?

Also, why do you think that paper does not address the option of pumping in more ocean water and diluting it? (It's paywalled - if you'd like a PDF I can get you one.)

It's Gizmodo. These "news" outlets are largely staffed by comms majors who couldn't find jobs elsewhere. You know that kid at the back of the class that never paid attention or missed half the semester, but somehow barely managed to graduate? Those are Gizmodo/Buzzfeed/etc. writers.

Stupid question: Being that a large fraction of the problematic plants seem to exist close to or within desert countries, couldn't you simply pump it into the desert? I figure, if you find an appropriate area, you'll have not much of an ecosystem to destroy anyway and the area could eventually function as an enormous evaporation pond.

I think the issue is the scale of the operation. It's not that the desert doesn't have the capacity to absorb brine, it's that pumping all that brine into one spot creates a local ecological catastrophe. To avoid a concentration of toxins you need to spread it around, which is expensive.

My expectation is that the brine will have to go back into the ocean. The deserts a big, but the ocean is bigger. What the paper mentioned in the article points out is that you can't dump this all in one place.

If you're wanting to make fresh water there, it's probably because people do actually live there and want to do other stuff there, so any method of polluting the environment is going to have negative consequences.

For example if they are extracting fresh water from seawater, they are probably also already using groundwater as well which your proposal would pollute.

Saudi is enormous - no doubt there are vast expanses completely away from civilisation, and I'm guessing there are plenty of remote oil field areas that are already degraded to some extent. However: firstly as you hint at the desert does have an ecosystem, and secondly salt is not the only contaminant in the sea. I could imagine an Aral Sea type scenario where heavy metals, for example, were evaporated out in significant concentrations over time. Then with a little wind blowing the dust towards populated areas, you are in trouble.

I think you're underestimating how much of an ecosystem there is in a desert. It's often a fairly fragile one as well.

I admit I had not expected this to be a problem. The salt water comes from the sea, I'd expected it to be fine to release the salt back into the sea.

But I understand that untreated, this extra-salty water would, in large amounts, become a current of its own that's significantly different from regular sea water. And apparently there are added chemicals in it that I suppose were necessary for the desalination process? Shows how little I know about desalination, I guess.

Still, cleaning and diluting it and releasing it back into the ocean seems like the only workable solution. It just needs to be cleaned better and with an eye on the consequences of how and where this enters the ocean.

Is a bigger problem in shallow water. At open sea, salt will sink to the next deep water layer with the same density. (Marine organisms are relatively customed to deal with reasonable amounts of salt, the deeper the more customed).

Could be pre-diluted offshore with an unlimited amount of surface sea water available. But if there is more things than salt in the mix, or if we want to just dump it at the sea for saving some dollars, then we are creating a problem.

On the other thing, humanity needs salt, specially in badlands and deserts or in very cold areas. We could just refine, clean and then eat it.

There are no extra chemicals - the brine is just concentrated sea water. The chemicals are present in sea water, they've just been concentrated by removal of 40% of the water.

You can't dilute it; the entire point of the exercise is to obtain and not use up fresh water.

Probably the sensible answer is to dry it and bury the powder salt.

Of course you can dilute brine into sea water.

High concentration brine does not automatically mix into the sea water. It goes to the bottom of the sea and forms a separate layer. But you can use nozzle diffusers, mixer etc. and discharge into high currents.

This is what I thought too. Why not dump them out into long shallow 'trays' which can then dry out in the sun, leaving behind just the salt, which can then be stored/used/disposed of.

Also, I am not an expert.. but, couldn't we use the leftover salt for energy storage?


> Also, I am not an expert.. but, couldn't we use the leftover salt for energy storage?

I don't think salt is something that is in particularly short supply.

But wouldn't having it in a stable form as a mountain of salt be a decent storage solution? Or would the volumes produced be quickly untenable?

The mountain of salt will have a mass of at least 3.5% of the total amount of water you produce. It will be a lot more than that if you only use some of the water and let the rest evaporate.

For example, Israel produces more than 1 million tonnes of fresh water per day. That's 35,000 tonnes of salt, or 16,000 cubic meters -- enough to cover a football field to a depth of 3 meters -- every single day.

Can't this brine be mixed with cleaned sewage water to produce something similar to the original seawater wrt salinity and copper/chloride concentration?

> with cleaned sewage water

You're better off treating the 'cleaned' sewage water for reuse as drinking water, which is being done in many locations.

It’s saying for every 2.5L of seawater only 1L of freshwater is recovered and the rest is brine, which also includes chemical byproducts.

Why is this ratio so bad? What would it take to recover more water and produce more concentrated waste that could be managed differently?

Alternatively recover less water and have a waste that is only marginally more salty that seawater.


The desalinated water will end up back in the oceans eventually, so should the brine. Of course you can't just dump it back in directly, but if diluted and released responsibly, the ocean is the right place for the brine.

What do you dilute it with? You just spent a bunch of time and energy seperating water from it. I guess we should ship/pipe the brine to wastewater treatment facilities, and mix it with the treated waste before discharging it back into the ocean/river?

Seawater (edit: and air, too. one of the problems is the brine has little dissolved oxygen).

Put it in big leaky boats that drive around in 1000km radius circles?

I see this as an opportunity. Before you dilute the brine with sea water and pump it back into the ocean, ideally you remove the microplastics and perhaps some other problematic substances and thus clean up the ocean.

where's the money in that?

/depressed sarcasm/

Unfortunately the volumes of "cleaned" brine are just not significant. See my comment elsewhere in the thread.

I assume the brine is heavier than regular sea water. Could leading it through a pipe directly into the deep ocean be a (slightly) better option? There's less marine life there and it can slowly mix with the ocean water. Deep ocean water also has a higher salinity and lower oxygen content already.

> In fact, the study concluded that for every liter of freshwater a plant produces, 0.4 gallons (1.5 liters) of brine are produced on average.

How does removing water from solution makes more of that solution?

2.5 L of water go in.

1 L freshwater comes out of pipe A.

1.5 L wastewater comes out of pipe B.

I guess, it's more "X gallons of sea water result in Y gallons of drinkable water and Z gallons of brine", where Y=1.0, Z=1.5 and X >= Y + Z.

That's a good point, but I assume what they meant is that to output 1 liter of fresh water, the plant needs to process ~2.5 liters.

For every 2.5 liters seawater, the products are 1 liter fresh water and 1.5 liters of brine.

Easy solution, use brakish water or sewage for desalination rather than sea water. Not difficult. And stop flushing drinking water down the toilet.

That sounds like it might be part of a possible solution, but not an easy one.

Sewage contains other volatile products that would evaporate and condense along with water. Cleaning sewage water for use in drinking is probably much, much harder than doing it with just sea water.

No it really isn't. Most people just think it is disgusting. It is less energy intensive than sea water.


> And stop flushing drinking water down the toilet.

What do you suggest using instead?

Grey water

huh I always wondered about what they did with it. especially now that plastics are showing up in a lot of table salts...

Sounds like they just need to find a good use case for brine, turn it into some kind of fuel or additive.

The ever dreamed of space slingshot seems to be the only safest, everlasting option to dispose brine.

> The high concentrations of salt, as well as chemicals like copper and chlorine,

can we not harvest those?

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