Desalination Is Booming. But What About All That Toxic Brine? | Hacker News Reader

Desalination Is Booming. But What About All That Toxic Brine?

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73 pointsgeorgecmu73 comments

Does anyone working in the field know if a 100-1000x reduction in energy consumption of desalination is theoretically possible - using so called promised supermaterials based on graphene/nanotubes etc. or some kind of economies of scale ? Or are we limited by the law of physics here ?

I am really skeptical of promise of materials like graphene because although i have heard about magical properties for so many years now i have never heard of practical mass manufacturing completely upending an old school method for something. May be i am not knowledgeable enough.

This is one of the technologies that is increasingly important for the future of the earth especially in water poor countries with heavy population.

In the large scheme of things it might turn out cheaper to move population closer to the coasts, have desalination plants instead of other solutions to water scarcity assuming renewable energy costs reduce significantly as well along with a lot of surplus.

Water evaporated and leaves brine behind, at any temperature above 0C (even below through sublimation). Theoretically I guess you can imagine the sun evaporating the water that you capture, so you could have close to 0 energy input. So there is no physical limit I suppose. But you don't want to wait for the sun, you want to speed up that process, I don't know what the limit is there, when the speed matters (how much does it matter?).

Maybe with enough surface area, waiting for the Sun wouldn't be such a time-consuming task.

Any site doing this is more likely to use a mirror array for concentration, but I'm not sure offhand which shape(s) might be optimal for different reasons.

Anything close to a 100-1000x reduction in energy consumption is unlikely in the next 10-20 years. That said filters have steadily gotten better over the years (better throughput, more durable, etc.)

Also, the main thing to focus on is cost of water produced. If you design a new filter that is much more energy efficient but costs 100x more than the standard plastic filter, it may not provide much advantage.

There is a theoretical minimum energy required to desalinate water, because an entropy cost is involved. At room temperature, the cost works out to about 0.8 kWh per cubic meter, and our best systems seem to reach approx. 25% efficiency.

Thanks. It's quite a bit better than I expected.

The current state of the art (reverse osmosis) is already fairly good. The first link I found [1] demonstrates the increase in efficiency - we're talking about roughly 3 kWh/m3. I don't recall exactly, but I think that is in an order of 5 of the theoretic maximum.

At an average, rather immodest level of water consumption per capita (~1580 m3/annum), then this is about ~4740kWh per year, or 13 kWh per day. I'd say this is significant, but then:

For comparison, current energy use per capita in the USA is 7000kg-oil-equivalent [2] (or 81000 kWh [3]), so an additional 4740 kWh is about 5%.

The real problem is that people use absolutely indecent amounts of energy and water and other resources, usually for no good reason at all...

[1] https://s3.amazonaws.com/academia.edu.documents/45145253/The... [2] https://data.worldbank.org/indicator/EG.USE.PCAP.KG.OE?locat... [3] https://en.wikipedia.org/wiki/Tonne_of_oil_equivalent

Thanks for the stats -- I actually just installed a solar array on my house which should produce around 8000kWh/yr which is in the ballpark of how much energy our 2-person household would need to desalinate our own water, so it's nice to have a tangible metric (and to know it could be done on our own roof space)... ~$24k installed, does not include cost of desalination plant :D

Are those numbers right? 1580 m3/year is 4.3 m3 or 1100 gallons per day. http://www.theworldcounts.com/stories/average-daily-water-us... says 100 to 175 gallons per day per person.

I got that number from here - tried to find a more 'official' source, but water isn't as well documented as energy.

Note that those numbers when I last looked into it typically include industrial and agricultural water use - residential water consumption is usually approximately 15% of total water use, so that fits reasonably.

One problem is that in many countries, water consumers (e.g. farmers) are able to withdraw water from their own soil, and so nobody really knows how much water that is, although it's possible to make educated guesses.

[1] https://www.statista.com/statistics/263156/water-consumption...

Seems plausible within an order of magnitude. 1 pound of beef takes ~1,800 gallons of water.

Please do not spread this twisted truth.

1. Those numbers are from all the rain hitting the pasture divided by by the cows mass (that is eatable)

1.a including whatever it eats

2. The way it's told makes it seem that none of the water is reused which is not true Though beef is a water intensive 'crop' it is not as bad as certain people makes it out to be.

Edit: formatting

Are they taking into consideration the water it takes to produce the food that you eat in that 1100 gpd figure? Also, the amount of water that you use to shower/wash dishes/flush/water your lawn?

Wonder what level of energy is needed for water transportation and pumping inside cities. Btw for reference the water consumption per capita is much lower and very skewed in developing countries. It is all about access and fights over that. I hope for many coastal regions desalination might become the economically viable option

I think the problem of salt is a much bigger problem than we realize it. It's toxic, you can't burn it for fuel, and you can't really do anything with it except store it. Are there other ways of disposing of salt without repercussions?

If only there was a large body of water nearby in which it could be diluted...

From the fine article:

> But a less chattered-about problem is the effect on the local environment: The primary byproduct of desal is brine, which facilities pump back out to sea. The stuff sinks to the seafloor and wreaks havoc on ecosystems, cratering oxygen levels and spiking salt content.

The problem is that is where it currently goes... It is addressed in the article.

Yes: sell it.

Or dilute it. The solution to pollution is dilution.

>The solution to pollution is dilution.

For a while. The scale of human population and our increased per capita resource usage starts to make that less often viable.

Not for brine.

The salt comes from the ocean in the first place, and the water returns to the ocean relativly quickly. Unless something changes and we start to notably change the volume of water in the ocean, dilution is the only way to maintain the ocean chemistry. If we don't, then we would be reducing the salinity as the water returns without the salt.

(as a disclosure, i've only read a very small amount about these problems, so please take all of this with a grain of... salt)

The problem is that it isn't perfectly diluting, it's concentrating the salt in areas near the desalination plants, changing ecosystems and causing problems locally.

There's also the semi-related problem of salt that isn't from the ocean making it's way there, increasing the overall salt concentrations over time.

If we could find a way to use the salt from desalination (at least partially) somewhere else, then maybe we could help offset the "saltification" of the ocean and can more easily avoid destroying ecosystems around desalination plants. (it doesn't need to be an all-or-nothing solution, we could still dump some salt back into the ocean while keeping some out and used in other areas)

I suspect that diluting the brine has problems that weren't discussed. For example, it might consume much more energy than we think.

Also, what do you dilute it with other than... fresh(er) water?

Combine brine processing with sewage treatment? There's ample non-potable water whenever someone flushes the toilet, I would surmise.

It could be put to use for CSP or nuclear systems that leverages molten salt for hex with water with some processing.

Salt build up in agricultural soil seems like a looming problem but I'm not seeing a huge issue with the salt from desalination. Can't we continue to dilute and put the brine back in the ocean? Is it ideal, probably not, is it better than rerouting rivers and depleting aquifers, probably.

The pattern with human activity is that anything less than ideal will eventually kill us.

FTA:

> The primary byproduct of desal is brine, which facilities pump back out to sea. The stuff sinks to the seafloor and wreaks havoc on ecosystems, cratering oxygen levels and spiking salt content.

The issue is the dissolution process is slow enough that the salt has time to wreck havoc on the environment. And if you're taking river water or aquifer water to dilute the brine to a point near the local salinity why go through the whole desalination process to start with instead of using the water to dilute this byproduct?

It's easy to forget that at large scales the ocean doesn't really disperse things evenly. Surface salinity for example ranges from 30-40 g/kg across the surface of the ocean.

https://www.nasa.gov/sites/default/files/styles/full_width_f...

I think it's most likely that it would just get buried or piled up somewhere. Salt is not really a high value product, so I wouldn't be surprised if desal plants had to pay people to take the salt from them.

* Problem 1: It gets into the ground water.

* Problem 2: If dumped into the ocean, it increases the salt concentration (see: Middle East).

Disclaimer: Worked on some related projects on how to find a positive use for Brine.

Did you arrive at any possible positive uses for Brine?

I wish we had. No, our team failed to come up with anything that would mitigate the hazardous effects of brine. The scale of brine production is enormous. While there are inefficiencies in the supply chain (energy carrier for reverse osmosis, membrane quality and technologies), we closed the project with the insight we are actively deploying another technology that messes up our planet.

What about molten sodium energy storage?

We looked very briefly into energy storage and resource production (mining).

The scale is the problem. At the end, you still end up with lots and lots of inorganic material, which is toxic for the environment.

The amount of salt used in storage applications would likely not even make a dent in the amount of salt produced by large scale desalination.

Leakage into ground water would certainly be and issue if proper planning was not in place. I would have to think there are ways to prevent this leakage though. We have burying lots of coal ash for many years now and must have some best practices in place. Coal ash is more toxic than salt.

I'm casually wondering what the ecological impact of just dumping it into the Great Salt Lake or the Utah salt flats would be. Both are already so toxically salty that almost nothing is able to live there.

There's brine shrimp in the Great Salt Lake.

But there's also industry that extracts the salt from the Great Salt Lake, via evaporation. This shows that, if you've got salt to dump somewhere, there's actually a market for that. (That is, if it's pure. Others pointed out the problem of chemicals added to the salt water to make it easier to process.)

Yeah the issue is all the additives the desal plants add to protect their hardware.

The Jordanian plan is to pipe brine into the Dead Sea, which is already hypersaline.

I wonder given enough cheap salt, is there a possibility of it being useful for something? Like at least a cheap building material for desalination plants in areas where the deserts meet the coast, and the lack of rain would make it last longer or something.

Or (this might seem crazy) considering Antarctic sea ice is melting at increasingly faster rates, which isn't good in itself - is that causing the water at the far south latitudes to be lacking in salinity? Would additional salt there provide for keeping the ecosystems stable for longer at least? Granted shipping would be another issue.

The former may require some free market ingenuity, the latter may require some ingenuity and some sort of goodwill on the part of some governments.

Himalayan salt lamps?

there's a fun kim stanley robinson book gaming out climate change (called 50 degrees below, or in that series anyway) where they dump a ton of extra salt in the ocean near there for that exact reason. In the book, iirc, it sorta stalls some bad stuff from happening but doesn't end up being that helpful long term.

Salt is not toxic in all respects - salt lakes and rock formations have been natural environments in themselves, which have been present and integrated with more common ecosystems throughout natural history.

The challenge is how to understand and work with natural ecosystems well enough to not burden them with salt concentrations that harm them, and perhaps even to fit and enrich them.

The sun desalinates almost all the rain that falls to earth everyday from the oceans.

This site is a bit more radical in how they go about it, but I know that in Utah we have several structures build from salt quarried nearby(huge deposits near the Salt Lake) and then treated to be water resistant. I imagine a similar thing is possible but maybe not efficient.

http://buildingwithseawater.com/?myportfoliotype=the-salt-bu...

Form it into bricks and build things with it?

This article talks about newer technologies being "more efficient" in terms of the brine they produce, by which they seem to mean that you get more fresh water with less brine production.

How is this possible? Your input has a certain amount of salt and water in it, right? How do you take out the same amount of water, but leave less salt behind? Am I missing something?

I imagine you recycle brine into seawater somehow.

I think they are using the technology on brackish water instead of seawater, less brine in -- less out, but more water out.

I believe they're ignoring the concentration of salt in the brine, instead only counting the volume of 'highly salty water' that is output.

I'm curious what the mineral content is of the brine water. There are a few cyanobacteria, like spirulina, which thrive in alkaline water that other algae can't handle. One could likely use the run off to process high nitrogen content sewage water and produce spirulina which could be used for food, oil and ethanol production.

What about http://news.mit.edu/2015/shockwave-process-desalination-wate...?

I'm disappointed this article talks so much about brine, and so little about the even-more-dangerous Dihydrogen Monoxide that is a result of the process.

This is a very bad article - pure FUD.

Aquion Energy is making salt water batteries, that could be a good use for this stuff: http://aquionenergy.com

Sadly their FAQ states they’re in the process of rebuilding their business as a consequence of filing for bankruptcy.

That is unfortunate, but considering the opportunity presented by the need for grid-level energy storage for renewables or even by the need for domestic energy storage for solar as well as the apparent availability of materials it could be an attractive area for innovation.

I'm still kind of shocked lead acid is faring so poorly when it comes to grid storage. One of the oldest (the oldest?) battery chemistries, well understood, really cheap, mostly safe, simple, durable, serviceable, recyclable. (sidenote, submarine warfare was, for decades, powered by lead acid)

It's chief disadvantages are low power density and low power to weight ratio, neither of which matter for grid storage.

It just seems to have all the hallmarks of traditional industrial solutions. But, of course, lithium ion has the same advantage ubiquitous silicon semiconductors have- massive, massive economies of scale and endless R&D dollars.

Lead acid doesn't handle (input or output) current so well. Perhaps 5x or so than lithium.

Sure, so you buy more capacity. And since it's like 5x cheaper than lithium...

Bankruptcy doesn't always mean going out of business. And the IP is still probably good, and likely going to be liquidated and sold on to someone else (who will hopefully start a new business with the tech).

Use the waste byproduct for molten salt energy storage: https://www.maltainc.com. Not only efficient, but profitable even to do so.

Is there any constraint on what types of salt or salt compounds are usable for energy storage? Or does it not really matter for the most part?

Not really, though a commonly used thermal salt is the eutectic mixture of 60% sodium nitrate and 40% potassium nitrate, which can be used as liquid between 260-550 °C. Table salt, or sodium chloride, has a melting point of around 800 °C. So it really depends on what attributes your looking for.

TL;DR No inherent terrible problem, just issues as it scales.

With sea levels rising there's not going to be a global shortage of water.

This article is terrible. It contains lots of exaggerations and conflates all sorts of problems like the assumption that all energy usage means burning fossil fuels.

It came from the ocean. Put it back in the ocean.

From TFA:

>The stuff sinks to the seafloor and wreaks havoc on ecosystems, cratering oxygen levels and spiking salt content.

>Because this stuff is denser than typical seawater, it sinks to the seafloor and disrupts vibrant communities of life, which find themselves wanting far less salt and far more oxygen.

>But brine is more than just hypersaline water—it can be loaded with heavy metals and chemicals that keep the feedwater from gunking up the complicated and expensive facility. “The antifoulants used in the process, particularly in the pretreatment process of the source water, accumulate and discharge to the environment in concentrations that can potentially have damaging effects on the ecosystems,” says Jones.

That's exactly what the article is about. Putting it back in the ocean is the problem.

>> totaling 141.5 million cubic meters a day, compared to 95 million cubic meters of actual freshwater output from the facilities. Bad news for the environment, to be sure, but things aren’t altogether dire: Desal tech is rapidly evolving, so plants are getting far more efficient, both in the brine they produce and the energy they use.

Bad journalism. Bad science. A desal plant is essentially a brine production facility. A more efficient plant won't output less salt. It may be less by water volume but that water will just be all the more salty. This cannot be avoided short of piling the salt up on the land. Brine is bad, but when mixed in with the vast volumes of the oceans is a non-issue. All the brine produced by desal plants is nothing compared to the brine produced by sunlight on the ocean surface.

>> "But herein lies opportunity: The discharge can also contain precious elements like uranium."

Ya. Um, that is an entirely different story. Uranium from seawater is a thing today even without the brine. Some put the amount of natural uranium in seawater in the billions of tons. Every country in the world suddenly having ready access to a limitless supply of uranium? Desal might be the least thing to worry about.

it's indeed a bad article. Probably newer plants will have to dump their brine further away from shore, where it's dissipated easier? What is the effect of the brine on the local ecosystem? Is it on par with the warming of water by thermal plants? The article raises more questions than it answers.

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