As the world gets drier, do we need to turn to the ocean?
Sean Bothwell can understand why people think desalination is a silver bullet. When he was a kid living in California's Orange County, the ocean was always close by. It didn't make sense to him that all the water near him wasn't usable.
"I grew up thinking, like, why the heck aren't we desalinating?" said Bothwell, who is now executive director of the California Coastkeeper Alliance. "Why are people always saying that we need to save water and conserve?"
[...] For his part, after doing his graduate school thesis on desalination as an adaptation mechanism for climate change, Bothwell's mind began to change on the process of ocean desalination, and he finally understood its problems and limitations.
"I realized all the things that people don't understand about desal—of all the issues we work on, [the efficacy] is the toughest thing to communicate to people," he said. "Everyone thinks it's a good idea."
[...] It's not just what gets sucked into plants that poses a problem for the ocean. The potable water produced by desal plants has an evil cousin: the super-salty discharge that remains, a substance known as brine, which is roughly twice as salty as the original seawater. Brine is heavier than seawater and can sink to the bottom of the ocean, where it creates a deoxygenated dead zone. [...]
"Our ocean is already under a ton of different pressures: nutrient runoff, ocean acidification, climate change," said Bothwell. "You add desal on top of it, and it creates a dead zone."
[...] "One of the reasons desalination is so expensive is that it's energy-intensive—it's one of the most energy-intensive water supply options that we have," said Heather Cooley, director of research at the Pacific Institute. "In the places where we've seen people build it, we do see the rates go up. There are cheaper options that have fewer environmental impacts and impacts on communities."
[...] Communities could also do a lot more with efficiency measures and figure out ways to reduce the current amount of water they consume. "It's not uncommon to see emerald green lawns that are irrigated poorly," said Cooley. "If you look at our urban water use in California, half is for landscapes. There's a lot of doom and gloom around drought and around climate change and water use, but we have significant opportunities to be doing better than how we've been doing."
[...] As the world gets drier, there's no question that ocean desalination can fit into our water future. But tapping into the seemingly endless supply of the ocean is more complex than it looks at first blush. The promise of desalination is understandably alluring, but a focus on it while ignoring simpler solutions shows how some see climate change as a problem to be solved with technology, rather than finding ways to fix broken systems and to make do with less. Real, sustainable change comes from making the harder, systemic fixes first—not chasing after expensive technology.
"We need to do the cheaper things first," Cooley said. "We don't know what the future holds. And the things we're talking about doing are consistent with a good quality of life—it's just about using less water."
(Score: 5, Insightful) by MIRV888 on Saturday April 08 2023, @07:34AM (4 children)
I know they use seawater to extract salt via evaporation in large ponds for it's multitude of uses. I dunno if it scales, but it seems like the brine would be a better alternative.
(Score: 2) by EJ on Saturday April 08 2023, @11:31AM
I came here to post this. I can't think of any good reason they couldn't make use of the brine rather than just pumping it back out into the ocean.
They should even be able to find a way to use the brine for cooling on its way to the process to extract the salt for further use.
(Score: 2) by looorg on Saturday April 08 2023, @01:46PM
https://news.mit.edu/2019/brine-desalianation-waste-sodium-hydroxide-0213 [mit.edu]
One would assume it just doesn't have to be pumped into or under the sea again. Apparently there might be useful things you can do with it, or just let it dry and create salt? Very salty Salt perhaps but I'm sure there is a market for that. If you don't want to eat that you can use it in other things.
(Score: 4, Informative) by Immerman on Saturday April 08 2023, @02:32PM (1 child)
Agreed, sea-salt "farms" seem like a no-brainer companion business for desalination plants.
Then again there might be an issue of volume as desalination scales up: e.g. New York City consumes one billion gallons (~3 thousand acre-feet, ~4 million tonnes) of water per day. Trying to process a similar volume of brine per day could be a real challenge, and would produce around 100,000 tonnes of salts per day - about 1/8th of daily global salt consumption.
(Score: 2) by Reziac on Sunday April 09 2023, @02:36AM
And wouldn't this be a natural match, what with most of the concentration already done?
https://cen.acs.org/materials/inorganic-chemistry/Can-seawater-give-us-lithium-to-meet-our-battery-needs/99/i36?PageSpeed=noscript [acs.org]
And there is no Alkibiades to come back and save us from ourselves.
(Score: 4, Insightful) by Mojibake Tengu on Saturday April 08 2023, @09:18AM (13 children)
This one pop-sci article is just another example of post-modern total reasoning failure.
Here is why:
In classic atmospheric natural water cycle, the water is pulled from ocean by sun (call it cost-free energy) into clouds (some cost-free transport), raining, rivers and so, and later goes back to ocean.
This is understandable and explainable by schoolchildren.
What is absolutely natural that in this cycle, more salt(s) are continuously added to the oceans all time, washed out from continents by aggregated flows.
Although the scale is in orders bigger then industrial scale, the total amount is so small no one cares about that ocean-added natural minerals.
Compare to that, industrially desalinized water uses energy input but does not add any additional salt to the ocean when the water goes through pipes to drinkers.
The tech only returns the salt previously taken from the ocean and borrows the water for a while.
The water itself, when used, does not vanish anywhere, leaving its salt orphaned abandoned, sooner or later it goes back to the ocean too and reunites with its previously separated salt again.
So, unlike natural raining cycle, this is effectively a "zero-salt" production, actually.
Articles like that are driven by pure greed or envy, not by responsibility.
Respect Authorities. Know your social status. Woke responsibly.
(Score: 2) by driverless on Saturday April 08 2023, @11:23AM (4 children)
Except for all the crap that gets dissolved in the desalinated water before it ends up back in the ocean again.
Agreed, but it's in your post, not the OP.
(Score: 2) by PiMuNu on Saturday April 08 2023, @11:27AM (2 children)
> Except for all the crap that gets dissolved in the desalinated water before it ends up back in the ocean again.
Are you concerned about human waste (poo and wee) or pollutants?
(Score: 2) by driverless on Saturday April 08 2023, @11:28AM (1 child)
The phrasing was deliberately ambiguous and covers both.
(Score: 2) by PiMuNu on Sunday April 09 2023, @11:05AM
Presumably these pollutants, both bio and non-bio, are a problem regardless of the presence of brine?
(Score: 1) by khallow on Saturday April 08 2023, @04:45PM
My bet is that agricultural runoff also has increased levels of salt (total amount not concentration) in it due to the increased rinsing of soil.
(Score: 5, Informative) by Immerman on Saturday April 08 2023, @02:44PM (6 children)
The problem is not the global salt levels, it's the *local* salt levels.
As they say in the summary, when you dump brine into the ocean is DOES NOT MIX with the less-dense surrounding water (and if it did, it would just make it that much more salt in the water you're then trying to desalinate) Instead it sinks to the bottom where it pools and slowly flows along the sea floor out to sea (flowing MUCH slower than on land, since it's displacing slightly-less dense seawater rather than much less dense air).
It will *eventually* mix and stop being a problem - if nothing else it should eventually hit the ultra-cold rivers of fresh water flowing along the sea floor from the poles... though no telling what that might do.
BUT, it can easily flow for hundreds of miles before then, and in the meantime the resulting vast lakes and rivers of brine on the sea floor create dead-zones where the water is too salty for most sea life to survive.
And that's happening in shallow coastal waters, where the sea floor is an incredibly important part of the ocean ecosystem, so you're going to have serious knock-on effects.
(Score: 2) by GloomMower on Saturday April 08 2023, @03:05PM (5 children)
I'm a dummy about this topic. But why can't you mix the brine with just more ocean water you pump in so it isn't so drastic a difference before releasing to the ocean again? Keep getting more ocean water keep diluting until it is less of a issue then release.
I get initially they can't mix well, but isn't that solved if the water is warmed up? Does diluting the brine just take too much energy?
(Score: 3, Informative) by Immerman on Saturday April 08 2023, @04:26PM (3 children)
I suspect the biggest issue is that you'll tend to shoot yourself in the foot financially. There's also a definite lower limit on how diluted you could make it - you're adding salt to seawater, so it MUST become saltier - but with enough fresh seawater flow it probably isn't a problem - but even a 10:1 seawater:brine mix is still 18% higher salinity than normal, and I'm not sure just how sensitive most sea life tends to be - salt is a nasty, destructive substance in quantity.
In general though you don't have a lot of water flow along the sea coast - bays, coves, etc. mean the water "puddles" along the coast (and tend to extend much further into the ocean than just the above-water portions). It flows in and out with the tide, but you're mostly isolated from the the currents that could carry material away.
Add a desalination plant, and now you've created a slight inward flow of seawater from the ocean. So if you mix outgoing brine with seawater you'll just end up sucking it all up again in your water intake, which means it's that much more difficult to desalinate the water, and you create more brine per gallon of fresh water. And that loop will just keep going until you hit some new stable salinity for your local seawater. Which could well be salty enough to be a significant environmental problem.
You could presumably pump brine miles out to sea where it can mix into a large passing current... but that gets severely expensive in terms of both energy and maintenance. And desalination has some really high costs to begin with - like $0.30 to $0.70 per gallon. Increase that cost significantly to do it in an environmentally responsible manner, and it starts becoming a really hard sell.
And perhaps most importantly - it's really hard to compete with the environmentally destructive alternatives. And if history has taught us anything, it's that when politicians have to choose between money and safety, money almost always wins.
(Score: 1, Informative) by Anonymous Coward on Sunday April 09 2023, @01:51AM
Math fail.
Assume X salt per unit of seawater. The brine contains 2X.
Mix 10:1 and you have 12X/11water.
1.09X or a 9% increase in salinity.
And 1:10 is a very low mix ratio. The ocean is damn big. Run a pipe out to where there is even a minor current and stick a big agitator on the end. No problem.
(Score: 1) by khallow on Sunday April 09 2023, @03:27PM
As the AC replier noted, you can just run a pipe out a ways and put a mixer on the end. It won't be anywhere near $0.30 per gallon to do that. Reminds me of the saying "Dilution is the solution to pollution." Sure, that doesn't work when you have too much pollution to dilute. But it is a big reason why smoke stacks are so popular. The plume has a chance to mix with air and greatly dilute the dosage before anyone on the ground breathes it in.
(Score: 1, Informative) by Anonymous Coward on Sunday April 09 2023, @10:26PM
https://www.advisian.com/en/global-perspectives/the-cost-of-desalination [advisian.com]
This page says that cost to desalinate seawater ranged from 3 to 9 cents/gallon back in 2005.
Melbourne's desal plant (only one I could find figures for) costs about 0.5 cents/litre now (2 cents/gallon).
(Score: 2, Funny) by Anonymous Coward on Saturday April 08 2023, @09:30PM
If they mix it with sewage then we could potentially create an environmentally sound beverage for hipsters to drink, who we could then blame for being in debt because of their hipster tastes? Win win ka-ching.
(Score: 2) by PiMuNu on Sunday April 09 2023, @11:08AM
Taking a step further, why bother with desalination at all? Presumably the whole water system can be run as a closed cycle, with top up from rain water for industrial/agricultural usage and to deal with leaks.
(Score: 0) by Anonymous Coward on Sunday April 09 2023, @02:41AM
just let nature do all the work and collect all the fresh water that falls from the sky out over the oceans