How do you make salty water drinkable? The hunt for fresh solutions to a briny problem

[sl8]

https://www.nature.com/articles/d41586-024-02073-6

NEWS FEATURE
04 July 2024

How do you make salty water drinkable? The hunt for fresh solutions to a briny problem

Unconventional methods for desalination could create more drinking water, help many industries to deal with problematic brines and increase lithium supplies for batteries.

By XiaoZhi Lim

People have been separating salt from water for millennia, harvesting both salt and fresh drinking water from salty seawater. But there are limits to what can be done — sometimes with drastic consequences. When people in ancient Mesopotamia couldn’t work out how to desalinate their irrigation water and prevent salts from accumulating in their soils, their society collapsed. “It’s kind of the world’s oldest, most boring, but serious problem,” says Sujay Kaushal, a hydrologist at the University of Maryland in College Park.

This problem is now growing more pressing, as salinity levels creep up in fresh waters for a slew of reasons. Rising sea levels are pushing salt into coastal groundwaters, while excessive groundwater extraction in other places is drawing deeper, saltier waters up into aquifers. And human activities — from deicing roads to washing clothes and fertilizing fields — are polluting surface waters with many kinds of salt. Last October, Kaushal and his colleagues reported that salt levels in major streams and rivers around the world are booming; some bodies of water are now several times saltier than they were a few decades ago1. Freshwater salinization is a massive global problem, not just a regional one, he says.

A second, related issue is the growing burden of problematic waste brines. A variety of industries — from oil and gas extraction to the desalination plants that produce drinking water — create salty waste waters that are costly to dispose of. “We need to do something with the brine,” says Menachem Elimelech, an environmental engineer at Yale University in New Haven, Connecticut.

[...]

To do all that, scientists are now exploring techniques to separate salt from water more efficiently, using electricity, new materials and solvents. With a wide range of brine chemistries to tackle and a host of different goals, there isn’t one “killer” technology, says Shihong Lin, an environmental engineer at Vanderbilt University in Nashville, Tennessee. “This is like a thousand different problems,” says Lin.

[...]

[Progressive dog]

1. How much do you suppose the melting glaciers will dilute the salt?

We've got a lot of climate and population problems that may be unsolvable.

[sl8]

2. Good question.

Another factor to consider - as the temperature increases, ocean evaporation will increase, tending to increase salinity.

[Progressive dog]

3. Yes, I'm curious about how much study

of water salinity (or other pollution) has been done. It seems likely that there would be a lot.

[Blues Heron]

4. not much - the ocean is 12,000 feet deep on average, so even a 12 foot rise would only dilute by 1/1000th

[Progressive dog]

5. I found a best scientific guess as 230 feet.

Apparently a lot more than .1% of the worlds water is stored in glaciers.
https://www.usgs.gov/faqs/how-would-sea-level-change-if-all-glaciers-melted
There is still some uncertainty about the full volume of glaciers and ice caps on Earth, but if all of them were to melt, global sea level would rise approximately 70 meters (approximately 230 feet), flooding every coastal city on the planet.

[Blues Heron]

6. That would be a dilution factor of 1/50th less salty if it all melted, I could see that being perceptible but barely

[NNadir]

7. There was a recent review in EST on this topic.

It is here: Developing Salt-Rejecting Evaporators for Solar Desalination: A Critical Review Zhi Yang, Dawei Li, Yunxia Zhu, Xiangyu Zhu, Wentao Yu, Kaijie Yang, and Baoliang Chen Environmental Science & Technology 2024 58 (20), 8610-8630.

Unfortunately, the paper focuses on solar desalination, which of course is the natural way solar desalination works, apparently focusing on industrializing natural systems.

I have not had a chance to read the paper, but I'm aware of it. (Industrial solar turns me off; it's unacceptably problematic.)

I have been interested in this problem for quite some time, and discussed cleaner approaches to desalination - which I increasingly feel may become a requirement in the era of global heating - here: The Energy Required to Supply California's Water with Zero Discharge Supercritical Desalination.

To my way of thinking, it can be shown that isolated solidified sea salt is a form of stored energy, if one exploits ion selective membranes, which will control the rate at which salt is released back into the sea, and thus the risks of concentration if one accounts for diffusion rates. One can further mitigate the environmental cost if one thinks of where salts are returned to the sea.

It is however, a huge problem.

Thanks for the post.