Better desalination technology key to solving world's water shortage

Aug 04, 2011

Over one-third of the world's population already lives in areas struggling to keep up with the demand for fresh water. By 2025, that number will nearly double. Some countries have met the challenge by tapping into natural sources of fresh water, but as many examples – such as the much-depleted Jordan River – have demonstrated, many of these practices are far from sustainable.

A new Yale University study argues that seawater desalination should play an important role in helping combat worldwide shortages – once conservation, reuse and other methods have been exhausted – and provides insight into how desalination technology can be made more affordable and energy efficient.

"The globe's oceans are a virtually inexhaustible source of water, but the process of removing its salt is expensive and energy intensive," said Menachem Elimelech, a professor of chemical and environmental engineering at Yale and lead author of the study, which appears in the Aug. 5 issue of the journal Science.

Reverse osmosis – forcing seawater through a membrane that filters out the salt – is the leading method for seawater desalination in the world today. For years, scientists have focused on increasing the membrane's water flux using novel materials, such as carbon nanotubes, to reduce the amount of energy required to push water through it.

In the new study, Elimelech and William Phillip, now at the University of Notre Dame, demonstrate that reverse osmosis requires a minimum amount of energy that cannot be overcome, and that current technology is already starting to approach that limit. Instead of higher water flux membranes, Elimelech and Phillip suggest that the real gains in efficiency can be made during the pre- and post-treatment stages of desalination.

Seawater contains naturally occurring organic and particulate matter that must be filtered out before it passes through the membrane that removes the salt. Chemical agents are added to the water to clean it and help coagulate this matter for easier removal during a pre-treatment stage. But if a membrane didn't build up organic matter on its surface, most if not all pre-treatment could be avoided, according to the scientist's findings.

In addition, Elimelech and Phillip calculate that a membrane capable of filtering out boron and chloride would result in substantial energy and cost savings. Seventy percent of the world's water is used in agriculture, but water containing even low levels of boron and chloride – minerals that naturally occur in seawater – cannot be used for these purposes. Instead of removing them during a separate post-treatment stage, the scientists believe a membrane could be developed that would filter them more efficiently at the same time as the salt is removed.

Elimelech cautions that desalination should only be considered a last resort in the effort to provide fresh water to the world's populations and suggests that long-term research is needed to determine the impact of seawater desalination on the aquatic environment, but believes that desalination has a major role to play now and in the future.

"All of this will require new materials and new chemistry, but we believe this is where we should focus our efforts going forward," Elimelech said. "The problem of water shortage is only going to get worse, and we need to be ready to meet the challenge with improved, sustainable technology."

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4.5 / 5 (2) Aug 04, 2011
Why is this news-worthy?, there's no actual science here, only pointing out what a solution might look like, sheesh
4 / 5 (1) Aug 04, 2011
They could always make a series of clear solar dome/column type stills for desalinization.
1 / 5 (1) Aug 04, 2011
"there's no actual science here"

It is a press release from Yale University News.

What did you expect?
not rated yet Aug 05, 2011
Why filter at all, just pump the sea water inland, and use the sun to "distill" the water from the salt and what not. By definition, the areas that need the water have plenty of sun light, and are dry. I would envision huge solar distillaries, just black plastic with clear ribbed covers that would channel the "distilled" water to tanks to be stored.
not rated yet Aug 05, 2011
Why are we worrying about desalination, anyway? In all seriousness, there are two other major potential sources of fresh water already available. There is a large amount of fear building up in various communities regarding potential flooding of the planet caused by melting/sliding glaciers in Greenland and Antarctica. Why not do something about that potential problem now rather than waiting for it to happen?

Why not harvest the ice from the GIS and the WAIS and distribute it to thirsty nations like the nations of the Sahara? Why not take the ice and use it in one of the most ambitious geo-engineering projects in history?

Place it all over the interior Sahara and allow it to melt. It potentially would cool the deserts, quench the thirsty lands of the Sahara, and fill the drying interior lakes of Africa. This, in turn, would lead to more local water vapor and subsequently more rain in lands of drought. Jobs could be created for years to cut the ice and distribute it. Problems solved.
not rated yet Aug 05, 2011
Why not harvest the ice from the GIS and the WAIS and distribute it to thirsty nations like the nations of the Sahara? Why not take the ice and use it in one of the most ambitious geo-engineering projects in history?

I can't tell if you're serious or not...

Another option: let the water-deficient populations realize they should base their cities in more inherently sustainable areas in the first place.

Other than anthropocentric obstinance, what is the point of building a city in a desert? Or on a subsiding delta/island? To perpetuate these inherently flawed civic-centers is an exercise in futility. You're only expending resources when you shouldn't have to, because there shouldn't be a population there in the first place, because that ecosystem is obviously not meant to support concentrated populations of macro-vertebrates in the first place.

Don't build your house on the side of a volcano and then be pissed when a lava flow destroys it.
not rated yet Aug 05, 2011
I can't tell if you're serious or not...

I am deadly serious.

As to choosing where to build cities, people don't have a lot of choice where they are born. A number of countries are pretty much nothing but desert, some of which became such within historical times after the populations settled there.

Sometimes volcanoes come up from nowhere (I can think of a couple in Mexico and elsewhere in Central America), right in the middle of settlements.

And, deserts can be tamed and made inhabitable for populations of millions. It has been done all over the United States within historical times. The Salt Lake Valley, in Utah, is an example, as is Palm Springs, CA, and several others. With proper management this is possible here and the world over.

With Antarctica and Greenland holding over 80% of the planet's freshwater in the ice, there is no need for water shortages and we can use this ice to geo-engineer the planet to avert the disaster that is claimed to be waiting in the future.
not rated yet Aug 07, 2011
Why filter at all, just pump the sea water inland, and use the sun to "distill" the water from the salt and what not. By definition, the areas that need the water have plenty of sun light, and are dry. I would envision huge solar distillaries, just black plastic with clear ribbed covers that would channel the "distilled" water to tanks to be stored.

Perhaps an even better approach would be to use focused sunlight to heat the seawater, use the steam to generate power and then allow the steam to condense into distilled water. That way you get more power for the grid in addition to the desalinated water.

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