Seawater: Our Only Hope for a Drink

[Are_grits_groceries]

Desalination of seawater has become a necessity, but it has to be done right.
As any globe will reveal, there’s no shortage of water on Earth. Unfortunately, over 97 percent of it is too salty for us humans to drink, and only a tiny fraction of what remains is in the rivers, lakes, and groundwater that we’re able to easily access.

In much of the world, these freshwater supplies are growing scarce, and competition for these resources promises to be one of the hot-button geopolitical challenges of the next 50 years and beyond. As climate change worsens droughts, accelerates desertification, and whittles away glaciers (the water towers providing life to so much of the world), it’s no wonder that some experts are looking towards that enormous pool of salty water for a drink.
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In the past couple of decades, though, a more promising, scalable solution has surfaced—reverse osmosis. Bear with me as I revisit high school chemistry. Take a semi-permeable membrane that water molecules can travel through, but not larger sediments like salt. Put very salty water on one side and less salty water on the other, and water will travel through towards the salty side until the concentrations are even. That’s osmosis. Alternately, apply pressure to the saltier side, and water flows through the membrane, but the salt gets stuck. That’s reverse osmosis, and the result is fresh water. And that’s how most modern day desalination plants work.

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The upfront costs of building the plants are considerable—San Diego’s Poseidon Plant is budgeted at $300 million; Melbourne is fixing to spend $2.9 billion on one that’d be amongst the world’s largest—but after they’re built, the chief expense is the energy it takes to push the seawater through the membranes.

Then there are the environmental costs, which are slowing down the approval processes in regulation-heavy places like California. As ocean water gets sucked into the system, aquatic organisms can get sucked up with it. Then, besides drinking water, there’s the other byproduct of the process—very salty, and often hot, brine, which if released straight back into the ocean can create dead zones, worsening a problem already plaguing many coastal cities.
http://www.good.is/?p=16626

We are already way behind the curve on this. The water crisis is growing bigger every minute. Desalinization will work, but you can't just decide to plop down a plant in a short time and make everything hunkydory.

[Zynx]

1. I looked into Texas' program for desalination and there are certainly promising results, but

to pretend that the energy costs are not substantial or that there is no environmental impact is foolish.

[RaleighNCDUer]

2. As for the energy costs, make it a two-fer:

use tidal energy to power the desalinization plant. The tidal generators can not only power the desalinization, but also provide the energy to pump the fresh water inland.

[depakid]

13. Aussies are way ahead of that game:

In West Aistralia, the Perth Seawater Desalination Plant, Seawater Reverse Osmosis (SWRO) runs on renewable wind energy.

http://www.water-technology.net/projects/perth/

In South Australia, a plant near Port Augusta will run on solar thermal -and engage in commercial salt production.

http://www.ecosmagazine.com/?act=view_file&file_id=EC134p4.pdf

[Are_grits_groceries]

3. I agree.

I posted about the water crisis earlier, and someone brushed it off by pointing out the amount of saltwater available to be used. They seemed to think it was as easy as pie to fix it up.

[Zynx]

9. The amount of money that has to be spent on bringing desalination plants online

in sufficient quantities to meet the water problems is astonishing. Every aspect of the issue is actually very daunting. I hope people realize that before more series crises emerge.

[wildflower]

4. This may be a dumb question, but

Couldn't gravity be used? In the way a water wheel does? Then no energy would be required.

When I raise a cup of dirty water up above a coffee filter and pour it down, the water flows through to the cup, and the sediment remains in the filter. All I have to do is hold it there; gravity does the rest.

I'm not sure how this could be implemented on a large scale, but maybe it's feasible?

[blogslut]

5. I think salt bonds with water molecules

I am probably wrong because I don't know very much about anything.

[truthisfreedom]

6. When salt dissolves in water, it actually splits up into ions (atoms with electrical charge).

The salt is not a solid at that point. Gravity does not affect the mix... it stays mixed unless you use some sort of trick to remove it (boiling off the water, or passing it through a special membrane like this article is about.)

[Ezlivin]

7. How much would an R/O plant discharge in terms of waste water?

I have an under-counter R/O system in my home and was astonished to learn that it only recovers about ten percent of the water it uses. That means for every gallon of pure water it generates, it dumps nine gallons into my septic system.

RO units use a lot of water. They recover only 5 to 15 percent of the water entering the system. The remainder is discharged as waste water. Because waste water carries with it the rejected contaminants, methods to recover this water are not practical for household systems. Waste water is typically connected to the house drains and will add to the load on the household septic system. An RO unit delivering 5 gallons of treated water per day may discharge 40 to 90 gallons of waste water per day to the septic system. Source

[kentauros]

8. There may still be some not-so-energy-intensive methods out there.

I always like the one Henri Coanda came up with:

From Air Wells, Fog Fences & Dew Ponds

In the 1950s, the French inventor Henri Coanda designed an elegant method to desalinate water in Morocco (USP #2,803,591). He built a silo with reflective walls, mounted several inches over a tidal pool, angled so as to catch and multiply the sunlight, thus superheating the air in the chimney. The rising hot air drew in cold air from the bottom, and became super-saturated with moisture by the time it reached the top. Pure water flowed from the condensers there. The residual brine also is of great value to chemical industry and in the construction of solar ponds. The French government forced Coanda to cease operations because his device threatened their monopoly on salt production.

[amborin]

10. it's developers who are behind the 'desalinization' agenda; not environmentalists

it's amazing how successful these developers are at getting folks to believe desalinization is a good thing

they want desalinization so they can say: there are no obstacles to more and more development, of land that should be left open space, undeveloped....

[Are_grits_groceries]

11. It's not a question of good or bad.

It is probably going to be the only way to go in the coming years. Clean, fresh water is becoming scarce, and large companies are trying to get rights to it. Oil wars will pale in comparison to water wars.

[amborin]

12. you're right

but over population and over development are making the problem worse