
Turning Saltwater From Earth and Sea Into Drinking Water - iProject
http://www.nytimes.com/2012/06/10/science/earth/turning-saltwater-from-earth-and-sea-into-drinking-water.html?
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hendler
Interesting that there was no mention of Dean Kamen's "slingshot"

<http://www.wired.com/wiredscience/2008/03/colbert-and-kam/>

[http://www.thedailybeast.com/newsweek/2008/04/04/big-
problem...](http://www.thedailybeast.com/newsweek/2008/04/04/big-problem-neat-
solution.html)

~~~
thaumaturgy
Almost two years ago I commented in an HN thread about this,

"DEKA is a strange duck. They have some genuinely brilliant people there,
working on some genuinely revolutionary inventions -- but they just can't seem
to actually bring them to market. Or, they're not interested in bringing them
to market. ... I've yet to hear of the Stirling engine / water purifier being
deployed anywhere; ... I really don't "get" them. The best I can figure is
that everyone (influential) there is happy just to be working on these
puzzles, and they don't really care if anyone uses them or not."

(<http://news.ycombinator.com/item?id=1793446>)

That opinion seems to be withstanding time's test.

~~~
planetguy
Actually, I'd say the truly brilliant people are in the marketing department,
building huge hype for something which... presumably doesn't work as well as
advertised or else we'd have heard about it again in the intervening three
years. I don't know precisely what _is_ wrong with it, but it's safe to assume
that there's something.

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danielharan
As for energy, it's probably much cheaper to reduce consumption. This is a
hidden subsidy to agriculture and industry.

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adnam
Desalination is less of a problem than pumping water to farmland, industry and
residences high above sea-level.

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excuse-me
Where do you get the saltwater high above sea-level?

~~~
epochwolf
I think they are talking about pumping desalinated seawater over a thousand
miles inland.

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brunnsbe
Out in the archipelagos in Finland (and I guess also Sweden) converting salt
water into drinking water is becoming more common as it's quite easy when the
salt amount in the Baltic Sea is quite low compared to the oceans.

~~~
excuse-me
They are having to start drinking WATER in Finland? Has the booze finally run
out?

~~~
brunnsbe
You need some water to create booze. ;-)

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ChuckMcM
Most people believe that bottled water is just tap water marked up a few
thousand percent, it would be interesting if these desalinator plants sold
bottled water. They could run at a profit apparently, and they could make an
interesting argument:

"Conserve our precious natural water sources by drinking -Wapure-, purified
water."

This would then make it a _good_ thing to drink bottled water since you would
be keeping cows and what not alive.

~~~
zcid
My issue with drinking bottled water is the bottles. Estimates are around 1
billion bottles thrown away each year in California alone.

[http://www.consrv.ca.gov/index/news/2003%20News%20Releases/P...](http://www.consrv.ca.gov/index/news/2003%20News%20Releases/Pages/NR2003-13_Water_Bottle_Crisis.aspx)

~~~
ChuckMcM
This is one of those things where I wish the report would include their
methodology. This report was brought up during the "Great Bottled Water
Debate" at Google and a couple of people wondered how they came up with their
numbers.

As it turns out, if you sit at a dump site (at least in Northern California,
and Google is fortunate to be built right next to one) and watch the trash
being unloaded you will note that there is little recyclable material left in
the trash when it gets there, further the waste management company does some
separation as well because they get to keep any money they get from the
recyclables that get that far (unlike the ones in the cans at the curb which
they split with the city).

What was clear though was that between a fairly large homeless population
which relies in part on recycling fees and waste management contracts that are
structured to provide a disproportionate benefit to the waste management
company, they both get paid for disposing 'X' tons of waste which is measured
on the way in, and they get paid for 'Y' tons of recyclables they recover post
ingress weigh-in so its a double win for them.

The result is that in California there are several mechanisms in place which
select for recycling. This results in very little recyclable material actually
getting into landfills (which is good) but it also makes statements like the
one you link, essentially false.

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6ren
Question: why do desalination plants use a filtering system, instead of
evaporation? (like that desert survival trick of spreading plastic over a
hole)

(guessing) Is it because (1) evaporation is actually very energy inefficient
compared to filtration, especially at scale; or (2) evaporation doesn't
separate out impurities that also evaporate.

~~~
kijin
(1) is definitely a factor. It takes a very large amount of energy to boil
water.

<https://en.wikipedia.org/wiki/Desalination#Methods>

> _Reverse osmosis plant membrane systems typically use less energy than
> thermal distillation, which has led to a reduction in overall desalination
> costs over the past decade._

But the wikipedia article says that 85% of desalination worldwide still uses
distillation.

~~~
ams6110
Seems like a good area to use solar energy though. Water is easy to store and
if you can make enough on sunny days to carry you through nights and overcast
times, efficiency doesn't really matter as much since your energy source is
"free."

~~~
planetguy
I'm sure it's possible, and that someone has sat down and done the
mathematics, and figured out that it's just not worthwhile.

The most efficient way to do it is to use solar thermal, not solar electric,
power -- build a huge array of mirrors to focus on heaters which boil your
water and distill it out. But it's not really "free" -- you need a lot of
land, a lot of mirrors, and a staff of people who keep the mirrors clean and
replace the broken ones.

Oh, what the hell, I'll do the maths myself. To heat up and boil one litre of
water from 20 degrees C takes 2.6 million joules. Sunlight, on a sunny day, is
one kilowatt per square metre; let's generously assume we can get 50%
efficiency over the eight hours of the day when the sun is high in the sky
[don't forget, this is solar _thermal_ power, it's more efficient than
photovoltaics]. So each square metre of collecting area in our plant can boil
5.5 litres of water per day. The desal plant in this article produces 27.5
million gallons per day so to replace it with solar we'd need nineteen million
square metres, or nineteen square km, of mirrors. That's a _lot_ of mirrors,
and a lot of squeegee men.

If you wanted a solar-powered desal plant I'm sure you could do it cheaper
using photovoltaics plus reverse osmosis.

~~~
phreeza
Wouldn't it be possible to somehow recover the latent heat of the boiling
water when it passes back into the liquid phase, minus the salt? I'm pretty
sure I learned the theoretical maximum efficiency for this in my undergrad
physics class but I can't quite remember.

~~~
kijin
Maybe you could use the steam to pre-heat the water that enters the system? If
the water is at 60C instead of 20C to begin with, that will reduce the amount
of energy needed to boil it. Besides, all that steam needs to be condensed
back to water anyway if people are going to drink it. (I think that's what
they already do in advanced "multi-stage" distillation plants.)

Theoretically, you could also add a steam turbine to make some extra
electricity on the side, but I don't know how efficient such an add-on might
be.

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antidoh
California, with its long coastline and big brain and capital pools, could
transform itself into a fresh water sheikdom.

~~~
arethuza
Your comment about California having a "long coastline" got me wondering how
it compares to other places. It turns out that even if you measure the length
of the coastline quite generously (i.e. tidal shoreline) the length of the
California coast is 3,427 miles.

That sounds pretty impressive until you compare it with places with more
crinkly coastlines - Norway has ~13,000 miles of coastline and even tiny
little Scotland has 6,158 miles.

However, I suspect that there won't be much call for de-salination in Norway
or here in Scotland (where it has been raining for most of the last week).

~~~
josefresco
You don't even need to leave the US to find a state with a _longer_ coastline.
Maine's comes in at 4,568 miles

~~~
jonknee
That's a bit deceptive though because that figure for Maine includes all the
islands and what not. Maine isn't very big, there's no way it has that much
actual coastline.

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hexagonal

      (Production of desalinated water costs 2.1 times more than 
      fresh groundwater and 70 percent more than surface water, 
      according to El Paso Water Utilities.) 
    

Copyediting fail. How about "110% and 70% more"?

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cheatercheater
Can you couple this with osmosis based energy production for double win?

[http://www.renewableenergyworld.com/rea/news/article/2010/10...](http://www.renewableenergyworld.com/rea/news/article/2010/10/osmosis-
re-emerges-as-a-promising-power-source)

~~~
planetguy
No, because thermodynamics is a bitch.

Desalination works by reverse osmosis and costs energy. Rather a lot of
energy, in fact.

Osmosis-based energy production goes by forward osmosis and produces energy.
However if you were paying attention back there when I said "thermodynamics is
a bitch" it should come as no surprise that the energy you get out by wasting
your fresh water isn't as much as the energy you put in to get it in the first
place.

~~~
cheatercheater
> it should come as no surprise that the energy you get out by wasting your
> fresh water isn't as much as the energy you put in to get it in the first
> place

Agreed, but maybe the effect can be used to alleviate the cost of getting the
fresh water? For example, it doesn't cost so much to heat up a building once
it's been heated up if it has heat exchangers in its HVAC: the output heat is
used to heat up incoming hot air. A wasteful process can be made more
efficient with stupid tricks.

