Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

utexas.edu

Post reply on HN
Print view View original

41–50 of 61 posts

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#41

Post by efsavage »

sbierwagen wrote: post #25
efsavage wrote: post #19

I don't put much stock in those who make claims like "the next world war will be over water", because we have a massive supply of water (the ocean) and a massive supply of energy (the sun) to power whatever we need to do to make it drinkable. A floating desalination plant powered by an x000-acre floating solar platform, pumping clean water back to shore, and dispersing slightly saltier water across a wide area, doesn…

The process doesn't even have to be super efficient Economics are important. We didn't go back to the moon because it was too expensive, and we're not going to see massive-scale desalination because it's also too expensive: http://physics.ucsd.edu/do-the-math/2012/10/the-energy-water... California uses 46 billion gallons of water per day. Supplying 25% of this via desalination would require 36 GW of thermal-equivalen…

A very informative article, thanks for linking.

However, his estimates for the energy required were very conservative, and even if these numbers don't work out with today's water prices, they do make sense at a certain point that is likely lower than one encouraging violence. That effectively provide a cap where we start to go this route if necessary, and the vast supply means that we shouldn't go above that for very long.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#42

Post by backprojection »

usablebytes wrote: post #39

Why do we usually utilize science to fix the wrong problem? Shouldn't we be making more efforts on 1) Growing more trees 2) Reducing environmental pollution 3) Controlling human population ???

Because the earth isn't designed to take care of us. If we had stayed a small pre-industrial society, we would still eventually die of something - there are myriad ways species go extinct.

The only way to ensure long-term survival is to develop science and technology quickly enough to solve problems (both natural and artificial) as they come up.

This includes solving problems created by past generations, who necessarily did not have access to the knowledge needed to avoid creating those problems in the first place.

It's certainly not guaranteed that we will do so fast enough.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#43

Post by ars »

tsotha wrote: post #40
ars wrote: post #22

Earlier quoted context omitted.

Do you think they clean your local city water? They don't. They filter it a bit, then add chlorine to deal with biologicals, and that's it.

But municipal water typically comes from rain or snowfall. The distillation has already been done.

You wish.

No, it usually comes from a river. And guess where the waste water from a sewage treatment plant goes?

Right back into the same river, only downstream. And that's where the next city down the line picks it up.

That water gets recycled multiple times on the way to the ocean, by each city on the river.

That's not a bad thing! But the water can hardly be called distilled.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#44

Post by bdcs »

monochromatic wrote: post #3

I'd love to see an energy-conservation analysis of this technique. How many joules per liter does it actually require?

I have come back from the land beyond the paywall: Importantly, this device operates with an energy efficiency of 25 mW h L−1 (25±5 % salt rejection, 50 % recovery), which is near the theoretical minimum amount of energy required for this process (ca. 17 mW h L−1).

For that last number, the authors cite ref [1], which does an entropic analysis of unmixing solutions and looks at the minimum (reversible) work required therefore.

[1] Y. A. Cengel, Y. Cerci, B. Wood, Proc. ASME Adv. Energy Syst. Div. 1999, 39, 537–543;

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#45

Post by ars »

sbierwagen wrote: post #37
ars wrote: post #26

Earlier quoted context omitted.

The absolute minimum energy you need is 2.2kJ per liter. A 4x4 inch solar cell could do that in about 2 hours. However I suspect that you'll never actually desalinate water for that amount of energy in a portable system. The very best commercial systems manage to do it with about 3 times the energy of the minimum. More common ones are about 10 times the minimum.

The absolute minimum energy you need is 2.2kJ per liter. Where's that number from? For what process?

Mixing saline and fresh water releases energy. To "unmix" them you have to supply energy.

See: http://en.wikipedia.org/wiki/Osmotic_power

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#46

Post by ars »

kunil wrote: post #29

"consumes less energy and is dramatically simpler than conventional techniques." I remember a video that shows some kind of filter (it looked like a plastic sheet). They were simply pushing water against it and you get clean water from salty water. I don't think it gets easier than that. However if I remember correctly the filter gets unusable after a while

You need energy to "push" the water through the membrane. A LOT of energy.

It's called reverse osmosis if you want to look it up.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#47

Post by ajuc »

usablebytes wrote: post #39

Why do we usually utilize science to fix the wrong problem? Shouldn't we be making more efforts on 1) Growing more trees 2) Reducing environmental pollution 3) Controlling human population ???

There's more than 8 000 000 000 of us, if everybody were just doing the thing with the greatest priority it would be very ineffective division of work. Like digging one hole with 1000 people.

As a humanity we can (and should) multitask, especially when it comes to science and inventions, because you never know which seemingly pointless path can lead you to a great breakthrough.

Imagine everybody since antiquity worked only on the greatest humanity problems as they've seen it at the time. No useless stuff like music, so no irrational numbers for example :)

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#48

Post by adventured »

sbierwagen wrote: post #25
efsavage wrote: post #19

I don't put much stock in those who make claims like "the next world war will be over water", because we have a massive supply of water (the ocean) and a massive supply of energy (the sun) to power whatever we need to do to make it drinkable. A floating desalination plant powered by an x000-acre floating solar platform, pumping clean water back to shore, and dispersing slightly saltier water across a wide area, doesn…

The process doesn't even have to be super efficient Economics are important. We didn't go back to the moon because it was too expensive, and we're not going to see massive-scale desalination because it's also too expensive: http://physics.ucsd.edu/do-the-math/2012/10/the-energy-water... California uses 46 billion gallons of water per day. Supplying 25% of this via desalination would require 36 GW of thermal-equivalen…

These types of x-y-z is impossible due to cost assumptions have always been made throughout modern history, and they often end up being wrong. You're judging everything based on today's technology. When in fact technology tends to leap forward massively at times due to necessity, and it's rarely foreseen. The same leaps will happen again and again and again.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#49

Post by Luyt »

Ellipsis753 wrote: post #28

"The new method requires so little energy that it can run on a store-bought battery." What a silly measurement. I can buy a laptop battery or a car battery at a store. Also it does not give any idea of how much water could be produced from the battery. A teaspoon per battery probably isn't too great. (Although at the moment they get only nanoliters of salty water from it of course).

A similar silly unit is used to measure 'green' energy: "This windmill can power 10.000 households". As if we're too stupid to understand a kWh figure.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#50

Post by alan_cx »

XorNot wrote: post #24
djloche wrote: post #20

Earlier quoted context omitted.

Water shortages are political in nature. The technical and logistical parts have been solved for a while.

Still doesn't sell massive war - shortages are political in regions where people generally have nothing. Wars - technological ones of the type major powers would fight - are expensive. Far more expensive then any amount of desalinization we would need to build.

It could easily mean massive war, if a war is politically required. One country holding out water supply to another country for whatever reason. Say such a country has a big friend, like say the US?

Not to say it will happen, I believe and hope it wouldn't happen, but it could.

Post reply on HN