Maya Demise Due To Drought?

Don't hold your breath. The present efficiencies of Reverse Osmosis is pretty close to the thermodynamic limit. If the thermodynamic limit is 1.06 kWh/m^3 then the present plants are operating at about 2 kWh/m^m. (The limit varies with targeted input & output salinity). Unfortunately, the difference between ultimate and actual efficiency is because the plant has to pump the water out of the ocean and into the water distribution system....in addition to through the reverse osmosis membrane.

One the other hand, this is pretty good. No desal technology can compete with pumping fresh water straight out of the ground or river.

 

Maybe not. But when the fresh water's either gone or poisoned, which is already the case in many parts of the world, desalination will be vital.

Jayman and I had a lengthy discussion awhile ago about the topic. He seemed to think the idea of evaporating seawater and capturing the condensate within a 'greenhouse'-type structure seemed to hold promise. I'm not sure reverse osmosis is necessary.

 

We have two separate discussions.

The first is the efficiency of reverse osmosis. It's about as good as it gets. In fact it is so efficient that over half the power is needed for conventional infrastructure pumping from source to destination and all intermediate treatment/storage/brine removal. It's a mistake to think that most of the power is needed for the desal step. This means that the economic problem is the cost of handling/pumping water and the big capital cost of the plant to begin with. With a evaporating plant, there is still the capital cost and a more complicated energy scheme since more of the solar power has to be converted to electricity. That's why distilling plants have been abandoned for Reverse Osmosis plants. RO plants are very, very productive and reliable for the energy consumed.

The second discussion is the need for water where the country is too poor to afford any big industrial plant, RO or distilling. This is an economic problem causing the poisoning, not a technological limitation.

 

I recall the design we bantered about involving a simpler energy scheme. The seawater was heated directly by the sun, without any conversion losses of electrical generation. It was more or less an evaporation pond with a cover.

 

I read it as cost, and my eyes skipped energy Let's rephrase and say if someone gets the cost of desalination down - including energy that will go a long way to solving irrigation problems in areas close enough to salt or brackish water.

For energy on a coast line just include wind turbines or wave electrical gerators But you need to include this cost. There are also combined ideas, for example using natural gas to turn a turbine to create electricity, then using that heat to help desalinate the water. or...

or
http://www.gizmag.com/ibm-solar-powered-desalination/14760/

 

Nothing's been proved. There may have been multiple factors. One possibility is the salinity of irrigation water, which raises the salt content of the land. There is a threshold where rather suddenly the preferred crops will no longer grow. A drought would exacerbate the problem as it would require more irrigation.

Lots of theories, lots of evidence, but no cut-and-dried answer.

Your conclusion is true though: Climate change can wipe out a civilization.

Just one more example of the harm done by superstition and religious bigotry: All that valuable knowledge lost!

Yep. I had forgotten. But when you remind us, I remember that.

You still need to pump the water into the pond, and then to the end users, and dispose of the salt. If the salt is to be sold, it will need to be cleaned. If the water is to be used for domestic purposes, it must be treated.

Getting the energy for this renewably is a good idea. We should be getting all our energy renewably. But using "greenhouse" evaporation still doesn't look all that much different, energy-wise, than RO. It may be a better method, but only marginally. Not an enormous breakthrough. And it requires more land, which will be easy in some places and hard in others. The idea could help, but will not give us energy-free potable water.

This thread is making me thirsty. Excuse me while I slurp down a glassful... It's nice to live in the pacific Northwest.

 

New (13 Feb) online at PNAS "The water footprint of humanity"

which tallies up indirect consumption, for example cattle raising and cereal growing. The paper may end up having historical significance in that it was edited by NAS member Peter Gleick. You know that he is a water-resources guy, when not doing Heartland Transplants.

Don't know if we will be seeing that again

 

Do you discount a paper because of the editor? Probably not I could only pull up the abstract which seems interesting. Americans use about twice the water as those in India and China. I wonder if there is a big difference for those in dry states as oposed to wet states.

As an aside, I have a Danish friend who is working here. Last weekend we were talking about if the high prices for utilities work to reduce consumption over there. He said one of the things he noticed about Americans is they leave the water flowing when brushing their teeth, in Denmark they only have it on when needed. My running coach is from burundi and he has a charity to get clean water to people there. You can bet that when he had to go down to the well to fetch water, that they did not waste a lot of it.

 

Austingreen "Do you discount a paper because of the editor? Probably not "

Interesting sidenote.Gleick was one of the authors of a critique of the lastest Spencer paper.
Resulting in the bizarre resignation of the Editor of the journal "Remote Sensing".And the even more bizarre apology letter from the editor to Keith Trenbirth.
Instant karma for Gleick.

 

I never do that. And though I am a pacifist, I take "military"-type showers: Get wet quickly, turn off the water and soap up leisurely, turn it back on and rinse quickly, dry off leisurely.

I take comfort in the fact that water shortages are likely to ht my region long after they've hit other places, but I use as little water as I can. (Except for drinking, where I drink as much as I can.)

Truth disclaimer: I live in a neighborhood with an association, and the association waters the lawns. I would never water a lawn on my own. But my front lawn is tiny, and the back lawn is part of a common area, not really "mine" at all, and not large.

When I lived in North Dakota I gave each bedding plant in the garden one cup of water when I put it in the ground, and that was all the water I gave my garden, and I didn't water the lawn. If it didn't rain, the lawn got brown and I didn't have to mow. When the rain came, it got green again. If there was too little or too much rain, my garden suffered. But even then only a very bad drought or a full-on flood prevented me from getting lots of veggies.

 

Bumped because of a new study about India monsoons and agriculture and civilization

Past in monsoon changes linked to major shifts in Indian civilizations

Clever sampling of Godavari River sediments offshore. Y'all probably know that basically every river has a sediment cone offshore. Libraries of paleo-information just waiting for somebody to take a look.