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rommel543
2010-Dec-14, 09:57 PM
This probably belongs under the science area, but I rarely go out of the OTB section these days since I'm am at work when I'm on here. :whistle:

So I was reading that environmental scientists have predicted that a cyclical drought should be hitting the south west soon, something to out-do the dirty 30s, and it got me thinking about irrigation and aqueducts. I know desalination plants exist but from what I read about them they are terribly in-efficient and use a lot of energy for the amount of water they produce. So I was wondering, what would be the best method for desalinating a large volume of water?

I think it's reverse osmosis that is currently used in most plants. The need to pre-treat the water to avoid fouling of the filters by bacteria growing slime on them, and it take a lot of energy to run the high pressure pumps. They also have a low return rate for the amount of water that gets pushed through.

At first I figured boiling/evaporating would be the quickest but probably uses the most amount of energy to complete. This could be mitigated by using solar or wind power, but then your cost of infrastructure goes up.

What other ways are there to desalinate sea water?

Ronald Brak
2010-Dec-15, 12:32 AM
I don't know of any other practical way to desalinate water besides reverse osmois and vacuum distillation (lowering pressure to boil/evaporate). Reverse osmosis appears to have a slight edge over vacuum distillation (boiling). But costs can depend on various factors, including if there is a source of waste heat from power stations or other sources that can be used. Treating sewage to make it drinkable and transporting water are alternatives to desalination that can be cheaper.

Jens
2010-Dec-15, 05:16 AM
Not anything about other methods, but about the boiling one, there are plans to put power generation plants in deserts, which use mirrors to concentrate solar rays into a boiler and to have the steam drive a turbine. The nice thing about it is that if you build it close to the sea, you can also use it to distill seawater.

rommel543
2010-Dec-15, 02:38 PM
Well thats my thinking, desalinate sea water and then pipeline it to the southern states where it's needed for agriculture. It's not like pipelining water is a really big deal, we already have a water pipeline from here into the northern states.

Ronald Brak
2010-Dec-15, 03:24 PM
Well thats my thinking, desalinate sea water and then pipeline it to the southern states where it's needed for agriculture. It's not like pipelining water is a really big deal, we already have a water pipeline from here into the northern states.

Unfortunately desalinated water is so expensive farmers simply can't afford to use it if they have to pay what it actually costs. They won't be able to compete with farmers who don't have to pay for desalinated water. (Of course that may change if ecological disaster devastates food production and pushes food prices up.) Also, pipeing water is very expensive in terms of energy if it has to go up hill. Here in Australia expensive desalination plants are being built basically to stop city dwellers taking away water from agriculture. It's easier to get city dwellers to pay more for water because for them it's only a small part of their overall budget, so it's not worth it for them to kick up a big stink about it. But if a farmer has to pay more for water they can easily go broke so they often fight it tooth and nail.

rommel543
2010-Dec-15, 03:44 PM
This may sound kind of odd but if you dug a large hole and filled it with sea water would the natural filtering of the soil help remove the salt and minerals or would you just be increasing the mineral content of the ground water? One of the other problems in the south west is they are sucking so much water from the ground sink holes are developing. If we were able to replenish the ground water by pumping sea water to a dry lake bed and letting it filter through the ground it may assist in the replenishing.

Before you bash me I'm just trying to brain storm a way to get fresh water to the agricultural area in the south west. Living where I do getting water isn't a problem, sometimes we get too much in fact so it bothers me to hear about other areas that have droughts going on.

Mister Earl
2010-Dec-15, 04:00 PM
I've had an idea for this kind of thing for a while now. it's kind of hard for me to put my ideas down in type, so forgive me ahead of time if I'm about to confuse everyone.

Ok. Step one: Dig out a series of basins to store seawater. Step two, cover them all in greenhouse-style plexiglass or plastic. Arrange the roof so evaporated water can condense on the roof and drop down into a collection system. Step three, rig up a system that would pump water from the ocean into the basins. Work out a rotation so there's always one or two basins that are being cleaned out (salts and such). You could rig up solar panelling between the basins to power the pumps, and you'd need storage tanks, of course, for the purified water. And if you had a handy and cheap way of cleaning out the sea salt of impurities, you could sell that, too. In my head, it seems to be an efficient system with few moving parts susceptible to problems. But then again, if this kind of thing were THAT easy to do, someone out there would probably be doing it already.

Ivan Viehoff
2010-Dec-15, 04:10 PM
Here in Australia expensive desalination plants are being built basically to stop city dwellers taking away water from agriculture.
Which is so foolish. Far cheaper to buy out the farmers, cease large scale irrigation, and use the water in places where it has a higher value. In many cases in Australia the irrigation is causing environmental damage by salination of the land, so you kill two birds with one stone. I read an article once which suggested that when you took into account the financial business support schemes, and the cheap water they got, and the effect of the environmental damage they caused, a lot of the large-scale arable agriculture in Australia was not actually contributing to the economy.

BigDon
2010-Dec-15, 04:11 PM
Cleaning sea salt in quantity isn't difficult. Ask Morton Salt Company to lend you an engineer or two.

Ivan Viehoff
2010-Dec-15, 04:16 PM
This may sound kind of odd but if you dug a large hole and filled it with sea water would the natural filtering of the soil help remove the salt and minerals or would you just be increasing the mineral content of the ground water?
"Filtering" out salt doesn't work because salt is so soluble. The salt would sink into the ground and make it useless. So not a good idea.


I'm just trying to brain storm a way to get fresh water to the agricultural area in the south west. Living where I do getting water isn't a problem, sometimes we get too much in fact so it bothers me to hear about other areas that have droughts going on.
See previous post on damaging effects of giving cheap water to farmers in Australia. The fact that farmers find water priced at its true resource value too expensive is telling you something - the agriculture is not actually economic. That suggests that you would obtain economic gain in SW USA by doing less water-intensive agriculture, or even just less agriculture, so that more of the water is available for high value uses, and thus avoiding further highly expensive or highly environmentally damaging water extraction schemes.

MAPNUT
2010-Dec-15, 04:59 PM
Antarctic icebergs.

korjik
2010-Dec-15, 05:47 PM
This probably belongs under the science area, but I rarely go out of the OTB section these days since I'm am at work when I'm on here. :whistle:

So I was reading that environmental scientists have predicted that a cyclical drought should be hitting the south west soon, something to out-do the dirty 30s, and it got me thinking about irrigation and aqueducts. I know desalination plants exist but from what I read about them they are terribly in-efficient and use a lot of energy for the amount of water they produce. So I was wondering, what would be the best method for desalinating a large volume of water?

I think it's reverse osmosis that is currently used in most plants. The need to pre-treat the water to avoid fouling of the filters by bacteria growing slime on them, and it take a lot of energy to run the high pressure pumps. They also have a low return rate for the amount of water that gets pushed through.

At first I figured boiling/evaporating would be the quickest but probably uses the most amount of energy to complete. This could be mitigated by using solar or wind power, but then your cost of infrastructure goes up.

What other ways are there to desalinate sea water?

Since your location says Canada, I have to ask what southwest are you talking about?

If you are talking the US southwest, then what definition of southwest are you talking about? :)

If you are talking California, Arizona, Utah, New Mexico and Nevada, then if there is going to be a lage scale, Dust Bowl-like drought, then it would be far better to close down as much of the agriculture as possible and try to get more natural vegetation in place. That would be far better at a dust bowl prevention than trying to get more water available.

If you are adding in Texas, Oklahoma, Colorado and Kansas to that, then the problem is a bit different. It may be better to try to divert some fresh water from the northern midwest than to try to do large scale desalination. There are some fairly large natural resevoirs up that way.

Of course, it would probably be easier just to not have huge cities in the middle of deserts....

Yeah, LA, I am looking at you. You to Phoenix

:)

rommel543
2010-Dec-15, 06:21 PM
Since your location says Canada, I have to ask what southwest are you talking about?

If you are talking the US southwest, then what definition of southwest are you talking about? :)

I found the article again that I was mentioning..

Hot With Decades of Drought: Expectations for Southwestern United States (http://www.sciencedaily.com/releases/2010/12/101213151405.htm)


An unprecedented combination of heat plus decades of drought could be in store for the Southwest sometime this century, suggests new research from a University of Arizona-led team. A 60-year drought like that of the 12th Century could be in our future.
.....

"Major 20th century droughts pale in comparison to droughts documented in paleoclimatic records over the past two millennia," the researchers wrote. During the Medieval period, elevated temperatures coincided with lengthy and widespread droughts.

.....

"We're not saying future droughts will be worse than what we see in the paleo record, but we are saying they could be as bad," said lead author Connie A. Woodhouse, a UA associate professor of geography and regional development. "However, the effects of such a worst-case drought, were it to recur in the future, would be greatly intensified by even warmer temperatures."


From what I gather they are talking about the agricultural states that run from Nebraska through to Kansas, New Mexico, Texas, Arizona, etc.




If you are talking California, Arizona, Utah, New Mexico and Nevada, then if there is going to be a lage scale, Dust Bowl-like drought, then it would be far better to close down as much of the agriculture as possible and try to get more natural vegetation in place. That would be far better at a dust bowl prevention than trying to get more water available.


What are we going to replace it with for food? The worlds population is increasing and with it the demand for food and natural resources.



If you are adding in Texas, Oklahoma, Colorado and Kansas to that, then the problem is a bit different. It may be better to try to divert some fresh water from the northern midwest than to try to do large scale desalination. There are some fairly large natural resevoirs up that way.

Of course, it would probably be easier just to not have huge cities in the middle of deserts....

Yeah, LA, I am looking at you. You to Phoenix

:)

The problem with grabbing from the North is it's already a source of water for much of the US and Canada. With the lack of snow fall and warmer temperatures they are seeing a drop in water levels there as well. The east is showing drops in the water levels in the Great Lakes and the glacial run-off that provides for the west is quickly dropping as well.

Great Lakes water levels alarmingly low, officials say (http://ottawa.ctv.ca/servlet/an/local/CTVNews/20100529/great-lakes-water-100529/20100531/?hub=OttawaHome)



The Canadian Hydrographic Service issued a warning earlier this month that water levels were at potentially dangerous levels on the lakes system, which stretches from Lake Superior in northwestern Ontario to Montreal.

The water is running so low that boaters risk running aground on rocks that would usually be well under water, the service said.

...

The U.S. Army Corps of Engineers reported this month that in April, the biggest of the Great Lakes lost about three centimetres during a time when spring runoff usually swells the lake by as much as eight centimetres


http://www.pc.gc.ca/canada/pn-tfn/itm2-/2003/au/index_e.asp

A quick stop at the Athabaska Glacier in Jasper National Park confirms that this is the case. As you approach the glacier, dated cairns mark the previous positions of the toe of the glacier, documenting its retreat throughout the twentieth century. In fact, most Rocky Mountain glaciers are shrinking. Late summer reduction in the water levels of glacier-fed streams and rivers has also been documented. This decrease is again linked to the shrinking size of the glaciers.

But what of the future? Global climate models suggest that increased melting will be partially offset by increases in snowfall. In the case of the higher elevation icefields, increased snowfall may keep pace with increased melting. Lower lying glaciers, however, are expected to continue shrinking rapidly; some will disappear altogether.In the short term, while the glaciers are melting back, the water levels of glacier-fed streams and rivers will increase. But as glaciers disappear and the glacial ice diminishes, so will their ability to regulate the water levels of these streams and rivers.



There are also concerns here that if we start supplying more water to the US, Canada will begin to run short for it's own needs.

Ivan Viehoff
2010-Dec-15, 11:29 PM
What are we going to replace it with for food? The worlds population is increasing and with it the demand for food and natural resources.
A lot of agriculture in the US SW is unnecessarily water intensive. They grow rice in the desert, stuff like that. You could grow just as much calorific value with a lot less water. As for abandoning really marginal land in Arizona, etc, well currently US agricultural subsidies have put lots of Mexican farmers out of business, and they are often fairly low yield operations, so there is probably a lot of scope for re-expanding agriculture in Mexico and increasing its efficiency. And if you get really short of food, you can slightly reduce the output of animal feed and put the land growing animal food to human food. Also all that corn grown for bio-ethanol is utterly pointless, of no environmental benefit overall. So there is plenty of land and water to feed yourselves in the USA, you are just using it rather inefficiently because of distorting subsidies. After sorting that out, you'd still probably be able to eat more meat than us Europeans. Of course we have distorting subsidies here too.

Solfe
2010-Dec-16, 12:52 AM
Sorry about introducing a tangent, but did The Dust Bowl or the Dirty Thirties impact Mexico directly?

More on topic, I saw a solar boiler system that was using salt to store heat. Desalinization of ocean water, plus the need for salt sounds like "solution via waste utilization."

I wish I had a harebrained idea that was actually easy to implement. :)