# Desalination: What is the future of water



## K. Riehl (Jun 21, 2009)

I'm starting this thread to see if any of the fine minds here on the Chrons has any insight into Desalination on a large scale.

If we do have large scale population increases plus climate change then we don't really have any other option than perfecting desalination. In searching via Google I see a large number of environmental sites that seem to be down on the idea. Too much power used, too much of an impact on the environment, etc.. most are listed here:

Why Desalination Doesn't Work (Yet) | LiveScience

Please comment and let me know what you have heard, read, and what you think the future of fresh water will look like.


----------



## TheEndIsNigh (Jun 21, 2009)

Dune!!!!


----------



## Dave (Jun 21, 2009)

TheEndIsNigh said:


> Dune!!!!


Quite! Didn't the Sun power that.

I know that the island of Malta experimented with desalination in the 1970s after severely overpumping it's water table until Sea Water contaminated the the aquifer. You couldn't drink the tapwater there and it felt salty if you showered in it. It is probably still the same.

Malta was only able to do that because it got dirt cheap oil from Gaddafi's Libya. When the relations with Libya soured they were no longer able to afford it.

Power is the key problem. I think that Nuclear Power is the only feasible way to run these plants. France has them and it has a high % of nuclear power. In 2007 Sarkozy entered into an agreement to provide Libya with nuclear technology to power a desalination plant.

Thames Water in England has been given permission to build a desalination plant. They argue that there is no other choice given the population growth in London and South East England, the lack of space to build reservoirs, and the increasing frequency of droughts. It would used for short periods to top up existing supplies.

In the UK there has been much discussion of building a Water Grid so that the higher rainfall in the less populated North and West could be transported to the more populated South and East. I don't see that ever happening, and it is very long term. They did this on a small scale with Kielder Reservoir in Northumberland, built to supply the projected future demands of industry on Teeside. By the time it was completed in the 1980s, the industry had largely gone away, and it was no longer required.

The answer must include using less water (and not just domestically with bricks in toilet cisterns and turning off the tap when you brush your teeth) industry and agriculture use far more water than households. In some places in the world rivers have been reduced to a trickle because of irrigation and the irrigated land itself is becoming contaminated with salts due to evaporation. To me that makes no sense.


----------



## Urien (Jun 21, 2009)

Water is just a matter of cost. If you're willing and able to pay more then you can build desalination plants. 

A national water grid might be a better solution for the UK. It's not that difficult an engineering problem. Especially given the frequency (until the last couple of years) of water shortages in the south-east of England. Also it has the benefit (relative to desalination) of not needing the extra generating capacity.

If somehow we could utilise the methane generating power of livestock then perhaps we could solve two (or is it three?) problems at once. I think I'm not quite sure whether I might not be unsure of what I'm not quite saying there.


----------



## Nik (Jun 21, 2009)

IMHO, that article called it correctly. 'Reverse Osmosis' is NOT easy, and scales hard.

My small corner of BigPharma had two modest RO units and a 'still. The 'still just had to be dismantled and 'pickled' to de-scale at six month intervals. That was fun.

We kept the 'still because the only 'consumables' were an o-ring a year, and some industrial-grade hydrochloric acid for de-scaling. And all *that* took was 'due care'...

Each RO unit had a sludge catcher, a de-ioniser column, a two-stage high-pressure pump, a pre-filter, a UV steriliser and the RO membrane cartridge. (Not necessarily in that order ;-) The RO system had to be purged and sanitised, monitored, logged, cosseted, cajoled, re-booted, adjusted, fed reagents and disposables. 

Only two of us were allowed to play with the gizzards...

Remember, that's using 'City-grade' potable tap-water as feedstock. That's with chlorine in the water to suppress bio-growth. That's with pharma-grade users, and an *essential/expedite* flag on the consumables budget...

IMHO, even if membranes improve by 50%, the pre-treatment and pumping requirements still make the system horrible expensive.

One way around is to have 'free' water pressure to work with. Either you have a renewable energy source like hydraulic wave-power, or you put the mega-RO unit / Hydro-station on shore of DeadSea and tunnel the Med through the hills then dowwwwn by those thousand-some feet...

Probably cheaper to mine Glaciers...


----------



## zachariah (Jun 21, 2009)

Buy a million of these and pop them somewhere hot. If I was doing a near-future SF story around the idea, I'd have a tunnel leading almost horizontally from the sea to a sub sea-level arid zone (like death valley USA) which would be flooded (with the added benefit of lowering sea levels) and turned into a giant Watercone. Hey presto, remove the threat of rising sea levels and give everyone free fresh water in one go! Where's my Nobel prize?


----------



## chrispenycate (Jun 21, 2009)

The only problem with solar distillation is scale; after all, all the 'natural' fresh water on the planet is generated that way. It would be fairly easy to produce industrial quantities, and the nicest thing is that it works best on hot desert: maximum day to night time temperature differential, and minimum risk of cloud. If you had a few dozen square kilometres of Sahara to play with it needn't even be expensive.

Seawater is run in a black trough down the centre of a glass house or polytunnel. The temperature inside gets very high (if you're using plastic sheeting, you're probably forced to choose high temperature plastics) and the water evaporates, bringing the internal humidity up to 100%. Then the ever more concentrated brine goes further along the tube, until we either: a) dump it into the sea somewhere (essentially sterilising a lump of ocean) or b) make an inland salt lake.

At night in the desert the temperature falls rapidly, an the water condenses on the walls and runs down to be collected.

You can build one, and it will work; no alchemy, nothing sophisticated, a couple of big plastic bags and you'll get a couple of litres of water (and some blocks of salt. Unfortunately, we need millions of litres of water, which involves vast surface areas, ways of pumping the liquids (both seawater and fresh), storage tanks, monitoring of salinity/viscosity (if the system gets blocked by its own salt sludge you have to be able to increase the flow so it doesn't actually solidify.)

It doesn't have to be seawater, although that is the most abundant raw material on the planet; since it is distillation almost any soluble impurity will be removed, so industrial waste water would work, too, though I would avoid nuclear cooling water.

Pumping the seawater to a temporary high reservoir could be done with conventional techniques, or a combination of wave and tidal power (probably not from the Mediterranean, though; not enough tide) Or windmills. Theoretically, as water vapour is lighter than air, you could make it condense at altitude and use gravity feed to distribute it; practically the geometry of this might cause more problems than it solved.

Then there's the possibility of just increasing rainfall in a small region, causing a continuous updraught which generates a permanent thunder head, raining into a large synthetic lake…


----------



## Wiglaf (Jun 21, 2009)

Desalinization is strongly opposed by the environmentalists.  The idea of mitigating the effects does not appease them.  You may wait a decade and still not have the permits.  As for solar desalinization, it would take up too much animal habitat and be blocked by the environmental lobby.  Burning more natural gas is out of fashion and environmental and NIMBY groups make it impossible to get permits for renewable energy plants.  No one will allow for the building of a second nuclear power plant.  If you have a population advantage, you may be able to get a distribution system built.  However, it will be expensive, involve lawsuits, and those in wetter areas may threaten to secede.  You will also have to go through this every time you want to improve the system.  Also an endangered fish may cause the courts to force you to turn off the pumping systems.  Toilet-to-tap will be strongly opposed by the populace. Collecting run-off is problematic as it is more contaminated than treated waste water will ever be.  You can not buy it from an agricultural area that through exemplary conservation has a surplus; your current supplier will sue to have the deal blocked and/or refuse to sell you what they are currently supplying you.  You can channel run-off into gravel beds and cat-tail fields and allow it to be treated in that manner before replenishing the ground water.  If you do that, you can then dig productive wells.

At least that is how it works here.  The solution to water shortages is lots of money and a good team of lawyers.


----------



## TheEndIsNigh (Jun 22, 2009)

Chris: I like your idea. Why not adapt it. If the plastic pipe/tube was floating in the sea and split into two layers salt water on top condensed fresh water below then all that would be required is to pump the salt water up to the higher level and one to pump out the fresh water from the bottom. It doesn't matter (in fact it's preferable) if not all the water is extracted. That would just mean that a slightly more saline solution is dumped back in the ocean at the other end of the pipe. Some method would be needed to ensure only vapourised water passed into the condensing region - it'll be possible somehow - maybe a gortex type material that allows vapour but not water through. If the pipe/tube was rectangular in cross section that might help. The top layer could be flushed at night to remove any salt deposit buildup at the edges.


----------



## skeptical (Jun 22, 2009)

The problem with solar desalination is scaling it up big enough to make a significant difference.   Very expensive.

The problem with distillation is massive energy costs.    Reverse osmosis is, generally, still the cheapest, and it is getting cheaper due to major advances in RO membrane technology.    I really see it as the future.  For city water supply at least.

So where does the water go?   Most of it goes to irrigation.   Under current water useage, there is no way we can use* any* kind of desalination to meet current and future needs for agriculture.  The amounts of water needed are just too incredibly massive.

However, we can reduce dramatically the amount of water needed for irrigation.   Too much is used in terribly wasteful methods, such as whole field flooding.   Replace all that with trickle field irrigation, and the amount of water needed drops to about one third.   This is difficult, but more likely to be done than any kind of desalination for agriculture.

There are other techniques.   The best solar desalination is called sun and rain.   Most of the natural rainfall is currently wasted.   A lot can be gained by reducing that waste.  For example :  it is easy and low tech to dig a bloody great hole in the ground, in a natural hollow, and let monsoon rain flow into it, to be stored for the dry season.   OK, it needs plastic liners, and a cover to reduce evaporation, but it is still relatively easy and cheap to do.


----------



## Wiglaf (Jun 22, 2009)

skeptical said:


> The problem with solar desalination is scaling it up big enough to make a significant difference. Very expensive.
> 
> The problem with distillation is massive energy costs. Reverse osmosis is, generally, still the cheapest, and it is getting cheaper due to major advances in RO membrane technology. I really see it as the future. For city water supply at least.
> 
> ...


You are basically right about desalinization plus it has an environmental impact due to the left over salt and contaminants that must be disposed of.  The 21 plants proposed in California would be capable of producing <4% of our usage.
As for reduced agriculture usage, what waste?  Usage has been halved and output doubled.  Further reductions are only possible by changing to less thirsty crops.  Who wants to eat cactus?  They sell it in the supermarket but it doesn't seem to be their biggest seller.  Crop irrigation is a science.  They don't just spray water arround willy nilly.  They use special machines to see to it that water is distributed evenly.  That way the entire crop can receive the minimum amount of water without having to slightly over water some parts.  The waste in in homes.  The problem is that agriculture is 80% of water usage.


----------



## Wiglaf (Jun 22, 2009)

skeptical said:


> For example : it is easy and low tech to dig a bloody great hole in the ground, in a natural hollow, and let monsoon rain flow into it, to be stored for the dry season. OK, it needs plastic liners, and a cover to reduce evaporation, but it is still relatively easy and cheap to do.


 If we had monsoon rain, we wouldn't have a water problem in the first place.  Although some control of runoff would be wise as if global warming does happen rainfall will increase while snowpacks will decrease.  Water rationing in the summer and flooding in the winter would suck.


----------



## skeptical (Jun 22, 2009)

Wiglaf
My comments were supposed to be global in context.  You are talking of California.   Fine.  But California has to sort out its own solutions.   Mind you, I would be seriously dubious about any suggestion that there is no room for increased irrigation efficiency.


----------



## Drachir (Jun 22, 2009)

Tuas Seawater Desalination Plant - Seawater Reverse Osmosis (SWRO) - Water Technology

Perhaps this is the answer.  Apparently large scale reverse osmosis works quite well and it is acceptable from an environmental point of view as it uses much less energy than conventional systems, which also makes it much more cost effective.  

BTW environmentalists are quite right to object to desalination based on vast energy requirements, especially given the the current problems with energy dependency.


----------



## skeptical (Jun 22, 2009)

Drachir's reference clearly shows the potential of reverse osmosis desalination.   However, it is worth remembering that it supplies only 10% of the needs of an urban population of 4,500,000 people.  That is :  a plant costing $US 140 million supplies 450,000 city dwelling people with their water.

Since agricultural irrigation requires many times that amount per person, this is a clear indication of the fact that, while desalination is great for supplying safe drinking water, it is NOT the answer for total fresh water supply.


----------



## chrispenycate (Jun 22, 2009)

Perhaps we should be following the 'Oath of Fealty' scenario and towing in the icebergs breaking off the Antarctic shelf to corners of civilisation where they would be useful?

Lot of water in one of those lumps. Not a long term solution, and I can't think of a low energy propulsion method; sails would have to be so enormous.


----------



## skeptical (Jun 22, 2009)

Just throwing some numbers at you.

A typical suburban dweller in the wealthy West uses about 200 litres per day per person for drinking, washing, laundry, flushing toilets, sprinkling lawns etc.  Thus a city of one million people needs 200 million litres per day.   And that is not taking into account industrial use.

The minimum food requirement for an adult person requires crops grown on 1000 square metres of land, assuming no animal protein in the diet.   Crops need about 10 mm of water per day to grow vigorously.  Some of this may come, of course from rain, but the rest must come from irrigation.  That represents a total of 10 cubic metres per day water.  Assuming half comes from rain, we must still allow for 5,000 litres per person per day of irrigation water.

For a million people that means 5 billion litres of water per day for irrigation, even assuming everyone is vegan!


----------



## Ursa major (Jun 23, 2009)

skeptical said:


> Crops need about 10 mm of water per day to grow vigorously.


 
Is that right?

That's 3650mm per annum, 3.65m or 143.7 inches (i.e. just short of twelve feet.)


It seems rather a lot.


----------



## Drachir (Jun 23, 2009)

skeptical said:


> Drachir's reference clearly shows the potential of reverse osmosis desalination.   However, it is worth remembering that it supplies only 10% of the needs of an urban population of 4,500,000 people.  That is :  a plant costing $US 140 million supplies 450,000 city dwelling people with their water.
> 
> Since agricultural irrigation requires many times that amount per person, this is a clear indication of the fact that, while desalination is great for supplying safe drinking water, it is NOT the answer for total fresh water supply.




I agree that it is not the answer currently, bit it is a start.  A decade ago the costs would have been much greater, so perhaps in the future the cost may be lowered further.  Of course, we could always begin to use water more efficiently.  I know that is a startling thought but too often the approach to water use is to look for other sources instead of using what we have more carefully.


----------



## skeptical (Jun 23, 2009)

Ursa
You are correct.

However, remember my earlier comments about the wasteful nature of most irrigation.   To maximise crop growth, normally a hell of a lot of water is used.


----------



## Wiglaf (Jun 23, 2009)

skeptical said:


> Just throwing some numbers at you.
> 
> A typical suburban dweller in the wealthy West uses about 200 litres per day per person for drinking, washing, laundry, flushing toilets, sprinkling lawns etc. Thus a city of one million people needs 200 million litres per day. And that is not taking into account industrial use.
> 
> ...


 Annual withdrawls from water resources per capita in North America is 1,664 cubic meters per year.  The second highest is Asia at 644 cu meters.  The world average is 623 cu meters.
You are right about the world being more wasteful for crops(in another post); the US and China use between 1/3 and 1/2 the water for the same output as India and Brazil.
The industrialized countries use more water but poor countries have more wasteful agriculture.


----------



## Urlik (Jun 23, 2009)

a better solution (excuse the pun) is to grow crop hydroponically.
this would also help keep nitrates from poluting rivers.


----------



## zachariah (Jun 23, 2009)

Geothermal - blast a giant hole in the bottom of the sea floor and build a...er...thing...to collect the freshly boiled water. The heat will provide electricity too. I'll collect my second Nobel now thanks.


----------

