12 April 2008

Solving the World's Water Problems I: Desalination

One of the most serious environmental problems for humans of Earth is the shortage of clean water for drinking and other human uses. Perhaps 1 billion people lack access to clean freshwater. But since 97% of the water on Earth is salty water, one promising method to create clean water is desalination. Desalination is expensive due to high energy costs, but some progress is being made on that front.
The specific (per unit of produced potable water) energy of desalination has been reduced from over 10 kW h m-3 in the 1980s to below 4 kW h m-3 (refs 78, 83)....For zero per cent recovery, that is, the removal of a relatively small amount of water from a very large amount of sea water, the calculated theoretical minimum energy for desalination is 0.70 kW h m-3 of fresh water produced. This theoretical minimum increases to 0.81, 0.97 and 1.29 kW h m-3 for recoveries of 25, 50 and 75%, respectively, suggesting that further improvements in the energy efficiency of RO desalination are still possible.

...Recent work by the Affordable Desalination Coalition78, 84 has demonstrated a remarkably low specific energy of seawater desalination, at 1.58 kW h m-3, under ideal conditions (that is, new membranes, no fouling, and low water flux) at 42% recovery. This value is relatively close to the theoretical minimum energy for seawater desalination at that recovery, suggesting that next-generation fouling-resistant RO membranes will be able to desalinate sea water with lower energy consumption. __Nature__via__SoftMachines
A large part of Earth's human population lives close enough to salt water seas and oceans for desalination to play a much larger role in clean water access, as the energy issue is managed by more efficient technologies, and more plentiful energy supplies.

Advances in nanotechnology promise significant improvements in clean water efforts. Here is a PDF download discussing nanotech approaches to providing clean water from Foresight.org. More on nanotech solutions to clean water problems.

Eventually, plants will be gene-engineered to take up saltwater in their roots, purify to freshwater, and collect the freshwater in an interior cavity that can be tapped for a freshwater supply. I expect such plants to be developed in 5 to 10 years time.

Update: OTEC--ocean thermal energy conversion--offers other routes to clean water. Low pressure distillation of warm seawater and atmospheric moisture condensation by cold seawater. Here are two websites that try to monitor progress in OTEC:
Hawaii Energy Options

And a bonus 2 visionary looks at potential uses of the ocean from:

John Craven
S Ramachandran

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Blogger Snake Oil Baron said...

Might it be possible for people in coastal areas to make small, pipe sized tunnels through some of the mountains which cast rain shadows in many areas so that waste water could be treated on the other side where high temperatures and clear desert sunlight could be used to aid in the destruction of pathogens and the reduction of sewage to a low water, high energy product for further processing? If done in covered ponds the system could capture the water vapor for agriculture or desert reclamation projects. Designing fatter wind towers which could also function as condensation tanks would mean you could drop the water around each tower via underground drip irrigation (in the mornings and late afternoons when evaporation is less but photosynthesis is still possible) and turn the surrounding land from desert to prairie/pasture. It would be a case of desalinating at the coast, using it for people, agriculture and industry and then using it again when released in the treatment process. Energy from the dehydrated sewage could be sent back to the coast for desalinization and other uses.

Saturday, 12 April, 2008  
Blogger al fin said...

Interesting idea, Baron.

Municipal waste sludge can be converted to energy, but is probably best done locally rather than piping it long distances.

In the southwestern US and other dry sunny regions, solar energy will be used to power desalination as well as pumping stations to pump the fresh water inland.

Geoengineering schemes to increase rainfall over some dry coastal areas will also help to boost agricultural development in many areas of the globe.

Bio-energy for desert areas will come from algal hydrocarbons, with algae grown in salt water ponds, among other approaches.

Sunday, 13 April, 2008  

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