Saturday, July 01, 2006

Pt.3 H2O /Nano Filters

Cheap Drinking Water from the Ocean
Carbon nanotube-based membranes will dramatically cut the cost of desalination.
A water desalination system using carbon nanotube-based membranes could significantly reduce the cost of purifying water from the ocean. The technology could potentially provide a solution to water shortages both in the United States, where populations are expected to soar in areas with few freshwater sources, and worldwide, where a lack of clean water is a major cause of disease.

The new membranes, developed by researchers at Lawrence Livermore National Laboratory (LLNL), could reduce the cost of desalination by 75 percent, compared to reverse osmosis methods used today, the researchers say. The membranes, which sort molecules by size and with electrostatic forces, could also separate various gases, perhaps leading to economical ways to capture carbon dioxide emitted from power plants, to prevent it from entering the atmosphere.

The carbon nanotubes used by the researchers are sheets of carbon atoms rolled so tightly that only seven water molecules can fit across their diameter. Their small size makes them good candidates for separating molecules. And, despite their diminutive dimensions, these nanopores allow water to flow at the same rate as pores considerably larger, reducing the amount of pressure needed to force water through, and potentially saving energy and costs compared to reverse osmosis using conventional membranes.

Indeed, the LLNL team measures water flow rates up to 10,000 times faster than would be predicted by classical equations, which suggest that flow rates through a pore will slow to a crawl as the diameter drops. "It's something that is quite counter-intuitive," says LLNL chemical engineer Jason Holt, whose findings appeared in the 19 May issue of Science. "As you shrink the pore size, there is a huge enhancement in flow rate."


A carbon-nanotube membrane (quarter shown for scale). The nanotubes are located at the center of each square. Despite their tiny size, they can filter water more efficiently than current larger membranes. (Credit: Science)

Interesting use of nanotechnology to help solve the problems with desalination. I always had the vision that many of the deserts that are close to oceans to be turned into vast areas of productive farmland or new cities built.

Another minor issue that has some interest in Santa Barbara is schemes to prevent water runoff and thus raise the ground water level by retaining water on the land.
One scheme that has drawn attention by a few of the city council members is semi-porous cement. One of the best filters to purify the runoff is the ground itself, but I think there are simpler and more cost effective ways to make a dent in reducing runoff.

My suggestion was to use Dry Wells to capture the runoff from rooftops and drain runoff. I presented it to my council person and showed how many of the gutters in town drain right onto the road or even worse onto the sidewalks instead of using the dry wells to capture the excess runoff. Here is a good diagram and instructions of the use of one:

And a cross section of one:

Gravel-less Drywell Leach Pit Kits

Grey water links:
CLOSED-LOOP MUNICIPAL WASTEWATER RECYCLING SYSTEM
Grey Water Systems
Recycling Gray Water for Home Gardens
ALTERNATIVE GREY WATER SYSTEMS
Less water than the Sudan?
Grey Water /Australia
Solving Problems with Nano-Filters

Carlsbad Desalination Project

HT Jason: Gates Foundation: 'We need to reinvent the toilet' - On The Left
Gates Foundation: 'We need to reinvent the toilet' - CNN.com

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