Saturday, July 16, 2011

A solution to the 'clean water' crisis?

Around the world, it's estimated that up to 20% of people live without access to pure drinking water and/or improved sanitation. The cost of purifying water is one of the major elements holding back the improvement in water supplies. However, a new and very low-cost technology may change that. Water Online reports:

Researchers at Rice University are spinning a bit of nano-based magic to create "coated sand" that has enhanced properties for water purification. The breakthrough may benefit developing countries where more than a billion people lack clean drinking water.

Beds of sand are commonly used throughout the world to filter drinking water. The particle size of sand and surface modifications determine the efficiency of sand in removing contaminants from water.

The Rice researchers' technique makes use of graphite oxide, a product in the chemical exfoliation process of graphite (aka pencil lead) that leads to single-atom sheets known as graphene via subsequent reduction.

. . .

Nanosheets of graphite oxide can be tailored to have hydrophobic (water-hating) and hydrophilic (water-loving) properties. When mixed in a solution with sand, they self-assemble into coatings around the grains and keep the hydrophilic parts exposed. Adding aromatic thiol molecules to the coatings enhances their ability to sequester water-soluble contaminants.

Ajayan, a Rice professor in mechanical engineering and materials science and of chemistry, and his collaborators from Australia and Georgia conducted experiments to compare this coated sand with plain sand and activated carbon granules used by municipalities and in-home filtration systems.

The researchers ran two model contaminants -- mercury (at 400 parts per billion) and Rhodamine B dye (10 parts per million) -- through sand and coated sand placed into filtration columns. They found coarse sand's adsorption capacity of mercury was saturated within 10 minutes.

The coated sand continued removing mercury for more than 50 minutes and resulted in filtered water with less than one part per billion. (The Environmental Protection Agency's maximum contaminant level goal for mercury in drinking water is two parts per billion.)

Results for water treated with Rhodamine B dye were similar.

The researchers found coated sand sequestered contaminants just as well as the commercially available active carbon filtration systems they tested.

There's more at the link. Here's a video report on the research.

This may not seem like a big deal to First World readers. However, when you've lived and traveled in the Third World as much as I have, and understand the deadly effects of unfiltered, polluted, disease-bearing water sources, this is potentially a monumentally important development. I hope the researchers at Rice can successfully commercialize this research, and make it available for implementation. They'll save literally millions of lives if they succeed.

It also has implications for organizations like the US military. If they can set up a 'coated sand' filtration system (which doesn't need an external power supply for its operation) they can potentially purify any local water source to support their operations, while cutting down on their power and fuel resupply requirements. When you consider that it's costing the US military about $400 per gallon to get gasoline to the front lines in Afghanistan, every gallon of fuel saved can make a measurable difference to military budgets!



Anonymous said...

I wonder if it can be tweaked to pull the salt from seawater? THAT would be even bigger than this.


Peter said...

@Antibubba: Look up 'reverse osmosis'. It's a relatively new filtration technique that can produce potable water from seawater. Not quite the same principle as 'smart sand', but also very useful.

Anonymous said...

I know about it, but it's power intensive and not terribly efficient. A passive desal solution would be a huge step towards clean water anywhere.


Janeen said...

The "magic" coated sand removes contaminants like pathogens and heavy metals through sorption processes. In general terms contaminants are removed from water when they stick (or sorb) to the coated sand.

Ionic compounds like salt (i.e. sodium chloride) break down into their constituent ions in water. Chloride ions are extremely hard to remove from water. There are no known sorption processes capable of accomplishing this.

So, no. Coated sand systems will not desalinate seawater.