Porous layers of slurry, zapped with electricity, may revolutionise the treatment of contaminated clay soils
WHAT'S good for the stomach is good for the earth. Reclaiming clay soils contaminated with toxic waste is a pain at the best of times. Now a technology, inspired -- believe it or not -- by the layered Italian pasta, lasagne, may do the trick. Already Monsanto, General Electric, Du Pont and the US Environmental Protection Agency are busy trying out the new method (New Scientist, Vol 141, No 1913).
Named after the gastronomic source of its inspiration, the lasagne technique, devised by Philip Brodsky, a researcher with Monsanto, essentially combines existing technologies used by hydraulic and petroleum engineers with methods already available for degrading chemicals.
This method has evoked much interest in clay soil areas in the US, which make up at least half of the country's toxic waste sites. Removing pollutants that seep into clay is difficult because they settle into the microscopic pores in the clay. Trace contaminants slowly percolate into the groundwater.
The new approach treats contaminated soils -- even under buildings -- by creating porous, horizontal layers a la lasagne in the soil and then passing an electric current through them. The layers, separated by contaminated layers of clay, are created by injecting a slurry of water and sand at various depths, through a process known as hydrofracturing. Pollutants are broken up within these treatment layers using microorganisms that can digest organic waste, or iron filings that speed up the breakdown of industrial waste.
A pipe that serves as an electrode is drilled through these layers and voltage passed through it. The current draws water and the toxic chemicals out of the contaminated clay and onto the treatment layers, a process called electro-osmosis.
Initial tests have been encouraging. Monsanto researchers found that within weeks thelasagne method removed 99 per cent of para-nitrophenol, copper and trichloroethylene. They also say that this method will enhance traditional clean-up techniques because it gathers all the contaminants under one roof, where they can be bashed into submission using several methods of decontamination for different wastes.
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