When it comes to cleaning up contaminated soil, there is no quick and easy method – or at least, not yet. That said, a chemical engineer at Northeastern University believes that using lasers may be a better way to go than any currently-used techniques.
Working with graduate students Wenjun Zheng and Sichao Hou, associate professor Ming Su tested his theory on simulated soil composed of porous silica, that was contaminated with a carcinogenic chemical known as DDE. A product of the infamous insecticide DDT, DDE fluoresces when exposed to ultraviolet light, making its presence in soil easy to detect.
When a high-powered laser was shined on the contaminated artificial soil, the DDE was instantly heated to thousands of degrees Celsius. This was sufficient to break its chemical bonds, converting it to innocuous smaller molecules like carbon dioxide and water. Almost immediately after the laser was used, the ultraviolet light caused no fluorescence, indicating that there was no longer any DDE present.
The laser technique should reportedly work on all types of contaminants, although it has yet to be tested on ones other than DDE.
Presently, contaminated soil frequently has to be removed from the ground and washed off-site with organic solvents before being returned. Not only is this expensive and time-consuming, but it also leaves toxic liquid waste to be dealt with. There are methods of treating soil on-location, although these only work on certain types of soil, or in the case of using plants/microbes, take a long time to have a pronounced effect.
By contrast, lasers could conceivably be used on-site on all types of soil and pollutants, delivering instant results. Su envisions a system in which a truck would drive across contaminated ground, towing a plow-like apparatus equipped with multiple fiber optic lasers that would treat the soil.
A paper on the research was published this week in The Journal of Applied Physics.
Source: American Institute of Physics
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