A new method developed at Northeastern University in Boston, Massachusetts (US), uses high-power lasers to thermally decompose soil contaminants. Directly breaking down toxins and pollutants, the researchers say this decontamination approach could be cheaper and more efficient than conventional decontamination solutions.
The proof-of-principle study shows how such a high-power laser system could be employed — theoretically on a large scale — to thermally decompose soil contaminants. “We are using an infrared laser with wavelength of 10 um,” confirms Ming Su, associate professor of chemical engineering at Northeastern.
The laser light zaps harmful substances by heating up the pollutant locally, reaching temperatures of thousands of degrees Celsius — hot enough to break down the chemical bonds of the pollutant, fragmenting them into smaller, safer molecules, such as carbon dioxide and water. In principle, the team believes, all types of contaminants can be removed using laser light.
The professor says current methods for ridding soil of unwanted substances are toxins are inefficient, take a long time and, what is most concerning, may cause more contamination. By contrast, the approach presented by Su and his team may offer a solution to these drawbacks. What is new and unique about this technique? “It is rapid, highly efficient, and there is no secondary contamination,” emphasizes the expert.
Many conventional decontamination approaches require digging up the contaminated soil and transporting it to a special facility off site for cleaning. The soil then has to be returned and adequately reinstalled, which is a laborious process that costs significant time and money. One widely used method is rinsing out pollutants from the contaminated soil with water or organic solvents. The problem is that rather than completely eradicating contaminants washing often only dilutes them. Then what to do with the contaminated water? The organic solvents themselves can become harmful secondary contaminants.
Another previously employed decontamination method is soil vapor extraction, where air is pumped into the ground to remove volatile organic compounds. But experts say this solution only works on permeable or homogeneous soils. Biological approaches to break down pollutants using plants or microbes, on the other hand, are often too slow to deal with acute toxication and only work with certain contaminants and in low concentrations.
Saving thousand of acres of agricultural land
Key applications for this new laser-based decontamination method will be pollution removal and soil recovery. “It may save thousands of acres of land for agricultural purpose,” replies Su when asked what excites him personally the most about the outcome of this study.
The kinds of substances this new laser-based method could destroy are organic contaminants and metal ions. The biggest advantage of using lasers, according to the professor, is that they can be used at the site of decontamination.
The next step for Su and his colleagues in this endeavor will be prototyping a laser plow for large-area scanning.
The study is detailed in the article “Laser induced rapid decontamination of aromatic compound from porous soil simulant,” published in the Journal of Applied Physics.
Written by Sandra Henderson, Research Editor Novus Light Technologies Today