Environmental engineering experts in America have turned to acoustic technology to help the US Air Force get rid of its hazardous chemicals.
The innovative sonochemical process, developed by academics from the University of Arizona College of Engineering, involves the use of sound waves to destroy the complex molecular structures of toxic materials, reducing them to innocuous water and carbon dioxide.
The key to the process is the cavitation, or bubble formation, that strong sound waves induce. The small bubbles which form in toxic substances following exposure to sound waves tend to swiftly implode, resulting in sharp shock waves.
These intense shock waves in turn generate huge amounts of heat energy which lead to extremely high temperatures, conducive to the destruction of chemicals. In addition to this, the bubble implosions also produce highly active oxidizing radicals, which are capable of rending the molecular structure of surrounding matter, thus destroying it completely.
While cavitation has already been used for medical purposes, most prominently in the form of shock-wave lithotripsy, which can remove kidney stones without the need for invasive surgery, Manish Keswani, assistant professor at UA's Department of Materials Science and Engineering and Reyes Sierra-Alvarez, professor at the Department of Chemical and Environmental Engineering, now believe the process is ideally suited to the treatment and disposal of certain hazardous chemicals.
Toxic PFCs, which include perfluoroalkyl sulfonates and carboxylates and serve as a key ingredient in fire-fighting foams, are hardy chemicals which are difficult to break down and readily capable of abiding for lengthy periods of time in the environment, as well as the tissue of living organisms.
Cavitation promises to break down the molecular bonds of toxic PFCs via the generation of heat energy and oxidizing radicals in a manner which is both quick and cost-effective. The method is believed to be capable of achieving temperatures in excess of 5,500 degrees Celsius, more than sufficient to render the dangerous chemicals innocuous.
The chief innovation of the acoustic technology developed by the UA engineers is a dual-transducer system which generates multiple sound frequencies, a feature which will hopefully render it capable of processing larger volumes of material.
Keswani and Sierra-Alvarez have been awarded a contract worth almost a quarter of a million US dollars by the Air Force Civil Engineering Centre to apply this technology to the dispatch of its vast stockpile of fire-extinguishing foam, which totals almost 11 million litres in volume.
The researchers hope to take advantage of this opportunity to further refine their system, using an electrochemical probe to determine the most propitious chemical and acoustic conditions for destruction of the hazardous chemicals.