The cleaning power of sound waves on the back of a
truck
Embargo 10am Monday 21 August
A young researcher in Sydney is
cleaning up contaminated soil by blasting it with ultrasound.
Andrea Sosa Pintos from CSIRO
Industrial Physics has shown that toxic and carcinogenic pollutants, such as
polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs),
can be decomposed quickly, easily and cheaply using a portable treatment unit.
“Chemical analysis of the soil and
water after we’ve treated it confirms that more than 90 per cent of pollutants
have been destroyed,” she says.
Present soil remediation techniques
such as landfill disposal, incineration and bioremediation, have many
limitations. “None of these provides a complete or cost-effective solution. And
some of them can be time-consuming.” says Sosa Pintos.
“Our process is very simple. We generate high-power ultrasound waves in a slurry
of the contaminated soil in water,” Sosa Pintos explains.
The soil and water are mixed and the
slurry is pumped through a treatment unit where it is exposed to the ultrasonic
waves. The whole process only takes a matter of minutes, as opposed to hours and
days, or even months using other techniques.
“Ultrasonic waves travelling through
the mixture create micro-bubbles. When these bubbles burst on the surface of the
soil particles, they release intense shock waves which can generate temperatures
of up to 5000 degrees Celsius. Any chemical contaminants on the
surface of the soil particles bear the brunt of these bursts of energy and are
blown apart,” she says.
Importantly, the surrounding liquid
stays cool, eliminating the possibility that the remnants of the toxic compounds
can recombine to form dangerous by-products, as sometimes happens using other
technologies. Dioxins are formed during incineration, for instance.
The pilot plant Sosa Pintos and her
colleagues have developed can already process about a tonne of soil a day. For a
commercial scale system a more efficient feeder unit including a higher capacity
pump would be required.
Sosa Pintos says. “If the right
engineering company were interested, within a couple of years we could develop a
commercial treatment unit able to be hauled to contaminated sites on the back of
a truck.”
The combination of high destruction
rates, very low energy costs, and the convenience of on-site treatment, makes
high-power ultrasound a promising option for soil remediation.
Andrea Sosa Pintos is one of 16 Fresh
Scientists who are presenting their research to school students and the general
public for the first time thanks to Fresh Science, a national program hosted by
the Melbourne Museum and sponsored by the Federal and Victorian governments, New Scientist,
The Australian and Quantum Communications Victoria. One of the Fresh Scientists will win a trip
to the UK courtesy of the British Council to present his or her work to the
Royal Institution.
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