Air Date: Week of September 22, 2000

Cynthia Graber reports on research that uses sound to banish the smell from hog waste.

Transcript

GRABER: Hog farms don't usually make great neighbors. Noxious odors drift off lagoons of animal waste, plaguing people who live downwind. Now, scientists are using sound to help get rid of the smell. A vibrating machine sends sound waves at about 20 kilohertz through wastewater. The force of these ultrasound wavelengths create small vacuum bubbles in the water. When these bubbles collapse, they release pressure and heat, activating certain chemical reactions. Scientists aren't exactly sure how it all works, but somehow this pressure speeds up reactions already occurring in the pig waste, helping speed the transition of stinky hydrogen sulfide and ammonia into significantly less smelly sulfur and nitrogen. Vacuum bubbles collapsing in water do emit a faint shriek. You'll have to get close to hear it. But those lagoons may let out a yelp as they're being scrubbed clean. That's this week's technology update. I'm Cynthia Graber.