ULTRASOUND PRINCIPLES

Ultrasound is present in a wide range of intensities in frequencies beyond our human hearing limit (20KHz or more). Sound propagation, in a medium like water, is accomplished through waves that exhibit a continuous transition through the medium in a two-phase pattern: rarefaction (negative pressure); and compression (positive pressure). During these alternating cycles, the magnitude of negative pressure in the areas of rarefaction eventually becomes sufficient to cause the liquid to fracture, causing “cavitation.” Cavitation is the rapid creation, growth and explosive collapse by implosion of microscopic bubbles. The collapse and implosion of a myriad of cavitation “bubbles” through an ultrasonically activated liquid, produces the cavitation effect commonly associated with ultrasonics. Ultrasound applied at high intensity and low-to-medium frequencies generates cavitation in water. The use of cavitation to rupture or disintegrate biomass is the prime application of ultrasound for sludge treatment and minimization.