Sonochemical sterilization

The synergetic effects observed during the sterilization of Bacillus subtilis var. niger ATCC 9372 by the combined action of ethylene or propylene oxide with high intensity airborne sound waves (34.8 kHz) were investigated. It has been shown that the number of surviving spores deposited on paper strips decreases exponentially with the sound intensity at sample level. Reductions of the order of one third of the time required for standard propylene oxide sterilization have been observed by using the combined action of sound waves with gaseous sterilization. At the present time maximal synergetic effects seem to be achieved for the following experimental conditions: propylene oxide concentration 500–1000 mg/litre, acoustic intensity 161–162 dB, contact time 80 min, temperature 60°C and relative humidity 40%. The basic mechanism involved in sonochemical sterilization seems to be more of a physical (accelerated gas diffusion) than of a chemical nature.