Abstract
We have investigated the inactivation of Saccharomyces cerevisiae and Cryptosporidium parvum by ultrasonic irradiation. Cryptosporidium parvum is one of the most serious poisonous protozoa that causes the waterborne disease and has high resistance to chlorine because of the hard oosyst. After ultrasonic irradiation, the viability of Saccharomyces cerevisiae was observed by the colony counting technique, and that of Cryptosporidium parvum was evaluated by the infectivity test using mice. In this study, the flow ultrasonic reactor with several frequencies (23.7, 44.6, 98.7, 144, 168 kHz) was used for the irradiation of ultrasound. The influence of the height of the reflector on the formation of OH radical and the inactivation of yeast cells was investigated at each frequency in batch system. The sonolytic inactivation of Cryptosporidium parvum was carried out with batch and flow systems at a sound frequency of 23.7 kHz. The addition of NaClO (1 ppm) to the suspension on the infectivity test was found to be effective, suggesting the oosyst might be damaged by the shock wave induced from the cavitation.
