Legionella pneumophila in sterile distilled water was not detected after ultraviolet irradiation by FLONLIZER®, a new‐type sterilizer, at a flow rate of 82.5 to 364.8 liters/hr. When irradiated by FLONLIZER® at a flow rate of under 324.0 liters/hr, no viable cells of legionellae, other heterotrophic bacteria and bacterivorous protozoa were detected in the cooling tower water, which was found to contain L. pneumophila. No viable cells of L. pneumophila and L. bozemanii suspended in sterile distilled water were detected after the irradiation with UV‐doses of over 6.16 × 103 μW·sec/cm2. At the irradiation of low UV‐doses under 1.06 × 104 μW·sec/cm2, the viable count of legionellae recuperated by photoreactivation from UV‐damage increased with the exposure time under a white fluorescent lamp. However, in the samples irradiated with UV‐doses of over 3.52 × 104 μW·sec/cm2, equal to the FLONLIZER®, legionellae did not recuperate even after 18 hr illumination with a white fluorescent lamp. FLONLIZER® is thus expected to act as a sterilizer which can control the legionellae inhabiting cooling tower systems placed in outdoor space.

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The kinetics of the inactivation of Bacillus subtilis spores by ozone alone and ozone with UV irradiation were investigated in a circulation system of a 5.3 1 of saline suspension (106 spores/m1) under various conditions of ozone concentration (3.0 and 7.0 mg// in inlet gas) and UV intensity (3,413 and 13,650 gw/cm2). The spore inactivation by ozone with UV irradiation was more effective than by ozone alone in the presence of organic compounds such as tryptophan and ribose. The combination treatment of ozone and UV is considered to be a useful disinfection method for practical use.

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