Ultraviolet germicidal irradiation and titanium dioxide photocatalyst for controlling Legionella pneumophila

Legionella pneumophila, a causative agent of Legionnaires disease and Pontiac fever, is an important microbe to be addressed. Total recovery rates of Legionella pneumophila were evaluated in a chamber by three sampling methods: AGI-30 impinger, impactor, and nuclepore filtration and elution. Our results demonstrated that impingers are likely to perform better than impaction and filtration methods. These might be related to the stronger sampling stress from impaction and dehydration stress from filtration. With regard to control techniques, ultraviolet germicidal irradiation (UVGI) and titanium dioxide photocatalyst (PCO) were considered to be promising to inactivate Legionella pneumophila. In this investigation, the influences of UV dosage and relative humidity on UVGI effectiveness and relative humidity and face velocity on germicidal effectiveness of titanium dioxide (TiO2) coating filters were evaluated in a laboratory test chamber. It was indicated that a very low UVGI dosage of 289 to 860 muWsec/cm(2) was required to produce a 5 log decrease in concentration of Legionella pneumophila. Our results demonstrated that penetrations of Legionella pneumophila were in the range of 0.04-0.27 for the TiO2-coating filter with UV light. It was recommended that UVGI and the TiO2 catalyst filter do provide a good germicidal capacity for Legionella pneumophila.