OP-II-3

PP-II-34using titania or Ag-doped titania solution, dried at room temperature and calcined at773K for 2 hours. Thus we could obtain titania or Ag-doped titania thin film inside theglass tube. 200ml of test solution included L. pneumophila was filled in the glass tubeand circulated at a flow rate of 200ml/min. Black light lamps (6W x 4, wave length300-400nm) located outside the glass tube was switched on to irradiate UV light, andthen the sample was collected at intervals to estimate the presence of viable bacteria.RESULTS AND DISCUSSIONFig.1 shows the survival rateof L. pneumophila with processtime on titania thin film (P-Ti) andAg-doped titania thin film (Ag-Ti)under UV irradiation. The datafollows a first order rate law, andthe estimated rate constants(min -1 ) shows in the figure.Without photocatalyst and no UVFig. 1. Survival rate of L. pneumophila with process time.irradiation (Control) did notdisinfect L. pneumophila. On the other hand, under UV irradiation, the survival rate ofL. pneumophila decreased gradually without photocatalyst. In addition, in the case ofusing titania and Ag-doped titania thin films under UV irradiation, the survival rate ofL pneumophila decreased rapidly. Surprisingly, Ag-doped titania could slightlydisinfect L. pneumophila without UV irradiation. Fig. 2 shows the SEM images ofL. pneumophila after the treatment for 24h. The cell wall of L. pneumophila wasdestroyed by Ag-titania thin film. Although the leakage of the endotoxin was detected,the endotoxin was photocatalytically decomposed after 24h of treatment.(c)(a)(b)Fig. 2. SEM images of Legionella pneumophila treated with (a) control, (b) UV irradiationand (c) Ag-doped titania thin film under UV irradiation for 24h.Reference[1]. E. Obuchi et al., Kagaku Kogaku Ronbunshi (in Japanese) 21, 1075-1081 (1995).395