Inactivation of Giardia by Ozone and Its Disinfect Mechanisms

This study was to investigate the effect of ozone （ O3 ） inactivation on Giardia in water by the fluorescence staining method. In order to elucidate the dominant mechanisms of inactivation, cell surface or inner cell components damage were comparatively examined by scanning dectron microscopy （SEM）. Results suggested that O3 had a stronger effect on inactivating capability. Firstly, when the concentration of O3 was above 2.0 mg/L and the contact time was up to 5 min, it showed a significant inactivating effect. Secondly, the effect of turbidity on inactivation was also found to be significant in synthetic water; when turbidity increased, the inactivating effect decreased. Thirdly, the inactivating rates were improved with a temperature increase from 5 to 25℃, but decreased when the temperature were out of this range. The inactivating capability of O3 was stronger under acidic conditions than alkalic conditions. Lastly, when the concentration of organic matter in the reactive system was increased, probably due to the competition between G/ard/a and organics on O3, the inactivating rate was decreased; in addition, the cellular morphology of Giardia varied with different contact times. At contact time of 30 s, cells were rotundity and sphericity; at 60 s they became folded, underwent emboly, and burst; and at 240 s, the cell membrane of Giardia shrinked and collapsed completely.