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Background: Ozone (O3) is an unstable gas used commonly for oxidation and disinfection. It is approximately 20 times more soluble than oxygen in water. Ozone is a protoplasmic oxidant affecting the bacterial proteins and inactivates cellular enzymes. It can destroy molds, bacteria and viruses. The present study was conducted to assess the disinfecting ability of ozone on the surface microorganisms.
Materials and methods: Eight species of pathogenic bacteria in different concentrations (102, 105, 107 and over than 107 cells per milli liter) were treated with ozone gas. An aluminum chamber with a total capacity of 300L was set within a safety cabinet, where the ozone generator was installed. Different concentrations of 8 species of bacteria were treated with ozone gas at different times (30, 60, 90, 120, 180 minutes). Before and after ozone treatment, the number of bacteria was determined by breed counter method.
Results: Among different bacteria treated with ozone, Bacillus cereus revealed the highest resistance to the germicidal effects of ozone. Indeed, concentration of >107 cells/ml of this microorganism was inactivated by the highest ozone concentration (30 ppm). Staphylococcus aureus and Micrococcus spp. with concentration of 107 cells/ml were inactivated with lower ozone concentration (10 ppm), however, Escherichia coli and other gram-negative bacterial pathogens (107 cells/ml) were inactivated in higher concentration of (15 ppm) ozonation.
Conclusion: In order to achieve surface sterilization, ozone should be employed with a concentration of 30 ppm, however, if inactivation of nonsporulative bacteria is desired lower ozone concentration of 15 ppm will be adequate.

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Background: Water used in the pharmaceutical industry should have special physicochemical and microbiological characteristics. One of the quality items of pharmaceutical water is level of microbial content. For this reason selection of effective disinfection method is the main item for design of pharmaceutical water systems. Water systems can be maintained at temperature below 10 ºC and more than 70 ºC but maintaining of water at ambient temperature could increase of microbial content. In this condition use of disinfectant is useful for reducing of microbial content. Some of them such as chloride, ozone and hydrogen peroxide due to good results have more application.
Materials and Methods: In this study, effect of three disinfectants chloride, ozone and hydrogen peroxide with 1 ppm concentration, consider on five microorganisms Pseudomonas aeruginosa, Staphylococcus aureus, candida albicans, Aspergillus niger and E.coli.
Results: Counting and decreasing of microorganisms showed the efficiency of disinfectants.
Conclusion: Finally ozone was selected as the best disinfectant due to high efficiency.