Inactivation ofEscherichia coliusingozone and ozone ‐ hydrogen peroxide

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Abstract
The purpose of this study was to compare the inactivation efficiency of ozone and ozone‐hydrogen peroxide. Escherichia coli (ATCC 11775) was used as the test organism in 500 ml batch reactors to which ozone was added from a concentrated side‐stream solution. Two types of laboratory water were used: a 0.05 M phosphate‐0.01 M bicarbonate buffer (pH 6.9) designed to prolong the life of dissolved ozone; and a 0.05 M phosphate buffer (pH 6.9) containing hydrogen peroxide at a weight ratio of 10 parts hydrogen peroxide to 1 part ozone designed to rapidly decompose the ozone. It was found that the half‐life of ozone in the bicarbonate buffer was approximately 180 s after immediate demand was satisfied compared with approximately 20 s in the hydrogen peroxide system after immediate demand was satisfied. Differences in the inactivation of E. coli between the two systems were indistinguishable for the first 60 s of contact time. For contact times of 120 s and greater, the bicarbonate buffer continued to support inactivation of E. coli whereas no further inactivation was observed in the hydrogen peroxide system. The ozone residual was below detection limits in the peroxide system by the end of 60 s. It was concluded that the maintenance of an ozone residual was important for obtaining the best disinfection performance. Therefore, chemical application points should be carefully selected in the process train to optimize disinfection prior to advanced oxidation.