Inactivation of Bacillus subtilis spores with ozone and monochloramine

Abstract

The inactivation kinetics of Bacillus subtilis spores with ozone and monochloramine was characterized by a lag phase followed by a pseudo-first-order rate of inactivation. The lag phase decreased and the post-lag phase rate constant increased with increasing temperature within the range investigated (1–30°C for ozone, 1–20°C for monochloramine). The corresponding activation energies were 46,820 J/mol for ozone and 79,640 J/mol for monochloramine. The CT concept was found to be valid within the concentration range investigated of 0.44–4.8 mg/l for ozone, and 3.8–7.7 mg/l as Cl 2 for monochloramine. The inactivation kinetics of B. subtilis spores with both ozone and monochloramine varied with pH within the range of pH 6–10 investigated. The fastest ozone and monochloramine inactivation rates were observed at pH 10 and 6, respectively. Different stocks of the same strain of B. subtilis spores had different resistance to ozone and monochloramine mainly because of discrepancies in the extent of the lag phase. B. subtilis spores might not be conservative surrogates for C. parvum oocysts for ozone disinfection at relatively low temperature mainly due to the spores having a lower activation energy compared to that for the oocysts. In contrast, the activation energy for monochloramine was comparable for both microorganisms but differences in the extent of the lag phase might result in the spores being overly conservative surrogates for the oocysts at relatively low temperature.