Evaluating bacterial aerobic spores as a surrogate for Giardia and Cryptosporidium inactivation by ozone

The inactivation kinetics of two strains of bacterial aerobic spores were investigated in a batch reactor for two pH levels (6.3 and 8.2) and various ozone dosages (0.5–2.5 mg/l). The kinetics of ozone decomposition was found to satisfactorily fit a first-order decay model. The CT (concentration×contact time) values were calculated using the modified Hom equation with exponential disinfectant decay. Lower pH resulted in lower CT values. The environmental spores tested were not as resistant to ozone as the reference strain of B. subtilis. Comparison of CT values for aerobic spores with published data suggests that bacterial spores could be a surrogate for evaluating the ozone inactivation of G. lamblia cysts and C. parvum (oo)cysts during drinking water disinfection. However, more information on the resistance of naturally occurring populations of bacterial spores would be needed before they are used as an indicator of ozone disinfection efficiency.