Chemical inactivation of Cryptosporidium parvum in water

Inactivation of Cryptosporidium parvum oocysts in water using single or sequential microorganism reduction chemicals was studied. Experiments were conducted at bench-scale in oxidant demand-free 0.05 M phosphate buffer. Animal infectivity using neonatal CD-I mice was used for evaluation of oocyst infectivity following treatment. Inactivation kinetics were determined for single treatment using ozone, chlorine dioxide, free chlorine or monochloramine, and sequential treatment using ozone followed by free chlorine or monochloramine.; Survival curves for the C. parvum oocysts after ozone treatment were characterized by an initial lag and a slight tail-off at high levels of treatment. For chlorine dioxide, free chlorine and monochloramine treatment, the survival of the oocysts declined linearly with the C_avg t (arithmetic average of initial and final concentration x contact time) products. Temperature was a critical factor for C. parvum oocyst inactivation and the inactivation rates decreased dramatically at low temperatures. Water pH was not a significant factor affecting the inactivation rate constant of ozone (pH 6 to 8) or chlorine dioxide (pH 6 to 11). A non-linear Incomplete gamma Hom (I.g.H.) model with temperature correction was developed for ozone inactivation, and Chick-Watson models with temperature correction were developed for chlorine dioxide, free chlorine and monochloramine inactivation. Between 1 and 37°C, every 10°C drop of the water temperature resulted in the reaction rate constant decreasing by a factor of 2.2 and 2.3 for ozone and chlorine dioxide, respectively, corresponding to activation energies of 52 and 55 kJ/mol.; Evident synergy was observed for sequential inactivation using ozone followed by free chlorine or monochloramine. Factors that affected sequential inactivation included the level of ozone primary treatment, and the C _avgt product of the secondary treatment and water temperature. Gross kills of the sequential treatment were greater for higher levels of ozone pre-treatment and increased linearly with the C_avgt products of the secondary treatment. High water temperature was favorable for both gross kill and inactivation synergy. For 1.6 log-units of ozone primary kill, the efficacy of free chlorine or monochloramine secondary treatment was comparable, and their reaction rate constant increased by a factor of about 1.7 for 10°C increase in water temperature.