Sequential inactivation of Cryptosporidium parvum using ozone and chlorine.
Inactivation of bovine-derived C. parvum oocysts was studied at bench-scale in oxidant demand free 0.05 M phosphate buffer using free chlorine alone or ozone followed by free chlorine at temperatures of 1 degrees C, 10 degrees C and 22 degrees C at pH 6. Animal infectivity using neonatal CD-1 mice was used for evaluation of oocyst viability after treatment. Kinetic models based on the linear Chick-Watson model were developed for free chlorine inactivation and ozone/free chlorine sequential inactivation for 0.4 or 1.6 log-units of ozone primary kill. At 22 degrees C. ozone pre-treatment increased the efficacy of free chlorine for about 4-6 times depending on the level of ozone primary kills. Gross kills of the ozone/free chlorine sequential inactivation were a function of ozone primary kills and increased linearly with the free chlorine C(avg)t (arithmetic average of the initial and final residual x contact time) product. Temperature was critical for both single and sequential inactivation, and the efficacy of free chlorine after 1.6 log-units of ozone primary inactivation decreased by a factor of 1.8 for every 10 degrees C temperature decrease. Given an ozone primary kill of 1.6 log-units, the free chlorine C(avg)t products required for a gross kill of 3.0 log-units were 1000, 2000 and 3,300 mgmin/L for 22 degrees C. 10 degrees C and 1degrees C, respectively.
Li
H
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Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Canada. hanbin@ualberta.ca
Finch
G R
GR
Smith
D W
DW
Belosevic
M
M
D000818:Animals; D002417:Cattle; D002713:Chlorine / Q000737:chemistry*; D016785:Cryptosporidium parvum / Q000472:pathogenicity*; D007700:Kinetics; D008962:Models, Theoretical; D010083:Oxidants, Photochemical / Q000737:chemistry*; D010126:Ozone / Q000737:chemistry*; D013696:Temperature; D018508:Water Purification / Q000379:methods*
D010083:Oxidants, Photochemical; D002713:Chlorine; D010126:Ozone