Giardia and Cryptosporidium pose two major concerns for the water industry. Waterborne diarrhea caused by these persistent pathogenic protozoan is one of the most frequently identified waterborne diseases in developed countries. The current enumeration techniques for routine
monitoring of Giardia cysts and Cryptosporidium oocysts are imprecise and there are no perfectly reliable indicators of the presence of protozoan parasites or their removal by treatment. Therefore, it is crucial to assure that disinfection processes in public water systems are
achieving adequate level of inactivation at all times. This study focused on the use of aerobic spore forming bacteria (B. subtilis) as a surrogate for inactivation of C. parvum and G. muris with ozone. The inactivation data of B. subtilis spores and G. muris
cysts obtained in this study showed that B. subtilis spores can be used as a conservative surrogate to verify the removal efficiency of G. muris as they would overestimate CT requirement (over an order of magnitude) during the ozonation process. Comparison of survival
data of B. subtilis spores from this study with survival data of C. parvum in the literature showed that B. subtilis spores were less resistant at higher ozone CT. However, the relation between survivals of C. parvum oocysts and B. subtilis spores
can be expressed using multiple linear regression. Using inactivation data of B. subtilis spores, an approximately up to 2-log reduction of C. parvum by ozonation was verified. B. subtilis spores could be used as a simple and rapid surrogate for on-site disinfection process
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