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Abstract
Major waterborne cryptosporidiosis and giardiasis outbreaks associated with contaminated
drinking water have been linked to evidence of suboptimal treatment. Cryptosporidium
parvum oocysts are particularly more resistant than Giardia lamblia cysts to removal
and inactivation by conventional water treatment (coagulation, sedimentation, filtration
and chlorine disinfection); therefore, extensive research has been focused on the
optimization of treatment processes and application of new technologies to reduce
concentrations of viable/infectious oocysts to a level that prevents disease. The
majority of the data on the performance of treatment processes to remove cysts and
oocysts from drinking water have been obtained from pilot-tests, with a few studies
performed in full-scale conventional water treatment plants. These studies have demonstrated
that protozoan cyst removal throughout all stages of the conventional treatment is
largely influenced by the effectiveness of coagulation pretreatment, which along with
clarification constitutes the first treatment barrier against protozoan breakthrough.
Physical removal of waterborne Crytosporidium oocysts and Giardia cysts is ultimately
achieved by properly functioning conventional filters, providing that effective pretreatment
of the water is applied. Disinfection by chemical or physical methods is finally required
to inactivate/remove the infectious life stages of these organisms. The effectiveness
of conventional (chlorination) and alternative (chlorine dioxide, ozonation and ultra
violet [UV] irradiation) disinfection procedures for inactivation of Cryptosporidium
has been the focus of much research due to the recalcitrant nature of waterborne oocysts
to disinfectants. This paper provides technical information on conventional and alternative
drinking water treatment technologies for removal and inactivation of the protozoan
parasites Cryptosporidium and Giardia.