Modeling chlorine inactivation requirements of Cryptosporidium parvum oocysts

Chlorine and monochloramine inactivation of Cryptosporidium parvum oocysts was studied using bench-scale experiments in 0.05-M phosphate buffer at pH 6 and 8 at 22 degrees C. Animal infectivity using neonatal CD-1 mice was used as the criterion for oocyst viability. Inactivation data were fitted to a robust kinetic model, the incomplete gamma Hom (I.g.H.) which can account for first-order disinfectant decomposition. For chloramination a two-step disinfection approach was evaluated in which chlorine species were applied sequentially with free chlorine followed by ammonium chloride and preformed monochloramine (if necessary). Increasing levels of free chlorine pretreatment were shown to reduce the subsequent monochloramine concentration and/or contact time required for a given level of inactivation thereby demonstrating synergism. Incomplete gamma Hom models were used to generate design graphs that can aid engineers in establishing disinfection requirements for controlling Cryptosporidium parvum in drinking water.