Chlorine dioxide, cryptosporidium, and disinfection by-product formation

This paper briefly summarizes a study reported elsewhere in which the inactivation kinetics of Crytosporidium parvum using CIO2 were examined using an MPN cell-culture infectivity assay. The results indicated that the kinetics were largely independent of three water matrices tested, however they were strongly influenced by the source of the oocyst isolates. CT values corresponding to 2-logs of inactivation varied more than 10-fold among oocysts obtained from 3 different laboratories. The most well-established of the inactivation databases was used to derive an inactivation vs. CT relationship. This relationship was then used as part of a case study aimed at investigating the required CIO2 doses and by-products associated with different levels of Giardia and Cryptosporidium control in a natural water (Grand River, Ontario, Canada, TOC = 5.5 mg/L. CIO2 was able to provide greater than 3-logs of Giardia inactivation under most conditions (varying pH and temperature) before exceeding current U.S. chlorite regulatory limits (1 mg/L), however Cryptosporidium inactivations of only up to approximately 0.2 to 0.3-logs (40% to 50%) could be provided while maintaining compliance, based on the preliminary (and arbitrary) inactivation kinetic model. Nevertheless, the predicted ability of CIO2 to provide some Cryptosporidium control indicates that it may serve productively as part of a multi-barrier approach for ensuring safe drinking water.