Inactivation of Giardia Cysts by Ozone after Residual Disappearance

Abstract

Kinetic models for inactivation of microorganisms by chemical disinfectants have described the instantaneous rate of kill as a function of the instantaneous residual. Laboratory batch experiments were conducted exposing cysts of Giardia muris to low doses of dissolved ozone in water from Lake Audubon, ND, and Vancouver, BC. Viability was assessed by excystation. Substantial inactivation was found to continue following disappearance of ozone residual, indicating that the fundamental postulate of modeling chemical disinfection may not be universally applicable. The mechanism for this effect, the extent of applicability, and the alternative modeling frameworks needs further study. However, this finding, if generalizable, has significance particularly in treatment of wastewater for reuse, and may provide a pathway for achieving greater log removals while keeping disinfectant byproducts low.