Development of a mathematical model of Cryptosporidium inactivation by ozonation

Abstract

A new mathematical model was developed to express the processes of Cryptosporidium inactivation by ozonation. In this model, five different stages were considered as state variables of Cryptosporidium oocysts for accurate expression of the inactivation. ATP, in vitro excystation and DAPI/PI permeability assays were used to describe the oocyst amounts of different stages. Some reaction constants were estimated by the structure components of oocysts or by the stoichiometry of reactions, while the others were by the oocysts population changes in ozonation. The calculated values of this model were well consistent with experimental inactivation data. Three-log inactivation of sporozoites required about 0.04 mgO3 per unit oocyst (mgC) from the simulation results. Before ozone reacts with sporozoites, more ozone was consumed to oxidize other parts of oocysts and DOC produced. The main path of inactivation of oocysts by ozonation was estimated to be P1 (intact oocysts)→P2 (oocysts with damaged outer oocyst wall)→P4 (oocysts without excystation function)→P5 (oocysts with inactivated sporozoites and no excystation function) from experimental and simulated results.