Evaluation of Ozone Effectivity on Removal of Giardia Cysts in Water

Introduction. Giardia, a flagellate protozoan, is a sort of intestinal parasite in human and animal bodies. Despite of man-to-man conventional method of transferring, this parasite is one of the main causes of water born diseases, and addition of conventional rates of chlorine to water cannot remove it. Ozone is an excellent disinfectant and can inactivate the most resistant microorganisms. It is used periodically to disinfect drinking water. The aim of this study is to evaluate the rate of ozone used for removal of giardia cysts in water.Material and Methods. This is an experimental study and corona discharge method is used to generate ozone. Giardia cysts were separated by concentration density slope with sucrose, counted 10 times with Thoma lam and then the mean was calculated. This solution, containing 120,000 cysts/lit, was ozonated in 5, 7 and 9 min with the density of 1.3 mg/lit in city water, distillated water and physiology serum. In another test, the effect of elapsed time on ressistance of giardia cyst was evaluated for a 6-day period, in the first, 3rd and the 6th day for various minutes of 1, 3, 5, 7 and 9 with the density of 2 mg/lit in the city water.Results. Durations of 5 and 7 minutes could not remove all of the cysts, but after ozonation for 9 minutes, all of the cysts were removed. When tests were performed in distillated water and physiology serum, all of the cysts were removed completely. In another test, all of the cysts were removed in the durations of 7 and 9 minutes of the first day, while in the third and the sixth day, the efficiency of cyst removal rate decrease in the 7 and 9 minutes and fresh cysts were observed.Conclusion. Distillated water and physiology serum caused disturbance in the test and resulted in incorrect data, so decolorized city water is used in this pilot study. As time elapsed, environmental conditions caused difficulties for cyst life continuing. Cyst's cell wall gets resistant and removal of all of giardia cysts with first day Ct is impossible.