Date of Award

Fall 1995

Project Type


Program or Major


Degree Name

Doctor of Philosophy

First Advisor

Aaron Margolin


Safe supplies of drinking water free of pathogenic agents such as viruses and protozoa are essential for humankind. The evaluation of current treatment practices for the removal of pathogens has become increasingly important with the occurrence of waterborne disease outbreaks. Shortcomings associated with chlorine have prompted the need to assess alternative disinfectants.

The overall objective of this research is to compare chlorine and chlorine dioxide as disinfectants for surface waters using Giardia muris cysts, bacteriophage MS2, total and fecal coliforms, and heterotrophic bacteria. Concentration x time (CT) values for the inactivation of Giardia muris cysts and MS2 bacteriophage as a function of pH and temperature by chlorine and chlorine dioxide at the bench and pilot scale are established.

Results indicate that chlorine dioxide is more effective against G. muris and MS2 than chlorine at the bench scale. Chlorine dioxide is more virucidal at pH 9.0 than at 6.0 and 7.0 and chlorine at all pH values tested. Chlorine, however, is more virucidal at pH 6.0 than at higher pH values. For both disinfectants, G. muris log reductions are not significantly different among any of the pH values tested. The effect of temperature on inactivation rates at the bench scale was inconclusive.

Pilot studies indicate chlorine dioxide is not as effective as chlorine in inactivating G. muris and MS2. However, the variation and small number of data points limits the statistical power of analysis of pilot results.

Differences between bench and pilot scale studies for the log reduction of both organisms by chlorine and chlorine dioxide are observed. Results indicate that G. muris cysts are approximately 30 times more resistant than MS2 to chlorine and 45 times more resistant to chlorine dioxide. Low levels of turbidity, total and fecal coliforms, and heterotrophic bacteria do not affect the disinfectants' ability to inactivate G. muris and MS2.

Results of this study indicate that chlorine dioxide exhibits strong disinfecting capabilities. It should be considered as a viable alternative to chlorine.