MODELING WATER-TREATMENT CHEMICAL DISINFECTION KINETICS

Various empirical and probabilistic kinetic inactivation models that c an be used to assist in the design and analysis of potable water disin fection systems were reviewed. Models were derived for both disinfecta nt demand-free and demand conditions. Ozone was used to inactivate het erotrophic plate count bacteria that were grown in natural water under low nutrient conditions and enumerated using R2A agar at 20 degrees C for 7 days. Experiments were conducted at 22 degrees C in 0.05 M (pH 6.9) phosphate buffer in bench-scale, batch 250 mL reactors. This disi nfection data set, characterized by tailing-off behavior, was used to assess Chick-Watson, Hem-type, Rational, Hom-Power law, and Selleck mo del fit to the observed logarithmic survival ratios. It was found that the Chick-Watson model did not adequately represent the ozone disinfe ction kinetics. A Hom-type model incorporating a first-order disappear ance term for ozone residual was found to best describe the observed i nactivation of heterotrophic plate count bacteria. Named the incomplet e gamma Hom model, it was found to be a robust kinetic model. The prop osed incomplete gamma Hom model can be used to generate simple design charts for a wide range of disinfectant types, organisms, and conditio ns, as an aid to the design of water disinfection systems.