AWWA WQTC56981

Spores of the non-pathogenic aerobic bacterium Bacillus subtilis have frequently been proposed as indicators for assessing the Cryptosporidium parvum inactivation in ozone contactors. The objective of this study was to demonstrate how a cultured strain of spores can be used to measure the hydrodynamic performance of ozone contactors through challenge experiments. Ozone inactivation of cultured Bacillus subtilis ATCC 6633 spores was measured and compared to inactivation of C. parvum determined in a earlier published study. A kinetic model based on a multi-target mechanism was found to adequately describe spore inactivation at temperatures of 3C, 12C and 22C, and at pH 6 and 8. Although the B. subtilis spores shared similar resistance to ozone as C. parvum oocysts, important differences between the respective inactivation characteristics were observed. The potential use of the spores for measuring hydrodynamic performance of ozone contactors was evaluated by simulation. Kinetic models of microorganism inactivation were inserted into a CFSTR-in-series mixing model of hypothetical back-mixed ozone contactors and inactivation was computed using segregated flow analysis. The analysis revealed that for certain ozonation conditions, the spores are considerably more sensitive to the effects of back-mixing than are C. parvum oocysts. B. subtilis spores may therefore serve as conservative indicators of the hydrodynamic performance of existing ozone contacting systems or as tools to study and optimize the design of ozone contactors in drinking water treatment. Includes 16 references, tables, figures.