Disinfection of Bacillus subtilis spores with chlorine dioxide: a bench-scale and pilot-scale study

Chlorine dioxide (ClO2) inactivation of Bacillus subtilis ATCC 19659 spores was examined at pilot-scale during periods representative of winter and summer temperature extremes at the Britannia Water Treatment Plant in Ottawa, Canada. In addition, bench-scale experiments using the same source water (Ottawa River, Ontario, Canada), as well as buffered and unbuffered laboratory waters were conducted using B. subtilis spores. Bench-scale inactivation of B. subtilis spores by ClO2 was similar to reported values for Cryptosporidium parvum (both organisms being more resistant to ClO2 than Giardia lamblia), suggesting the possibility that these spores may be used as potential indicators for protozoan parasites. Additionally, spore inactivation was observed to be influenced by pH in laboratory (distilled deionised water) water but not in Ottawa River water. At pilot-scale, spore inactivation was influenced by water temperature: a ClO2 dose of 2.5 mg/L resulted in a spore inactivation of approximately 2.0 log10 and 0.5 log10 at water temperatures of 23.2d egrees C and 5.2 degrees C, respectively. Chlorite concentrations remained below both the US EPA maximum contaminant level of 1.0 mg/L and the maximum contaminant level goal of 0.8 mg/L for up to 2.0log10 B. subtilis inactivation.