Inactivation of bacillus subtilis spores and formation of bromate during ozonation

Inactivation of B. subtilis spores with ozone was investigated to assess the effect of pH and temperature, to compare the kinetics to those for the inactivation of C. parvum oocysts, to investigate bromate formation under 2-log inactivation conditions, and to assess the need for bromate control strategies. The rate of B. subtilis inactivation with ozone was independent of pH, decreased with temperature (activation energy of 42,100 J mol−1), and was consistent with the CT concept. B. subtilis was found to be a good indicator for C. parvum at 20–30°C, but at lower temperatures B. subtilis was inactivated more readily than C. parvum. Bromate formation increased as both pH and temperature increased. For water with an initial bromide concentration of 33 μg l−1, achieving 2-logs of inactivation, without exceeding the 10 μg l−1 bromate standard, was most difficult at 30°C for B. subtilis and at mid-range temperatures (10–20°C) for C. parvum. pH depression and ammonia addition were found to reduce bromate formation without affecting B. subtilis inactivation, and may be necessary for waters containing more than 50 μg l−1 bromide.