To meet newly proposed bromate standards, ozone doses should be decreased, thus also decreasing the risk of renal cell cancer, but the risk of infection with Cryptosporidium parvum will increase at the same time. The present study was designed to evaluate and balance these two risks, using a probabilistic risk assessment, which involves calculating the disease burden, expressed in the number of disability adjusted life-years (DALY) as developed by Havelaar et al. In the case of Neuilly-sur-Marne ozone contactors, four ozone doses were studied at 5°C and at 22°C. Results showed a sharp decrease of the disease burden with the application of ozone, and then a slight increase as the ozone dose was increased. Minimal DALYs were obtained with ozone doses of 1.5 mg/L at 22°C and 2.5 mg/L at 5°C. Nevertheless, these two ozone doses do not comply with the 10 μg/L bromate standard, as an average of 12 at 5°C and 11 at 22°C are produced.

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