Controlling bromate formation

A pilot-scale study, based on a fractional factorial experimental design, w as performed to evaluate the indirect impact of preozonation (0-1.5 mg/L) a nd/or the addition of powdered activated carbon (PAC) (0-20 mg/L), and the direct impact of intermediate ozone (O-3) dose (1.2-3.0 mg/L), pH (6.0-7.5) , and hydraulic residence time (HRT-12-18 min) on bromate (BrO3-) formation . Under the conditions of this study, neither preozonation nor PAC addition had a significant impact on BrO3- formation observed at the outlet of the pilot contactor. The most influential parameter was pH, followed by interme diate O-3 dose. A cross-effect (interaction between pH and intermediate O-3 dose) was also statistically significant. Consequently, the impact of pH d epression on BrO3-formation was shown to be O-3-dose-dependent. During thes e experiments, the BrO3- standard of 10 mug/L was achieved with O-3 doses o f < 1.6 mg/L and a pH of < 6.3. These conditions were consistent with 2-log -but not 3-log-inactivation of Cryptosporidium.