AWWA ACE54407

With the inclusion of bromate as a regulated parameter, the Southern Nevada Water System (SNWS) has undertaken a pilot testing program to verify the bromate formation at 2-log Cryptosporidium inactivation and to investigate possible bromate mitigation techniques and its effect on biologically activated filtration. The first 3 months of the pilot evaluated three bromate mitigation techniques, the addition of a small amount of prechlorine, the addition of a small amount of preammonia, and the combination of prechlorine and preammonia. Results show bromate formation would likely exceed the proposed MCL of 10 ppb when ozone was added to produce a 2-log Crypto inactivation and no mitigation technique was used. Bromate formation could be reduced without a mitigation technique by lowering the inactivation to approximately 0.75-log to meet the project goal of 5 ppb and to approximately 1.0-log to meet the MCL. The addition of a small amount of prechlorine did not significantly reduce bromate formation when compared to no mitigation technique. However, preammonia addition and the combination of prechlorine and preammonia addition did significantly reduce bromate formation to 5 ppb at 2-log Crypto inactivation. Although a dose of 0.5 mg/L of ammonia alone was required to meet the bromate goal, adding 0.5 mg/L of prechlorine followed by ammonia allowed the ammonia dose to be reduced to 0.1 mg/L and still meet the 5 ppb goal. Includes 2 references, tables, figures.