BCDMH Disinfection for CSO

Effective disinfection of combined sewer overflows (CSOs) has been achieved using BCDMH, a bromine disinfectant. Over the last five years a total of six facilities have been constructed to provide rapid disinfection in metropolitan Tokyo. Results have been favorable prompting further expansion and use of this technique within Japan. BCDMH (1-bromo-3-chloro-5,5-dimethy lhydantoin) when dissolved in water produces hypobromic acid, an active biocide. This bromine compound is commonly used in industrial, spa and pool applications. It is comparable with NaCIO in terms of toxicity and disinfection and there are no halogen related derivatives prompting subsequent dehalogenation. BCDMH is superior to NaClO with regard to 1) reaction time, 2) degradation, 3) volumes required, 4) dosing rate; and 5) handling. The speed of reaction reduces the need for disinfectant contact tanks, a critical factor in land constrained Tokyo. Required retention time is 3 minutes or less compared to 15 minutes for NaClO. Performance data has shown that an injection rate of 2 – 7.5 mg/L (chlorine equivalent) reduces 103 – 106 CFU/mL of [h1]coli-form to less than the Japan standard value of 3,000 CFU/mL.[h2] Based on the testing completed in Japan, CSOs would be effectively disinfected to a 200 [h3]CFU/100 mL using a 6 mg/l (chlorine equivalent). Performance data, technical designs, system integration and operational processes will be presented.