Bromochlorodimethylhydantoin as a Drinking Water Disinfectant: A Case Study in a Small Drinking Water System

While most drinking water treatment plants use traditional disinfectants such as chlorine or chloramine, we discovered a small plant that for several years had been using bromochlorodimethylhydantoin (BCDMH), a disinfectant typically used for spas. In this plant, serving ∼3400 residents, solid BCDMH tablets were dissolved in water and injected directly into the groundwater to control iron-reducing bacteria. While BCDMH hydrolyzes to form HOCl and HOBr as disinfectants, 5,5-dimethylhydantoin (DMH) is produced as a byproduct in stoichiometric amounts to the milligrams per liter levels of disinfectant applied. Due to concerns over high levels of DMH that could be released for human consumption, this chemical was quantified for the first time in drinking water and the well water feed, as well as a broad group of 51 chloro-, bromo-, and iodo-disinfection byproducts (DBPs) from five different classes. Nontarget analysis utilizing gas chromatography–high-resolution electron ionization mass spectrometry was also conducted to screen for other potential DBPs and contaminants. Results revealed 5.3 mg/L levels of DMH in the BCDMH-treated well and 24 μg/L in the finished drinking water (diluted by blending with chlorinated water from three other wells) as well as unique brominated DBPs, including brominated hydrocarbons.