Use of Enhanced Coagulation to Reduce DBPs

The Stage-1 Disinfectants/Disinfection By-Products (D/DBP) Rule was promulgated in December, 1998. This regulation establishes maximum residual disinfectant levels (MRDLs) for several disinfectants, as well as new or revised maximum contaminant levels (MCLs) for certain DBPs: chlorinated organic DBPs, such as THMs and HAAs, as well as inorganic DBPs. such as bromate and chlorite. Because naturally occurring organic matter (NOM) reacts with chlorine to form DBPs, the D/DBP Rule includes a treatment technique for improving NOM removal. Utilities must achieve a certain level of NOM, or disinfection by-product precursors (DBPPs) removal bv what is termed `enhanced' coagu1ation. The requirements of this regulation (i.e., the MCLs, MRDLs, and enhanced treatment) must be met by both large and small-sized Subpart H systems that use conventional treatment. Many large utilities, especially those which participated in the Information Collection Rule, are already meeting the Stage-1 MCLs for DBPs and the TOC removal requirements of enhanced treatment, or are in the process of making modifications to treatment to achieve compliance. Smaller-sized utilities, however, are typically presented with more challenges to achieving compliance. This paper focuses on DBPP removal by enhanced coagulation, with an emphasis on the challenges faced by smaller utilities, and the tools available to them for complying with the D/DBP Rule. A case study is presented to illustrate the traditional approach to determining enhanced conditions, and the impact of this regulation on small systems. A separate discussion is also provided to introduce an emerging technology for improving precursor removal. This technology is magnetized ion exchange, and it is an adsorption process that can be used by small systems needing to reduce precursors prior to disinfection.