The Relationship Between Pre-filter Chlorine Addition and Enhanced Disinfection Byproduct Formation

In this work, the issue of how pre-filter chlorination of drinking water causes an increase in disinfection byproduct (DBP) formation is examined. Chlorination and granular media filtration are two widely used practices in drinking water treatment. It is also common to apply chlorine ahead of the filters. However, this has been shown to elevate disinfection byproducts (DBP) levels. Experiments were performed at full- and bench-scale using filter influent and effluent from working filters and several anthracite/sand filter columns operated in parallel. The filter influent for the bench-scale experiments was clarified water from the Warner Water Treatment Plant operated by the Aquarion Water Company in Fairfield, Connecticut. In several filters, pre-filter chlorine was supplied to the clarified water influent feed line. The results of this work indicate that DBP precursor accumulates as particulate natural organic matter builds up on filter media over the course of a filter run. Contact with chlorine works to deplete the precursor present from the media surface and leads to subsequent reactions with chlorine, creating DBPs. This effect is eliminated by elimination of chlorine from the influent, where a build-up of NOM can be found on the filter media. 11