Purchasing and selling treated water as a product is common place in the water industry. One practice involves the wholesaler of the treated water and the wholesale purchaser of the commodity. The wholesale purchaser, commonly referred to as the consecutive system (CS), in turn distributes water to retail customers. The public water system (PWS) that treats source water and then sells it to a wholesale purchaser is defined as the wholesale system (WS).

Water wholesalers and consecutive systems (CS) are responsible for serving approximately one-third of the US water customers. Typically, long residence times are associated with a WS/CS approach. These long residence times can lead to high formation of disinfection by-products (DBPs) in the distribution system. The primary goal of this research was to develop and evaluate DBP control strategies (e.g. water age management or alternative treatment options) for CSs that can facilitate their compliance with the Stage 2 Disinfection By-product Rule (D/DBP Rule). Project objectives were to develop relationships between DBP formation and chlorine residuals and chlorine demands, conduct a bench-scale hold study (HS) to model the DBP concentrations in a distribution system using the simulated distribution system approach (SDS) that was developed by the United States Environmental Protection Agency (USEPA), and conduct field-scale DS and bench-scale HS sampling quarterly for eight utilities located within the continental United States. The SDS approach resulted in identifying system specific trends and indicated that HS data can in general be used as a conservative indicator of distribution system DBP formation. The study also evaluated the following alternative disinfection methods for controlling DBP formation: booster chlorination, conversion to chloramine, and chlorine dioxide as a primary disinfectant. This enabled a comparison of DBP formation under varied disinfection practices as alternative for reduction of DBP formation in both the WS and CS networks.

Relationships in both DSs and HSs were developed between the chlorine residual, chlorine demand and DBP formation in order to identify correlations between water age and chlorine demand with respect to DBP formation. Comparisons of HS data to DS data for the eight utilities lead to identifying relationships between water age, chlorine residuals, and chlorine demands with regard to TTHM and HAA5 formation. Results indicated that water age management will have a minor impact on DBP formation for high water age systems, with much of the DBP formation occurring within the first 24 hours. However, a strong relationship between the chlorine demand and TTHM formation was found in both the DS and HS samples indicating that HSs are effective at modeling DS TTHM formation. Booster chlorination showed to be an effective reduction strategy for low water age cases and conversion to chloramine illustrated a stop in formation of DBPs at the point of conversion. The use of chlorine dioxide, used as the primary disinfectant with chlorine used as the secondary disinfectant, proved effective in oxidizing DBP precursor compounds, thus minimizing DBP formation.