Developing a Model for Disinfection By-Products in a Water Distribution System

Abstract

The characteristics of disinfection by-products (DBPs) formation in the distribution system of Hiroshima City were investigated. Then a model was developed for predicting DBPs based on the formation kinetics. In previous studies, many factors, such as water temperature, pH, amount of chlorine residual (Cl2), type and amount of organic substances, and residence time were confirmed to affect DBP formation experimentally. These factors, except for Cl2 concentration, were observed to have a significant influence on DBP formation in the real distribution system. However, there was not a distinct relationship between DBPs and Cl2 concentrations at the sampling location using a reaction time of over 30 hr. We attempt to predict DBPs in the distribution system from considerations of the above DBP formation kinetics that follow; DBPs＝DBPs-eq×(1−exp(−k×(t＋c))) Here, DBPs-eq is the DBP concentration at equilibrium, k is the parameter of the DBP formation rate after the effluent is in the distribution reservoir (after approximately 10 hr), t is the residence time in the water distribution system, and c is the parameter of the residence time based on the DBP formation pattern in the distribution system. The equation with the input variables of water temperature and residence time was developed from the relationship between the coefficients in the equation and the factors mentioned above. The ratios of the predicted DBP concentrations to the observed DBP concentrations in the case of dichloroacetic acid and trichloroacetic acid were 0.79 (0.60-1.23) and 0.82 (0.73-1.04), respectively. The model is helpful for managing the DBPs in water distribution systems.