AWWA WQTC60733

The objective of this study was to characterize the reactivity of disinfection byproduct (DBP) precursors occurring in a water distribution system (DS) and to evaluate the global effect of residence time on modified organic matter (MOM) reactivity. The paper discusses a case study of Quebec City's (Canada) water utility distribution system. Four sampling points were selected for data collection. The first was located before post-chlorination within the plant. This point provided information about the initial conditions of MOM. The three other points were located along distribution pipes, i.e. at the beginning, the middle and the extremity, with approximate residence times of water of 3, 12 and 15 hours, respectively. The location of these points allowed evaluation of the impact of residence time on the formation of DBPs and changes in MOM throughout the pipes. Four sampling campaigns were conducted at each point. In order to characterize MOM reactivity, samples were first concentrated by reverse osmosis until a volume concentration factor of 10 was reached. Fouling organic matter remaining on the membrane was recovered by an alkaline solution wash. The retentate and the alkaline solution were considered as two distinct fractions. A portion of the retentate was fractionated with two non-ionic macroporous resins. The methodology developed for the fractionation was inspired from the method used by L. Labouyrie-Rouiller and the adsorption of the organic matter was conducted following manufacturer recommendations. MOM reactivity was investigated using experimental chlorination tests on fractionated and non-fractionated samples under controlled conditions of pH, temperature and chlorine dose. Measurements of pH, conductivity, turbidity, total organic carbon (TOC), UV-absorbance and temperature were carried out for all samples collected and all produced fractions. Includes 14 references, figures.