Determination of chlorine decay and chlorine-fluoride diffusion coefficients in water distribution networks

Drinking water is traditionally disinfected at the treatment plant before it is fed into the water distribution network. There are different methods to disinfect drinking water. Among them chlorination is the most commonly used disinfection method. The decay of chlorine added into drinking water is related to the age and type of the pipe. Chlorine decay that occurs at the inner surface of a pipe due to biofilm accumulation is called wall decay. The other form of decay, that is bulk decay, is due to flow of water in the pipe causing residence time for water. Especially in North American countries, fluoride is added into drinking water to prevent tooth decay. Unlike chlorine, fluoride does not decay as the concentration moves some distance in the network. Hence fluoride is called as a tracer, it may be also used in the calibration of pipe networks. In the first section of this thesis, chlorine decay constant rates (bulk decay constant) corresponding to different Reynolds number were determined under constant temperatures. For this purpose, high density polietilen (HDPE) pipe was used. Due to the use of a new HDPE vii pipe and non-existence of biofilm layer wall decay is ignored in the experimental calculations. In the second section, the aim was to find apparent diffusivity and dispersion coefficients of both chlorine and fluoride lacking in the literature. Chlorine and fluoride were injected into the experimental pipe section under different flow regimes ranging from laminar to transitional (Re=0-20000). Observed and recorded results were correlated with the numerical solution of the two dimensional convective-dispersive equation. By comparing the results of the experiments and numerical simulations, apparent diffusivity coefficients for both chlorine and fluoride corresponding to different Reynolds number were derived. Using this information Taylor dispersion coefficients were derived for both chlorine and fluoride by using the analytical solution of the one dimensional convectivedispersive equation.