AWWA ACE93173

Chlorine decay in distribution systems is created in part by the consumption of chlorine due to reaction at the pipe wall. Reactivity of the pipe wall is a function of pipe diameter, flow velocity, nature of the pipe material, amount and nature of deposits, etc. Pilot studies and field experiments have been performed to evaluate the influence of various parameters on the chlorine consumption due to reactions occurring at the liquid/solid interface. Results show that: the influence of the pipe wall in the overall chlorine consumption depends on the geometry of the pipes (surface/volume ratio) with an increasing diameter, the contribution of pipe water reactivity is reduced; hydrodynamic conditions affect the rate of chlorine decay - chlorine diffusional mass transfer toward the surface can be a limiting factor and in the case of laminar flow conditions, one observes a reducing of the rate of chlorine decay; and the chlorine concentration level is also involved in the rate of chlorine decay throughout the distribution network - the lower the chlorine concentration is, the higher the rate of chlorine consumption is. Results obtained from pilot and full scale experiments confirm that chlorine decay can be predicted according to apparent first order kinetics. These results also show that modelling in the distribution network needs to take into account numerous parameters. A more precise strategy of chlorination adapted to each configuration of material, water quality, hydraulic conditions, etc. will be possible after the integration of such results in the quality model.