Combined chlorine dissipation: Pipe material, water quality, and hydraulic effects

Effects of water chemistry, temperature, pipe material, and hydraulic conditions on total chlorine dissipation were investigated using laboratory- and pilot-scale experiments. Chlorine demand in the bulk phase depends on water chemistry, and the bulk-phase dissipation constant (k(b)) generally increased with increasing dissolved organic carbon. A 10 C rise in temperature resulted in a threefold increase in kb. Pipe material significantly influenced total chlorine dissipation rates in the following order: galvanized iron > unlined cast iron > polyvinyl chloride (PVC) > lined cast iron. Total chlorine consumption predominantly occurred at the wall surface in small-diameter unlined cast-iron and galvanized-iron pipes and predominantly in the bulk phase for lined cast-iron and PVC pipes. The mass transfer coefficient (k(f)) and the overall dissipation constant (K) increased with increasing Reynolds numbers. The wall constant (k(W)) is an intrinsic pipe property and is therefore a true constant; an increase in k(W) with increasing Reynolds number was observed. However, this may be attributed to dynamic changes in particulate surface area associated with release of corrosion products from the pipe surface.