Chlorine decay and DBP formation under different flow regions in PVC and ductile iron pipes: Preliminary results on the role of flow velocity and radial mass transfer

摘要

A systematic experimental study was conducted using a pilot-scale drinking waterdistribution system simulator to quantify the effect of hydrodynamics, total organic carbon(TOC), initial disinfectant levels, and pipe materials on chlorine decay and disinfection byproduct(DBP) formation. The first phase of the experiments focused on the variables of flowrate and pipe materials and their effects on the formation of trihalomethanes (THMs) a primarycategory of DBPs in chlorinated drinking water. Different from previously reported bench-scaleinvestigations, this experimental study was to determine chlorine decay and DBP formationkinetics under simulated field conditions and to contrast the effects of new PVC and aged ductileiron pipe materials. In this paper, we report the experimental findings on the rate of THMformation under stagnant, laminar, transitional and turbulent conditions, and further attempt toaddress the effects of the pipe materials on the reaction kinetics.The results indicate that the second-order DBP formation model of Clark (1998) cansufficiently describe the variations in total trihalomethanes (TTHM) concentrations. Thedetermined reaction constants are smaller under stagnant and turbulent flows in the new PVCpipes than the aged ductile iron pipe. The latter has a high rate of DBP formation accompanyingwith rapid chlorine residual loss. It is suggested that these observed differences are a result ofthe mass-transfer enhanced wall demand in the aged ductile iron pipe. Implications for rechlorinationin the distribution network operations are discussed.