Role of typical pipes in disinfection chemistry within drinking water distribution system

Deep insight into the forces driving chloramine decay in different pipe materials is the key to taking sound action to cope with pipe water quality deterioration. By using the newly developed RTCDM (refined Total Chloramine Decay Model) and pipe section reactor, the role of four typical pipes in disinfection chemistry was qualitatively and quantitatively compared, and the mechanism of pipe wall mediated chloramine decay was further described. As for the four typical pipes studied, the characteristics of deteriorating water quality, especially for accelerating total chloramine decay was in the order of cast iron pipe > steel pipe > cement lined ductile iron pipe > polypropylene-random pipe. Cast iron pipes, cement-lined ductile iron pipes, and steel pipes of long service age are characterized by one or two driving forces leading to TCR decay. Aged cast iron pipes could take up chloramine by Fe(0) and microbes (especially nitrifiers) spreading over the inner wall. Aged steel pipe is characterized by aggressive electrochemical corrosion and weak nitrification. Lime and gypsum leaching is the main cause, and nitrification/denitrification may also occur in aged cement-lined ductile iron pipe. Polypropylene-random pipes have a minimum effect on disinfection chemistry. This knowledge is of value in speculating the reasons leading to TCR loss in the full scale distribution system.