Residual chlorine management based on quantitative estimation of chlorine consumption by inner wall surfaces of distribution pipes

Abstract

In real residual chlorine management practices, a simple criterion is required for evaluating chlorine consumption by inner wall surfaces of water distribution pipes. The amount of chlorine consumed by 1 m2 of the inner wall surface of a pipe per hour (J-value) can be used for this purpose. To estimate the J-value for a pipe, a zero-order rate equation was adopted for chlorine reduction caused by a pipe wall, based on laboratory experimental results. The J-value was closely related to characteristics of the pipe material. The J-value for old unlined metallic pipes was extremely large (J > 18 mg m−2 h−1), whereas that for plastic polymer pipes was very small (J < 0.08 mg m−2 h−1). The J-value for cement mortar lined pipes increased exponentially with increasing water temperature. This paper proposes an effective method on the basis of J-value for residual chlorine management practices. First, this method is used to identify those pipes which consume relatively more chlorine than other pipes. Maximum allowable residence time (MART), within which the required minimum chlorine concentration can be maintained, can also be estimated by this method. MART is useful to determine necessary and sufficient measures for shortening water residence time in identified pipes.