KINETICS OF CHLORINE DECAY

Proper understanding, characterization, and prediction of water qualit y behavior in drinking water distribution systems are critical to ensu re meeting regulatory requirements and customer-oriented expectations. This article investigates the factors leading to loss of chlorine res idual in water distribution systems. Kinetic rate equations describing the decay of chlorine were developed, tested, and evaluated using dat a collected in field-sampling studies conducted at several water utili ty sites. Results indicated that chlorine decay in distribution system s can be characterized as a combination of first-order reactions in th e bulk liquid and first-order or zero-order mass transfer-limited reac tions at the pipe wall. Wall reaction kinetic constants were inversely proportional to pipe roughness coefficients. Wide variations in both bulk reaction constants and wall reaction constants were observed amon g the sites.