Abstract
As a part of its "Safe, Better Tasting Tap Water" project, Tokyo Waterworks is installing additional chlorine injection (rechlorination) equipment at the water supply stations in order to stabilize and reduce the residual chlorine concentration in the entire service area by lowering the amount of chlorine injected at the purification plants. To effectively install the rechlorination equipment, the residual chlorine concentration prediction formula has been applied with time, water temperature, organic substance concentration (TOC) as the independent variables. Following certain adjustments to the prediction formula to take into consideration the decomposition of chlorine in the water supply station service reservoirs and in the transmission and distribution pipelines, the factors that caused the calculated concentration of residual chlorine to be higher than the actual concentration are now accounted for in the adjusted formula and the calculated values and actual values are closely aligned. Through the adjusted formula, it was determined that twelve water supply stations in the 23-ward area and seven in Tama area require rechlorination facilities given the reduced residual chlorine concentration at the purification plant outlets. As a result of this research, all necessary procedures are taking place to install the required equipment.
