An Empirical Model for Bulk Chlorine Decay in Drinking Waters

The current chlorine decay models involve complex calculations, and they are impractical for rapid chlorine dose/decay product calculations. This problem limits their applicability to treatment systems. Previously, less attention was paid to developing empirically based bulk chlorine decay models for predicting chlorine decay pathways. In order to bridge this gap, we developed a chlorine decay model based on kinetic data. The model was calibrated using well-characterized humic substances to simulate the natural organic matter content in water. Subsequently, the decay model was utilized to make chlorine decay predictions in the water of the Greater Kandy Water Treatment Facility, Sri Lanka. The chlorine decay predictions are in accordance with model calculations on a short-time scale (less than 5 h). Accordingly, it was noted that the chlorine dose of 1.6 mg/L was found to be inadequate for maintaining the mandatory residual chlorine balance at 0.2 mg/L at distribution. Furthermore, the reported average total of trihalomethanes (TTHMs) below 20 μg/L leaves room to increase the initial chlorine dose.