Chlorine Reactivity with Organic Matter: A Modelling Approach for Surface Waters in Portugal and Angola

Abstract

Water quality is an essential requirement for human consumption. One of the key quality criteria is the absence of bacterial contamination, necessitating disinfection as the final step in water treatment, which is commonly achieved through chlorination. During chlorination, chlorine is consumed through the oxidation of the organic compounds present in water. This study focused on examining chlorine consumption in raw water from the Bengo River (Angola) and water at the outlet of the Lever Water Treatment Plant (Portugal). Specifically, the decay kinetics of chlorine in water samples were investigated through a series of experiments. In the first series, the chlorine concentration was varied while maintaining a constant level of organic matter (expressed as oxidability using KMnO₄) at temperatures of 25 and 35°C. In the second series, the chlorine concentration was held constant while the oxidability varied. Various kinetic models have been applied to the experimental data to describe the decay of chlorine and organic matter. The parallel first-order model yielded the most satisfactory representation of chlorine consumption kinetics.