Mechanistic Modelling of Chlorine Decay in Reclaimed Water Containing Ammonia

Abstract

Keeping an effective disinfectant residual concentration in reclaimed water is still a challenge due to its high levels of ammonia and organic matter when compared with those in drinking water. Particularly, in reclaimed water containing ammonia, chloramines formation is expected. This paper presents a novel mechanistic chlorine decay model, integrating the reaction schemes of monochloramine auto-decomposition with a kinetic mechanism accounting for reactive chlorine species decay in the presence of organic matter. A parallel second order mechanism, where monochloramine reacts both with fast and slow organic matter reactive fractions, was identified as the most suitable and a successful calibration of the model was achieved. Further studies are being conducted to promote the ease of use of the model by correlating the model parameters with quality parameters related to the organic matrix of the waters.