Reactions between aqueous chlorine and ammonia: a predictive model.

• Online Access: http://hdl.handle.net/2047/d10017227

The Unified Plus Model was proposed in this study as a predictive tool for reactions between aqueous chlorine and ammonia. Based on the Unified Model (Jafvert 1985), the reaction scheme was changed by removal of Reaction 10 and inclusion of trichloramine hydrolysis reaction. The rate coefficient for monochloramine formation was re-evaluated to incorporate the latest reported values (Qiang and Adams 2004). To ensure the user-friendly nature of a mechanistic based model, Visual Basic for Application was used as the programming language and Excel was used as the interface. The Unified Plus Model was calibrated and validated to the following ranges of initial conditions, pH 6.5 - 9.5, temperature 4 - 30°C, total carbonate buffer concentration 9x10-4 - 1x10-2 M, and initial chlorine to ammonia molar ratio (Cl2/N)0 0.5 to 2.0. It can reasonably predict chloramine species concentrations in synthetic solution using the initial conditions within the above ranges. The potential applications of the Unified Plus Model were demonstrated through case studies. With some moderate modifications, the model can be used to generate breakpoint curves, which can demonstrate the effect of open system as well as degree of mixing on the speciation of chloramine species. This model was also used to successfully reproduce the observed breakpoint phenomenon during switching between monochloramine and chlorine. An attempt was made to incorporate the effect of NOM (Duirk, 2005) and to simulate disinfectant loss in a full scale system.