Date of Award
Although chlorination of ammonia and nitrite ions have been studied comprehensively, the kinetics of chlorination in water matrices containing ammonia in the presence of nitrite ion have not been fully understood. The coexistence of the two nitrogen compounds is a phenomenon most often encountered during biological nitrification of municipal wastewaters. The spatial variation of the nitrogen species generates unpredictable complications in the effectiveness of chlorination as the disinfection process. The focus of the research study was the examination of chlorine residual speciation and the fate of ionic nitrogen species, i.e. nitrite and nitrate ions, under various experimental conditions. The experimental matrix consisted on three initial ammonia concentrations (0.036 mM, 0.107 mM, and 0.214 mM) at pH levels of 6.0, 7.0, and 8.0. At each ammonia concentration, three chlorine to ammonia molar dose ratios (MDRs), and four nitrite ion to ammonia molar concentration ratios (NRDs) were tested. The results revealed instantaneous free chlorine partitioning between the nitrite ion and ammonia in all experimental conditions. As NDR increased, the fraction of chlorine combined with ammonia decreased, thus resulting in lower chlorine residual concentrations. The kinetic profiles of chlorine residuals and nitrite ion revealed that higher NDR contributed to rapid monochloramine decay and increase in dichloramine formation. The rise of reaction pH resulted in decrease of the immediate nitrite ion chlorination, while
dichloramine concentration decreased and monochloramine concentration increased at all tested experimental conditions.
The chlorination kinetics of ammonia in the presence of nitrite anion was modelled using KINTECUS, a software available free of charge through the internet. The results indicated that at pH 7.0, the nitrite ion and ammonia chlorination rate constants were higher than those observed at pH 6.0 and 8.0. As the pH increased, the rate constant of the reaction between nitrite ion and monochloramine decreased. Lastly, the rate constant of dichloramine formation increased as the pH increased in the chlorination of water matrices with varying concentration of nitrite ion and ammonia. These results have direct implications for the chlorination of water matrices containing varying concentrations of nitrite ion and ammonia such as effluent of the Biological Nitrogen Removal (BNR) process.
Estahbanati, Shirin, "Dynamics of Simultaneous Nitrite Ion and Ammonia Chlorination in Complex Water Quality Matrices and their Impact on Chlorine Residual Speciation during Disinfection" (2021). CUNY Academic Works.
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