Modelling drinking water chlorination at the Breakpoint: II. Calculation of the chlorine and chloramine concentrations along municipal pipe

Abstract

A B S T R A C TThis study is focused on the determination of added chlorine dose in low ammoniacal concentration contained in distribution pipe of drinking water. The chlorine concentration in disinfected water varies between events of lack and excess that must be regularly controlled. The chlorine transport from the inlet to the outlet of pipe is carried out in turbulent flow where the phenomena of diffusion and convection are in charge to convey chlorine and chloramines formed along the polyvinylchloride pipe. The chlorine decay is principally due to ammonia consumption in the water bulk. The chlorine demand serves to generate inorganic chloramines and the formation of an uncertain intermediate, which helps to destruct them, and the reactions series of formation-destruction are referring to Breakpoint chlorination. The set of presented reactions at Breakpoint chlorination are not clear and the observed rate constants are not similar in the researchers found in the literature. Then, their choices are not easy because they cause large differences between the experimental profiles of disinfectants concentrations taken from literature and the predicted profiles of disinfectant concentrations investigated in the present paper. The set of differential equations are resolved simultaneously by the method of finite differences. Therefore the concentrations of free residual chlorine, ammonia, monochloramine, dichloramine, trichloramine, nitrogen hydroxide and total chlorine are calculated at different points constituted the municipal pipe.

Review of chloramine decay models in drinking water system

“…Environmental Science: Water Research & Technology Critical review process. 9,10,12,18,19,24 The earlier model was chloramine autodecomposition model developed by Jafvert and Valentine. 18 Their model consisted of several reactions' schemes including hydrolysis, redox, equilibrium and disproportionation reactions.…”

“…Driss et al 9 proposed a numerical method to predict the chlorine and chloramine residual concentrations at various points in the distribution system. The model is based on a set of reactions obtained from previous models that occurred at the breakpoint condition or in low ammoniacal water.…”

“…The breakpoint reactions can be affected by many factors including pH, temperature, initial molar ratio and contact time. 9,80 The model considers the flow regime as well, that largely affect the mass transport in pipes. Under turbulent flow condition, a comparatively better match with the observed data was evident.…”

“…1,[5][6][7][8] Historically, the chlorinated disinfection process has been successful in limiting bacterial and viral contamination. 5,9 However, a major drawback of chlorinated disinfectants is that they are highly reactive to organic and inorganic compounds in water and form disinfection by-products (DBPs). [10][11][12] Some of these DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs) have been suspected to cause birth defects, cancer and other long term health threats.…”