Variable Chlorine Decay Rate Modeling of the Matsapha Town Water Network Using EPANET Program

Abstract

A variable chlorine decay rate modeling of the Matsapha town water network was developed based on initial chlorine dosages. The model was adequately described by a second order rate function of the chlorine decay rate with respect to the initial chlorine dose applied. Simulations of chlorine residuals within the Matsapha water distribution network were run using the EPANET 2.0 program at different initial chlorine dosages and using the variable decay rate as described by the second order model. The measurement results indicated that the use of constant decay rate tended to underestimate chlorine residuals leading to potentially excess dosages with the associated chemical cost and side effects. The error between the two rate models varied between 0% and 15%. It is suggested that the use of water quality simulation programs such as EPANET be enhanced through the extension programs that accommodate variable rate modeling of chlorine residuals within distribution systems.

Effect of Dividing the Water Transmission Pipe Line in Modeling Residual Chlorine, Case Study: Isfahan Water Transmission Line

“…Different methods of disinfection is applied to preserve water quality [1][2][3]. The main reasons to disinfect the drinking water is due to pathogenic microorganisms entering through the drinking water distribution system [4,5]. The residual amount of the disinfectant during storage and distribution of drinking water is the most important factor to select the kind of disinfectant.…”

“…The required time for fast reactions is about 3 to 4 h [7]. Several studies are performed to investigate on the most suitable bulk decay coefficients [3][4][5]10,16]. The SR model is simulated by combined concentration of chlorine and other substances in the kinetic equations of decay.…”

“…where kf is the mass transfer coefficient (length divided by time), kw is the wall reaction rate coefficient (length divided by time) and D is the pipe's diameter [5,16,18,19]. The wall decay coefficient depends on characteristics of the distribution pipes such as diameter, age, roughness, pipe material and the volume of biofilm formed on the pipe surfaces [7,9,11].…”

“…EPANET is a series of modeling software package developed by the United States Environmental Protection Agency's (EPA) for the hydraulic and quality simulation of water distribution systems [2,3,5]. The water quality simulation in the EPANET2.0 is limited to only a single chemical species.…”

“…They proposed a new method for designing, installing and disinfection operation in water distribution systems by optimizing the amount of injected chlorine [17]. Tiruneh et al [5] found that second order kinetics for bulk decay calibration was more accurate than first order model in simulation of the Matsapha town water network. Applying first order model for simulating chlorine wall decay in EPANET s/w, the value of the wall coefficient by trial and error procedure was obtained 0.05 m d -1 [5].…”