Reviews  Chlorine Residual Models  DBP Models  DBP Correlations  Precursor & DBP Models
(See also: DBP Degradation, Chlorination Chemistry)
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Citation  Notes  Abstract 

Fisher, I., G. Kastl, and A. Sathasivan. 2012. A suitable model of combined effects of temperature and initial condition on chlorine bulk decay in water distribution systems. Water Research 46:32933303. 
2site 2nd order model  The tworeactant model meets basic suitability criteria, including accurate prediction of chlorine residual over hundreds of hours, commencing with chlorine concentration 04 mg/L. This model was augmented with an equation that increases the decay coefficients with temperature according to Arrhenius theory. The augmented model was calibrated against decaytest data sets to obtain a single invariant set of parameters for each water. Model estimates of chlorine residuals over time closely matched decaytest data, over the usual operating ranges of initial chlorine concentration (14 mg/L) and temperature (3.528 degrees C). When the augmented model was fitted to partial data sets, it also predicted the data reserved for validation very well, suggesting that this model can accurately predict the combined effect of initial chlorine concentration and temperature on chlorine bulk decay in distribution systems, using a single set of invariant parameters for a given source water. 
Kohpaei, A.J., and A. Sathasivan. 2011. Chlorine decay prediction in bulk water using the parallel second order model: An analytical solution development. Chemical Engineering Journal 171:232241. 
All distributed drinking water receives some form of disinfection and a minimum disinfectant residual should be maintained at the customer tap. The most popular disinfectant is chlorine. Chlorine reacts with compounds in water and hence decays. Description of chlorine decay is often difficult, due to a complex set of reactions and an initial fast reaction followed by a slower reaction. Before any attempt could be made to understand the decay characteristics in the distribution system, chlorine decay in bulk water has to be correctly described. The parallel second order reaction model was found to be one of the most suitable models for this purpose. However, widespread use of this model is hindered by its complexity, most importantly the nonexistence of an analytical solution. In this paper, an analytical solution for this model was developed by initially assuming that the ratio (alpha) of slow and fast reaction rate coefficients is small. The estimated parameters and the chlorine residuals predicted by the numerical analysis and the proposed solution were compared for the chlorine decay data sets obtained from the literature as well as laboratory analysis. The results showed that the proposed analytical solution was very accurate for the prediction of chlorine decay behaviour in all samples.  
Fisher, I., G. Kastl, A. Sathasivan, and V. Jegatheesan. 2011. Suitability of Chlorine Bulk Decay Models for Planning and Management of Water Distribution Systems. Critical Reviews in Environmental Science and Technology 41:18431882. 
Effective disinfection planning and management in large, complex water distribution systems requires an accurate network water quality model. This model should be based on reaction kinetics, which describes disinfectant loss from bulk water over time, within experimental error. Models in the literature were reviewed for their ability to meet this requirement in real networks. Essential features were identified as accuracy, simplicity, computational efficiency, and ability to describe consistently the effects of initial chlorine dose, temperature variation, and successive rechlorinations. A reaction scheme of two organic constituents reacting with free chlorine was found to be necessary and sufficient to provide the required features. Recent release of the multispecies extension (MSX) to EPANET and MWH Soft's H2OMap Water MSX network software enables users to implement this and other multiplereactant bulk decay models in real system simulations.  
Fisher, I., G. Kastl, and A. Sathasivan. 2011. Evaluation of suitable chlorine bulkdecay models for water distribution systems. Water Research 45:48964908. 
2site 2nd order model  The firstorder model is unsuitable due to inaccuracy and inability to represent rechlorination. Three potentially suitable, simple, reactant models were compared. The singlereactant model was found to be unsuitable, as it was inaccurate when restricted to using a single set of invariant parameters. The tworeactant model was more suitable than the variableratecoefficient model, although both models were accurate under the same restriction. The tworeactant model was then calibrated against datasets consisting of multiple decay tests for five distinctly different waters. It accurately predicted data reserved for validation over the chlorine concentration range of 06 mg/L, using a single set of invariant parameters, and is therefore the simplest, generally suitable model for simulating chlorine profiles in distribution system networks. 
Brown, D., J. Bridgeman, and J.R. West. 2011. Predicting chlorine decay and THM formation in water supply systems. Reviews in Environmental Science and BioTechnology 10:7999. 
Although numerous disinfection byproducts (DBPs) have been reported in the literature, only a small number have been addressed in either quantitative or health effects studies. The DBPs that have been quantified in drinking water are generally present at low to mid mu g/l levels or below. Approximately 50% of the total organic halide (TOX) formed during the chlorination of drinking water and more than 50% of the assimilable organic carbon (AOC) formed during ozonation of drinking water is still not accounted for and little is known about the potential toxicity of many of the vast number of DBPs present in drinking water. The presence of free chlorine is a prerequisite to THM formation. Therefore, a robust understanding of the mechanisms of both chlorine decay and THM formation are fundamental to the management of THMs in water supply systems. This paper presents a review of work undertaken to improve our understanding of these key phenomena and highlights areas of vulnerability in our knowledge and so recommends areas of future research.  
Clark, R.M., Y.J. Yang, C.A. Impellitteri, R.C. Haught, D.A. Schupp, S. Panguluri, and E.R. Krishnan. 2010. Chlorine fate and transport in distribution systems: Experimental and modeling studies. Journal American Water Works Association 102:144155. 
The purpose of this study was to address the loss of free chlorine in corroded metal and polyvinyl chloride (PVC) pipes subject to changes in velocity. The study demonstrated that in older unlined metal pipes, chlorine residuals disappear rapidly with increased velocity but remain stable in PVC pipe. It is clear from the experiments reported in this article that there are differences between the wall demand characteristics of unlined metallic and PVC pipe and that these differences have regulatory implications. The authors also found that although distribution system modeling is an important activity that should be maintained and even expanded, no model is perfect and utilities must maintain a carefully constructed calibration program when models are used.  
Jonkergouw, P.M.R., S.T. Khu, D.A. Savic, D. Zhong, X.Q. Hou, and H.B. Zhao. 2009. A Variable Rate Coefficient Chlorine Decay Model. Environmental Science & Technology 43:408414. 
Chlorine is the most widely used water disinfectant in the world. As a result, optimal chlorine usage is essential for both human and environmental health. Chlorine decay models can be used to predict residual concentrations in water distribution networks and optimize chlorine dosing. However, the coefficients of current chlorine decay models are often dependent on the loading conditions and are therefore impractical for daytoday water distribution network modeling purposes and chlorine dosing optimization studies. This study proposes and assesses a novel numerical chlorine decay model with four parameters that are independent of the loading conditions for a given water sample. The model is based on kinetic equations derived from the rate law for concurrent bimolecular second order reactions with chlorine and will be referred to as the variable rate coefficient (VRC) chlorine decay model. The performance of the proposed model is compared with another model reported in the literature, and the VRC model is also assessed for reliability with data sets that are omitted during model calibration. The VRC model is consistently found to be in agreement with the experimental data.  
Huang, J.J., and E.A. McBean. 2007. Using Bayesian statistics to estimate the coefficients of a twocomponent secondorder chlorine bulk decay model for a water distribution system. Water Research 41:287294. 
Most chlorine decay models for the bulk phase in a water distribution system consider only chlorine concentration and time. Clark first proposed a twocomponent secondorder chlorine decay model based on the concept of competing reacting substances. A corrected mathematical formulation is developed and, because the recent findings suggested that not all natural organic matter (NOM) is involved in the chlorine decay process, an additional parameter is introduced. A parameter assignment method employing Bayesian statistical analysis incorporating Monte Carlo Markov chain (MCMC) with Gibbs sampling to make inferences, is employed in the estimation of model parameters. Three parameters are estimated for the model, namely the ratio of chlorine to TOC, the chlorine reaction rate, and a fraction factor of TOC which represents the true amount of TOC involved in chlorine decay process. Water samples taken from Goderich in the summer of 2005, are used for estimating the parameters. (c) 2006 Elsevier Ltd. All rights reserved.  
Chowdhury, Z.K., L. Passantino, R.S. Summers, L. Work, N. Smith, L. Rossman, and J. Uber. 2006. Assessment of Chloramine and Chlorine Residual Decay in the Distribution System. AWWARF 

Hallam, N.B., F. Hua, J.R. West, C.F. Forster, and J. Simms. 2003. Bulk decay of chlorine in water distribution systems. Journal of Water Resources Planning and ManagementAsce 129:7881. 
Mathematical models of chlorine concentration in water distribution systems require the bulk decay coefficient to be quantified. The coefficient needs to be determined with respect to independent variables if models are to maintain their predictive capability as seasonal and water treatment operational changes occur. Reported herein are experiments undertaken to determine the functional dependence of the bulkfree, chlorine decay rate coefficient on total organic carbon concentration, initial chlorine concentration, temperature, and the number of rechlorinations. The resulting equation gives satisfactory results during annual cycles and the introduction of granular activated carbon treatment at a water treatment plant.  
Gang, D.C., T.E. Clevenger, and S.K. Banerji. 2003. Modeling Chlorine Decay in Surface Water. Journal of Environmental Informatics 1:2127. 
This paper presents a chlorine decay model based on the possible chlorine decay mechanisms. To evaluate this model, four raw surface and alum treated waters (Chester, Garden City, Maysville, and Lake Vandalia) were used. The chlorine residual at the end of the study period was maintained at the same concentration to avoid effects of chlorine concentration difference. Results show that this model predicts the chlorine residual extremely well, consistently yielding correlation coefficients greater than 0.98. Alum treatment substantially increased the fraction of rapidly reacting functional groups by 24% and decreased the specific chlorine demand (SCD) by an average of 14.4%. Therefore, alum coagulation processes may preferentially remove natural organic matter (NOM) having a slower reaction rate (with chlorine), higher specific chlorine demand, and higher chlorinated DBPs production.  
Powell, J.C., J.R. West, N.B. Hallam, C.F. Forster, and J. Simms. 2000. Performance of various kinetic models for chlorine decay. Journal of Water Resources Planning and ManagementAsce 126:1320. 
A number of computer packages have been developed for modeling chlorine decay in water distribution networks. However, there is uncertainty as to the kinetic model that they should use for the decay mechanism. This paper explores the performance of six different kinetic models for the decay of free chlorine in over 200 bulk water samples from a number of different sources. The paper also presents the results of surveying the longitudinal decay profile of free chlorine in two in situ pipe stretches. It concludes that, for network modeling purposes, it is generally reasonable to assume firstorder kinetics for bulk and overall decay. 
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Francis, R.A., Vanbriesen, J.M. and Small, M.J. (2010) Bayesian Statistical Modeling of Disinfection Byproduct (DBP) Bromine Incorporation in the ICR Database. Environmental Science & Technology 44(4), 12321239.  Statistical models are developed for bromine incorporation in the trihalomethane (THM),trihaloacetic acids (THAA), dihaloacetic acid (DHAA), and dihaloacetonitrile (DHAN) subclasses of disinfection byproducts (DBPs) using distribution system samples from plants applying only free chlorine as a primary or residual disinfectant in the Information Collection Rule OCR) database. The objective of this study is to characterize the effect of water quality conditions before, during, and posttreatment on distribution system bromine incorporation into DBP mixtures. Bayesian Markov Chain Monte Carlo (MCMC) methods are used to model individual DBP concentrations and estimate the coefficients of the linear models used to predict the bromine incorporation fraction for distribution system DBP mixtures in each of the four priority DBP classes. The bromine incorporation models achieve good agreement with the data. The most important predictors of bromine incorporation fraction across DBP classes are alkalinity, specific UV absorption (SUVA), and the bromide to total organic carbon ratio (Br:TOC) at the first point of chlorine addition. Free chlorine residual in the distribution system, distribution system residence time, distribution system pH, turbidity, and temperature only slightly influence bromine incorporation. The bromide to applied chlorine (Br:Cl) ratio is not a significant predictor of the bromine incorporation fraction (BIF) in any of the four classes studied. These results indicate that removal of natural organic matter and the location of chlorine addition are important treatment decisions that have substantial implications for bromine incorporation into disinfection byproduct in drinking waters. 
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Citation  Notes  Abstract 

Summers, R.S. and Chowdhury, Z.K. (2001) Water Treatment Plant Model, Version 2, User's Manual, p. 126, Center for Drinking Water Optimization.  Successor to the 1992 model  The basic modeling approach includes estimation of: (1) NOM removal by individual unit processes; (2) Disinfectant decay based upon demands exerted by NOM and other sources; and (3) DBP formation based upon water quality throughout the treatment plant and in the distribution system. The model simulates DBP formation under given treatment conditions and permits the user to evaluate the effects of changes in these conditions on the projected disinfectant decay and DBP formation. By using the model under different treatment scenarios, the user can gain an understanding of how the input variables affect disinfection and DBP formation. It must be stressed that the model is largely empirical in nature. 