Research On A Single Parameter Mathematical Model For Variable Chlorine Decay Rates In Water Distribution Systems

Excessive residual chlorine concentration in water supply pipe network will produce peculiar smell and disinfection by-products.Too low residual chlorine concentration is likely to cause secondary pollution and affect water quality safety.Therefore,monitoring and control of residual chlorine concentration is of great significance.Through the research and application of the residual chlorine attenuation model of the water supply pipe network,a more accurate water quality model is established to simulate the change of residual chlorine concentration during the operation of the water supply pipe network.The simulation results can provide a basis for the water quality safety management of the water supply pipe network.The first-level model of the bulk chlorine decay model is widely used in water quality simulation due to its simple calculation,few parameters and good fitting effect,but the accuracy of the bulk chlorine decay model still has a large room for improvement.In recent years,the idea of the variable decay reaction rate of residual chlorine has emerged and a lot of research has been carried out on this.Among them,the representative model is VRC which has the advantages of high accuracy and good reliability.However,the VRC model has too many parameters and complex structure.So,It can not be applied in water quality simulation of water supply network.Considering the advantages and disadvantages of the first-order model and the VRC model,a single-parameter variable reaction rate model(SPVRC model)for the chlorine decay of bulk water was proposed.In this model,the total reaction coefficient and chlorine reactant concentration are regarded as global variables,which are defined as the new reaction coefficient K.When the temperature is constant,K is only related to the concentration of chlorine reactants.The mathematical expression of K and chlorine reactants is established,and the attenuation of K is continuous and decreases gradually with time.K0 is only one parameter in this model.The relationship between SPVRC model parameters and temperature is established through the Arrhenius relationship,and the method of parameter calculation and model adjustment in the process of secondary chlorination and water mixing is proposed.Residual chlorine decay experiments were designed at different temperatures,secondary chlorine addition and water mixing.SPVRC model was used for fitting analysis of experimental data.The accuracy was evaluated through goodness of R2,SSE and RMSE.Compared to other residual chlorine decay model of bulk water,SPVRC modelhas more advantages in the following aspects:The consumption of chlorine reactant concentration is used to express the degree of progress of the reaction,and through the mathematical relationship to establish its relationship with the reaction rate coefficient.When the second chlorine addition occurs,,the consumption of chlorine concentration of reactants don't mutate.So,the calculation process is more simple.SPVRC model proposed the simulation method of residual chlorine decay in water mixing.Arrhenius was used to establish the relationship between model parameters and temperature,which improved the applicability of the model.The model contains only one parameter and can reflect the law of overall activity attenuation of chlorine reactants in the reaction process.The model are both simple and accurate,which lays a foundation for subsequent application in epanet.The initial chlorine concentration of the model uses the theoretical value calculated by adding chlorine to the volume of the water sample,rather than the optimal value calculated to improve the applicability of the model,which reduces the workload of the simulation process.