The Dynamic Model Of Trihalomethanes Based On The Chlorine Decay In The Water Distribution Systems

After chlorine is put into the water as a disinfectant, it will keeping decaying, which will lead not to meet the requirement of chlorine remained at the end of the water distribution system. On the other hand, chlorine will react with the organics in the water and produce some poisonous byproducts, such as trihalomethanes(THMs). Although much work has been carried out to solve this issue, an efficient solution has not been found due to the difficulty of site sampling, the gap between site circumstances and lab experiments and limited research method. Water quality research could be done by the establishment of Zhejiang University water distribution simulation platform. Based on this platform, this thesis describes the chlorine decay, the production of trihalomethanes and the dynamic model of trihalomethanes based on chlorine decay in the water distribution systems.Firstly, we describe the relationship between the chlorine decay and the production of trihalomethanes theoretically, which further result in the dynamic model for trihalomethanes based on chlorine decay in the bulk water. Meanwhile, combined with C programming, orthogonal experiments are set up to get the optimized parameters of the improved model, whose accuracy is verified.Secondly, by lab experiments, this model's reaction degree was decide m=n=1, compared with Cl2 and the organics. Besides, the quantitative relationship between THMFP (Trihalomethanes Formation Potential)and TOC (Total Organic Carbon) is set up, which significantly reduces the burden for model establishment. Up till this stage, this model has been fully approached, along with two additional experiments to verify this reliability and accuracy.Thirdly, the loop D of water distribution system simulation platform, which is made by the mostly used material-cast iron, is chosen as the experimental loop. Based on theory and experiment, the chlorine decay model for water distribution systems is improved compared with traditional methods, which only takes laminar flow, ruling out states, into account. The result indicates that models considering both the turbulent flow and laminar flow performs better than ones only considering laminar flow, and the traditional multi-factor regression model.After obtaining the revised chlorine decay model for water distribution system, a dynamic model for trihalomethanes based on chlorine decay model is achieved by theory analysis and experiment approaches. Results indicate that this model fits better than traditional multi-factor regression model.Finally, taking the practical facts that water distribution system is mostly built in combination of several pipe materials into consideration, two set of multi-material experiments were carried out, i.e. loop B/C/D under same experimental conditions. The results show that the stainless pipe performs with greatest decay of free chlorine, iron comes second, and PE comes last. In the view of production of trihalomethanes, PE produces more than the others, iron comes second and the stainless steel comes last. The disparity of the trihalomethanes formation between these materials results from their decay rate for free chlorine, and is scarcely related with its mechanism of production.