Research On Booster Disinfection In Water Distribution Network And Its Application In Southern China Area

Water distribution network system plays an important role in urban water cycle. Various kinds of reactions will occur during the transportation of drinking water in the network systems which makes the water quality deteriorate before used. In the process of water distribution, to maintain protective levels of residual chlorine can protect drinking water against bacterial growth and then ensure water supply security.On account of its high disinfection efficiency, easy using and low cost, aqueous chlorine has been widely used in disinfection process. However, there are some problems in conventional one stage chlorination, such as uneven distribution of chlorine concentrations, higher overall consumption of chlorine and more productions of disinfectant by-products(DBPs), while booster disinfection does well in them. Therefore, it is significant to investigate the kinetics of chlorine decay and water quality variation with adoption of booster disinfection.Compared with jar test and static pipeline experiment, dynamic pipeline experiment is much closer to the network systems since it can simulate how water quality changes with different water age or in diverse operational conditions. I n this research, chlorine decay rule and water quality variation under booster conditions were discussed through dynamic pipeline experiments using water after filtration or chlorination in B Waterworks. Results showed lower chlorine decay rates after rechlorination with sodium hypochlorite. Under the same disinfectant dosage, booster disinfection maintained a relatively stable high residual concentration for a longer time and produced less chloroform in upstream node of the network system. Rechlorination conducted at a lower residual chlorine concentration was beneficial to reduce the productions of chloroform. Furthermore, in PE pipe chlorine decayed much slower and the productions of chloroform is less than in steel pipe with cement mortar lining.Using single disinfectant, there are limitations. In this paper, experiments were done to investigate whether the combination of chlorine and chlorine dioxide maintains their advantages and decrease their disadvantages. Results showed that the composite disinfectant contains about 60% chlorine dioxide which is generated by chlorine dioxide generator fed with hydrochloric acid and sodium chlorate. Dosage of the composite disinfectant had positive correlation with the concentration of chlorate. Meanwhile, the disinfectant could drop the p H of water. Chlorine decay data was analyzed through exponentially fitted method and results showed that decay rate of the composite disinfectant is slower than that of sodium hypochlorite. Furthermore, the composite disinfectant could decrease the content of organic matter. As a result, less chloroform would form.Biofilm biomass on dynamic pipelines of circular network simulator is different from it on pipelines of urban network systems for the different hydraulic conditions between them. In order to build the relationship between them, chlorine decay rate k’ and the rate of bulk water kb’ of corresponding straight pipeline with the same diameter were calculated on the basis of distance proportionality coefficient α and the first order chlorine decay model built in chapter 3. Diameter was mainly considered and chlorine consumption per unit contact area was assumed equal. Then relationship of chlorine decay rates among pipes with different diameters was built using contact rate β. After all, chlorine decay forecast model of network systems based on dynamic experiment through circular network simulator was proposed. Because of the removal of a waterworks, the water supply system of N city has changed and it is selected as an example in this research. The model proposed was applied to simulate chlorine decay under single dose or booster disinfection conditions. Results showed that booster disinfection provided a more even distribution of disinfectant concentrations, dropped the total dosage of chlorine while satisfying residual chlorine demand of terminal nodes in the network system and produced less chloroform.