The Combined Disinfectants' Influence On Water Quality In Different Pipes

Disinfection plays an important role in drinking water's quality and safety The traditional chlorine is well known for its simple operation and low cost, while by-products in disinfection process which can lead some serious problems cannot be ignored. Combined disinfectants, which can make full use of the single disinfectant advantages and reduce its disadvantages has a broad application prospect. In present study, three kinds of combined disinfectants as chlorine dioxide-chlorine, chlorine dioxide-chloramine and chlorine-chloramine and two kinds of pipe?the iron pipe and the PE pipe? were chosen to study combined disinfectants' influence on water quality in different pipes.The bulk water of the experiment was sampled from a waterworks' sand-filter's effluent in Changsha. The disinfectants were added in bulk water. Then the bulk water was, respectively transport into the iron pipe network and PE pipe network for static immersion and dynamic simulation experiments. The sampling was conducted at 1h,6h, 12 h, 24 h during the experiment The main water test?i.e. the beaker test? was also conducted for comparison. Results showed that:?1?The decay rate of combined disinfectant was lower than single disinfectant;different pipes had different effect on decay rate; The decay rate in descending order was: ductile iron pipe>PE pipe>main water and static>dynamic in the same pipe.?2?Combined disinfectants were more effective in disinfectant by-products' controlling than single disinfectant. Chlorine dioxide dominated combined disinfectants can control the production of CHCl₃ effectively and also reduced the organic disinfection by-products ClO₂^- andClO₃^-. Chlorine- chloramine disinfectants produced less CHCl₃ than single chlorine. The by-products increased in pipe network.The by-products' concentrations in descending order was: ductile iron pipe>PE pipe>main water, and static>dynamic in the same pipe.?3?TOC of water in pipes increased with time, while there was little change in main water. TOC in dynamic pipe was higher than static pipe; and the TOC concentration was positively correlated with the chlorine dioxide concentration due to the chlorine dioxide' stronger corrosion to the pipe wall which could lead TOC increasing.?4?The pH was mainly influenced by chlorine and chloramine. The pH was almost unchanged when chlorine dioxide was added.; Turbidity and iron content were mainly affected by the hydraulic scouring; dissolved oxygeny in ductile iron pipe declined with time when campared to bulk water, while there was little change in PE pipe and main water.