Characteristics Of The Transformation Of Nitrogen And Phosphorus In Reclaimed Water Distribution System And The Influence Of Disinfectant To Biofilm

The object of this study was to investigate the transformation of nitrogen and phosphorus in reclaimed water distribution system by sampling from simulate and actual pipe.The finished water of WTRP(Wastewater Treatment and Reuse Plant) was adopted as influent to study the change of water quality. Meanwhile, the influence of high-concentration disinfectant on microorganism in the biofilm and their activity were investigated to provide a helpful reference for the control of microorganism in reclaimed water distribution system.A series of CDC Biofilm reactors were used to model the distribution pipe in this experiment, and the removable polypropylene coupons were used for biofilm growth.Reclaimed water and biofilm were sampled from the model distribution system.The result of water quality indicated that the concentration of residual chlorine and NH4+-N were decreased along the pipe, but NO3--N and p H were increased along the pipe. The trend of NO2--N was increased firstly but then reduced. Meanwhile, the result of biofilm measurement indicated that biofilms formed in the model network had the capability of nitrification, denitrification and phosphorus enrichment. And these phenomena were confirmed through the detection of the water quality from actual pipe. Moreover, molecular biology techniques including PCR、DGGE and DNA sequencing were used to analyze the diversity of bacteria in biofilm formed in model distribution system. Bacterias including nitrifiers, denirifiers and phosphorus-accumulating bacteria(PAOs) were co-existed extensively in the biofilm.Due to the complexity of the actual reclaimed water, the co-existence of various ions and the interaction of microorganism, as well as the material of pipe affecting the content of phosphorus in the distribution system. A bench-scale experiment was established to study the influence of chemical interaction and biological effect on the phosphorus concentration in reclaimed water. The result showed that the exist of iron ion, aluminum ion and calcium ion reduced the existence of phosphorus, although the low existence of these ions in reclaimed water, and the maximum removal rate of phosphorus was up to 22.76%. Furthermore, the phosphorus removal rate for the combination of biological and chemical action was as high as 88.71%, which meant biological effect was the main approach of phosphorus removal in reclaimed water distribution system.Finally, the study used a bench-scale approach to investigate the disinfectant susceptibility of different microorganism in the biofilm from a model pipe of reclaimed water under the high dosage of disinfectant. The result showed that the complete viability loss on biofilm bacteria did not occur under high concentration disinfectant. And the microorganism could be recovered without disinfectant. The change of nitrifying and denitrifying activity of biofilm was not the same under the disinfection as well as at the recovery phase. The content of EPS in biofilm was decreased gradually after disinfection for 3h and recovery for 7d. In a word, disinfectant of high concentration can’t control the biofilm microorganism of reclaimed water pipe completely.