A Simulation Study On Rules Of Water Quality Variation In Sewer Networks

Urban sewage pipe network is an important part of urban sewage system, and thequality of sewage water may change during the process that the sewage water isconveyed to sewage treatment plant through the sewage pipe network. Based on theabove, the urban sewage in pipe network was selected as the research object, thevariation of the water quality were studied by circular flow of the simulative pipeline,the changes of different carbon sources were discussed and the basic characteristic ofthe pipeline bio-film was studied, also the relationship between concentration andparticle size of suspended solids was analyzed, in the meanwhile, the effect of differentflow rates on water quality change was studied, totally, certain reference for theforecast of influent quality in the sewage treatment plant was provided.The research results showed that when the sewage circular flow6h under thehydraulic conditions of30m3/h,0.53m/s, full of0.5, grade of3‰, both of physicalsedimentation and biological degradation could make some contribution to removingdifferent components. Among them, the removal rate of total organic matters (TCOD)was10.79%, while the contribution rates of physical sedimentation and biodegradationwere68.85%,31.15%respectively. The removal rate of nitrogen pollutants was11.15%, while the contribution rates of physical sedimentation and biodegradationwere both50%. The changes of nitrogen pollutants caused by biological degradationwere mainly that organic nitrogen in the water was transformed into NH3-N, and NO3-N was denitrified into N2. The change of the total phosphorus was relatively slight,which was related to the stable oxygen environment in the pipe.Further research results showed that the type of organic matters in the process ofsewage transmission had also changed, rapid easily biodegradable organic matters and slow biodegradable organic matters had been removed in a certain degree, but thevolatile fatty acids especially acetic acid increased obviously, the reason was mainlythat organic matters were hydrolyzed to generate volatile fatty acids under the action ofmicroorganisms. In order to grasp the biodegradation of wastewater in the pipe further,the pipe bio-films in different periods were detected through tiny electrodes, scanningelectron microscopy, and the PCR-DGGE technology. The results showed that theaverage thickness of sewage pipes bio-film was1094μm, the surface was of differentporosity, and biological components were relatively rich. The results for the particlesize of the suspended particles in sewage pipe showed that under the conditions ofconstant hydraulic flushing, the median of particle size had a tendency of graduallyreducing, and suspended solids sedimentation was more likely to occur when themedian of particle was more than21μm.Paper also studied the effect of different flow rates on water quality change, theresult showed that when the flow rate was small, the contaminant removal rate wasrelatively large, which was related to the obvious biodegradation and easiersedimentation of suspended particulate matter. As the flow rate increased, the effects ofphysical sedimentation and biodegradation on the contaminants removal were reduced,but biodegradation was increased than physical sedimentation relatively.