Characteristics Of Water Quality Variation And Biotic Succession In Sewer Networks

As the important part of urban sewage system，urban sewage pipe network hadbeen used to collect and transport urban sewage, industrial wastewater and rainwater inthe traditional sense, but in recent years, it has been found that the quality of sewagewater will change constantly after a long period and long distance transporting, thischange is mainly caused by the degradation of the biofilm sewers.A long-1200m urban sewage pipe network was built, the simulative urban sewagewas selected as the research object, the variation rule of sewage water quality along thepipeline was studied, and the pH, DO, thickness, structure and microbial populationvariation of the biofilm were investigated through the microelectrodes, ScanningElectron Microscopy and Molecular Biology Technology along the network, totally,certain theoretical basis for the microscopic changes in the urban sewage pipe networkwas provided.Under the hydraulic conditions of0.12±0.02m3/h,0.16m/s, full of0.6,25mm ofpipe diameter, temperature of26±2℃, simulation test was conducted, also keeping thedissolved oxygen of pipeline0.1±0.05mg/L at the same time. The results showed thatthe dissolved organic matter (SCOD) average removal rate was34.0%along the pipes;the average removal rate of nitrogen(TN) pollutants was12%along the pipeline, thechange was mainly because the organic nitrogen in the water transformed into NH3-N(NH3-N concentrations rose by an average of20.8%), and NO3-N was denitrified intoN2(NO3-N concentrations reduced by an average of76.6%); The change of the totalphosphorus was relatively slight, which was related to the stable oxygen environment in the pipe; SO42-showed deceasing tendency along the pipe, the average removal rate was23.1%.The results of microelectrodes show that the pH of biofilm changed little, DOshowed decreasing trendency along the pipe, the average biofilm thickness showedrising tendency during the initial period along the pipe because of the large hydraulicscour,and reached the peak at800m, due to a lack of easy absorption of nutrients, thethickness of the biofilm decreased obviously. Scanning Electron Microscopy analysisresults showed that the pipeline biofilm structure change was bigger along the pipe, theinitial surface structure of the biofim was smooth, but the structure along the pipe wasloose gradually.Rough biofilm structure increased the biofilm specific surface area, it wasconducived to microbial growth and development, accordingly, the water pollutantswere removed effectively. The network biofacies in the biofilm was studied through thebiological detection technology of PCR-DGGE, the total bacteria DGGE profilesshowed that the biofilm microbial flora was the most abundant in the initial200m pipe,the flora similarities of Cs value reduced gradually along the pipe, this indicated that thebiofilm flora experienced a certain succession along the pipeline, and formed stableflora structure exists gradually. The total bacteria DGGE graph edge banding rubbercutting sequencing and phylogenetic analysis further indicated that the Bacteroidetesand Trichococcus along the pipeline have been exited much all the time, Enterococcus,Thiomonas and band3of Bacillu showed deceasing tendency along the pipe, band8ofBacillu appeared a rapid increasing in400m then reduced at1200m again,Virgibacillus and Pullulanibacillus increased slowly, Mesotoga belonged to newmicroflora. SRB DGGE graph edge banding rubber cutting sequencing andphylogenetic analysis further indicated that the Desulfomicrobium, Desulfomicrobiumand Desulfomicrobium have been exited much all the time along the pipeline,Desulfobulbus and Desulfotomaculum decreased slowly, Desulfomicrobium increasedslowly.