Study On Laws For The Incipient Motion Of Sewer Sediments With Biological Activities

This paper generalizes the harm of the sediment deposits and summarizes the physical characteristics,internal biochemical reactions and the transport laws of the sewer sediments.In view of some shortcomings in the study,considering the inhomogeneity and high organic matter of sewer sediment,micro-observation and macro-scouring test are combinated to study laws for the incipient motion of sediments in drainage.The main contents are as follows:(1)Real sewer sediments have been used to analyze the physical properties such bulk density,particle size distribution,organic matter content and so on,and explore the incipient motion of sediments under different water flow intensities.Then propose to use the characteristic particle size as the criteria for judging the initiation of sediments.The result shows that the sediments are inhomogeneous and they are grouped by particle size at different water flow intensities.When reaching the threshold shear stress,the median diameter of bed load of the initiated sediment is in the range of d54 to d63 in the whole sample.The d60 of the entire sediment can be used as the criteria for judging the initiation of sediments.(2)Inorganic quartz sand with different particles has been used as experimental material to explore the effects of biological activities on the specimen under exogenous organic matter culture by adjusting the temperature,dissolved oxygen and nutrient solution.Scanning Electron Microscopy(SEM)and Laser Scanning Confocal Microscope(LSCM)have been used to observe the surface morphology of the inorganic sand and the initiation laws of the samples have been observed through the flushing test of the open channel flume.The result shows that the biofilm formed on the surface of the sand bed and among particles improves the overall anti-erosion ability and enhances the critical shear stress by reducing the surface roughness and enhancing the connection among the particles.But the effect of enhancement is weakened due to the aging of biofilm.Finally,the enhanced effect of the biofilm is analyzed quantitatively,and the Shields formula and the entrainment probability of sediments are modified.(3)Real sewer sediments are reconstituted by wet sieving to explore the effects of endogenous biological activities on the sediments by adjusting the temperature,dissolved oxygen and nutrient solution.SEM and LSCM are used to observe the surface morphology of the sediment and X-ray Computed Tomograpgy(XCT)is used to observe the internal structure of the sediments.In addition,the initiation laws of the sediment are explored through the flushing test of the open channel flume.The result shows that,unlike the inorganic sand,the biological activities in the sediments not only produce the biofilm that enhances corrosion resistance,but also consume the organic matter and produce the gas,so that the whole sediments swelle and the anti-erosion capacity is weakened.Based on the existing theories,the effects of biological activities on sediments with different organic matter contents are analyzed quantitatively.