Study On Erosion Characteristics And Transport Principles Of Sewer Sediment In Sewerage System

Sewerage system is one of the most critical infrastructures in a city. However, in the long-term working process, sewer sediment is prone to appear in drainage pipelines due to unreasonable design, or imperfect operation management, etc. Since the existing research on erosion characteristics and transport principles of sewer sediment is insufficient, this paper uses the method of combining on-site investigation and model test to study the erosion characteristics and transport principles of sewer sediment. The main contents are as follows:(1) Jiaxing, in Zhejiang Province has been used as the demonstration areas to study apparent characteristics, particle size distributions, content of volatile organic compounds and other indicators of sewer sediment under the conditions of both separated drainage system and combined sewer system. The result shows that, compared with separated drainage, sediment of combined sewer system shows organic characteristics more obviously, which contains a higher content of volatile solid and smaller diameter.(2) Real sewer sediment has been used as experimental subject to explore the sediment structure and anti-erosion variation with different levels of biological action by adjusting the temperature, dissolved oxygen, training time and other environmental conditions to control the strength of microorganisms in sediments in the laboratory. The result shows that, compared with lower temperature and anaerobic conditions, higher temperature with adequate oxygen supply promotes biological effects. In addition, the influence of biological effects on sediment characteristics depends on volatile organic content of the sediment inside as well. When contents are lower, biological effects are not obvious, and sewer sediments showed inorganic particle properties. On the contrary, when contents are higher, biological effects intensified the loose degree of the internal structure of sewer sediments, and finally weaken the ability to resist erosion. (3) Real sewer sediments with different volatile organic contents have been used as experimental subjects to study the dynamic erosion rule of sediment samples under the step change in steady flow with different levels of biological effects conditions. The result shows that variations of anti-erosion ability of sediment with different volatile solid content during the experiment are disparate. For sewer sediment with high content of VS(16.01%), anti-erosion ability has been weakened during the experiment. For sewer sediment with low content of VS(5.12%), a strengthen of anti-erosion ability has been observed during the experiment. For sewer sediment with VS content of10.96%, variation of anti-erosion ability is related to shear force, anti-erosion ability is strengthen under weaker shear force of0.21N/m2～0.58N/m2, while anti-erosion ability is weaken under weaker shear force of0.64N/m2～0.73N/m2.(4) In consideration of intermittent flow in sewer system, pipe model is used to analysis erosion characteristics and transport principles of sewer sediment with high VS content under erosion of instantaneous flow. The result shows that cohesion of sewer sediment has been enhanced during biological process, as a result, sewer sediment is transported in a form of particle group while being flushing. On the other hand, the influence of shear force on erosion rate is much more obvious than that of flushing duration because of the cohesive characteristics.