Biological effects on incipient motion behavior of sediments with different organic matter content
2021
Zhou, Yongchao | Yao, Xinyu | Gu, Yueqi | Qian, Dong | Thong, Chan Kei | Zhang, Yiping | Zhu, David Z. | Zhang, Tuqiao
PURPOSE: The organic content in urban sewer sediment can significantly influence sediment erosion behavior because of biological activity. In this experimental study, the erosion behavior of sediments with different organic content was investigated to develop a mathematical relationship between the critical shear stress and biological activities. MATERIALS AND METHODS: Before testing, sediment samples were incubated under two environmental conditions: aerobic conditions with high biological activities and sterile conditions with low biological activities. With different incubation periods, samples were subjected to the scouring test in an open channel flume, by which the incipient motion of sediments was determined. RESULTS AND DISCUSSION: Experimental results show that the sediment erosion resistance is simultaneously subject to the strengthening and the weakening effect induced by the biological activity, which is dependent on the incubation period and organic content. For low organic content sediment (volatile solids content < 4%), the biological activity can strengthen the sediment erosion resistance and increase τc, while τc of higher organic content sediment is distinctly reduced. CONCLUSIONS: The biological activity can both strengthen and weaken the sediment erosion resistance. The strengthening effect is attributed to the biofilm formation in the biological activity, whereas the weakening effect is due to the sediment volume expansion by the gas bubble formation. These effects depend on the incubation period and organic content within sediments, which can be used to predict the incipient motion of sediments by modifying the biological influence coefficient. Finally, Shields curves were modified to account for the biological activity.
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