ANALYSIS OF SETTLING VELOCITY OF PARTICULATES IN FLOWS IN DRY AND WET WEATHER FROM THE COMBINED SEWER
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摘要: 排水管道可接纳雨水径流和旱流污水,雨天形成雨污混合水,水流中部分颗粒沉降至管底形成沉积物。对比分析上述各环节中颗粒物的沉降速率特征,有助于提高对雨污混合水的管控效率。研究选取某合流管段,采集雨污混合水、雨水径流、管道沉积物及旱流污水,并采用淘析分离方法,开展颗粒物沉降速率(SV)特征分析,基于此建立颗粒物沉降速率与质量占比的拟合关系。结果显示,雨污混合水中颗粒物SV≥0.265 mm/s的比例与管道沉积物相近,且与雨水径流及旱流污水存在一定差异,说明在雨天水流运行过程中,部分管道沉积物被冲起,使雨污混合水中颗粒物SV得到显著提升。进一步分析显示,在每个SV下,降雨量越高,低于该SV的颗粒占比更少,且不易沉降的颗粒态污染物占比将会更高。该结果一方面说明,在较高雨量下SV较高的颗粒物更多被冲刷进入雨污混合水中;另一方面也说明,当雨天管网水量增加时,将会有更多不易沉降的颗粒态污染物进入管网下游,重力沉降设施的拦截效率将会显著下降。不同污染物的富集情况显示,PAHs、Cd、Cr和Pb在SV≥0.265 mm/s的颗粒物中占比较高,因此当设定SV=0.265 mm/s对雨污混合水进行重力沉降处理时,PAHs、Cd、Cr和Pb 4类有害污染物将会得到有效削减。基于上述数据建立了颗粒物SV与质量占比关系特征,即x=lnB/(A-y)(R2>0.95),该结果有助于实现特定SV下的颗粒物及颗粒态污染物质量比的快速转化。Abstract: The drainage pipes accept rainwater runoff and dry flow sewage, and form the combined sewer consisting of rainwater and sewage in wet weather. Some particles settle to form sediment. Comparing the settling velocity (SV) of particles in the above-mentioned routes will help to improve the control efficiency of wet weather flow. A section of the combined sewer was selected to collect water and sediment samples. The elutriation separation method was used to analyze the SV of particles. Based on this, the fitting relationship between SV and mass ratio was established. The results showed that the proportion of particulate matter with SV≥0.265 mm/s in the rain-sewage combined sewer was similar to that of the sediment, but was different from the stormwater runoff and dry-weather flow. This indicated that during the rainy days, some sediments were eroded, significantly promoting the SV of particles in wet-weather flows. Furthermore, under each SV, the higher the rainfall, the smaller the proportion of particles below that SV, and the higher the proportion of the unsettled particulate pollutants. The results showed that: a) more particles with higher SV were eroded into the wet-weather flow under higher rainfall; b) when the flow increased, more unsettled particulate pollutants entered the downstream of the pipe, resulting in the reduction of the gravity interception efficiency. In addition, PAHs, Cd, Cr and Pb accounted for high proportions of particles with SV≥0.265 mm/s. Therefore, when SV=0.265 mm/s was set for gravity sedimentation treatment measures, PAHs, Cd, Cr and Pb will be effectively reduced. Based on the above data, the relationship between SV of particulates and the mass ratio can be established, namely x=lnB/(A-y)(R2>0.95), which was helpful to realize the rapid transformation of the mass ratio of particles and particulate pollutants under the specific SV.
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Key words:
- wet weather flow /
- settling velocity /
- particulate /
- drainage system
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