西安市城市主干道路面径流颗粒物沉降性能及粒径分布研究

Study on particle sedimentation property and size distribution of urban trunk road runoff in Xi'an City

在西安市城市主干道南二环路建立路面径流采样站,利用自制流量等比例采样装置,采集2009年4—9月的16场降雨路面径流,采用累积曲线法试验研究路而径流中颗粒物的沉降性能和粒径分布,并就降雨特征对径流中颗粒物粒径分布影响进行分析。结果表明,沉降可有效去除颗粒物,沉降60 mm和2 h平均去除率分别为78.4%和86.3%。要达到450%、60%和80%的沉淀去除率,表面负荷应分别为1.1～9.3 cm/min、0.6～5.9 cm/min和0.1～2.7 cm/min。沉淀去除率每提高10%,表面负荷相应减少1.3～3倍。径流中颗粒物粒径分布呈宽幅变化,d_(10)、d_(50)、d_(90)分别为3～23 μm、17～56 μm和40～65 μm,表明径流中颗粒物以粒径3～65μm的细颗粒为主。最大降雨强度与颗粒物粒径相关性较强,其他因子与颗粒物粒径相关性不强,降雨强度足影响径流中颗粒物粒径分布的主要因素。

The present paper is aimed at providing a detailed analysis of the particle sedimentation features and size distribution of the urban artery roadways＇ raining water runoff in Xi＇ an City. As is known, air panicle is one of the chief pollutants in urban roads runoff, acting as the carrier of other environmental pollutants, such as organic mixtures and/or heavy metals. The concentrations and forms of such panicles can also bring about negative influence on human efforts on environmental protection by spreading this or that sort of pollutants. In addition, it is also one of the chief means for removing particles in sewage treatment. Such pollutants mixed with atmospheric particles can also be got rid of along with the run-off stormy water at the same time. Since panicle size distribution has direct impacts on the sediment efficiency and determines＇the designing parameters of water-clog collecting ponds or sewage-collecting tunnels. In our research, the runoff water collected from 16 storm events were sampled in proportion to the total amount of the storming events and accomplished through analyzing the rainfall time at the city＇ s southern second circular road in Xi＇ an City by means of self-made volume-proportional collecting devices from March to November in 2009. The precipitation features of the 16 storm events, such as their maximum rainfall intensity, the volume of the rainfall, their respective duration and each storm＇s antecedent dry period, were observed and traced simultaneously. The cumulative curve was adopted for tracing the settling features and particle size distribution. Besides, influence of precipitation features on the particle size distribution was also taken into account through correlation analysis method. The muhifaceted analysis results showed that the runoff water sedimentation turns to be an effective method for tracing the regularity of the road runoff panicles. Though the removalefficiency of the different runoff events with the same settling time varied widely, the average removal efficiency for 60 minutes＇ settling were worked out at about 78.4% and 86.3% for 2 hours＇ storming respectively. In order to achieve the removal rates of 45%, 60% and 80 %, the surface loads of the sedimentation tanks of ours were 1.1- 9.3 cm/min, 0.6 - 5.9 cm/min and 0.1 - 2.7 cm/min respectively. The surface load proved to decrease 1.3 - 3 times whereas the required particle settling removal efficiency increased 10%. The particle size distribution of road runoff varied greatly from region to region as well as from the storm event to event. The d10, d50, d90 of particles in artery roadway runoff in Xi＇ an City turned to be 3 - 23 μm, 17 -56μm and 40 -65 μm respectively. The results of our anal- ysis demonstrate that particles in the runoff water were mainly fine particles and much more attention should be paid to the pollution intensity as well as the movement and changing regularities of the minute particles with the diameter of 3 - 65 μm in the road runoff treatment field. The correlation analysis result of precipitation characteristics with particle size distribution reveal that the maximum rain intensity tends to bring about the most significant impacts on the particle size distribution while the other precipitation factors were also found less related with it, which shows that the maximum rain-fall intensity serves as the most important factors that determine the particle size distribution of the road runoff.