Pollution Characteristics And Control Technology Of Heavy Metal In Urban Rainfall Runoff

With the rapid development of urbanization in China,the proportion of impervious water on the underlying surface of the city is increasing.During the non-rainfall period,various pollutants accumulate and are washed and dissolved into the runoff during rainfall,especially heavy metal pollutants.Due to its characteristics of refractory degradation and bioaccumulation,heavy metal pollutants have a Long-term potential impact for human body after entering the water environment.Therefore,it is great significance to study the characteristics of runoff in time and space and its control techniques for heavy metal pollutants.This paper firstly takes the rainfall runoff in Changzhi City as the research object,and selects the roof and pavement of representative residential areas,commercial areas and industrial areas.The characteristics of runoff in time and space of heavy metal pollutants(Cd、Cu、Zn and Pb)in rainfall runoff are studied by monitoring the rainfall of several fields in each functional area,and the annual pollution load is estimated.The study found that the main conclusions can be summed up as follows.(1)The same field of rainfall in the same functional area,the concentration of heavy metals in the runoff of roof and pavement is similar to the change of runoff time.For the same functional area,the heavy metal pollution caused by runoff in each field is generally higher than that of the roof.The peak concentration of heavy metals in rainfall runoff generally lags behind the peak of rainfall intensity.The correlation between SS and heavy metals in each functional area is better,and the correlation between Cu and Zn,Cu and Pb,Zn and Pb is better,and the correlation between other heavy metals is poor.(2)In the residential area,there is no initial scouring effect on the four heavy metals in the 20170714 rainfall runoff,and some of the other monitoring sites have some initial scouring effects on heavy metals.In the commercial area,there is no initial scouring effect on heavy metals in 20170904 rainfall runoff,and the initial scouring effect occurres on the 20170714 rainfall runoff roof and pavement.In most of the other sessions,some heavy metals have an initial scouring effect.All the monitored rainfall runoffs in the industrial zone have an initial scouring effect on some heavy metals.(3)From the heavy metal runoff EMC of each rainfall runoff,it can be known that the heavy runoff heavy metal Cd has the highest pollution degree,which is inferior V,and Cu,Zn and Pb are all above III water bodies.Using the average concentration method combined with the SCS model,it can be calculated that the sum of the annual loads of heavy metals Cd,Cu,Zn and Pb in the roof and surface runoff of Changzhi City.The annual load of heavy metals Cd,Cu,Zn and Pb in the roof and surface runoff of Changzhi City is 649.04kg/a,1141.17kg/a,3176.73kg/a and 188.02kg/a,respectively.The annual load per unit area of heavy metals Cd,Cu,Zn and Pb in the roof runoff is0.14kg/(hm~2·a),0.24kg/(hm~2·a),0.69kg/(hm~2·a)and 0.04kg/(hm~2·a).The annual load per unit area of heavy metal Cd,Cu,Zn and Pb on the road surface is 0.15kg/(hm~2·a),0.39kg/(hm~2·a),0.85kg/(hm~2·a)and 0.07kg/(hm~2 a).Based on the characteristics of heavy metal pollution in rainfall runoff,this paper combines the low-impact development measures of sponge city to propose the technology of heavy metal pollution control in rainfall runoff--bioretention facilities.Using artificial simulation of rainwater,the influent amount,the influent time,the influent concentration and the filling four factors affecting the removal of heavy metals in the bioretention facility were selected.Each factor was selected at three different levels,and orthogonal experiments were carried out on plant bioretention facilities and plant-free bioretention facilities.The experiment results show that the bioretention facilities have better removal effects on copper,zinc,lead,cadmium,chromium and arsenic,and the removal rates are above 70%.Among the four factors,the filler has the greatest influence on the removal rate of heavy metals,followed by the water inflow time.Plant retention facilities have higher rates of removal of heavy metals than those without plants.