| Urban surface runoff is the second major pollution source that affects the quality of urban water environment.Roofing,as an important part of urban impermeable area,plays an important role in urban non-point source pollution.Urban roof rainwater runoff with a certain potential for development and utilization that its collection convenient and water quality relatively good.xi'an is a water source and water quality both seriously short city.The collection and utilization of roof rainwater runoff will be an effective way to solve the water problem in xi'an.In this study,runoff sampling points were set in typical cultural and educational areas of xi'an city,and runoff water samples were collected by artificial time interval sampling method during the rain period.The roof runoff of 11 typical rainfall events from August 2016to September 2018 containing the three seasons of spring,summer and autumn were sampled,monitored and analyzed and the monitoring indexes were SS,COD,TN,TP,NH3-N,turbidity,heavy metal Pb,Zn,Cu,Cr,Ni,Cd and PAHs.Initial rainwater was defined according to the change of pollution index concentration with runoff time.Studying on the initial roof rainwater runoff of Xi'an is crucial to clear its pollution level,Control runoff pollution,realize the rainwater utilization and ease the pressure of water use in xi'an.What's more,the studies about heavy metals and PAHs of initial roof rainwater runoff in xi'an are barely reported and the main purposes to monitor the heavy metals and PAHs of initial roof rainwater runoff are to study the pollution level,change characteristics,and then give the concentration range on the asphalt felt roof which is the most important roofing type in xi'an.It provides reference value for the following study on heavy metals and PAHs of the initial rainwater runoff of such roofs in xi'an.Study on the removal efficiency of the initial rainwater runoff pollutions with making use of the designing coagulation orthogonal and percolation column filtration tests in accordance with the quality of the initial rainwater runoff in Xi'an.Furthermore,To design the interception device in accordance with the characteristics of initial rainwater runoff quality and quantity as well as the roof rainwater funnel's structure in the local situation of Xi'an combined with LID?LOW Impact Development?technology and to study the permeability,work status,pollution interception efficiency and replacement cycle of interception device.The test results are as follows:Study on the characteristics of roof rainwater runoff water quality and the analysis of initial roof rainwater runoff at a cultural and educational area in Xi'an shows that:?The roof rainwater runoff pollutants'standard deviation coefficient of each event rainfall varies greatly which is mainly related to the characteristics of each event rainfall.?For the same type of underlying surface,runoff pollutant concentration has a similar change rule with runoff time,that is,the runoff pollutant occurs zigzag fluctuation with runoff time and finally tends to be stable.?The rainfall intensity is related to the energy of the pollutants being washed away from the underlying surface.The higher the rainfall intensity is,the stronger the ability of runoff formed by rainfall to wash surface pollutants,which affects the water quality of the runoff.?COD,TP,turbidity and heavy metals Pb,Zn,Cu,Cd,Ni and Cr in roof rainwater runoff are all significantly correlated with suspended matter SS,indicating that suspended matter SS is an important carrier of organics,heavy metals and other pollutants.?The first 30-40 minutes of a rainstorm event and the first 40-50 minutes of a heavy rain event and the first 20-60 minutes of a moderate rain event and the first 40-80 minutes of a light rain event can be defined as the initial rainwater runoff in Xi'an.?The water quality of initial roof rainwater runoff is poor and the concentrations of initial roof rainwater runoff pollutants are high.The water quality of roof rainwater runoff is improved later.?The concentration ranges of SS,COD,turbidity,TP,NH3-N and TN of initial roof rainwater runoff are respectively 24.6524.13 mg/L,79.89927.67 mg/L,34.38169.45 NTU,0.051.69mg/L,5.2329.24 mg/L,7.6933.66 mg/L.The concentrations of heavy metals Cr,Pb,Zn,Cu,Ni and Cd of initial roof rainwater runoff respectively ranged from 30.57 to 621.2 ug/L,44.36 to 197.75 ug/L,163.25 to 935.44 ug/L,27.04 to 220.68 ug/L,14.89 to 145.29 ug/L,1.12 to 6.89 ug/L,and the its PAHs concentrations ranged from 124.37 to 340.62 ng/L.The coagulation precipitation of the initial roof rainwater runoff shows that:?SS and COD are the main control items of runoff water quality.The optimal dosage of PAC,PFS and aluminum sulfate for runoff water quality of the same roof runoff is respectively 50 mg/L,60mg/L and 60 mg/L.Under the optimal dosage,the removal rate of SS and COD of runoff by PAC,PFS and aluminum sulfate was:PAC>PFS>aluminum sulfate.?When PAC dosage was 50 mg/L and PAM dosage was 0.4 mg/L,removal rates of SS,COD,TP,turbidity and TN of the initial roof rainwater runoff were respectively 97.21%,90.51%,100%,93.99%and18.70%,and then the removal effect is the best.?The range analysis of coagulation orthogonal test shows that the removal order affecting coagulation on SS,COD,turbidity,TP and TN is PAC dosage>hydraulic condition>PAM dosage.?Sedimentation test was carried out under optimum orthogonal coagulation condition and the pollutant removal effect of rainwater runoff was the best at 120 min of static precipitation.Decontamination law of initial roof rainwater runoff and key parameters'design by interception device of rainwater funnel show that:?The less the geotextile mass per unit is,the more velocity the permeability will be and the relation of filtration flux with filtering head of geotextile proves to be linear.Under the same filtration head,the smaller the geotextile mass per unit is,the higher the filtration velocity will be.?The geotextile with a certain amount of pollutant requires more filtration pressure than the clean geotextile The more the quantity of pollutant,the more the pressure needed for geotextiles filtration.However,the relationship between geotextile filtration velocity and filtration pressure is still linear under a certain amount of pollution.?In the case of no overflow,the interception devices made of geotextiles have certain pollution interception effect,which can effectively reduce the pollution load of initial roof rainwater runoff and improve runoff water quality.?According to the rainfall characteristics of xi'an and the use of type 87 rainwater funnel,The overflow loophole of interception device at least 0.0154 m2,that is,the opening rate should not be less than 13.7%.and the effective filtering area heights of interception device made by geotextile of 500 g.m-2 must be at least 568 mm in case that the roof flooding when the storm hitting of every five-year recycling interval turns to repeat.?The effective filtering area heights of interception device made by geotextile of 500 g.m-2 respectively must be at least479 mm,520 mm,547 mm 568 mm in case that the roof flooding when the storm hitting of every two-years,three-years,four-years,five-year recycling interval turns to repeat.Experimental study on the treatment of initial roof rainwater runoff with combination packing of quartz sand,zeolite and activated carbon shows that:?The three percolation columns set in the test all had certain treatment effect on the initial roof rainwater runoff and reduced the pollution load of the initial rainwater.?The removal rates of SS,COD,TN,TP,turbidity,heavy metal Pb,Zn,Cu,Cr,Ni and Cd of the initial rainwater by the three filter columns were consistent with the overall change trend over time,that is,the removal efficiency increased with time and finally tended to be stable.?The filtration column was filled with 30 cm zeolite,20 cm activated carbon and 30 cm quartz sand from top to bottom can have the best removal effect of the initial roof rainwater runoff pollutants. |
PDF Full Text Request