Investigate Migration And Transformation Of Typical Pollutions In Rainwater Runoff And Its Impact Between Each Other When Flowed Through LID Practices

In order to relieve road runoff pollution,waterlogging and water shortage in urban city and built a sustainable development one,sponge city construction based on low impact development(LID)facilities have been carried out in several big cities in our country,and it will be gradually expanded into more cities' planning and design.In this study,we not only investigated the impact of LID practices on rainwater runoff volume and typical contaminants(N,P,heavy metals,TOC et al)in rainwater runoff,but also applied spectrum techniques,such as UV-Vis,3D-EEMs,2D-COS and so on combined with analysis methods,parallar factor(PARAFAC)analysis and principal component analysis(PCA)to characterize dissolved organic matter(DOM)and its complex behavior with heavy metal ions various in LID practices.Green roofs and grass swale were selected in our study.The major results obtained as follows:(1)According to the rainwater volume control experiments,we found all green roof practices had about 10 min runoff rentention time for two hours long and over three years rainfull event.Stormwater runoff reduction rate of green roofs with 5 cm soil layer was between 16.56-24.69%,and 32.69%for 10 cm soils layer.We also found that green roofs with turfy soil layer had a little good performance on stormwater runoff reduction rate than that with rural soil layer.These results demonstrated that runoff reduction rate had a positive relation with substrate thickness and the types can cause a effect on it,whereas the types of plants had little impact on it.(2)The road runoff quality control experiments showed that green roof can effectively improve the pH value of road runoff,indicating that green roof practices can ease receiving water acidify and bulidings corrosion.We also found that green roof had a bility on reduce the concentration of N03--N,Pb and Zn in rainwater runoff,but it can release pollutants to receiving water environment,such as NH3-N?TN?TP?TOC and Cu.As the pretreatment practices of runoff,the pollutants removal efficiency of surface layer of grass swale were 73.43%,59.98%,22.72%,40%,10.06%,5.52%,6.84%and 2.8%for TSS,COD,TN,TP,Cu,Cd,Pb and Zn,respectively,whereas the removal efficiency of soil layer were 89.16%,74.17%,52.02%,53.33%,37.87%,40.22%,33.19%and 39.56%for them,indicating that grass swale had a good performance on purifying road runoff and alleviate the downstream water polluted risk,especially for ground water.(3)According to 3D-EEMs analysis,the fluorescence intensity of two protein-like component peaks in green roof influent DOM was decreased gradually in green roof with time,at the same time,the fluorescence intensity of newly emerged humic-like peaks was increased.The humification degree of green roof effluent DOM was increased with rainfull time increasing.The fluorescence intensity of two protein-like peaks and two humic-like peaks were gradually decreased when flowed through grass swale surface,especially for protein-like fluorescence peaks,whereas the protein-like peaks in grass swale bottom effluent DOM were almost disappeared and the fluorescence intensity of humic-like peaks were significantly decreased.The humification degree of grass swale effluent was decreased.(4)Based on the results of UV-Vis analysis,we can conclude that aromatic degree,molecular weight,types and abundance of active functional groups(such as-OH,-COOH,C=O,COOR,et al)of green roof effluent DOM were increased,while them in grass swale effluent were decreased,especially for bottom effluent.(5)All green roof DOM samples were successfully divided into four components by parallel factor(PARAFAC)analysis:three humic-like components(C1,C2 and C3)and one protein-like component(C4).The PCA result showed that these three humic-like substances had positive relation.Five components were obtained in grass swale DOM samples by PARAFAC analysis:three humic-like components(C1,C3 and C4)and two protein-like components(C2 and C5),and the component C1 appeared positive relation with C3,whereas C4 presented positive relation with C2 and C5.(6)In order to analysis and evaluate effluent of green roof and grass swale impact on the bioavailability and mobility of heavy metals in road runoff,2D-COS was applied in this study.The green roof effluent samples were more susceptibility to the variation of metal ions concentration(Cu2,Pb2+ and Zn2+)than influent samples according to two-dimensional synchronous correlation spectra(2D-SYN-COS),and the complex sites were increased on the direction of humification.The complex ability of DOM with Cu2+ was increased and with Zn2+ was decreased slightly,indicating that green roof effluent can increase the transfer ability and bioavailability of Cu2+ in water environment.This result also demonstrated that the reason of green roof released Cu to effluent runoff and absorbed Pb and Zn.The effluent DOM of grass swale presented lower sensitiveness to the variation of metal ions concentration(Cu2+ and Pb2+).The complex ability of grass swale surface effluent DOM with Cu2+ was decreased,while grass swale bottom effluent DOM with both Cu2+ and Pb2+ were decreased.