Migration And Transformation Of Dissolved Organic Matter And Heavy Metals In Runoff Rainwater Of LID Facilities

The water problem in China's cities is becoming more and more prominent?water shortage,water pollution,frequent guilt?,which seriously restricts the sustainable development of cities.How to scientifically use rainwater to alleviate the contradiction of lack of urban water resources and effectively reduce stormwater runoff has become a topic.In response to the problem of stormwater runoff pollution,the United States has proposed the concepts of low impact development?LID?for rainwater,and designed rainwater control facilities throughout the site planning and design process.Technically,it mainly controls from the source,the middle and the end.These technologies are of great significance for the control and utilization of urban rainwater pollution in China.The purpose of this study is to conduct in-depth research on the migration and transformation of typical pollutants in runoff rainwater?such as organic matter,heavy metals and organic pollutants?in LID facilities,in order to provide technical support for alleviating urban water problems and sponge city construction.In this study,a simulated experimental device was used to evaluate the water purification performance of runoff rainwater in four different urban functional areas after treatment with grassy swale and ecological concrete revetment.UV-visible absorption spectroscopy,three-dimentional exicitation emission matrix spectroscope fluorescence spectroscopy,simultaneous fluorescence spectroscopy and other fluorescence spectroscopy were measured,PARAFAC,principal component analysis,correlation analysis and two-dimensional-correlation spectroscopy were also used to analyze the characteristics of the DOM in Beijing rainwater runoff samples in LID facilities.The subtle process of processing the DOM by the LID facility is quantified by tracking changes in the DOM spectrum.The concentration of TN and TP in the runoff water before runoff through the LID facility is relatively high.TSS and TOC decreased by 50.00%to 95.23%in the runoff,and the removal rates of TP,TN and TOC in the roadside area,classical garden area,core commercial area,and residential area four functional areas reached 96.22%-99.45%,81.87%-99.72%and 94.40-95.52%,respectively.The removal rate of heavy metal?HM?ions Cu²⁺,Zn²⁺,Pb²⁺and Cr²⁺in the grass swale treatment was 30.95%-97.39%.The removal rate of heavy metal ions in the treatment of ecological concrete revetment can reach 83.15%⁹9.10%in the four functional areas,and the purification effect is obvious.The spectral parameters indicate that the DOM has a relatively high humification and aromaticity after treatment at the LID facility,and the aromatic and molecular weight of the runoff DOM in the four functional areas follow the order in which the effluent is greater than the influent.Based on the analysis of three-dimentional exicitation emission matrix data PARAFAC,the four functional areas'runoff rainwater was treated to be decomposed into three main components of DOM,including two humic components and one proteinoid component.Through principal component analysis and correlation analysis,it can be found that the change of DOM component in rainwater runoff varies greatly with functional area and after treatment.DOM and other pollutants in runoff pollution are mainly positively correlated.Nutrient pollutants can be treated by ecological concrete together with DOM,and heavy metal pollutants may be purified together with DOM.Through fluorescence quenching titration experiments and calculation of complexation constants,it was found that Cu²⁺in the effluent of the grassy swale can simultaneously react with protein-like substances and humus-like substances,and Cu²⁺reacted with protein-like substances more strongly than humus-like substances.Pb²⁺in the inflow and outflow of rainwater runoff from ecological concrete revetment can also react with protein-like substances and humus-like substances at the same time,and Pb²⁺is more sensitive to humic substances than to protein-like substances.In addition,the results of 2D-COS indicate that the binding sites and sequences of different LID facilities and runoff rainwater will be affected after the LID,and the complexation sites will change,but the total binding law is the same,and the binding ability and site of the two heavy metals is different.It can be found clearly that the intensities of peaks were high in grassy swale G2,indicating that the samples were more susceptible to the change in fluorescence intensity under external perturbation.The intensities of peaks indicate more susceptibility to humus-like materials with the addition of Pb for samples of ecological concrete revetments.This study can deepen the understanding of the interaction,migration and transformation of typical pollutants in rainwater and its environmental effects,and help to make better use of rainwater to ensure urban water supply.