Study On Ecological Control Technology And Mechanism Of Stormwater Runoff

Concerning the"urban waterlogging and serious water contamination",and other social and ecological environmental problems resulted from the accelerated urbanization process,it is urgent to effectively control and utilize the urban stormwater runoff.Although a great number of purification materials has been used during the rainfall-runoff control process,there is still a lack of systematic studies concerning the reduction in capacity under specific water quality and volume conditions.Contamination accumulation degree of purification materials,and the impact on the underground water ecology.The urban rainfall runoff ecological combination system is a treatment system designed and based on traditional low impact development technology.This includes the development of water quality,water features and the migration path of urban road rainfall runoff.This system mainly includes the permeable pavement and in-place filtering technologies such as modified bioretention systems and ecological resistance control processes such as ecological ditches.Based on the idea of non-point source contamination purification,this can be achieved through the"impoundment,seepage,purification and drainage"of the runoff,the rainfall runoff ecological combination system is designed.This paper investigates the reduction features of various units and combination systems upon the runoff contaminants and optimizes the parameters of single facilities.We aim to demonstrate the operation process parameters and mechanisms of pavement runoff contamination bio-ecological resistance control technologies.The main research conclusions from the study are as follows:(1)Based on the purification performance results of different types of permeable pavement,with the extension of rainfall duration,the effluent water quality that permeated from the permeable pavement generally got worse.The effluent water qualities for different types of permeable pavements were ranked as follows;steel slag permeable brick(SP-B)>permeable ceramic brick(CP-B-ceramic)>cement permeable brick(CP-B-cement)>permeable asphalt pavement(PAP).Compared with the initial infiltration runoff,the permeable pavement had better control effects of the levels of nitrogen,phosphorus and heavy metals.However,the effluent water quality did not conform to surface grade V water standards.The reduction capacities of the four types of permeable pavements against the thermal contamination load were ranked as follows:SP-B>CP-B-cement>CP-B-ceramic>PAP,and the thermal contamination load reduction rate of permeable asphalt pavement were less than 20%.The higher the infiltration runoff temperature,the longer the rainfall return period and the higher the rate of reduction in thermal contamination.The degree of heavy metal contamination on the subgrade soil surface layer was higher than that on the middle and lower layers.As shown from the heavy metal evaluation results,at a depth range of 10–40 cm,the soil was subject to medium contamination and Cu and Pb factors contribute to the highest contamination index contribution rate.The heavy metals carried during the process of runoff infiltrated from the permeable pavement and accumulated in the subgrade soils.(2)The results from the simulated rainfall experiment showed that the reduction capacities of the 3 groups of the retention systems against the contaminants were ranked as follows;BSM+5%BC(sand/soil media+5%biochar)>BSM+5%BC+biological matrix(sand/soil media+5%biochar+biological matrix)>BSM(sand/soil media).Based on the experimental results,the basic features of the biological retention system were evaluated against the matrix factors and the permeability coefficients.Considering the impacts of concentration of water contaminants,the design return period and the antecedent dry time,the water quantity regulation effects were respectively established using the multiple quadratic regression equation.The quantitative coupling relationship between the contaminant concentration removal effect and the impact factor was used to estimate the regulation effects of the retention facilities under different rainfall conditions.(3)According to the removal features of contaminants in the runoff,the appropriate hydraulic load of the subcritical flow ecological ditches was selected as0.3 m~3/(m~2·d).The swamp morning glory and water mifoil had the strongest adaptability in the ecological ditches and were used as the alternative dominant plant in the ecological ditches.Compared with the fluidized bed matrix,the gravel matrix was more suitable for the growth of plants.Under the subcritical flow status,the surface grade V water was adopted as the effluent water quality standard.The average appropriate lengths of the gravel matrix and the fluidized bed matrix ditches required for the effluent were used for the up-to-the-standard calculation according to the fitted equation,respectively as follows,4.57 and 4.01 m.(4)The cumulative proportion of phosphorus on the matrix of ecological ditches that adopt the gravel as the matrix can be ranked as follows:Ca-P(calcium bound phosphorus)>Fe/Al-P(iron/aluminum bound phosphorus)>PA-P(potential active phosphorus)>WA-P(weakly absorbed phosphorus).The cumulative proportion of phosphorus formed on the matrix of ecological ditches that adopts the biological stuffing as the matrix can be ranked as follows:WA-P>Fe/Al-P>PA-P>Ca-P.The contents of heavy metals on the matrix of two ditches are generally ranked as follows:Zn>Cu>Pb,and front end>middle end>rear end.The contents of heavy metal forms can be generally ranked as follows;residual form>reduced form>oxidized form>weak acid extractable form.The proteobacteria,actinobacteria,bacteroidetes,patescibacteria,firmicutes,chloroflexi and acidobacteria are the dominant species in the ecological ditches.Amongst these species,proteobacteria had the maximum abundance proportion in these two ditches and were the commonly shared dominant species.Saccharimonas,trichococcus,burkholderia,lentimicrobiaceae and dermatophilus were the dominant species in the ecological ditches.(5)The runoff regulatory effects of actual pavement runoff and artificial rainwater on the multi-level ecological combination system were respectively adopted to conduct a comparison experiment.As shown from the results,under different infiltration water qualities,all of the effluent water qualities of the multi-level ecological combination systems conformed to the surface grade II water standard.The corresponding stability applied to the urban rainfall runoff treatment.The permeable asphalt pavement was the main unit that intercepted the suspended solid.The biological retention system had the strongest absorption capability upon TP and heavy metals.The ecological ditches had rich biological actions and a stronger purification capacity for nitrogen,phosphorus and other organic materials.(6)Based on the HYDRUS-2D model,the critical parameters for sensitivity analysis were made for the permeable pavements,the ecological retention and ecological ditches.As shown from the results,the rainfall return period(V)and the influent concentration(c)were the sensitive parameters that affected the migration of contaminants in the permeable asphalt pavement and ecological ditches.The inflow concentration(c),matrix pore size distribution(n)and stuffing isothermal absorption constant(K_d)were sensitive parameters that affected the migration of contaminants in the biological retention system.Through the calibration and verification of the model,this study obtained the reliable hydrologic power and the water quality feature parameters of the multi-level ecological combination system to simulate the given rainfall conditions.The research achievements may provide a theoretical basis for the pavement runoff contamination of bio-ecological control technology.In summary,this paper systematically explores the removal efficiency of three detention facilities for nitrogen,phosphorus,organic pollutants,suspended solids and heavy metals in rainwater runoff under different rain intensities and concentrations.At the same time,the three detention facilities have been studied and compared.The removal characteristics of different pollutants and the use of Miseq high-throughput sequencing technology to investigate the microbial community structure of the biological retention system and ecological ditches in the operating phase,revealing the relationship between the microbial community characteristics and water purification.According to the construction characteristics of urban roads,a preliminarily established rainwater runoff bio-ecological combination treatment system provides theoretical guidance for the development of road runoff pollution control technologies.