Research On Runoff Control Of Modified Zeolite Packed Bioretention Ponds

As one of the low-impact development measures,bioretention ponds have a certain mitigation effect on urban waterlogging and non-point source pollution that must be solved urgently.The traditional bioretention pond packing（Bioretentio Soil Medial,BSM）has low removal efficiency for rainwater runoff pollutants,and the nutrient leaching phenomenon will occur in the soil in the early stage of rainfall.The packing layer is an important structural layer of the bioretention pond.Modification helps to increase the retention capacity and pollutant reduction capacity of the bioretention pond,thereby improving the overall hydrology and water quality regulation performance of the bioretention pond.In this study,natural zeolite（Natural Zeolite,NZ）was used as the main research body for modification,and EDTA-Modified Zeolite（EDTAMZ）,Ca（OH）₂-modified zeolite（Ca（OH）₂-Modified Zeolite）were prepared,Ca MZ),Fe₂O₃-modified zeolite（Fe₂O₃-Modified Zeolite,Fe MZ）,Mn O₂-modified zeolite（Mn O₂-Modified Zeolite,Mn MZ）4 kinds of modified zeolite,and the modified zeolite and traditional bioretention pond filler ratio for research The object,the comprehensive evaluation of the rainwater runoff storage and interception capacity of the modified zeolite packing ratio is carried out by the analytic hierarchy process,and the bioretention pond is used to conduct a comprehensive analysis of the simulated rainfall experiment,and then screen out the organisms with strong rainwater runoff storage and interception capacity retention pool packing.This paper can provide a more reliable basis for the selection of the components of the improved packing bioretention pond,and also provide some guidance for the relevant design and construction standards in practical projects.The main conclusions of this study are as follows:（1）The isothermal adsorption experiments were carried out on the zeolites obtained by the four modification methods.The results showed that the adsorption effect of the four modified zeolites on NH₄⁺-N and SRP in rainwater was significantly higher than that of NZ.When the concentration in rainwater was 80 mg/L,the adsorption capacity of EDTAMZ,Ca M,Fe MZ and Mn MZ for NH₄⁺-N was 2.92mg/g,2.64 mg/g,2.55 mg/g and 2.37 mg/g,the adsorption capacity for SRP was 0.76mg/g,3.01 mg/g,0.81 mg/g and 0.80 mg/g,while the adsorption capacity for NZ was NH₄⁺-N The adsorption capacity of and SRP was only 1.78 mg/g and 0.68 mg/g.Since the metal ions supported on the surface of the modified zeolite can form complex bonds with strong binding ability with NH₄⁺-N and SRP,the adsorption effect of the modified zeolite on NH₄⁺-N and SRP is enhanced.At the same time,the modification process oxidizes the reduction of the zeolite surface The surface of the zeolite is rough and porous,thereby improving the pollutant adsorption capacity and efficiency of the modified zeolite.（2）Dynamic adsorption experiments were performed on the mini-columns with5%,10%,and 15%of 4 kinds of modified zeolites and natural zeolite added to BSM,respectively.The results show that:from the point of view of the runoff reduction rate,the runoff reduction rates of BSM+5%Mn MZ and BSM+5%EDTAMZ are 15.95%and 15.74%,respectively,which are obviously better than the runoff reduction effect of the other two packing ratios of the experimental column.The modified zeolite packing has a good control effect on the average concentration of SS in the effluent of the bioretention tank,in which BSM+10%Mn MZ shows stronger SS retention capacity.for NH₄⁺-N and SRP,all experimental columns are in The concentration of NH₄⁺-N within 30～60min of runoff was higher than that of inflow,and the reduction effect of NH₄⁺-N was only shown in the later stage.With the increase of the zeolite ratio,the reduction effect of the experimental column on NH₄⁺-N was improved,and the removal efficiency of NH₄⁺-N by the BSM+15%Mn MZ dynamic adsorption device was 97.56%.The removal efficiencies of BSM+10%EDTAMZ and BSM+15%Mn MZ were 95.76%and 96.86%after inflow for 60 min.Comprehensive comparison shows that Mn MZ and EDTAMZ can show significant removal ability of NH₄⁺-N and SRP in stormwater runoff.（3）Carry out AHP weighted assignment judgment on the retention capacity,adsorption capacity,pollution interception capacity and modification cost of 6 fillers with different proportions.The weighting of each alternative is as follows:BSM+10%Mn MZ（0.2590）>BSM+10%EDTAMZ（0.2508）>BSM+10%Ca MZ（0.1709）>BSM+10%Fe MZ（0.1317）>BSM+10%NZ（0.1072）>BSM（0.0804）,BSM+10%Mn M Z and BSM+10%EDTAMZ The dynamic adsorption has the best effect on the regulation of stormwater runoff stagnation and pollution interception.（4）The simulated rainfall experiments were carried out on 6 kinds of 10%zeolite ratio packing bioretention ponds.The results showed that the average reduction rate of rainwater runoff in the actual operation of the improved bioretention ponds was 21.16%～21.63%,while the traditional packing bioretention ponds were only 42.76%.the improved bioretention pond has a significantly better control effect on the SS concentration in rainwater than the traditional packing bioretention pond,and the BSM+10%Mn MZ packing bioretention pond has the strongest and most stable control of SS.（5）The average load reduction rates of modified zeolite-filled bioretention ponds to NH₄⁺-N,NO₃^--N,TN and TP in rainwater are 66.57%～77.88%,54.97%～72.26%,30.48%～71.76%and 78.43%～94.99%.Among them,the average reduction rate of NH₄⁺-N by adding 10%EDTAMZ filler bioretention pond is 77.88%,and the average load of NO₃^--N in adding 10%Mn MZ filler bioretention tank is72.26%,which shows that Mn MZ and EDTAMZ are added as modifiers to traditional fillers can significantly improve the effect of bioretention ponds on stormwater runoff stagnation and interception.