The Removal Efficacy And Mechanism Of Heavy Metal From Runoff By Permeable Pavement System Based On Enhanced Materials

As one of the most typical sponge facilities,permeable pavement system(PPS)had a high prospect of application in China.However,compared to other sponge facilities.PPS had relatively weak control of runoff pollution,especially for heavy metals(HMs),And there was no systematic understanding about the migration and transformation behavior of HMs in stormwater runoff as well as in facilities.In this study,new enhanced infiltration materials(construction waste brick,coal gangue,activated carbon,multi-walled carbon nanotube,multi-layer graphene)were applied in PPS and the control efficiency and mechanism of typical HMs(Mn,Pb,Zn,Cu,Cd and Ni)in runoff was investigated.This study systematically investigated the application value of the selected fillers in terms of material leaching,hydraulic performance,dynamic process,long-term operation capability,and adaptability to different working conditions.The morphological distribution and transport of HMs in the system were also analyzed.This study aimed to provide references for the operation and maintenance of the PPS.The results showed that:(1)Construction waste brick permeable pavement system(CW)and coal gangue permeable pavement system(CG)could significantly improve the water storage capacity and infiltration capacity of the system.The six PPS had a low concentration of dissolved HMs,and the metals were mainly Mn and Zn.The effluent concentrations of HMs in different PPS showed a basically consistent trend: a sharp decrease in the early stage,followed by different degrees of increase.Compared with traditional permeable pavement(TR),Activated carbon permeable pavement system(AC)had the best enhancement effect on the removal of HMs,and followed by multi-layer graphene permeable pavement system(MG)and multi-walled carbon nanotube permeable pavement system(MCN).Each structural layer of the PPS had a certain ability to remove Pb,Cu,and Cd.Mn,Zn.and Ni were more dependent on the surface layer and bedding materials.The lower and middle parts of the bedding layer were prone to the precipitation of HMs.The enhanced materials could significantly affect the pattern of HMs.The pattern stabilized with increasing depth,and migration became gradually weaker.The enhanced materials increased the proportion of Fe-Mn oxide bound state of Mn and Pb,and three carbonaceous materials significantly reduced the residual state of most HMs.(2)When the rainfall intensity was below 10 a,the removal rate of HMs tended to increased with the increase of rainfall intensity.When the rainfall intensity reached20 a,the removal of HMs got worse.The rainfall intensity had little effect on pollutants with higher removal rates(e.g.,Pb,Cu,and Zn)and PPS with better removal performance(e.g.,MCN,MG),but significantly interfered with pollutants with lower removal rates(e.g.,Mn,Ni,and Cd)and PPS with poorer removal performance(e.g.,CW,CG).The control of HMs by the PPS improved significantly with the increase of dry period.The order of the influence of the drying period on the removal of HMs in the PPS was: CW >CG > TR > MG > MCN> AC.The initial concentration had less influence on the dynamic change trend of the PPS.Carbonaceous materials could better adapt to the change of initial concentration in the role of surface particulate matter,the surface layer played a more important role in the removal of HMs from the PPS.In particular,the effect was more pronounced for HMs with a greater proportion of particulate matter forms(e.g.Pb and Cu)(3)With the increase of operating time,the control capability of PPS for HMs gradually weakened.The performance of CW,CG and TR deteriorated significantly with the growth of service life.AC,MCN and MG could improve the long-term pollution control performance of PPS.With the cleaning process,the outflow concentration of each PPS gradually decreased.The cleaning outflow of 5 years pollution was mainly dominated by Mn and Zn,and the proportion of HMs outflow was more uniform during 10 years.The cumulative concentration order of PPS outflow was: CG> CW > TR > AC > MG > MCN.The ecological risk evaluation results showed that the bedding structure is the most seriously polluted,followed by the surface layer.Cd was the main ecological risk potential source,followed by Pb and Cu.The pollution status of several PPS was CG>MCN > MG >AC > CW.The dominant bacterial phylum in the PPS was Proteobackteria,with the abundance of each modified filler ranging from 43.62% to 70.92%.The community distribution at the level of "genus" is uniform.The dominant bacterial group of activated carbon was Acinetobacter.This study provides novel approaches for the resource utilization of solid waste and the engineering application of carbonaceous materials,which could expand the selection range of PPS and other facilities and promote the development of sponge city in China.