Effect Of Substrate Configuration On Constructed Wetland Performance And Greenhouse Gas Flux

Constructed wetland（CW）,known as a new ecological sewage treatment technology technology,has the advantages of low cost,low energy consumption,simple operation and convenient operation and maintenance and has been widely used indomestic wastewater,industrial effluent,agricultural wastewater and other wastewater treatment filed.However,the emission of greenhouse gases（GHGs）,mainly including carbon dioxide（CO2）,methane（CH4）and nitrous oxide（N2O）,has become a global problem in the process of treating wastewater in CWs,which have attracted widespread attention of all walks of life.Finding a green and efficient way to mitigate the net global warming potential（GWP）on the basis of maintaining pollution removal efficiency has been a priority task that needs to be solved.In this study,based on the vertical subsurface flow CWs,we set up different substrate types（gravel,walnut shell,manganese ore and activated alumina）and combinations,studied the influence of substrate feature on the CO2,CH4 and N2O emission flux,analysised the relationship between substrate characteristics and microbial community combining the change of the microbial community structure and diversity in wetland,revealed the mechanism of substrate configurations affecting GHGs flux,and provided a new strategyand theoretical basis for mitigating GWPs and strengthening the performance of CWs.The main research conclusions are as follows:（1）The removal effects of pollutants of CWs with various substrate types were significantly different,especially the best sewage purification performance was found in CWs with manganese ore.And the removal rates of COD,NH₄⁺-N,TN and TP in CWs with manganese ore were 90.1%±4.3%,84.1±3.7%,65.1±4.0%and 97.1±2.2%,respectively.（2）Compared with single substrate CWs,composite substrate CWs has its unique advantages.For example,CWs with substrate combination including walnut shell and manganese ore fully solved the problem of denitrification inhibition,although it also leads to the decrease of COD and TP removal efficiencies.（3）The GHGs fluxes of CWs with various substrate types were significantly different,especially the obviously decrease of N2O and significantly increase of CH4emission fluxes was in CWs with walnut shell substrate,which greatly promoted the global warming potential of the CWs.On the contrary,the average CH₄ emission flux in manganese ore CWs is only 2.00 mg m^-2h^-1,which makes a significant contribution on the mitigation of greenhouse effect of CW.（4）The combination of substrates significantly affects N₂O and CH₄ emission fluxes.When walnut shell substrate is combined with manganese ore substrate or activated alumina substrate,the CH4 emission flux will be significantly reduced,and there was the lowest N₂O emission flux in CW with walnut shell and manganese ore substrates.（5）The results of microbial analysis suggested that the substrate configuration mainly affected the microbial community structure to achieve good sewage purification effect and lower GHGs emission fluxes.