The Transmission Of Methane In Vertical Flow Constructed Wetlandplanted Cyperus Alter

Methane?CH₄?emission from constructed wetlands plays a key role in the concentration of methane in the global atmosphere,and is the main source of methane emissions.CH₄ is first produced by Methanogens in the substrate,and oxidized by Methanotrophs,then released into the atmosphere through three ways.The three ways includes plant transmission,bubble propagation and diffusion transmission,and plant transmission is the main way.Therefore,this study of CH₄ transmissioninternal plants in constructed wetlands has great significance for the control of CH₄ emission from constructed wetlands for the protection of the ecological environment.In this paper,the CH₄ transport and emission in a vertical flow constructed wetland planted Cyperusalternifolius were studied by macroscopic experiment and microscopic simulation.On the one hand,artificial vertical flow constructed wetlandswere constructed then the CH₄ emissions of four vertical flow constructed wetlands was monitored by using anonlinesingle chip microcomputer to control gas detectors.On the other hand,after the end of the emission monitoring experiment,the methane transmission efficiency of the height of the stem of Cyperusalternifolius was analyzed at0-25 cm,25-60 cm and 60-95 cm respectively.In microscopic experiments,electron microscope scanning was used to dissect the roots and stems of Cyperusalternifolius,so as to construct the three-dimensional structure inside the plant.Methane monitoring data as the basic initial data was used to simulate the movement of CH₄ inside the root and stem trachea of irregular plants from the microscopic point of view in order to explore the transmission route of CH₄ inside the vegetation.The simulation model is compared with the experimental results in this paper to verify the reliability of the model.The results show,under natural conditions,planting 3 plants in the strong ye ars and planting 9 plants in the strong years were in the same trend of CH₄ emis sion from spring?March,April,May?to winter?December,January and February?,and CH₄ emission flux was the largest in October.The CH₄ emission fluxes of planting 3 plants at young age and planting 9 plants at young age were the large st in summer,527.083 and 917.708 g/m^2/day respectively.The CH₄ flux of planting3 plants in the strong years and planting 9 plants in the strong years were the l argest in autumn,939.167 and 1004.167 g/m²/day respectively.Dissolved oxygen,conductivity,TC and TN are also factors affecting CH₄ emission.In this study,po lynomial regression model was used to get the relationship between CH₄ transport efficiency and temperature:y?28?-0.005x₁²?10?0.203x₁-1.882,?R²?28?0.582,P?28?0.013?.The relationship between CH₄ transfer efficiency and substrate temperature wasalso obtained[y?28?-0.012x₂ ²?10?0.412x₂-3.24,?R²?28?0.618,P?28?0.005?].Temperature and substrate temperature were the two most important factors affecting CH₄ emission,accounting for 60%and 19%respectively.By studying the transmission efficiency of methane in different parts of the single plant of Cyperusalternifolius,the methane release efficiency in different parts of Cyperusalternifolius was significantly different at 0-25 cm,25-60 cm and 60-95 cm?p<0.05?,and the average transport amount of CH₄ was the largest in the development period.The average transport capacity of CH₄ in the 25-60 cm part of the stem was 0.192g/m²/s at the growth period.The average CH₄ transport in mature 0-25 cm section was0.033 g/m²/s at the stem.The average CH₄ transport in the 25-60 cm parts of the stem was 0.078 g/m²/s during the senescence.In this study,the multiphase flow porous medium model,effect of instantaneous interface,small Reynolds number laminar flow,interphase force,wall drag force,and temperature change on transmission are considered as simulation mechanism.The movement rule of methane in roots and stems through the establishment and simulation of CH₄ transport mathematical model in root and stem of Cyperusalternifolius were investigated and monitored.According to the annual average CH₄ emission as the import condition,it was found that the relationship between the transport of methane between the main roots and the porosity of the four layer basin is very consistent.CH₄ is mainly transmitted along the direction of the catheter,and the transverse transmission exists but is very small.The proportion of CH₄ transmission volume distribution from the inside to outside of the four regions?C1?C2?C3?C4?is 24.3%,22.9%,31.3%and 21.5%,respectively.According to the daily emission rule of methane as an import condition,a series of changes of stratified flow,fluctuating flow and slug flow occur successively.The proportion of the two regions?C5?C6?of the export of Cyperusalternifolius stems from inside to outside accounted for 59.1%and 40.9%respectively.The emission efficiency of CH₄ at top outlet was 83%and the CH₄ emission efficiency was 16%.The CH₄ emission efficiency range of the stem top exit was 76%-82%,and the proportion of stem skin escaping from Cyperusalternifolius was 16%-20%.In this study,it was found that the microstructures of the leaves are more complex and diverse than the roots and stems,so that how to unify and simplify the simulation of the structure of the leaves is the difficult point in the next step.Plant size seriously affects the law of internal flow field,and the simulation of micro size is a difficult point for academic circles.The transport of methane in Cyperusalternifolius should undergo a complete life cycle from the substrate-root-stem-leaf-atmosphere,and it is difficult to select a reasonable material as verification test because the physical size of the main root is too small.The above will be the focus of the next stepfor CH₄ transmission in constructed wetland.