Construction And Operation Effect Analysis Of New-type Subsurface Flow Constructed Wetland System In Winter

At present,the shortage of water resources and the pollution of water environment have become a worldwide problem.As an emerging wastewater treatment process,constructed wetland has the advantages of low construction cost,high efficiency,convenient maintenance and management,and has the functions of ecological restoration and landscape beautification.It is in line with the international concept of miniaturization and decentralization of wastewater treatment,which is widely promoted in most countries all over the world.However,the treatment of wastewater by constructed wetlands will be affected and restricted by many factors,such as temperature,dissolved oxygen（DO）,matrix properties,plant types,soil microorganisms and so on.These factors limit the purification effect of constructed wetlands,which in turn limit the promotion and application of wetlands.Temperature is a limiting factor of constructed wetlands among them,which restricts the promotion and application of constructed wetlands in cold regions,because the removal of nitrogen and phosphorus and other pollutants by the wetland system is significantly reduced under low temperature environment.Particularly,winter temperatures will drop below zero in most parts of northern China,so that many wetlands will be frozen and unable to operate normally.Based on this,this paper has carried out the research on a new type of constructed wetland in winter.The main research contents and results are as follows:（1）Aiming at the problem that the wetland is affected by the low temperature,which causes the removal effect of wastewater to be reduced,this paper proposes a new type of constructed wetland structure,which uses shallow geothermal energy to increase the internal temperature to ensure that the wetland system can run normally in winter.（2）Before the construction of the wetland,in order to determine whether the internal temperature of the wetland can reach the expected goal under the condition of shallow geothermal energy,a groundwater-heat transport model was constructed.The simulation results show that under the action of shallow geothermal energy,the final outlet temperature can reach the expected temperature,indicating that the proposed new-type wetland structure in winter is feasible.（3）In order to verify the removal effect of wetlands,a new type of wetland structure was constructed,and experiment was conducted.The results show that the wetland can operate normally and no freezing phenomenon occurs in winter under the effect of shallow geothermal energy,indicating that the wetland under shallow geothermal energy insulation can ensure normal operation in winter.（4）Through experiment,the removal effect of nitrogen,phosphorus and other pollutants in the wetland system was studied.The results showed that the average removal rate of TP,TN and NH₄⁺-N in the wetland system reached 77.7%,54.8%and 44.5%respectively in winter,and the overall removal effect was good.（5）Comparing the removal effect of wetland system on pollutants such as nitrogen and phosphorus with other thermal insulation methods,the results show that the wetland structure proposed in this paper has the advantages of good effect,no pollution,simple maintenance,etc.,which has good practical value.