| In recent years,the development of industry and the growth of population have led to the worsening of water resources crisis,which not only affects the sustainable development of cities,but also endangers the survival of human beings themselves.The problem of water pollution needs to be solved urgently.As a kind of efficient,reliable,low-cost and ornamental wastewater treatment technology,constructed wetland has been widely used at home and abroad.However,with the increase of urban population,there is less and less land suitable for the construction of constructed wetlands in cities,while the traditional wetland needs a larger area.In addition,a large amount of rainwater on roofs and overpasses is an important factor aggravating urban water pollution.How to make full use of the water head of these high-rise buildings to solve the hydrodynamic problem of constructed wetlands is also a problem we are facing.The contents of this paper include:1)In view of the above problems,this paper proposes a space-saving new spiral composite constructed wetland,and compares the performance of new spiral composite constructed wetland with that of ordinary composite constructed wetland through constructing comparative tests.During the test,samples were collected at the water outlets of two wetlands every three days,and the COD,NH4+-N and TP were detected.2)The experimental results showed that:（1）Under the same conditions,the average removal rates of COD,NH4+-N and TP in the new spiral composite constructed wetland are80.25%,72.60%and 81.50%,respectively,which are better than those in the ordinary composite constructed wetland（73.23%,62.11%and 77.56%）.（2）Compared with the common ordinary wetland,the spiral stepped composite constructed wetland designed in this paper can make the sewage drop from a high place,which solves the problem of sewage migration and eliminates the pumping link.In addition,spiral constructed wetland can be used for wastewater treatment with high head,and dropping water aeration can also increase the content of dissolved oxygen in sewage,which is conducive to the removal of pollutants in water.（3）In the case of large number of wetlands,the spiral stepped constructed wetland is more space-saving than the ordinary composite constructed wetland and the stepped constructed wetland that needs to be built on the slope.It is flexible in combination,simple in maintenance,and has ornamental value.Therefore,it can become the first choice of technology in the case of land resource shortage.3)With the development of computer technology,pollutant degradation simulation with the help of models has become an effective means of research.Therefore,in order to verify the feasibility of using the model to simulate the constructed wetland and to provide reference for the application of the wetland model in actual engineering,this paper uses the PREWET model and the CW2D model to simulate the surface flow constructed wetland and the subsurface flow constructed wetland respectively,and carries out the numerical simulation of COD and TP migration in the new spiral composite constructed wetland.The simulation results show that the simulation results of COD and TP are 83.16%and 85.00%respectively,both of which are slightly better than the experimental results of 80.25%and 81.50%,but the error is small.Therefore,the simulation results are very reasonable,and it is feasible to use CW2D model and PREWET model to simulate the constructed wetland.4)On the basis of verifying the feasibility of using CW2D model to simulate the constructed wetland,in order to reduce the upfront cost,a spiral slide type constructed wetland to be built in an urban park was simulated.The results show that the removal rates of COD,NH4+-N,NO3--N and TP in the subsurface flow constructed wetland reach 92.87%,84.47%,91.67%and 95.22%,respectively,achieving a good purification effect,which can become a kind of landscape sewage treatment system and can be put into construction. |
