Research On Physical Clogging Process And Practical Application Of Horizontal Subsurface Flow Constructed Wetlands

The party’s 20 th congress proposed "building a livable,working and beautiful countryside".In recent years,the discharge of rural domestic sewage in China has increased sharply,and the dispersion of residents has brought severe challenges to rural centralized sewage treatment.A distributed sewage treatment process,namely a small horizontal subsurface flow constructed wetlands,is widely used,but physical clogging has always been a difficult problem in its operation.Therefore,this thesis studies the physical clogging process of horizontal subsurface flow constructed wetlands,in order to provide more reasonable domestic sewage treatment methods for rural areas.The main research work is as follows:In order to understand the hydraulical behavior of the physical clogging process of the horizontal subsurface flow constructed wetlands,the physical clogging process of the horizontal subsurface flow constructed wetlands experimental system was studied by TSS concentration determination and Na Cl tracer experiment.The results showed that the porosity of the system decreased by 6.31% during the experiment,and the deepening of the blockage process,the short circuit and mixed flow of the system.The actual hydraulic retention time(0.281h)was most affected by the blockage,and the decrease rate was faster than the theoretical hydraulic retention time(0.073h).In order to reveal the physical clogging process of the horizontal subsurface flow constructed wetlands,CFD-EDM was used to numerically simulate the hydraulics of the experimental system,construct a spatial and temporal distribution model of physical clogging,and verify the feasibility of the numerical simulation through tracer experiments.The spatio-temporal distribution model was used to analyse the TSS concentration,material accumulation and porosity values at any point in the system at any time,revealing the physical clogging process of the internal structure of the system.In order to prolong the time for blockage to occur in the horizontal subsurface flow constructed wetlands,the physical clogging spatial and temporal distribution model constructed by CFD-EDM was used to optimise its structure,and the effect of baffle setting on the flow field and particle accumulation effect of the physical clogging model was investigated.The results show that the baffles can effectively improve the particle deposition efficiency,and that vertical baffles are more effective(15% longer time for complete blockage to occur and 21% higher hydraulic efficiency).Therefore,the addition of vertical baffles in the design of horizontal subsurface flow constructed wetlands structures can effectively extend the physical clogging time and improve the hydraulic performance.Finally,based on the structural optimization scheme of horizontal subsurface flow constructed wetlands and combined with the actual use needs,a small horizontal subsurface flow constructed wetlands sewage treatment system suitable for rural areas is proposed.And this system practice is applied to the domestic sewage treatment and landscape construction of prosperous Village,Ruian city.