Hydraulic Characteristics Of Composite Vertical Subsurface Flow Constructed Wetland Based On CFD

In recent decades,the problem of water environmental pollution has become increasingly prominent.With the gradual improvement of people's awareness of environmental protection,people realize that green mountains and green waters are the gold and silver mountains.As a new decontamination technology,constructed wetland has obvious advantages compared with the traditional secondary wastewater treatment plant,such as less capital investment and low operating cost.The hydraulic law of wetland system has a profound influence on the efficient operation of wetland.In this study,the fluid dynamics numerical model of wetland was established by using OpenGeoSys software to simulate and analyze the hydraulic characteristics of constructed wetland with vertical subsurface flow.The main research contents and conclusions are as follows:(1)The hydraulics characteristics of the composite vertical subsurface flow wetland were simulated and compared with the numerical model based on the 8 tracer experiments and the established numerical model,so as to verify the effectiveness and credibility of the model.To model the parameters in the saturated permeability coefficient K and the inflow discharge Q respectively set up multiple magnitude of wetland simulation,studied the influence of these two parameters on the simulation curve:based on the matrix permeability coefficient K,inflow flow rate Q,respectively,set up multiple scale model parameters influence forecast:with the increase of particle size of the matrix,the permeability coefficient K increase,the hydraulic efficiency of wetland showed a trend of decrease,to say the saturated permeability coefficient can indirectly reflect the effects of particle size of the matrix wetland hydraulic efficiency,with the decrease of the particle size of the matrix can reduce the hydraulic diffusion inside the wetland system,making the hydraulic efficiency is optimal.With the increase of inflow Q,the theoretical hydraulic residence time decreases,and the hydraulic efficiency of wetland increases.However,it is not in the design and operation process of subsurface flow wetland that the larger the inflow flow and the smaller the wetland matrix will make the purification efficiency of the wetland better.It is necessary to analyze the combination from various aspects reasonably to achieve the optimal operation efficiency of the wetland.(2)The correction of the numerical simulation model to predict four matrix approach(transverse 1,lateral 2,longitudinal 1,2)the efficiency of artificial wetland and artificial wetland system under different substrate laying way hydraulic characteristics and the treatment effect is different,including:(1)when the compound wetland system hydraulic retention time,certain matrix of the change of the mode of laying has certain influence on the running efficiency of wetland,lateral 2 configuration wetland system hydraulic efficiency value is 0.68,has good effect in the four kinds of situations;(2)from the perspective of engineering practice,in the case of the hydraulic efficiency difference is not large,the vertical layering because of the complexity of the way of laying,it is difficult to make it reach the best hydraulic state,and the horizontal 2 distribution of the wetland system short circuit value is 0.64,short flow,dead zone and other phenomena in four cases with the smallest probability;The maximum effective volume ratio of transverse 2 is 0.87.The short flow phenomenon is small in the wetland system with relatively large effective volume,which indicates that the effective volume is large in the lateral 2 wetland system.In summary,the operation efficiency of the horizontal 2 wetland system is the highest.(3)Under the premise that the matrix laying method achieves the optimal efficiency,the influence of different outlet locations on the hydraulic performance of the corresponding wetland system model was studied,and the hydraulic efficiency index was compared,and the conclusion that the lower outlet wetland operation efficiency was the highest was obtained.