| During the construction of the sponge city in Chongqing,when the source-based emission reduction cannot be carried out due to the high development of the land,the terminal rainwater control facility(SCM)is usually set up at the end of the drainage pipe to achieve the goal of runoff control and pollutant reduction.However,because Chongqing is a typical mountain city,the terrain slope of the waterfront area is large,and the drop between the water outlet and the waterfront is large,resulting in a high flow rate of water out of the drainage pipe,which is easy to cause strong hydraulic erosion to the SCM and affect the normal operation of the facility.Therefore,based on the field investigation of the drainage outlet in the main city of Chongqing,this paper adopts the"drop sill"to dissipate energy according to the high drop terrain.FSDF),the optimal design configuration was determined,and the hydraulic energy dissipation mechanism was preliminarily verified;at the same time,when it was difficult to set up large-scale SCM due to the tight land use in the waterfront zone,a modular zeolite media filter device was innovatively proposed(MZMF),systematically investigated the removal characteristics of MZMF to SS under different water inflow and suspended solids(SS)concentrations,and based on the analysis of the spatial distribution of SS in MZMF,the effect of filter media layering on the decontamination performance of MZMF was explored,and put forward the corresponding optimization design scheme;finally,the paper explores the reoxygenation capacity of FSDF,and proposes the combined layout scheme of FSDF and subsequent SCM at the end of the drain.The main conclusions are as follows:(1)The numerical simulation results of the FSDF using the FLUENT software combined with the k-εturbulence model and the VOF model under the PISO algorithm are basically consistent with the experimental results of the physical model.The average errors of water depth and velocity are 9.14%and 7.64%,respectively,and the maximum relative errors are 11.50%and 9.20%,and the flow state of the numerical simulation is basically consistent with the flow state of the physical model,which meets the accuracy requirements and can be used for subsequent simulation research.(2)Using the constructed numerical model,the hydraulic process simulation of 7kinds of drainage energy dissipation facilities is carried out.The results show that the energy dissipation rate of the solid baffle falling sill energy dissipation facility is as high as 90%,and the outlet water velocity of the energy dissipation facility has nothing to do with the influent flow rate.It is only related to the height of the drop threshold and increases with the increase of the height of the drop threshold.The analysis of velocity vector,pressure distribution and turbulent flow characteristics shows that the higher the height of the drop sill,the water flow is easily affected by the potential energy to form a hydraulic vortex in the triangle area of the drop sill(the area where the vertical plane and the horizontal plane intersect),and the flow velocity is caused by the baffle blocking the flow.The significant change in the vector direction makes the energy dissipated to the greatest extent in the triangular area,and finally causes the maximum pressure of the water flow in the horizontal direction to decrease along the way to achieve the effect of hydraulic energy dissipation.(3)The MZMF device constructed with zeolite medium is suitable for runoff rainwater with different SS concentrations,and the interception rate increases with the increase of the treated water,but the infiltration rate(IR)decreases with the increase of the treated water,and shows a slow decline,rapid There are three stages of decline and stabilization.When the geotextile is not added for filler layering,the IR of MZMF can be reduced from the initial 30 m/h to 1.5 m/h,and the maximum processing capacity should be controlled within 55 m~3/m~2.The effect of SS concentration on the interception rate of MZMF is not significant,but the accumulation of SS interception makes the interception process show typical three stages:front,middle and late,in which the interception rate in the early stage is only 50%～60%,and it can be increased in the middle stage to 80%～85%,while in the later stage it can be as high as 89%～93%.The removal of SS by MZMF is dominated by surface filtration,supplemented by internal retention.During internal retention,most of the SS is retained at 1/2 the depth of the zeolite media filter material layer,and a small amount can reach 2/3 of the filter material layer.According to the vertical distribution of SS in the device,the addition of geotextiles at 1/2 and 2/3 depth of the filter material layer reduces the initial IR(28.4 m/h)and the maximum processing capacity(50 m~3/m~2),but significantly improved the interception rate of MZMF in the early and middle stages of the treatment.The study confirmed that the use of homogeneous filler layering measures can significantly improve the interception rate of MSMF.In addition,optimized methods such as mixed media packing or layered assembled packing can also be used to enhance the MZMF’s ability to intercept sewage at the outlet.(4)The use of solid baffle drop sill energy dissipation facilities can also form turbulent flow in the process of water flow steps,and carry air to form bubbles to naturally aerate the water body,thereby realizing the oxygen enrichment effect of the water body under different water inflows.Under different flow rates,the DO of the water body from the first-level drop threshold to the outlet section increased by 1.30-1.55 mg/L,the reoxygenation rate was 13%-16%,and the recovery capacity per unit height was 3.25-3.75 mg/(L·m),effectively increasing the demand for DO for subsequent ecological pollution interception facilities.According to the different topographical and spatial characteristics of the waterfront,the thesis proposes two layout schemes for sewage interception:FSDF+MZMF and FSDF+MZMF+ecological sewage interception facilities(such as Pitang wetland).Among them,when MZMF is used as the main pollution interception measure,the FSDF should be arranged horizontally on both sides and in vertical series at the ends;and when MZMF is used in combination with ecological treatment facilities,MZMF and ecological pollution interception facilities should be placed in sequence with the end of FSDF Connect vertically. |
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