Optimization Of Urban Garden Design Based On Rainwater Purification

With the rapid development of urbanization,the urban underlying surface has undergone tremendous changes.The original large-scale permeable pavement is gradually covered by cement,asphalt and other impervious materials,which has greatly changed the urban water cycle,resulting in frequent urban waterlogging disasters,serious imbalance between water supply and demand,rapid depletion of groundwater,aggravation of non-point source pollution and so on.Sponge city construction is achieved through low impact development?LID?technology.In the process of LID design and construction,economic,practical and eco-environmental multi-source control and management measures are adopted to reduce urban rainwater runoff and its pollutants,in order to minimize the impact on the environment.Urban garden is an important part of sponge city planning and construction.At present,the structure of rainwater measures in domestic urban gardens is relatively single,which leads to the failure of garden green space to effectively deal with the surrounding rainwater runoff,and the phenomenon of flooding of urban gardens and aggravating non-point source pollution occurs from time to time.Therefore,it is of great practical significance to optimize the design of urban gardens.Taking the Yao Lake Campus of Nanchang Institute of Technology as an example,3typical underlying surfaces?roads,roofs and turfgrass?were selected as the research objects to collect and analyze rainfall runoff samples,and to explore the current situation and characteristics of rainfall runoff pollution in Yao Lake area of Nanchang.Through literature review and related experiments,two types of fillers and two types of vegetation suitable for rain garden in Wuhan city were selected,and they were combined to build rainwater garden test simulation device?ecological filter column?with different structural types.Rainwater garden simulation experiment was conducted with artificial rainwater,and the main pollutants in urban stormwater runoff were studied by different vegetation and fillers combination.At the same time,four different hydraulic loads were set up to explore the removal effect of main pollutants in rainwater runoff by ecological filter columns under four different hydraulic loads.Combined with the engineering application,taking the ecological science and Technology Park of Nanchang Institute of Engineering as the research object,this paper analyzes the current situation of the related rainwater facilities,and puts forward a set of optimized design plan according to the analysis results,which provides the basis for the promotion of the city garden and the construction of the sponge city in the future.Main conclusions are as follows:?1?Rainwater runoff pollution in Yao Lake area is serious,and there is varying degrees of initial scouring effect.The concentration of suspended matter SS in the rainfall runoff of Yao Lake area in the city is 1.98².93 times that of the two level standard of the pollutant discharge standard of the municipal sewage treatment plant.BOD5,COD,TN and TP exceed the 2.18².42,2.23².48,1.65².31,1.08¹.98 times standard values of class V water in the"surface water environmental quality standard"respectively.The variation of pollutant concentration in urban runoff with rainfall duration is characterized by higher concentration of pollutants in the initial runoff.The pollutant concentration index of each runoff falls rapidly after the first peak,showing a certain initial scouring effect.As time goes on,the pollutant concentration gradually drops to a stable level.?2?The isothermal adsorption tests of N and P of fillers such as green zeolite,ceramsite,red soil and coarse sand show that red soil has the strongest adsorption capacity of N and P,and the adsorption capacity of P is significantly weaker than that of green zeolite and ceramsite.Therefore,adding appropriate amount of green zeolite and ceramsite into red soil can significantly improve the adsorption efficiency of N and P.Considering vegetation growth and nitrogen and phosphorus adsorption effect of fillers,it is advisable to use the composite filler layer of"40%red soil+50%chlorozeolite/ceramsite+10%rotten leaf soil"in rainwater garden.?3?The experiments of water purification and vegetation physiological indexes of different types of ecological filter columns show that the load reduction rates of TN in the first four experimental simulation devices are 1.68%¹8.32%higher than those in the blank control device without vegetation,and the load reduction rates of NH₃-N in the first four experimental simulation devices are 6.22%²2.95%higher than those in the blank control device without vegetation,respectively.The load reduction rates of TP in each device are 6.22%²2.95%higher than those in the blank control device without vegetation.The average load removal rate is 67.42%⁸2.93%.The TP reduction effect of 4^#simulator is better than that of 1^#simulator,and slightly better than that of 2^#and 3^#simulator.The rose garden is the most suitable vegetation for planting rainwater gardens in the market.The rose and green zeolite vegetation packing combination scheme is the best rainwater garden configuration scheme.?4?With the increase of inflow hydraulic load q,the removal rate of pollutants in rainwater runoff will decrease.The difference of COD reduction rate is 10%¹5%under high and low hydraulic load conditions,TN and NH₃-N reduction rate is 5%¹0%under high and low hydraulic load conditions,and TP reduction rate is 20%³0%under high and low hydraulic load conditions.It can be seen that the change of inflow hydraulic load has a significant impact on the actual operation effect of rainwater garden.