Research On The Rainwater Collection And Utilization In Large-Scale Region Based On Water Quality Characteristics

At present,the construction of sponge city is booming in China,and collection and utilization of the rainwater is one of the important contents of sponge city construction.In this study,initial rainfall was defined as the runoff that had a higher contaminant concentration than the Grade A limit values for the“Discharge standard of pollutants for municipal wastewater treatment plant.”The Storm Water Management Model?SWMM?was used to simulate the rainy day outflow in the Huangxiao River area of Wuhan.To research the suitable initial rainfall criteria and initial rainfall storage pool setting schemes for large-scale areas in Wuhan.The sub-area was evenly embedded in the LID facility,and SWMM was used to simulate and analyze the influence of different layouts of the single LID facility on the water quality and quantity in the rainy day,than to seek the best combination LID.The rainwater runoff of several typical underlying surfaces in Wuhan was monitored and the physical form of the pollutants was analyzed to lay the foundation for the formulation of the rainwater treatment plan.According to the difference of climate environment in the north and the south,several typical cities were selected.SWMM was used to simulate the water quality and quantity of rainwater in large-scale areas,and the rainwater utilization schemes in the south and north were analyzed.The main findings are as follows:?1?SWMM was used to simulate the rainy day outflow in the Huangxiao River area of Wuhan.The variations in the initial rainfall duration,runoff depth,runoff ratio,and flushed contaminant ratio were analyzed under different rainfall intensities and catchment areas were obtained.The results showed that the initial rain runoff depth of7mm was suitable for the initial rainfall criterion of the large-scale rainwater drainage system in Wuhan.The setting scheme of the Wuhan preliminary rainfall storage tank should adopt at the end of the rain pipes.The comparative analysis of rainfall characteristics in the small-scale Poly Lafite community and the sub-catchment area of large-scale drainage system showed that the regularity of the initial rain characteristic parameters was same basically,the smaller the catchment area,the smaller the initial rain runoff depth.The initial rainfall runoff depth in the catchment area of 9.33ha was 3⁴mm.?2?Three LID facilities,namely,concave green space,permeable pavement and green roof,were added evenly in lage-scale area,and SWMM was used for simulation.The results showed that the setting standards ofthe concave green space,the permeable pavement,and the green roof werer 1%,3%,and 1%of the total catchment area.The reduction rates of total runoff,initial rain runoff,total pollutant amount and initial rain pollutant were about 32%?58%?63%and 72%.?3?The monitoring results of rainwater runoff on roofs,pavements and parking lots in Wuhan indicated:the pollution of the road runoff was the most serious,the pollution of the parking lot runoff was higher than that of the roof runoff except that the concentration of TN.Compared with flat roof,inclined roof pollution was more serious.Nitrogen in the runoff of the three underlying surfaces was mainly dissolved,and the dissolved nitrogen in the roof runoff was dominated by NO₃^--N.The NO₃^--N and NH₄⁺-H in the parking lot and the path flow were basically flat.If the initial rain was treated with a chemically enhanced primary treatment,the removal rates of COD,TN and TP could reach 45%,15%and 50%.?4?Selected typical cities in the north:Harbin,Dalian,Lanzhou,typical cities in the south:Wuhan,Hangzhou,Nanjing,using the generalization model of the large-scale area,combined with the local initial pollutant amount and rainfall sequence,simulated and analyzed the non-initial runoff ratio and non-initial runoff depth.The results showed:in the southern cities,the non-initial runoff was abundant,and the northern cities had less non-initial rainfall than the southern cities.Therefore,the northern cities could intercept some of the early rains for further treatment.The typical cases of rainwater utilization in the north and southwere selected for analysis.The results show that collecting rainwater for treatment could save water resources and brought economic benefits.