| Due to the rapid development of urbanization,the original pervious pavement is replaced by hardened pavement.A large number of pavement pollutants enter the natural water body with rainwater runoff,which seriously threatens the urban aquatic ecological environment.At the same time,in some old urban areas,due to the limited interception multiple of the combined drainage system,there is a combined overflow.Domestic sewage changes the quality of rainwater and aggravates the pollution of pathogenic microorganisms in urban waters.Rainwater filter is a common facility for urban nonpoint source pollution control.Generally speaking,rainwater filter includes biological retention filter and rainwater retention filter.In the process of renovation of urban sponge facilities in China,bio-retention filters are widely used.However,the purification capacity of single facility for heavily polluted rainwater is limited,and the removal effect of nitrogen and phosphorus is unstable,while the effect of bacteria removal is not clear.In order to improve the removal efficiency of rainwater runoff,combined drainage system overflow and road snow melting,this paper investigates the combination of rainwater retention filter and biological retention filter with modified zeolite filler as filter layer.Firstly,a modified filler for rainwater retention filter,copper-loaded zeolite,was prepared.Its surface characteristics and removal efficiency of representative pollutants under static conditions were measured,and compared with fine sand and natural zeolite.The results showed that the three kinds of fillers had certain removal capacity for COD,total phosphorus,ammonia nitrogen,etc.Among them,copper-loaded zeolite had the strongest removal capacity for pollutants;copper-loaded zeolite had the highest removal rate of Escherichia coli.,followed by natural zeolite,and fine sand;therefore,copperloaded zeolite could be used as rainwater.Modified packing for retention filter.Filling column experiment was used to investigate the effect of filling mode and proportion on pollutant removal efficiency of rainwater retention filter.The rainwater filter filled with natural zeolite and copper-loaded zeolite had better removal rate of Escherichia coli,chemical oxygen demand and ammonia nitrogen than layered filling type,and had little difference in phosphorus removal efficiency.At the filtration rate of 0.06 m/h,the influent pollutant concentration simulated biological retention filter.Under the experimental conditions of effluent pollutant concentration,the effect of 1:1 mixed filling is the best.The pollutant removal efficiency of rainwater retention filter decreases with the increase of filtration rate,and the load of chemical oxygen demand decreases the fastest.Therefore,the service area of the filter should be limited by chemical oxygen demand.A combined rainwater filter was formed by connecting a 1:1 mixed filled rainwater retention filter with a biological retention pond planted with iris and replaced with sandy loam soil.The treatment effects of polluted rainwater and snow melting with different rainfall intensities were investigated.The results show that the combined rainwater filter can treat the polluted rainwater and snow melting well.When the filtration speed is 0.10 m/h,the polluted rainwater and snow melting can meet the water quality standard of landscape environment.In the combined filter,the removal of total suspended solids,chemical oxygen demand and ammonia nitrogen is mainly carried out in the biological retention filter.The removal ratio of chemical oxygen demand increases with the increase of rainfall intensity,from 61.87% to 68.60%.The removal rate of total phosphorus is mainly in the modified filler rainwater filter,with the highest removal rate of 92.86%.The total removal rate of Escherichia coli.s stable at 98%.The removal rate of lead in the biological retention filter is increased with the increase of rainfall intensity.The removal rates of son,zinc ion,copper ion and cadmium ion are all above 99%. |
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