| As one of the important measures of low-impact development(LID),bio-retention facilities treat pollutants in rainwater mainly through a combination of physical,chemical and biological effects,especially the treatment of suspended solids,grease,heavy metals and viral microorganisms.good.However,the traditional biological retention facilities have problems of poor and unstable nitrogen and phosphorus removal,so it is necessary to improve the traditional biological retention facilities.First,the paper carried out static adsorption tests on different substrates and different combinations of substrates to obtain substrates for nitrogen and phosphorus removal.It is optimized and the optimal combination matrix ratio is determined through dynamic adsorption test.According to the initial rainwater runoff water quality of Nanchang urban roads,the impact of improved biological retention facilities of different structure types on the removal of pollutants from road rainwater runoff during different rainfall recurrence periods A comparative analysis was carried out.Using Design-Expert software to further optimize the external factors(recurrence period,confluence ratio,drought period before rain)and internal factors(height of submerged area)of biological retention facilities,and analyze the impact of improved biological retention facilities on runoff pollutants under optimal conditions Remove performance.The main research results are as follows:(1)Biological retention facilities are preferred for removing nitrogen and phosphorus static and dynamic attachment substrates.In the dynamic equilibrium process of nitrogen and phosphorus attachment and desorption of several substrates,sponge iron has the best adsorption performance for phosphorus,and zeolite has the best adsorption performance for ammonia and nitrogen;different combinations of substrates in the dynamic equilibrium process of nitrogen and phosphorus attachment and desorption,sponge The combined matrix of iron and zeolite has the best adsorption performance of phosphorus and ammonia nitrogen among the seven combined matrices,which is an order of magnitude higher than that of other matrices.Through the laboratory simulation test device,the volume ratio of zeolite to sponge iron is 5:5,3:7,A 7:3 dynamic adsorption experiment was conducted to study their removal efficiency for phosphorus and ammonia nitrogen.Taking into account the removal efficiency of the entire packed column for total phosphorus and ammonia nitrogen,the mixing ratio of zeolite to sponge iron 3:7 is the best choice.Therefore,a 3:7 mixed ratio of zeolite and sponge iron was selected as the improved matrix for the biological retention facility.(2)Study the impact of the improved bio-retention facilities on the removal of pollutants from the channel flow during different rainfall recurrence periods.Main conclusion:The difference in the structure of the biological retention facility greatly affects the removal efficiency of COD,TP,NH4+-N,NO3--N and TN due to the rainfall intensity,while SS is less affected by the rainfall intensity;the precipitation reappears During the period 0.5a and 1a,the removal of SS,TP,NH4+-N by the biological retention facility units No.1,2 and 3 is better,and the removal rates of SS are 70.8%,81.25%,78.04%;for TP removal The rates were 54.76%,89.89%,75.07%;the removal rates of NH4+-N were 61.63%,84.35%,and 82.17%,respectively.During the precipitation recurrence period 2a and 5a,the No.1,No.2 and No.3 biological retention facility units had better removal effects on COD,NO3--N and TN,and the removal rates of COD were 71.47%,81.84%and 85.03%,respectively;The removal rates of NO3--N were 43.85%,58.44%,73.21%;the removal rates of TN were 50.93%,65.83%,and 86.97%,respectively.In general,the effluent quality of Unit 1 bioretention facilities is poor,and only some of the indicators have reached the surface V water standard.The quality of the unit effluent of Unit 2 and 3 bioretention facilities has basically remained the same,even reaching the average level V water specification.Reached Class ? water specifications.(3)Comparative analysis of the removal effects of monomers of different types of biological retention facilities on runoff pollutants.The results show that the change in the structure of biological retention facilities does not interfere much with the removal effect of SS pollutants;the effect of reducing the precipitation intensity on the removal effect of the system facilities can be achieved by changing the type of filler and setting the submerged area on the structure.Among them,when the rainfall recurrence period is less than or equal to 2 years,the impact of changing the filler type on reducing the precipitation intensity is more obvious,and the setting of the submerged area is more effective when the recurrence period is 5 years or 10 years.The setting of submerged zone has certain promotion effec't on the removal of NO3--N and TN,and has a certain negative effect on the removal of TP and NH4+-N,and has little effect on SS pollutants.(4)Research on the purification efficiency of improved biological retention facilities by response surface optimization method.The results showed that the optimal conditions for the purification efficiency of the improved bioretention facilities using response surface optimization were the recurrence period 5a,the reflux ratio 10:1,the height of the submerged area 41.08cm,and the pre-rain drought period 4.46d.Under this condition,the average removal efficiency of runoff pollutants by the improved bioretention facilities has increased by about 5%to 10%compared with the prior optimization. |
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