Purification And Throttling Effect Of Multilayer Modified Filter Media On Urban Rainwater

At present,the vast majority of urban rainwater in China is directly discharged into the municipal pipe network for processing.There are two main problems with this approach: The city can On the one hand,the permeability ground of city reduced with the rapid growth of urbanization,therefore,the heavy rainfall in short periods can easily lead to urban flooding;on the other hand,pollutants in urban roads and houses can not penetrate into the soil,is discharged into water around the city and then affect water quality.More and more cities are not development because the improper rainwater treatment and are faced serious water shortage in China.It is concluded that the treatment of rainwater by infiltration,storage,treatment and drainage has important significance.The technology that is filtration and natural infiltration could treat urban rainwater,its treatment performance are that pollutants can be effectively intercepted and absorbed in rainwater runoff and that the filter layer can delay the time of runoff generation and reduce the amount of runoff.Therefore,it is great economic and environmental significance to study the urban rainwater treatment system with different combination of filtration and natural soil infiltration.The artificial water distribution is used to experimental water.According to the calculation,determination and analysis of the three actual runoff,the range of COD,ammonia nitrogen,total nitrogen,total phosphorus and turbidity in artificial water distribution were determined.With the analysis of three rain water quality: The contents of organic matter,ammonia nitrogen,total nitrogen and turbidity in the rainwater runoff are higher.In the early 20~30 min of rainfall,the concentration of pollutants in pavement and roof runoff is high.With the increase of rainfall in the rain,the late pollutant concentration decreased rapidly.The dry period is longer before rainfall,and the concentration of pollutants is higher in the initial runoff.The removal ability of each pollutant in runoff under different kinds of filter media was studied.The samples were selected from 0.5 ~ 1 mm quartz sand,1 ~ 2 mm quartz sand,0.5 ~ 1 mm zeolite,1 ~ 2 mm zeolite,1 ~ 2 mm ceramic,2 ~ 4 mm ceramic,0.5 ~ 1 mm broken brick,1 ~ 2 mm broken brick for the alternative filter.And then they are used for static adsorption experiments.Three filters were selected for subsequent modification and dynamic experiments.The best adsorption capacity of COD by different filters individually was: 1~2 mm ceramsite is 0.369 mg·g-1.The best adsorption capacity of ammonia nitrogen by different filters individually was: 0.5~1 zeolite is 0.066 mg·g-1.The COD and ammonia nitrogen adsorption of broken brick is better than quartz sand,but zeolite,ceramsite and quartz sand were selected as the filter media for the diafiltration system because broken pieces will be broken.Zeolite,ceramsite and quartz sand were selected for subsequent modification and dynamic testing.The three filters selected in the static adsorption experiment were modified for dynamic experiments.With the electron microscope scanning picture,the modified quartz sand was from the original smooth into a rough surface attached to the crystal particles,the surface of the ceramic particles becomed larger and its surface attached to the same crystal particles,the zeolite looked more fluffy and the pores were slightly larger.By X ray diffraction,it was found that the modified quartz sand increased the content of hematite(Fe2O3)and magnetite(Fe3O4),and the ceramsite increased components(?-Fe2O3)and goethite(?-FeO(OH)).Zeolite added soda stone(NaHCO3),natron(Na2CO3·10H2O)and ice salt(NaCl·2H2O).The static experimental results show that the modified ceramsite has the best adsorption effect on COD,the equilibrium adsorption capacity is 0.37 mg·g-1 and increased by 7.15% compared to unmodified.The modified zeolite had the best adsorption effect on ammonia nitrogen,the adsorption capacity was 0.074 mg·g-1and increased by about 12.12% compared with that before modification.The modified filter material is combined with the matrix soil,which was used to combine a single type of modified filter material and a combination of modified filter media with the substrate soil.Finally,dynamic experiments were carried out with various combinations of simulated soil columns.The results show that the matrix soil has no effect on the experimental results.When the single filter was combined with the matrix soil,the concentration of pollutants in the final effluent was lower than that of the pure soil control group.The average concentration of COD and ammonia effluent respectively was 15.12 mg·L-1,0.48 mg·L-1.Under the combination of the filter material and the substrate soil,the comparison of four different kinds of particle size and the thickness of the filter is carried out.On the scheme II-2(15 cm modified ceramic +10 cm modified quartz sand +5 cm modified zeolite),the average concentration of effluent COD was 12.24 mg·L-1,the average concentration of ammonia nitrogen was 0.71 mg·L-1.The runoff time was delayed by 325,190 min,and the runoff was reduced by 54.22,60.95 mm under the condition of heavy rain and rainstorm.Therefore,the effect of scheme II-2 on the contaminant removal efficiency and the effect of water saving is the best combination scheme.