Study On Water Runoff Pollution Of Ecological Ditch Integrated With Artificial Wetlands

With the continuous acceleration of domestic urbanization,urban surface runoff pollution is changing towards a larger total amount,heavier pollution and more complex composition.Due to the randomness and intermittence of urban surface runoff,the traditional water treatment technology is difficult to meet the needs of urban surface runoff pollution treatment,so there is an urgent need for economic and reliable urban surface runoff treatment technology.Aiming at the problem of urban surface runoff pollution,this study designed and optimized the ecological ditch constructed wetland combined system to reduce runoff pollution through ecological treatment methods in the process of runoff migration.By comparing the purification effects of polyethylene（PE）plastic filling ecological ditch and ceramsite+zeolite filling ecological ditch under different simulated working conditions,combined with the characteristics of microorganisms,the purification mechanism of ecological ditch with different structures is analyzed;A compound vertical flow constructed wetland was constructed to investigate the impact of rainfall intensity on the treatment efficiency of typical pollutants in runoff,and the variation law of runoff concentration along the flow path in the wetland was analyzed;The combined system of ecological ditch and constructed wetland was constructed,and its operation effects under different simulation conditions were analyzed.The effects of hydraulic load and operation interval on the purification effect of the system were investigated.The main conclusions are as follows:（1）Referring to the rainfall characteristics of Nanjing,by controlling different hydraulic loads and simulating different rainfall intensities,this paper explores the removal effects of ecological ditches constructed with different substrates on pollutants such as cod,TN and TP under different rainfall intensities.The nitrogen removal efficiency of ceramsite+zeolite filled ecological ditch is higher than that of polyethylene（PE）plastic filled ecological ditch;According to the removal characteristics of pollutants in runoff,the appropriate hydraulic load of ecological ditch should be selected as 0.3 m³/（m²·d）.Gladiolus has strong adaptability in ecological ditch and can be used as an alternative dominant plant of ecological ditch.Ceramsite+zeolite matrix is more suitable for plant growth than polyethylene（PE）plastic;Taking the surface V water as the standard,according to the fitting equation,the average suitable lengths of polyethylene（PE）plastic filler ecological ditch and ceramsite+zeolite filler ecological ditch are 5.81 m and 3.19 m respectively.（2）Proteus,actinomycetes,Bacteroidetes,patella,Firmicutes,Curvularia and acidobacteria are the dominant bacteria in ecological ditches;Proteus accounts for the largest abundance in the two ditches and is a common dominant species.Saccharimonas,trichococcus,Burkholderia,lentimicrobiaceae and dermatophilia are the dominant bacteria in ecological ditches.Compared with ceramsite+zeolite matrix ditch,the total amount of denitrifying functional bacteria in polyethylene（PE）filler ditch increased by 1.53%,and the TN removal rate increased by 14.1%,indicating that polyethylene（PE）plastic filler is more conducive to the attachment and growth of denitrifying microorganisms.（3）The compound vertical flow constructed wetland has high resistance to the change of hydraulic load when removing COD and TP.When the simulated precipitation intensity increased from light rain to heavy rain,the removal rates of the two pollutants decreased by only 7%and10%respectively.At the same time,when removing COD,NH₄⁺-N,TN and TP,the constructed wetland device is more efficient in treating pollutants at 0-60 cm along the way,and the pollutant removal capacity of ceramsite+zeolite filler is higher than that of plastic filler.The biological activity and adsorption near the water inlet are strong,and the vertical upward flow is more conducive to the extension of hydraulic retention time and the settlement of pollutants.Proteobacteria and bacillus are the main phyla of constructed wetland,which have strong ability of nitrogen and phosphorus removal.（4）The highest removal rates of COD,NH₄⁺-N,TN and TP in the ecological ditch constructed wetland combined system are 98%,87%,88%and 89%respectively.The removal effect is relatively stable.The constructed wetland can make up for the defect of weak resistance to hydraulic load impact in the process of nitrogen and phosphorus removal.At the same time,compared with other rainwater treatment technologies,ecological ditch constructed wetland system can better deal with urban surface runoff with long interval.At an interval of 3 weeks,the removal rates of COD,NH₄⁺-N,TN and TP were 94%,68%,76%and 47%respectively.When the hydraulic load of ecological ditch-constructed wetland system is 0.4 m³/（m²·d）and inlet COD206.1±3.93 mg/L,NH₄⁺-N 6.04±0.12 mg/L,NO₃^--N 4.02±0.06 mg/L,TP 1.07±0.06 mg/L.the effluent water quality meets the Surface Water Environmental Quality Standard（GB3838-2002）.