Research On Purification Mechanism And Dynamics Of Towns Runoff Non-point Pollution With Constructed Wetland

Currently, with the rapid development of urbanization and industrialization, theseriousness of non-point source pollution in towns has been exacerbated. The area ofimpermeable zone is increasing, and the sudden, shocking and random pollution of urbansurface water caused by runoff has become one of the main sources for water pollution in thecity. Dongguan is a typical city of the rapid industrialization in PRD(Pearl River Delta),runoff and sewage of which are mixed to discharge directly, which caused serious pollution tothe Dongjiang.A series of experiment about the treatment of towns runoff non-point source pollution byfold-flow constructed wetland were carried out, in order to providing feasibility forapplication of constructed wetland in this area. Wastewater treatment and landscape can becombined effectively by constructed wetland which has developed into an important controltechnology of non-point pollution for its economy and simplicity. Therefore, constructedwetland has a wide application prospect in runoff treatment.The results of hydraulic experiment carried out by the small scale device of fold-flowconstructed wetland showed that average porosity and the average permeability coefficient ofthe matrix with large porosity and good permeability were0.408and0.0688cm/s,respectively,. Firstly, the results of different experiment conditions showed that the wetlandsystem would appear the phenomenon of short-circuiting and stagnant water, and the actualflow would deviate from the ideal flow; secondly, with the same daily hydraulic loading,shorter cycle of intermittent influent flow would weaken the static diffusion of wastewater inthe wetland reducing the degree of short-circuiting; thirdly, with the same influent flow rate,intermittent influent flow not only made sufficient residence time of pollutants improving theremoval rate, but also promoted the flow penetration into lower part of wetland, which takefull advantage of the purification function of wetlands.Both the simulative and real purification experiments of the runoff got good pollutantsremoval rate which would not be influenced obviously by temperature resulting from thechange of the seasons. The results of anti-impact load experiment showed that constructedwetland system has strong anti-impact ability to pollutants concentration. Strong scour wouldtemporarily cause the decrease of phosphorus removal rate which would recover after20h.The removal rate of all pollutants increased to some degree since constructed wetlandhad been started, and the effluent quality was stable. The removal rate of CODCr, SS, NH4+-N,TP, Pb, Zn and Cu was up to more than90%. The average effluent water quality met the needs of Environmental Quality Standard for Surface Water (GB3838-2002) III. The ruleanalysis of the spatial distribution of the pollutants in wetland system showed that mostpollutants were removed in the first and second cell.The adsorption characteristics of phenanthrene in substrates from constructed wetlandwere studied with the balanced oscillation. The results showed that phenanthrene achievedadsorption equilibrium in20h. The adsorption isothermal lin on30℃could be describedbetter by Langmuir equation, which showed that the adsorption process was monolayeradsorption dominated by physical adsorption, supplemented by chemical adsorption.Temperature, pH, organic matter content of wetland substrate all influenced the adsorpt ioneffect of phenanthrene.The first order reaction kinetics model which was established with CODCr, TN, NH4+-Nand TP as indexes could simulate the pollutants removal law correctly. The correlationcoefficients of simulation equation about CODCr, TN, NH4+-N were more than0.96.Correlation coefficient of TP was0.9381, which was interrelated with the removal mechanism(physical mechanism dominates) of TP in wetland system. Consulted the runoff purificationdata in fold-flow constructed wetland with theoretical prediction data, and showed that theratio of the error within30%of the simulation results of CODCr, TN, NH4+-N, TP was up to65%.