Study And Modeling Of Phosphorus Removal In Constructed Wetlands Under Unsteady Inflow Condition

The sewage in the unsteady condition has varied characteristics from the traditional sewage,and the traditional sewage treatment technology might be insufficient under such conditions.Constructed wetlands are attractive alternative wastewater treatment technology which have been applied to treat various wastewater including unsteady sewage treatment.However,most of the current theories and models are based on steady state condition and in most cases they are insufficient to explain,and simulate the decontamination performance of wetlands under unsteady condition.,The mechanisms and influences of hydrodynamic characteristics on pollutants removal under unsteady conditions largely remains unclear,which greatly hinders the processing technology and development of constructed wetland under non-steady states.Therefore,it is of great practical significance to study the hydrodynamic characteristics and decontamination model of artificial wetland under unsteady condition,and to study the further development and application of constructed wetland technology.Current study was conducted on a horizontal flow constructed wetland and a vertical flow constructed wetland as examples.Based on the time line of multipoint tracer test,the residence time distribution of two kinds of artificial wetlands under different impact conditions were analyzed.Combined with the urban storm water runoff treatment of artificial wetland water quality and water erosion characteristics,TP removal efficiency test under unsteady conditions,the pollutants removal efficiency in studied constructed wetlands under unsteady conditions was analyzed.Based on the unsteady hydrodynamic characteristics coupled with the biokinetic reactions of the pollutants removal level we establish a model under unsteady condition,and the model was verified and analyzed under real conditions.The present study indicates that,under unsteady conditions,different hydraulic loadings make the change of water flow in artificial wetland.And the distance from the impact of the moment into the liquid impact by the impact of a larger impact,Single peak shock on the impact of about 20 h before the inflow of liquid is still affected,bimodal shock on the impact of about 40 h before the inflow of liquid is still affected.Based on the dimensionless time variable of the effluent flow,the RTD concentration curve under unsteady impact conditions was normalized,The treated RTD is not sensitive to hydraulic load,tracer dosage and so on,indicating that the artificial wetland itself has the law of water flow.The removal efficiency of TP was higher in the horizontal constructed wetland(54%)than that of vertical baffled constructed wetland(44%)with different baroque artificial wetlands under different unsteady influent conditions.The influent water flow of two kinds of artificial wetland pollutants is affected by the influent water and the change of water quality,but the impact of water quantity is more significant than the change of water quality.The RTDs of the constructed wetland experiment were simulated by the CSTRs + PFD parallel model.When the f = 0.890,z = 0.324,n = 2.2 and D = 0.279,the model was well fitted with the measured RTDs curve When the f = 0.849,z = 0.631,n = 1.6 and D = 0.110,the RTDs curves obtained by the model and the vertical baffled artificial wetland test have good simulation results.The parallel model can be used to model the pollutant removal based on the residence time distribution to predict the effluent concentration of pollutants in artificial wetlands under unsteady conditions.The main parameters of the model are the residence time distribution of the wetland and the first order reaction rate constant(d-1).When kv= 0.17d-1,the simulated effluent concentration of the vertical baffled artificial wetland TP has a good correlation with the actual effluent concentration under 5 times unimodal shock,when kv=0.12d-1,the simulated effluent concentration of the vertical baffled artificial wetland TP has a good correlation with the actual effluent concentration under 5 times bimodal shock.When kv=2.21d-1,the simulated effluent concentration of the horizontal baffled constructed wetland TP has a good correlation with the actual effluent concentration under 5 times unimodal shock,when kv=1.87d-1,the simulated effluent concentration of the horizontal baffled constructed wetland TP has a good correlation with the actual effluent concentration under 5 times bimodal shock.