Development Of High-efficiency Bioretention Filler With Wood Chip Biochar And Research Of Parameters Optimization

The improved bioretention with wood chip biochar can effectively improve the regulation ability of the traditional bioretention system,and the prospect of applying biochar to bioretention is very bright.This paper systematically researches three aspects:the development of improved filler,the experiment and analysis of the regulation effect of the improved bioretention system,and the optimization of the structural parameters of the improved bioretention facility.In this study,wood chips were used as raw materials to prepare 15 kinds of wood chip biochar under different processes.Through the detection of physical and chemical properties and yield analysis,combined with analytic hierarchy process(AHP),the best preparation process of wood chip biochar was selected.Then,the best wood chip biochar is added to the bioretention soil media(BSM)in three proportions of 2%,5%and 8%(w/w).Based on the analysis of its hydrological characteristics,water purification ability and cost,combined with the AHP,the best addition ratio of wood chip biochar was selected.Planting soil,BSM,BSM+5%WTR(w/w)and BSM+5%wood chip biochar(w/w)were used as fillers to build 1#,2#,3#and 4#four bioretention column small-scale test devices,designed 8 artificial rain tests for monitoring research.Based on the monitoring data of the small-scale test,the modified Morris classification and screening method is used to analyze the sensitivity of the Hydrus-1D model parameters.According to the sensitivity of each parameter,the parameter adjustment and model calibration of the Hydrus-1D model are performed.The Hydrus-1D model is combined with the response surface design method(RSM)in the Design-Export software.The Box-Behnken Design in RSM is used to design the test plan,and the Hydrus-1D model after the calibration is used to simulate to obtain the response value.The Analysis module in RSM fits the functional relationship between the response values in the model and various factors,and performs variance testing and regression analysis.Finally,the Optimization module in RSM can be used to predict the best design parameters.The main conclusions are as follows:?The best preparation process of wood chip biochar is:The system temperature of Muffle uniformly increased in rate of 20?/min from room temperature to 600?,and then pyrolyzed at 600? for 3h,cooled to room temperature finally;The best addition ratio of wood chip biochar improved filler is 5%.? The average water reduction rate of 1#,2#,3#and 4#bioretention column was 58.09%,22.35%,50.44%and 41.33%respectively.The load removal rate of 4#bioretention column to COD,TN,TP,NH3-N and NO3-N is all above 68%.The load reduction rate of 3#bioretention column on TN,NO3-N,TP and NH3-N is good,but the load reduction rate of COD is only 58.56%.The load reduction level of 2#bioretention column on various pollutants in rainwater is uneven.Among them,the load reduction rate of 2#bioretention column on NO3-N is-3.57-67.16%,and the average value is only 23.84%.?During the calibration period and the validation period,the determination coefficient R2 are all above 0.6,and the Nash efficiency coefficient NSE is above 0.5,which between the simulated and the measured results on water reduction rate and load reduction rate.The fit degree between the simulated values and the measured values is up to standard.?The results of the structural parameters optimization shown that the recommended thickness of the filler layer of BSM is the largest and the recommended thickness of the aquifer is the smallest,the recommended thickness of the filler layer of BSM+5%wood chip biochar is the smallest and the recommended thickness of the aquifer is the largest.? To meet the two requirements of 25cm?soil replacement layer thickness?120cm and 80%?water quantity reduction rate?85%with the maximization of pollutant load reduction rate as the optimization goal,all rainfall scenarios with a recurrence period of 3a&a confluence ratio of 20:1 and below can be handled for the bioretentions with filler of BSM,BSM+5%WTR and BSM+5%wood chip biochar.