| As an indispensable system in the construction of sponge cities,bioretention facilities can effectively reduce the amount of rainwater and purify pollutants of rainwater.Fillers play an important role in the regulation and control of rainwater by bioretention facilities.Research about improvement of fillers has been developed,but there are few studies on parameter optimization of bioretention facilities.In addition,there is little research on the use of biochar as a waste-utilizing material to improve the fillers of bioretention facilities.In this study,12 different corn stalks biochar(CSC)were prepared using different common corn stalks in northern China at different preparation durations and different firing temperatures,their physical and chemical properties were analyzed,and one of the corn stalks biochars was determined as bioretention fillers.The improved filler was added to the traditional biological retention facility filler BSM at a specific ratio.Three small-scale soil columns of BSM,BSM+5%WTR and BSM+5%CSC were built,and 8 simulated rain tests were carried out.There water quantity and quality were monitored to analyze the effect of its regulation on rainwater runoff.Based on the test data,the DRAINMOD model was validated and calibrated,and different scenarios were set up to simulate,in order to clarify the different factors such as the confluence ratio,the nitrogen influent concentration,the height of the aquifer,the thickness of the filler layer,and the depth of the submerged area on the control effect influences.The response surface method was used to optimize the design parameters of bioretention facilities,witch could provid a reference for the construction of bioretention facilities.The main conclusions of the research are:(1)As the preparation temperature increased from 400℃ to 600℃,the ash content of corn stalks biochar increased from 19.45%to 26.74%,the organic carbon content decreased from 7.89%to 7.25%,and the cation exchange capacity increased from 120.96 cmol/kg to 127.53 cmol/kg,the specific surface area increased from 5.32 m2/g to 217.36 m2/g.Its cation exchange capacity and specific surface area are generally higher than those of common bioretention fillers.Isothermal adsorption experiments were carried out on three types of biochar with good physical and chemical properties.The theoretical saturation adsorption capacity was ranked as CSC600-2>CSC600-1>CSC600-0.5.(2)Through 8 simulated rain tests,it was found that the peak flow reduction effect of BSM is unstable,and the peak flow reduction rate effect of BSM+5%CSC is more stable than 74%.BSM+5%WTR has a good effect on the peak lag of rainwater runoff,which is higher than the bioretention facility of BSM.The flood peak time of BSM+5%WTR and BSM+5%CSC in the 8 simulated precipitation tests both lag behind by more than 40min.(3)For the water quality detection of three soil columns in 8 simulated rain tests,the load reduction rate range of BSM+5%CSC for COD is 77.79%～94.51%,the average value is 86.96%,and the load reduction rate range for TN It is 78.57%～92.31%,the average value is 86.76%,the load reduction rate range for TP is 89.37%～98.63%,the average value is 95.11%,and the load reduction rate range for NH4-N is 87.71%～97.86%,average The value is 94.24%,and the load reduction rate for NO3-N ranges from 70.55%to 90.71%,with an average value of 82.08%.(4)Through the simulation of different scenarios,it is found that the lower the nitrogen influent concentration,the better the removal effect,and the ammonia nitrogen load reduction rate increases significantly;with the increase of the confluence ratio,the retention of the filler in the biological retention facility remains unchanged,and the water volume is reduced.Both the effect and the nitrogen reduction effect are weakened;as the aquifer depth increases,both the water volume reduction rate and the nitrogen load reduction rate show an increasing trend.Increasing the thickness of the filler layer,the water reduction rate increased from 60.54%to 67.16%,the nitrate load reduction rate increased by 4.97%,and the ammonia nitrogen load reduction rate increased by 0.52%;setting a submerged area within a certain range can enhance the removal effect of nitrate nitrogen.The removal effect of ammonia nitrogen has also increased,but too high an submerged area will affect the nitrification removal of ammonia nitrogen,the reduction rate of ammonia nitrogen load is reduced,and the removal effect of nitrate nitrogen also increases slowly.(5)The design parameters of bioretention facilities were optimized.When only the optimal nitrogen control effect is considered,to increase the nitrogen removal rate,the depth of the submerged area needs to be deepened;When the amount of water and the nitrogen control effect are both considered,and the submerged area is not as high as the case that nitrogen control effect is considered.Only when the optimal nitrogen control effect is considered,the optimized nitrate load removal rate is between 80%and 94%,and the ammonia nitrogen load removal rate can reach 100%;while considering the water volume and the optimal nitrogen control effect,the optimized water reduction The water reduction rate is between 60%-70%,the nitrate nitrogen load removal rate is between 80%-90%,and the ammonia nitrogen load removal rate is between 75%～100%.This result can provide a reference for the construction of bioretention facilities with biochar modified filler.(6)Actual rain monitoring was carried out on the rain gardens filled with BSM+10%WTR and BSM.The water reduction rate of the rain garden filled with BSM is 56.5～88.1%(median=72.8%).The removal rate of pollutant concentration of the rain garden filled with BSM+10%WTR is increased by 6.2%～36.4%,the load reduction rate is 6.2%～36.4%higher than the rain garden filled with BSM.When only the adsorption mechanism is considered and the NH3-N is the target pollutant,the operating life of the BSM+10%WTR,BSM and BSM+5%CSC rain garden is 39.6 years,27.6 years and 857.6 years respectively;when the NO3-N is the target pollutant,The operating life of the BSM+10%WTR,BSM and BSM+5%CSC rain gardens is 3.5 years,2.5 years and 48.4 years respectively. |
PDF Full Text Request