Research On The Application Of Biological Retention Pond With Biochar Modified Filler

Biological detention pond is an important low-impact development measure.By using plants and natural soil or artificial fillers to achieve the control of regional rainwater runoff and water quality,it is a low-efficiency stormwater management facility that is easy to construct and handle efficiently.In the context of China's vigorously promoting the construction of sponge cities,the research and application of biological detention ponds have received increasing attention.Based on the background of agricultural waste utilization,after finishing the experimental research on the basic properties of sponge properties related to the original greenbelt soil in Beibei District through field sampling,several biochars and commonly used improvement materials,river sand,were selected for improvement.The infiltration properties of the soil are used as filling material for the holding pond,and useful explorations have been made on the holding capacity of rainwater runoff,the overall design,and the optimization design of facility parameters using the best improved filling.The specific research contents are as follows:(1)Sampling and analysis of greenbelt soil with different land types and vegetation conditions in 8 regions and 24 sampling points in Beibei urban area,in order to explore the sponge body performance of native soil in greenbelt.From the analysis of the parameters of the sampled soil,among the 24 sampling points,the soil bulk density of 83.3% of the sampling points exceeded the limit of less than 1.35 g / cm3 stipulated in "Greening Planting Soil",but only 20.8% of the sampling points reached a minimum of 50 % Total porosity limit,and the difference in field water holding capacity at each point is small,basically between 20%.In addition,the measurement of the permeability coefficient shows that 79% of the sampling points can reach the minimum limit of 0.06 cm / min that can meet the soil permeability coefficient of detention facilities specified in the "Technical Specifications for Rainwater Control and Utilization in Buildings and Communities".However,the permeability is at an optimal level.Graded sampling points account for only 12.5% of the total number of sampling points.In general,the nature of the sampled green land soil is affected by multiple factors such as land use type,vegetation structure,and human activities.Soil compaction is more serious,the pore structure is poor,and the penetration capacity needs to be strengthened.It is difficult to use it directly as a sponge urban filler.Artificial improvement.(2)Through the design of four-factor and three-level orthogonal experiments,the effects of the addition of different types and proportions of biochar and different proportions of sand on the permeability coefficient and saturated water content of mixed fillers were found,and biochar and river sand were found.Reasonable addition can improve the water storage and water seepage performance of the filler,and the biggest impact is the proportion of biochar added.Through standardized processing methods,comprehensive consideration of the availability and cost of materials,and finally selected from 11 combinations of 4% rice husk charcoal?40% soil?56% fine sand mixed filler as the optimal combination for further research,At this time,the permeability coefficient is 0.348 cm / min,which is 17.4 times that of the original soil,which is much larger than the minimum 0.06 cm / min required by the sponge city guidelines.The saturated water content is 43%,and the water storage capacity can be increased by 32.7% based on the original soil.(3)Based on the optimal combination of fillers,a small biological retention pond device with two types of filler structures was constructed.The two devices were simulated twice with a recurrence period of 2 years and a duration of 120 minutes.Impact of one rainfall event on runoff capacity of detention ponds.The experiment found that adding rice husk charcoal as an independent internal aquifer layer at the same filler thickness helps to improve the rainwater runoff control capacity of the detention pond.Under the first rainfall condition,the runoff water volume of the No.2 detention pond with the aquifer was reduced The rate is 23.9%,which is 1.7 times that of the No.1 detention pond without the addition of an internal aquifer,and the reduction rate of flood peak flow is basically the same;in the case of secondary rainfall,the rainwater runoff control capacity of both detention ponds has significantly decreased At this time,the No.1 detention pond has a thicker mixed soil filler layer,which has better rainwater control capabilities.It is better than No.2 detention pond in reducing runoff rainwater volume and flood peak flow reduction.Finally,the feasibility of hydrological simulation of a single biological detention pond using SWMMH5.1 was verified by comparing actual device and softwaresimulated device effluent curves.(4)A brief summary of the overall design ideas of the biological retention pool,including a series of processes such as preliminary investigation and survey,site selection,morphological design,scale calculation and operation evaluation,and then based on SWMMH5.1 and Design-Expert,introduce The response surface optimization process of the structural parameters of the retention pool based on the response surface method is presented.Finally,the construction cost and social benefits of the biological retention pool are briefly analyzed.