The Application Of Modifying Soil By Biochar On Water Management

With the rapid development of domestic economy and the increase of urban pavement hardening,the peak runoff and total runoff of urban rainwater increase.The TSS,COD,ammonia nitrogen and total phosphorus content in road rainwater runoff are very high,resulting in more and more serious non-point source pollution,and urban water pollution is becoming more and more serious.In recent years,more and more attention has been paid to environmental protection by the government and all sectors of society.Sponge city construction has many pilot cities in the country.LID(low impact development)is an important part of the construction of sponge city.As a new concept of rainwater management,low impact development has attracted wide attention.In low impact development,permeation and filtration processes are critical.Biochar,with its porous structure,high adsorption efficiency and no secondary pollution,has become an excellent soil improvement material for increasing soil permeability coefficient and improving the ability of soil to remove runoff pollutants.In this paper,cotton stalks were pyrolyzed at 450 degrees Celsius to produce biochar,engineering river sand and clay as raw materials for soil improvement.Through laboratory simulation experiments,the permeability coefficients and the adsorption of TSS,COD,ammonia nitrogen and total phosphorus on 15 cm high-improved soil layer under the conditions of complete mixing of three materials,carbon and biochar models and different volume ratios of river sand,clay and biochar under the complete mixing model were studied.Removal effect.The concentrations of CDO,TP and NH4 in inflow and outflow of synthetic runoff were determined by spectrophotometry,and TSS concentration was measured by turbidimeter.The results show that the permeability of improved soils increases with the increase of the volume ratio of river sand to biochar.The permeability coefficient of the complete mixing model is higher than that of the Sand-Mixed carbon stratification and the complete stratification.The permeability coefficient of the soil in the 2:2:1 volume ratio of river sand,clay and biochar is 92.6 mm/h.The adsorption and removal efficiency of TSS,COD,ammonia nitrogen and total phosphorus by this model is also better than that by stratification and complete stratification of sand-soil mixed carbon.In the complete mixing model,the permeability coefficient in the 2:2:1 volume ratio of river sand,clay and biochar medium is lower than that in the other three groups,but the adsorption and removal efficiency of pollutants is higher than that in other groups.Comprehensive permeability coefficient and adsorption and removal efficiency of TSS,COD,ammonia nitrogen and total phosphorus in rainwater are the five indicators.A complete mixing model of 2:2:1 volume ratio of river sand,clay and biochar medium is selected as the best biochar soil improvement scheme.In the field simulation experiment of improved soil,turf mulching can reduce the infiltration efficiency of improved soil,protect soil structure better,and intercept TSS well.At the same time,it can absorb COD,ammonia nitrogen and total phosphorus,and prolong the service life of improved soil.In the field simulation,it takes a long time for the adsorption and removal of COD,ammonia nitrogen and total phosphorus to reach equilibrium,and the removal rate is similar to that without turf mulching after reaching stability.The adsorption and removal rates of TSS,COD,ammonia nitrogen and total phosphorus in improved soils are proportional to the lateral length of fluids flowing through the soil layer.For each biochar improved soil layer with an average length of 10 cm and a height of 15 cm after simulated runoff,the concentration interception of TSS and COD will increase by 0.038 NTU and 2.671 percentage points,and the removal rate of ammonia nitrogen will increase by 1.407 percentage points and total phosphorus.The adsorption removal rate will increase by 1.08 percentage points.The field simulation results show that the improved soil with the volume ratio of river sand,clay and biochar media of 2:2:1 has a strong adsorption and removal effect on TSS,COD,ammonia nitrogen and total phosphorus in rainwater.It can effectively control the non-point source pollution and peak discharge caused by urban road rainwater runoff and improve urban water environment.It is a more effective solution to urban rainwater management problems.