Study On Methane Emission Reduction Enhanced By Hydrophobic Biochar Modified Soil Cover

Landfill is an important anthropogenic methane emission source.Biochar can enhance methane adsorption and oxidation in landfill overburden,but the increase of permeability coefficient and water content caused by the addition of biochar can also affect the removal efficiency of CH₄.Therefore,this study through hydrophobic modification of biochar,uses biochar with hydrophobic properties to optimize soil cover.Hydrophobic biochar modified soil cover can not only prevents rainwater infiltration,but also promotes methane diffusion and adsorption in the cover,in order to maximize the effect of methane removal.（1）The ratio of biochar modification solution is 20%silane,72%ethanol and 8%water.When the volume of silane is 31.5mL,the optimum reaction conditions of biochar modification are 12 h of reaction,3 g of biochar,30℃of reaction temperature,4 h of drying time and 50℃of drying temperature,respectively.（2）Through the analysis of physical and chemical properties of soil,20%biochar modified soil and 20%hydrophobic biochar modified soil,it is concluded that the maximum dry density and plastic index of compaction of 20%hydrophobic biochar modified soil are less than that of soil,which proves that the addition of hydrophobic biochar not only increases the porosity and specific surface area of soil,but also facilitates the flow and adsorption of methane and oxygen,and strengthens its sparsity.At the same time,the content of phosphorus,potassium and organic matter in the modified soil was significantly higher than that in the soil itself,which was more conducive to the growth and reproduction of microorganisms and increased the number of methane oxidizing bacteria.（3）When the reactor started to run,the residual hydrophobic modifiers and hydrophobic functional groups replaced on the surface of biochar could inhibit methane-oxidizing bacteria.With the increase of operation time,the inhibition gradually weakened,and finally the methane oxidation ability of hydrophobic biochar modified soil was basically the same as that of biochar-modified soil cover.（4）Temperature has different effects on methane removal efficiency of each cover.The experimental temperature is 15-40℃.The results show that the optimum methane oxidation temperature of soil cover is 30℃.The optimum methane oxidation temperature of 20%biochar modified soil cover and 20%hydrophobic biochar modified soil cover is 35℃.（5）The oxidation ability of methane is different at different depths of the overburden.By analyzing the methane content in the range of 70 cm below the surface of the overburden,it is concluded that the porosity of the 20%biochar modified overburden and the 20%hydrophobic biochar modified overburden at the same depth is larger than that of the soil overburden,which is more conducive to the entry of oxygen in the air.Therefore,the oxidation effect is better,and the optimal oxidation depth of methane should be not less than 42cm.（6）Adding 5L water to each reaction column to simulate the effect of precipitation on the cover layer under natural conditions,which proves that adding hydrophobic biochar can significantly slow down the water entering the cover layer,and after precipitation,the water content of 20%hydrophobic biochar modified soil cover decreases fastest,and the methane oxidation ability recovers rapidly.