| Aiming at the contradiction between the waterproofness and the promotion of the adsorption and oxidation of CH4 of biochar modified soil cover in small?aged and abandoned landfill,the preparation of hydrophobic biochar and optimization of its preparation conditions were proposed,and the hydrophobically modified biochar was added to the soil cover to form a hydrophobic biochar soil cover?RH?.At the same time,an improved agent similar to the structure of biochar was found which has a porous structure and a large specific surface area and does not provide nutrients.Instead of biochar,it was added to the soil cover to form an inorganic ceramic material modified soil cover?RC?.RB and RC were compared with CH4oxidation performance with biochar-improved soil cover?RB?,respectively.The adsorption behavior and mechanism of CH4 in soil,?hydrophobic?biochar and its improved soil were investigated by conducting batch adsorption experiments.The main conclusions were listed below.?1?When the mass fraction of the modifier KH-570 was 7%,the amount of biochar added was 7g,and the modification temperature was 60°C,the surface of the modified biochar produced had the best hydrophobic properties,The contact angle was 143.99°,and the moisture absorption rate at room temperature for 24 h was 0.10%.?2?In the adsorption kinetics test,all the trends of the adsorption amount curves rose sharply in a short period of time,followed by the three processes of slow rise and little change in the end.With the increased of the initial concentration of CH4,the amount of CH4adsorption of the?hydrophobic?biochar and its 20%carbon-modified soil all increased.The addition of biochar and hydrophobic biochar significantly improved the adsorption of CH4 by soil,and the effect of adding biochar was particularly significant.In the isothermal adsorption experiment,the adsorption amount of hydrophobic biochar on CH4 was highest under the same temperature and pressure conditions,and with the increased of?hydrophobic?biochar addition,the adsorption of CH4 by?hydrophobic?biochar modified soil also increased.The pseudo-second-order kinetic equation and Freundlich isotherm adsorption model was more suitable than Langmuir isotherm adsorption model to describe the adsorption process of different amounts of?hydrophobic?biochar modified soil on CH4 adsorption.?3?When CH4 concentration in the simulated landfill gas was 35%,the total removal rates of CH4 by RB,RH,and RC were 95.80%,99.50%,and 64.98%,respectively.Both RB and RH showed good oxidation effect on CH4,but RH was the best.Compared with RB,RC had a lower removal effect on CH4,which indicated that the nutrients in biochar can promote the oxidation of CH4.With the increased of the simulated landfill gas inflow rate,the removal rate of CH4 by RB and RH increased,and the buffering capacity of RH on the increase the simulated landfill gas inflow rate was better.The optimal temperature for RB and RH to remove methane were both 30°C.?4?Under simulated rainfall conditions,the total CH4 removal rates of RB and RH were71.59%and 77.01%,respectively.The water content of RB and RH were 31.22%and22.68%,and the permeability coefficients were 1.15×10-7 and 7.68×10-8,respectively.RH had better oxidation ability for CH4 than RB,and was more waterproof.The hydrophobicity of biochar added to soil cover after hydrophobic modification was significantly better than that before modification.?5?The genus of bacteria with the greatest relative abundance at different depths in RB,RH and RC were Proteobacteria,and the dominant genus of methane-oxidizing bacteria were Methylobacter.The relative abundance of total methane oxidizing bacteria in the upper layer of RH was more than 13%higher than that of RB,the middle layer was lower than RB,and the lower part was not much different.However,RH made the distribution of flora in the cover layer more uniform,and was more conducive to maintaining the diversity and abundance of bacterial communities from environmental changes.The upper and middle layers of RC and RB were not much different.The relative abundance of total methane oxidizing bacteria in the lower layer of RC was more than 10%lower than that of RB.The removal effect of RB and RC on CH4 was combined to speculate that the improvement of methane oxidation efficiency was the result of the combined action of biochar porous structure and nutrients. |
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