Study On The Removal Of Trichloroethylene From Groundwater By Prb Filled With Biochar/Iron Composite Material

At present,the pollution of soil and groundwater in our country is serious and needs to be solved urgently.Overseas studies have shown that the effect of PRB technology in remediating contaminated groundwater is significant.In the restoration of chlorinated hydrocarbons,materials such as zero-valent iron are widely used and had significant effects,but functional materials such as biochar and biochar loaded with zero-valent iron are still in the experimental research stage.So far,the effect of magnetic biochar and zero-valent iron loading materials on the removal of pollutants has been studied by a small number of scholars.Research on the effects of different biochar raw materials and different loading methods on the removal of organic pollutants is rarely involved.There is little attention to the research on the application of biochar-iron materials in the PRB system.In addition,the optimal ratio of composite materials,the cooperative repair mechanism,and the permeability properties of materials in PRB applications require further research.This article aims to screen suitable biochar types,nano-zero-valent iron loading methods,and biochar-to-iron ratios as permeation reaction barrier in PRB technology.A series of indoor batch static experiments,column experiments,model box simulation experiments and micro characterization experiments were implemented.Based on the physical properties of biochar and the removal effect of biochar-iron materials on pollutants,the ratio and loading method of biochar-iron materials in the PRB system were determined.The synergistic mechanism of biochar-iron materials to remove organic pollutants trichloroethylene and its application effect in the simulated PRB system were revealed.The seepage characteristics of this biochar-iron material in PRB system engineering were analyzed.The main research contents and results are as follows:(1)Based on the principle of anaerobic pyrolysis of biochar,different biochars are prepared under different temperature and different biomass raw material conditions.The p H,CEC,specific surface area,porosity,and TCE adsorption performance of different biochars were analyzed.The results show that the CEC of coconut shell biochar and PSB is significantly higher than that of other biochars.PSB has a high-quality honeycomb and groove-like surface microstructure.The removal rate of coconut shell biochar and peanut shell biochar on TCE is as high as 80%,and its adsorption performance is better than that of rice husk biochar and masson pine needle biochar.Peanut shell biochar prepared at 500°C was selected as the supporting material of n ZVI.(2)The biochar-loaded nano-zero-valent iron material was prepared by the liquid-phase reduction deposition method and the ball-milling mixing method.Through batch test,chloride ion determination,kinetic test,isothermal test and p H gradient test,the removal effects of different preparation methods and different biochar-iron ratio materials on TCE were compared and analyzed.The results show that the biochar-iron materials prepared by the liquid-phase reduction deposition method and the ball-milling mixing method have significantly better TCE removal effects than the BC and n ZVI materials alone.The biochar-iron composite material prepared by the liquid-phase reduction deposition method has better TCE removal effect than the biochar-iron material prepared by the ball milling method.The removal rate of TCE by LBC-n ZVI materials with different biochar-iron ratios exceeds 95%.With the increase of the amount of n ZVI,the ability of L-BC-n ZVI and M-BC-n ZVI to remove TCE gradually decreases.L-5BC-1n ZVI has the best TCE removal effect,and the removal rate is as high as98.2%.(3)With the increase of the contact time,the removal amount and removal rate of TCE by the biochar-iron materials gradually increase,and eventually tend to balance.Within 4 hours of contact,the removal amount and removal rate of TCE increased rapidly.Within 4 to 24 hours,the removal amount and removal rate of TCE increased slowly.After 24 hours,the removal amount and removal rate of TCE tended to be balanced.The fitting results of the kinetic model show that the removal process of TCE by biochar-iron materials is more in line with the pseudosecond-order kinetic model.With the increase of the initial TCE solution concentration,compared with BC materials,the increase in the amount of TCE removal by L-BC-n ZVI and M-BC-n ZVI materials gradually increased.When the initial concentration of TCE solution was increased to 10mg/L,the removal amount of L-BC-n ZVI and M-BC-n ZVI material was as high as 25.95mg/g and 20.39mg/g.Biochar-iron materials are beneficial to the removal of TCE in a weakly acidic environment.When the initial p H was 6.0,the removal amount and removal rate of TCE reached the highest.(4)Through indoor column experiment and model box simulation experiment,the application effect and seepage mechanism of biochar-iron composite material in PRB system are analyzed.The results of indoor simulation experiments show that in a short period of time,the M-BC-n ZVI material in the PRB system has a significant removal effect on TCE,and the removal rate is close to 100%.With the passage of time,the biochar and iron materials in the system are continuously consumed,resulting in a significant decrease in the ability to remove TCE.Under the effect of 3d seepage,the biochar-iron materials have different degrees of sedimentation.The migration and loss of M-5BC-1n ZVI material is relatively low.Within 5days,the removal rate of TCE in the PRB system simulated by the model box exceeded 90%.In addition,the diffusion and precipitation of the media material can cause the reaction barrier in the PRB system to be inactivated or the permeability coefficient to decrease.(5)The microscopic results show that the biochar-iron material not only retains the strong adsorption effect of the BC material,but also forms a synergistic mechanism of adsorption and degradation under the action of multiple mechanisms due to the addition of n ZVI.It mainly includes the adsorption of BC and the reductive degradation of n ZVI.The adsorption of BC is formed by multiple mechanisms of pore filling effect,?-? interaction force,hydrogen bond force and electrostatic force.The reduction degradation of n ZVI mainly includes hydrogenolysis and reduction-elimination reactions of TCE.