| Biochar,as a new environmental function material,has been widely used in the control of soil organic pollutants in recent years.In this paper,the lime purple soil in hilly area of central Sichuan was used as the test soil.Biochar was produced from crop straw,and different ratios of biochar(1%and 5%,mass ratio)were applied to batch adsorption experiments and outdoor soil box experiments.The adsorption and migration mechanism of three hydrophobic antibiotics,namely sulfadiazine(SD),sulfadimidine(SMT)and tlorfenicol(FFC),in the purple soil were studied.The physi-chemical properties of the biochar before and after aging were characterized.The change of surface physi-chemical properties of the biochar during aging were also studied.The main conclusions are as follows:(1)Due to the leaching of soluble carbonate and salt-based ions(calcium,magnesium,potassium,etc.)from the biochar under natural rainfall and irrigation infiltration,as well as the oxidation of biochar surface,the acidic oxygen-containing functional groups(carboxyl,phenol,carbonyl,etc.)are increased,resulting in the decrease of pH and EC,and the increase of C-O bond content on the surface of biochar after aging.Mineralization of the biochar under biological and abiotic effects leads to a decrease in C content.The disappearance of organic membrane on the surface of fresh biochar during aging exposes some micro-pores which were covered by theorganic membrane,resulting in a significant increase in the specific surface area of biochar after one year of aging.In the field soil environment,the biochar surface was denuded or even some cracks were formed,local deformation and fragmentation also occured,which enhanced the connectivity of the pore channels and increased the average pore size.The types of functional groups did not change during theshort time aging process(1 year);the CEC values of fresh biochar after aging had no significant difference.(2)The three target antibiotics were physically adsorbed in five tested soils.The adsorption process of the three antibiotics on the charcoal was the result of multiple mechanisms working together.The application of biochar could significantly improve the adsorption of antibiotics on the purple soil,especially sulfamethazine and florfenicol,which had smaller Kow value.The enhancement was stronger with fresh biochar application,while it was weakened with aged biochar.(3)Because the unstable and soluble organic matter(DOM)in the aged charcoal soil decreases after aging,the contribution of DOM to the absorption of antibiotics is particularly significant for the lowest florfenicol in Kow value.Moreover,the decrease of DOM content resulted in the release of antibiotics which were originally adsorbed by charcoal soils,resulting in the decrease of antibiotic adsorption capacity of charcoal soils after aging.(4)Due to the addition of the charcoal-treated soil(5%mass ratio),the water content of biochar-permeable wall soil is higher than that of other soils,and DOC and pH are increased correspondingly.By comparing the three-dimensional excitation-emission fluorescence spectra of DOM extracted from the soil in the test boxes,it was found that the DOM content of the biocharcoal permeable reaction wall soil increased significantly compared with other soils.(5)Surface application of biochar can effectively control the transverse migration of antibiotics on the surface.The use of biochar-amended permeable reactive wall can effectively control the leaching and deep lateral migration of low concentration antibiotics in purple soil slope farmland. |
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