Study On The Effect Of Straw Biochar On The Adsorption Behavior Of Typical Antibiotics In Purple Soil

Straw biochar has great potential as a soil amendment for controlling antibiotic contamination,but there is a lack of systematic discussion on the assessment of biochar adsorption capacity for antibiotics in soil.In view of this,in this study,two weakly hydrophobic antibiotics,florfenicol and sulfadoxine-pyrimethamine,were selected as target contaminants for the calcareous purple soil,which is unique to the upper Yangtze River region and less attention,and four biochars were made from rape straw and rice straw at 300°C and700°C as soil improvers to systematically investigate the effects of biochar,purple soil,and mixed biochar-purple soil system（hereafter referred to as charcoal application soil）The adsorption of florfenicol and sulfadiazine was investigated systematically.A model was constructed and evaluated for the ability of biochar to adsorb antibiotics in charcoal application soils,and its ability and influencing factors were analyzed.This study can provide some feasibility basis for the control of antibiotic contamination by biochar in charcoal application soils.The main research findings are as follows.（1）As the pyrolysis temperature increased from 300 to 700°C,the C content of biochar increased and the H and O content decreased.All biochar contained functional groups such as hydroxyl,aliphatic,carboxyl and polysaccharides,but the aromaticity and stability increased and the polarity decreased;the total pore volume of biochar increased,the pore size decreased and the specific surface area increased by more than 61.99 times.The differences in the effects of biomass raw materials on the properties of biochar were not significant.（2）The isothermal adsorption characteristics of florfenicol and sulfadiazine in biochar,purple soil and sphagnum soil were in accordance with the Linear equation（R²>0.77,p<0.05）and Freundlich equation（R²>0.72,p<0.05）,the partition constant K_d ranged from 0.01 to55.74 L/kg,and the adsorption capacity constant K_F ranged from 0.01 to 112.09μg^1-1/n（cm³）^1/ng^-1.The free energy of adsorption of each adsorbent on florfenicol and sulfadiazine ranged from-19.60 to 7.08 k J/mol,all of which were less than 40 k J/mol and were physical adsorption.The elevated effect of high-temperature biochar on the adsorption of antibiotics on purple soil was stronger than that of low-temperature biochar.The adsorption mechanism of each test soil for florfenicol and sulfadiazine was partitioning and multilayer adsorption,and it was speculated that the adsorption mechanisms of low-temperature biochar and high-temperature biochar for antibiotics were partitioning and surface adsorption as the dominant mechanisms,respectively.（3）The partition constants K_BC for the adsorption of florfenicol and sulfadiazine by biochar in the sizing soil were obtained by constructing an evaluation model.the adsorption performance of low-temperature biochar in the sizing soil was enhanced by 0.43-fold to 1.31-fold,and the adsorption performance of high-temperature biochar in the sizing soil was reduced by 0.70-fold to 0.89-fold,indicating that the adsorption capacity of low-temperature biochar might be superimposed,while the adsorption capacity of high-temperature biochar was The adsorption capacity of high temperature biochar was suppressed.The redundancy analysis and correlation analysis showed that the adsorption performance of biochar in sizing soils was highly significantly and positively correlated with the pyrolysis temperature and specific surface area of biochar,and highly significantly and negatively correlated with（N+O）/C and H/C.