Adsorption And Migration Characteristics And Simulation Of Sulfadiazine In Soil And Components

With the increasing use of antibiotics,the pollution of antibiotics in soil has no longer been neglected and become the hot spots in the field of environmental research.Sulfonamides were one of the most widely used antibiotics in the world,a large number of drugs are discharged into the environment every year,and the level of emissions is increasing gradually.Sulfonamides antibiotics have greater harm to the environment duo to the slow degradation rate.In order to provide theoretical guide to research for the evaluation and repair of antibiotics in soil and groundwater,Sulfadiazine(SDZ)was used as the object of research to study its behavior of adsorption and migration.The study is divided into two parts.One is the effects of ion types,organic matter content and different heavy metals on the adsorption and migration of SDZ in soil.Besides the effects of pH,ion types and ionic strength on the adsorption and migration of sulfadiazine in soil components(kaolinite,montmorillonite and humic acid),the migration behavior of sulfadiazine in undisturbed soil column were studied.Fourier Transform Infrared Spectroscopy(FTIR)was utilized to investigate the changes of the kaolinite,montmorillonite and humic acid before and after adsorption.Based on the experiments,the static adsorption process was fitted by Langmuir,Freundlich and Linear equations.The other is using Hydros-1D software to simulate the migration of sulfadiazine in soil column,and the migration characteristics were analyzed.The migration of sulfadiazine in soil column was predicted by using the relevant parameters.The following conclusions were drawed:(1)Laboratory static experiments were conducted to investigate the influence of the ion style,organic matter and heavy metal on the adsorption of sulfadiazine.Lower ionic valence and higher levels of organic matter cause higher adsorption amount of SDZ.For different concentration of element Cd in the soil,the adsorption of SDZ is different.There is no influence for the adsorption of SDZ when the concentration of Cd was 100.0 mg/kg.The 10.0 mg/kg Cd will promote the adsorption of SDZ.However,the adsorption of SDZ will be induced when the concentration of Cd reached 1.0,300.0 mg/kg.When the elements Cu/Pb/Cd was coexisted,the order of the adsorption of SDZ was: Cd>Cu>Pb.The R2 of Freundlich and Langmuir to fit the experimental data was above 0.96.The Linear equation fitted better,R2 was above 0.98.So the Linear equation can best fit the adsorption of SDZ in the soil.(2)The kinetic adsorption of SDZ in soil and its components(such as kaolinite,montmorillonite,and humic acid)showed that the extent of adsorption was determined at the end of 24 hours.The order of adsorption amount of SDZ was humic acid>kaolinite>soil>montmorillonite.Laboratory static experiments were conducted to investigate the adsorption capacity of soil components for SDZ.There were no obvious effects on the adsorption of SDZ in kaolinite.In the montmorillonite,the adsorption capacity of SDZ was positively related to pH and negatively related to ionic strength.Na+ reduced the adsorption of SDZ in montmorillonite,but K+,Ca2+ and Mg2+ had little effect on its adsorption.For humic acid,ion type had some effects on the adsorption of SDZ,but pH and ionic strength had little effect on its adsorption.The correlation coefficient R2 of Freundlich equation was more than 0.8.R2 of Langmuir was above 0.78,R2 of Linear equation was above 0.92.Linear equation fitted best of all.(3)The BTCs of SDZ in undisturbed columns at the same soil profile of the different soil layers was different.The BTCs of the undisturbed column ?(15.0~30.0 cm)depth were shifted to the left of undisturbed column?(0.0~15.0 cm).In the deeper soil layers,the migration of SDZ was faster.This is mainly due to the physical and chemical properties of the soil.The organic matter,cation exchange capacity(CEC)of the former column is lower than the latter,while the pH was higher.Thus the adsorption of SDZ reduced and its mobility enhanced.(4)Different chemical factors have different effects on the migration of SDZ in disturbed soil columns.The higher the cationic valence and lower the organic matter content,the higher the peak of the BTCs of SDZ,the stronger of the migration.When the concentration of Cd was 10.0 mg / kg,the migration of SDZ was slowest,the peak is lowest.The other concentrations of Cd had little effect on the migration of SDZ.The elements of Cu Pb and Cd have different effects on the transfer of SDZ.SDZ moved faster when element Cu exsits in the soil column,the peak can reach 0.8,followed by Pb.The slowest migration was in Cd-containing soil.The pH of the effluent decreased at first and kept steady gradually and EC changed little.The concentrations of Ca2+ offered descending firstly than upgrade latter tendency.(5)The migration of SDZ in undisturbed soil column was simulated by one-site sorption model(OSM),two-site sorption model(TSM)and two-region model(TRM)respectively,and TRM model was used to predict the migration of SDZ under different water velocity.The results showed that OSM model fitted the data better than TSM model.The f is so small in TSM model,so there is barely instantaneous adsorption in undisturbed soil.TRM model showed that immobile water is also important for the adsorption of SDZ.TRM model fitted the data better than OSM model and TSM model,R2> 0.91,RMSE <0.061.In the process of prediction,when the water velocity increased from 0.017 cm/min to 0.030 cm/min and then to 0.100 cm/min,the migration of SDZ in the soil was also accelerating,and the concentration of SDZ in effluent was getting higher and higher.When the velocity reached 0.100 cm/min,SDZ can quickly break the soil and enter groundwater.(6)The migration of SDZ in the disturbed soil column was simulated by OSM model and TSM model respectively.The results showed that R2 was larger than 0.881,RMSE was less than 0.069 in the OSM model,R2 was larger than 0.907 and RMSE was less than 0.051 in the TSM model.The fraction of the instantaneous adsorption(f)was large,it indicating that transient adsorption was a very important process during SDZ's migration.Compared with the OSM model,the TSM model can simulate the migration process of SDZ better.The coefficients ? of the two models were all small.