Adsorption And Migration Characteristics Of Typical Antibiotics In Sewage Pond Soil

As an emerging pollutant,antibiotics have potential environmental risks.The study on the adsorption and migration characteristics of typical antibiotics can provide a theoretical basis for the control and remediation of soil and groundwater organic pollution.In this paper,four types of typical veterinary antibiotics,sulfamethoxazole（SMX）,roxithromycin（RTM）,enoxacin（ENO）,and chlortetracycline（CTC）,were selected as the target pollutant.The soil of the sewage pond discharged from the feces and urine of a pig farm in Yifeng County,Poyang Lake District,was selected as the research object.The adsorption and desorption characteristics of the target pollutants in the test soil were studied by static experiments supplemented by characterization methods.The migration laws were explored through soil column experiments.The simulation software fitted the migration of roxithromycin in the soil.The results of the study are as follows:（1）The soil tested is acidic sandy soil with loose granularity,the p H is between4.65～4.77,and organic matter content is 10.32～17.71g·kg^-1.（2）The adsorption and desorption kinetics showed that the target pollutants all have reached the adsorption and desorption equilibrium within 6 h.Under the same initial concentration,the adsorption and desorption capacity of RTM was larger than that of SMX;the adsorption capacity of CTC was larger than that of ENO,but the desorption capacity was smaller.（3）The adsorption and desorption isotherms showed that SMX was adsorbed in a stable form and was not easy to be desorption.There are strong intermolecular interactions between the test soil and RTM,such as ion exchange or strong electrostatic interaction,and the adsorption and desorption process of RTM is mainly chemical adsorption.There was strong adsorption between ENO and the tested soil.The desorption amount of CTC increased with the increase of liquid equilibrium concentration,and the desorption rate was lower.（4）Factors affecting adsorption:the increase of Ca²⁺strength is favorable for the adsorption of target pollutants,but not for desorption.The metal ions obviously promoted the adsorption of SMX and slightly inhibited its desorption.The adsorption capacity of SMX decreased with the increase of p H,and the desorption capacity increased with the increase of p H.Metal ions significantly inhibited the adsorption of RTM and slightly promoted its desorption.The effect of p H on RTM was consistent with that of SMX.Metal ions inhibit the adsorption of ENO and promote its desorption;the amount of ENO adsorption decreases with the increase of p H,while the amount of desorption increases with the increase of p H.Metal ions and p H had little effect on CTC adsorption and desorption.（5）The characterization results showed that there was no obvious change in the soil surface after adsorption of SMX.There were fine debris on the soil surface after adsorption of RTM,ENO and CTC.During the adsorption process,π-πinteraction occurs in SMX,complexation occurs in RTM,strong intramolecular hydrogen bonding occurs in ENO,and CTC is mainly due to surface complexation and cationic bridging.（6）Typical antibiotic migration experiments:The migration experiments of SMX,ENO and CTC all lasted 4440 hours,and RTM lasted 1752 hours.The recovery rates of the SMX outlet are:24.05%～95.90%,25.05%～68.60%and 23.15%～88.65%,showing a trend of gradual increase and continuous fluctuation;the RTM breakthrough equilibrium concentration is 22～25 mg·L^-1;ENO detected an obvious ENO curve only after 3500 h at K3,which was closest to the water inlet.After 4000 hours,CTC monitored the CTC concentration at the water outlet K3,which was closest to the water inlet,fluctuating continuously,and the highest was 7.68 mg·L^-1.The migration supplementary experiment:SMX penetrated the soil column for 24 hours,showing a gradually rising and stable trend without fluctuation;the supplementary experiments of ENO and CTC both lasted 332hours,ENO showed a fluctuating upward trend,and CTC showed a slow upward trend with no obvious fluctuation Phenomenon.（7）Hydrus-1D simulation software was used to fitting the concentration changes of RTM monitored by the experimental soil column,and the correlation coefficient was R²=0.7798.The surface soil can block the transport of antibiotics to some extent.SMX and RTM are not easily adsorbed in the surface soil and migrate smoothly in the soil layer,which may enter the groundwater system after polluting the surface soil.ENO and CTC are easily adsorbed by soil and migrate slowly in soil samples.ENO and CTC stored in soil for a long time may cause secondary pollution to groundwater.