Study On Remediation Of Tetracycline Pollution In Soil By Phosphate Modified Biochar

Tetracycline is a widely used broad-spectrum antibiotic,often used as a feed additive in the livestock and poultry breeding industry.Because tetracycline is not completely metabolized in animals,most of them are excreted in the original state or secondary metabolic state.Wastewater discharge from aquaculture and the use of tetracycline-containing livestock and poultry manure as organic fertilizer will cause a large amount of tetracycline to accumulate in the soil.When a large amount of tetracycline accumulates in the soil,the tetracycline will migrate along water bodies and food chains and other paths,causing potential harm to human health and ecological safety.Methods of removing tetracycline from soil include:high-temperature pyrolysis,chemical oxidation,biodegradation and adsorption.Among them,the adsorption method has received extensive attention due to its cheap cost and easy operation.As a product derived from the pyrolysis of waste biomass,biochar has a wide range of sources and low prices,and has become an environmentally friendly adsorbent that has been widely studied.However,the original biochar has a poor adsorption effect on tetracycline,and it is urgent to develop a biochar that can efficiently adsorb tetracycline.In this study,modified biochar with different phosphates（K₃PO₄、K₂HPO₄、KH₂PO₄和Na₃PO₄）were prepared.Through adsorption kinetics,the difference in tetracycline adsorption capacity of different phosphate modified biochar was studied.The specific surface area（BET）and infrared spectroscopy（FTIR）were used to characterize the obtained biochar to study the relationship between the material characteristics and the adsorption effect;and focus on the analysis of different pyrolysis temperatures,the number of phosphate metal cations,and the type of phosphate metal cations.The effect of the modification results is to compare and select the best adsorption material for subsequent tetracycline soil remediation.In addition,this paper studied the effects of tetracycline pollution on soil p H,ammonia nitrogen,nitrate nitrogen and available phosphorus through soil incubation experiments,and determined evaluation indicators.Finally,this paper selects K₃PO₄-800 modified biochar with the best adsorption performance and adds it to tetracycline contaminated soil to study its mitigation effect on tetracycline pollution in the soil.The main conclusions drawn in this article are as follows:（1）Compared with the original biochar,the phosphate modification process improves the adsorption performance of tetracycline.The overall trend is that the higher the pyrolysis temperature,the higher the adsorption performance,that is,K₃PO₄-800（124.51 mg/g）>K₃PO₄-400（24.64 mg/g）;the increase in the number of metal cations in the phosphate modifier will also improve its adsorption performance（K₃PO₄-800（124.51 mg/g）>K₃PO₄-400（24.64 mg/g））;In addition,the type of metal cations in the phosphate modifier will also affect its adsorption energy,the effect of K⁺is slightly better than that of Na⁺,K₃PO₄-800（124.51 mg/g）>Na₃PO₄-800（112.79mg/g）).Scanning electron microscopy（SEM）results show that the modified biochar has a richer pore structure;the specific surface area（BET）results show that the increase in pyrolysis temperature and phosphate metal cation content and metallicity will increase the specific surface area of the biochar material and pore volume;infrared spectroscopy（FTIR）results show that the modification will increase the richness of the functional groups of biochar materials.The adsorption process of potassium phosphate modified biochar conforms to quasi-first-order kinetics,and the adsorption process of potassium dihydrogen phosphate and dipotassium hydrogen phosphate modified biochar conforms to quasi-second-order kinetics.Through comparison and selection,the K₃PO₄-800 with the best adsorption performance was selected for subsequent adsorption thermodynamic tests.It was found that the adsorption process conforms to the Langmuir model,indicating that the adsorption process is physical adsorption,and the maximum adsorption capacity reaches 436 mg/g at 25°C,and the adsorption process It belongs to the endothermic spontaneous process.（2）Soil tetracycline pollution will affect soil p H,ammonium nitrogen,nitrate nitrogen and available phosphorus content and the corresponding enzyme activity.Tetracycline will decrease the p H of the soil by an average of 0.101（day 7）,but it is not significant（P<0.05）.After tetracycline enters the soil,the soil available phosphorus concentration drops by 7.47%at the highest,and ammonium nitrogen and nitrate nitrogen also drop by 16.46%and 12.69%respectively.At the same time,tetracycline also reduced the activities of soil urease and phosphatase.After treatment with tetracycline（25 mg/kg）,the soil urease activity decreased by17.85%,and the phosphatase activity decreased by 10.09%.Tetracycline affects the activity of soil enzymes,and also affects the content of inorganic nitrogen and available phosphorus in the soil,weakening the soil’s ability to supply nitrogen and phosphorus.（3）After adding K₃PO₄-800 biochar into the soil contaminated by tetracycline,the extractable concentration of tetracycline decreased significantly,and at the same time,it alleviated the effects of tetracycline pollution on ammonium nitrogen,nitrate nitrogen,available phosphorus,and phosphatase and urease activities.influences.When the addition amount was 2%,compared with CK,the concentration of extractable tetracycline in the soil decreased by an average of 55.29%（day 7）,effectively reducing the concentration of extractable tetracycline in the soil.When the addition amount was 0.5%,the ammonium nitrogen and nitrate nitrogen of the biochar treatment group were increased by 9.4%and 6.5%at the highest compared with the tetracycline treatment group.When the addition amount was 2%,the concentration of soil available phosphorus increased by 3.7%at the highest relative to CK.Compared with the tetracycline treatment group,after adding 2%biochar,the urease activity in the soil increased by 10.72%,and the phosphatase activity increased by 3.08%.It shows that the addition of K₃PO₄-800 modified biochar can effectively alleviate the impact of tetracycline pollution on the soil.