| In recent years,antibiotics have been frequently detected in natural water and agricultural effluents(concentration levels of ng/L-μg/L),becoming an emerging contaminant of social concern.Tetracycline is mostly used in human medicine and livestock farming because of its important role in disease control,promoting animal growth and improving feed utilization efficiency.However,tetracycline is not completely digested and absorbed by humans and animals,and 30%-90% of tetracycline is discharged into the environment through manure and urine,thus causing water and soil pollution and threatening ecological environment and human health.Adsorption method is widely used for the removal of antibiotics from water because of its high efficiency,easy operation and low cost,and adsorbent is the core of adsorption method.adsorbents.The adsorption mechanism and adsorption performance of each adsorbent were investigated by comparing the differences of adsorption characteristics of the six adsorbents on tetracycline with the characterization means and the adsorption kinetic model,isothermal adsorption equilibrium model and adsorption thermodynamics of the six adsorbents on tetracycline,while the optimal adsorption conditions of biochar,montmorillonite and polymeric aluminum chloride were screened by response surface design and applied to the actual methane.The following main conclusions were obtained:(1)The results of the adsorption model fitting showed that the Elovich model was more suitable to explain the adsorption process of tetracycline adsorption by the six adsorbents than the traditional pseudo-first-order kinetic and pseudo-second-order kinetic models,indicating that the adsorption process of the six adsorbents involved chemisorption and was controlled by several adsorption processes,constantly shifting to multilayer adsorption,among which the intraparticle diffusion process of activated carbon and chitosan was the possible rate-limiting step for the adsorption of tetracycline.The Langmuir model,Freundlich model and Temkin model were all well fitted,and the comparison of model fitting parameters yielded the largest adsorption capacity of montmorillonite,followed by biochar,and the smallest adsorption capacity of chitosan;the adsorption processes of the remaining five adsorbents except montmorillonite were heat absorption reactions.(2)The results of the adsorption test showed that when the initial tetracycline concentration was 120 mg/L,montmorillonite had the best adsorption effect on tetracycline in water,followed by biochar and then polymeric aluminium chloride.All three had more excellent adsorption characteristics than activated carbon,which is also a carbon material,zeolite,which is a clay mineral,and chitosan,which is a flocculant,respectively.Biochar,activated carbon,montmorillonite and zeolite have the highest adsorption capacity at p H 5and are suitable for the treatment of tetracycline in weakly acidic waters;Among the six adsorbents,montmorillonite,biochar and polymeric aluminium chloride have the shortest adsorption equilibrium time(12 h)and higher equilibrium adsorption capacity,in order of montmorillonite(104.09mg/g),biochar(26.35mg/g),polymeric aluminium chloride(22.04mg/g);All five adsorbents except montmorillonite can be heated to enhance the removal of tetracycline;The best solid-liquid ratio was 1.20g/L for biochar and activated carbon,0.80 g/L for montmorillonite and zeolite,and 0.40 g/L for chitosan and polymeric aluminium chloride,which could enhance the removal of tetracycline by heating,but the adsorption effect was not as good as the other four adsorbents.The adsorption effect was not as good as the other four adsorbents.(3)After fitting the response surface optimization test model and validation test,the best adsorption parameters of the adsorbent for tetracycline in water were obtained as follows: the solid-liquid ratio of biochar was 2.30g/L,the initial concentration was 24.00mg/L,the time was 9.8h,and the p H=5,the adsorption amount and the adsorption rate of biochar for tetracycline in water were 7.95mg/g and 77.58%,respectively;The adsorption amount and adsorption rate of tetracycline in water by montmorillonite were 27.91mg/g and 98.37%respectively when the solid-liquid ratio of montmorillonite was 1.90g/L,the initial concentration was 54.00mg/L,the time was 4.0h,and the p H=6;The adsorption of tetracycline in water was 49.95 mg/g and 13.89% at a solid-liquid ratio of 0.60 g/L,an initial concentration of 230.00 mg/L,4.0 h and p H=5.(4)The results of the optimized parameters of each adsorbent in biogas showed that biochar could effectively adsorb 78.62% of tetracycline in biogas environment with the adsorption amount of 8.51 mg/g;the adsorption rate and adsorption amount of tetracycline adsorbed by montmorillonite were 80.22% and 19.45 mg/g,respectively;the adsorption rate of tetracycline adsorbed by polymeric aluminum chloride was 64.41% and the adsorption amount was 253.00 mg/g.The experimental results showed that all three adsorbents have some application potential in the removal of tetracycline from methane. |
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