Removal Performance And Mechanism Of β-cyclodextrin Modified Biochar On Heavy Metals And Antibiotics In Aquaculture Wastewater

In recent years,with the rapid development of aquaculture industry,the pollution of heavy metals and antibiotics in aquaculture wastewater has become increasingly serious.At the same time,livestock and poultry manure contains relatively high concentrations of antibiotics and heavy metals.It will further pollute the water and soil environment.Because heavy metals and antibiotics have the characteristics of strong concealment,refractory degradation,and easy induction of resistance genes,they have become potential threats to the environment and human health.Therefore,the deep and effective treatment of antibiotic and heavy metal residues in aquaculture wastewater has become one of the research hotspots in the field of environment.Biochar（BC）is a porous carbon-rich material obtained by oxygen-limited pyrolysis of biomass.It has been widely used for the removal of pollutants in water due to its large specific surface area and abundant functional groups.However,the original biochar is difficult to separate from the aqueous solution after adsorbing pollution,and long-term immersion in water will cause the leaching of pollutants,which may cause secondary pollution.As a polymer,β-cyclodextrin（β-CD）has the structural characteristics of the hydrophilic outer edge and hydrophobic inner cavity;and can form inclusion complexes with pollutants,which can prevent secondary pollution while adsorbing pollutants.In order to control the pollution of heavy metals and antibiotics from the source and achieve the purpose of"using waste to treat waste",pig manure was used as raw material to prepare pig manure biochar（SMBC）in this experiment,andβ-cyclodextrin was used as a modifier.Modified pig manure biochar（β-SMBC）was prepared.The composition,morphology and structure of SMBC andβ-SMBC were analyzed by SEM,BET,FTIR,XRD,XPS,and elemental analysis.The adsorption properties and mechanisms of SMBC andβ-SMBC on tetracycline（TC）and zinc(Zn²⁺)in a single system were investigated.The co-adsorption characteristics and mechanisms of SMBC andβ-SMBC on TC and Zn²⁺in the binary system,as well as the synergistic and antagonistic effects of TC and Zn²⁺were investigated on the basis of a single system,and finally,the effects of the interaction of different factors on the adsorption effect were analyzed using response surface methodology.The main findings of the this paper are as follows:（1）The results of the adsorption studies of SMBC andβ-SMBC on TC showed that the effect of solution pH on TC adsorption by SMBC andβ-SMBC was greater,and the adsorption of TC was more favorable under acidic conditions.The adsorption kinetics of SMBC andβ-SMBC on TC can be better described by the pseudo-second-order equation,and the adsorption process is mainly divided into two stages:liquid film diffusion and internal particle diffusion.Meanwhile,the Freundlich model could better describe the adsorption behavior of TC on SMBC andβ-SMBC with the maximum adsorption amounts of 45.226 and 53.503 mg/g,respectively.Compared with SMBC,β-SMBC adsorbed TC better and the main adsorption mechanisms including electrostatic attraction,hydrogen bonding,andπ-πinteractions.Thermodynamic analysis showed that the adsorption of SMBC andβ-SMBC on TC is a spontaneous heat process.（2）The interaction mechanism of SMBC andβ-SMBC with Zn²⁺was revealed,and the main mechanism of Zn²⁺adsorption by SMBC andβ-SMBC was found to be the complexation reaction between oxygen-containing functional groups（-COO,-CO and-OH,etc.）and Zn²⁺.By comparing the FTIR before and after adsorption of Zn²⁺on SMBC andβ-SMBC,it was found that the stretching vibration of hydroxyl（—OH）was weakened after adsorption..The XPS characteristics of SMBC andβ-SMBC before and after the adsorption of Zn²⁺were investigated,and it was found that after the adsorption of Zn²⁺by SMBC andβ-SMBC,small and clear Zn2p characteristic peaks appeared near 1022 eV,and the appearance of Zn2p characteristic peaks indicated that Zn²⁺had been adsorbed on SMBC andβ-SMBC,and Zn²⁺formed Zn-R bonds with its surface functional groups during the adsorption process（R denoted as-COO,-CO,etc.）The effect of solution pH on the adsorption of Zn²⁺by SMBC andβ-SMBC was greater and more favorable to the adsorption of Zn²⁺by SMBC andβ-SMBC.（3）The presence of Zn²⁺in the binary adsorption system had less effect on the adsorption effect of TC,while the theoretical adsorption of Zn²⁺in the binary system was significantly greater than that in the single system,which suggests that TC promotes the adsorption of Zn²⁺on SMBC andβ-SMBC,and this difference may be because TC is a bridge between Zn²⁺and the adsorbent,enhancing the binding between Zn²⁺and the adsorbent,Zn²⁺may need to compete with functional groups on SMBC andβ-SMBC for TC to form Zn-TC complexes and compete with TC for adsorption sites on the surface of SMBC andβ-SMBC,i.e.,the interaction between TC and Zn²⁺is both competitive and synergistic,this may depend on the mass ratio between TC and Zn²⁺as well as environmental factors,and the adsorption process involves various adsorption mechanisms such as electrostatic attraction,surface deposition,hydrogen bonding,etc.The effects of SMBC andβ-SMBC on TC and Zn²⁺under different influencing factors were basically the same as those under a single system.The adsorption capacity of SMBC andβ-SMBC on TC weakened that on Zn²⁺increased with the increase of solution pH.The results of the response surface experiment showed that the fitting results of the response surface experiment data of SMBC andβ-SMBC on the adsorption of TC and Zn²⁺were significant.In the TC response surface experiments,the coefficients of determination R²of the SMBC andβ-SMBC models are 0.8687 and 0.9322,which indicate that the two models fit well with the actual experiments,and therefore the two models can be used as prediction models for the response values,respectively.In the response surface experiments for the adsorption of Zn²⁺,the coefficients of determination R²for SMBC andβ-SMBC were 0.9750 and 0.9056,indicating a significant correlation between the response values and the response variables,suggesting that more than 90%of the data could be explained by the equations obtained from the fits.