Mechanism Studies On Enhanced Sulfanilamide Removal From Water Using Functional Biochar Prepared From Cottonseed Husks By Microbial Modification

Sulfonamide antibiotic（SAs）contamination due to widespread application and incomplete biological metabolism is a global environmental problem.The adsorption and persulfate advanced oxidation methods based on biochar materials have become the research hotspots of SAs removal technology in water.However,whether as an adsorbent or catalyst,biochar often has limited functionality in the treatment of organic pollutants,requiring modification in practical applications.So far,researchers have developed various physical and chemical modification methods to directionally enhance the performance of biochar,but modified materials still have shortcomings such as poor adsorption and catalytic activity,unstable efficiency,and poor renewable performance.Moreover,the modification process has long reaction cycles,high energy consumption,and is prone to secondary pollution,which is not suitable for practical production and use.Therefore,simple and efficient green modification methods for biochar still need to be established in future research.This thesis proposed to use microorganisms to modify biomass precursors（agricultural waste cottonseed husks）.On the basis of obtaining biomass precursors with good pore structure and abundant surface functional groups,a variety of physicochemical modifications were carried out to obtain biochar materials with enhanced adsorption and catalytic performance of persulfate（peroxymonosulfate,PMS and perdisulfate,PDS）,which could be used to remove SA from water.At the same time,the change of chemical composition,transformation process of oxidant and pollutant on the surface of catalyst,and the application prospect of each technology in practical engineering was deeply discussed herein.The specific research contents and conclusions are as follows:（1）Biomass precursors（CSH-BMs）with well-developed pore structures and rich surface oxygen containing functional groups were obtained by planting pleurotus ostreatus in the cottonseed husks and utilizing enzymes secreted during the natural growth of microorganisms to degrade lignocellulose.Then combined with secondary high-temperature Na OH activation,the activated biochar adsorbents CSH-ACs with ultra-high specific surface area were prepared,which can quickly remove SA from water without being affected by various water components.The adsorption capacity could respectively reach 139.43,146.15,and 146.16 mg g^-1.The study found that compared to the CSH-AC₀ prepared from the original cottonseed husks,the BET specific surface areas of CSH-AC₄₀ and CSH-AC₈₀ chewed by microorganisms decreased,but larger pore sizes and pore volumes were obtained.In addition,due to the enzymatic hydrolysis of lignocellulose in the cell structure of cottonseed shell during the growth process of microorganisms,more aromatic compounds were enriched on their surfaces,and the oxygen containing group abundance,aromatization degree,and hydrophilicity of the obtained derived biochar CSH-AC₄₀ and CSH-AC₈₀ increased,resulting in an accelerated adsorption kinetic process.Finally,it was determined that the removal mechanism of SA by CSH-ACs mainly includes physical processes（pore filling,hydrogen bond interaction）and chemical processes（π-πstacking）though the study on the adsorption behavior of SA on CSH-ACs,characterization of the surface chemical composition of CSH-ACs before and after adsorption,and calculation of density functional theory（DFT）.（2）Using the microbial modified cottonseed husks in content（1）as the raw material,and taking advantage of the natural advantage of the fungus growth process that can enrich O on the surface of biomass,a biochar catalyst CSH-BC₈₀-800 with optimized C=O ratio,enhanced graphitization degree and good reuse performance was prepared by high-temperature carbonization at 800℃,which can achieve an SA removal rate of 84.8%within 120 minutes by activating PMS.It was found that the ¹O₂ produced in the CSH-BC₈₀-800/PMS system rather than·OH or SO₄^·-played a dominant role in the degradation of SA.At the same time,electrochemical experimental results showed that direct electron transfer from pollutants to PMS is also a key mechanism for SA removal.Based on the analysis of degradation intermediates,it was believed that SA was first caused by the cleavage of C-N and S-N bonds,and then ultimately mineralized and degraded through a series of benzene ring opening and hydroxylation reactions.（3）The biochar catalyst Fe₁-CSH-BC₈₀-500 with enhanced PDS catalytic activity was synthesized using cottonseed husks modified by microorganisms in content（1）as raw materials through low concentration Fe³⁺doping under pyrolysis conditions at500℃.The results show that Fe₁-CSH-BC₈₀-500/PDS system could achieve an SA removal rate of 82.48%within 180 minutes.It has been found that the formation of key active sites,PFRs,depended on the electron transfer of phenolic substances to metal ions in the biomass structure during the synthesis process.With the advantage of increasing content of aromatic compounds（mainly phenols）on the surface of biomass after microbial transformation,the abundance of PFRs on the surface of target biochar Fe₁-CSH-BC₈₀-500 obtained under low-temperature pyrolysis conditions increased,thus enhancing the removal effect of SA.SO₄^·-or·OH were the key active oxidation species that lead to the degradation of SA,while SO₄^·-or·OH were generated partly by the direct transfer of electrons from PFRs to PDS,and partly by the conversion of the intermediate·O₂^-.Compared with the non-free radical pathway in Content（2）,the degradation path of SA in Fe₁-CSH-BC₈₀-500/PDS system is simpler and the removal rate of TOC was higher.The oxidation ability of the Fe₁-CSH-BC₈₀-500/PDS system depended on the p H value of the solution,and the removal effect of SA was stronger under acidic conditions.The poor reusability of Fe₁-CSH-BC₈₀-500 was mainly due to the consumption of PFRs in the reaction and storage processes,but catalyst regeneration could be carried out by means of re pyrolysis.