Removal Mechanism Of Bisphenol A In Aqueous Solution By Walnut Shell Biochar Immobilized Strains Xenophilus Azovorans And Phanerochaetc Chrysosporium

Bisphenol A（BPA）is an environmental endocrine-disrupting organic pollutant,which can enter the natural environmental media directly or indirectly and endanger human health through the food chain.Among the removal methods of environmental organic pollutants,microbial remediation has received much attention from scholars because of its advantages of complete removal and no secondary contamination.At present,researchers have screened a variety of strains capable of BPA degradation,but their environmental conditions in pure culture systems are demanding and it is difficult to maintain microbial activity,and the BPA degradation efficiency is still low.How to improve the environmental adaptability of functional microorganisms and maintain high activity is still the key to promote the removal of BPA from environmental media.Biochar,as a carbon-based porous material,is widely used in soil fertilization and environmental pollutant removal,and it also has good biocompatibility as a microbial carrier.In this study,we first investigated the adsorption characteristics of walnut shell biochar on BPA,then investigated the degradation characteristics of strain X（Xenophilus azovorans）and strain BF（Phanerochaetc chrysosporium）on BPA under different influencing factors,and finally prepared two immobilized bacterial strains using walnut shell biochar as a carrier.Microbial immobilization remediation technology was used to explored the degradation characteristics and mechanism of BPA by the two immobilized strains.The dominant results of the research obtained were as follows:（1）Walnut shell biochar has a large specific surface area、well-developed pore structure and abundant chemical functional groups,which can be used as a carrier for microbial immobilization agents and also for the adsorption of pollutants.The adsorption of BPA by walnut shell biochar was more consistent with the pseudo-secondary kinetic model and the Langmuir model,the maximum adsorption capacity calculated from Langmuir isothermal model is approximately 21.702 mg g^-1;in the range of pH=3～9,the process of BPA adsorption by walnut shell biochar was not affected by the initial pH of the solution,but the adsorption capacity of BPA decreased with the further increase of pH to 11;the adsorption capacity of BPA increased slightly as the system temperature increased from 25℃to 35℃;the adsorption efficiency of BPA increased with the increase of dosage,but the adsorption capacity decreased;the effect of ionic strength on the adsorption of BPA by walnut shell biochar was not significant.（2）The 16Sr DNA sequence comparison results indicated that the screened strain X belonged to Xenophilus azovorans.The degradation rate of strain X reached 100%after 24 h in the pH range of 5～11,and that of strain BF reached 100%after 7 d in the pH range of 5～7;the optimum temperature for both strains was 35℃ and the optimum inoculum was 5%;strain X was suitable for BPA below 25 mg L^-1,and strain BF was able to completely degrade BPA at concentrations of 5～50 mg L^-1.The results of the degradation kinetics showed that the degradation half-value period t_1/2 of BPA was 77.02 h and 86.64 h for both strains,and strain X was able to degrade BPA faster.（3）The optimal immobilization ratio between carrier and bacterial solution was 1:10（g:m L）.The SEM results showed that after immobilization,the two strains were adsorbed on the surface of walnut shell biochar and in the pores and grooves,and strain X became fuller and increased after degradation of BPA;strain BF formed biofilm and adhered to the surface of walnut shell biochar.The FTIR results showed that the degradation of BPA by immobilized microorganisms was mainly related to methylene,C-O and C-H bonds.The immobilization treatment improved the adaptability of the strain to the adverse environment,and the effects of different pH（9～11）and temperature（25～35℃）on the degradation of BPA by immobilized microorganisms were not obvious;with the increase of the dosage,the efficiency of BPA degradation by immobilized microorganisms increased and the unit removal decreased,and the best dosage was 0.2 g;the degradation rate of immobilized microorganisms decreased with the increase of the concentration,the optimal substrate concentrations of the two immobilized bacterial agents were 10 mg L^-1 and 5 mg L^-1.（4）There are three main degradation products of immobilized bacterium agent X measured by HRLCMS,and there exists a possible degradation pathways of BPA;there are five main degradation products of immobilized bacterium agent BF whose degradation of BPA may have two pathways,and the degradation of BPA by two immobilized bacterium agents is mainly completed by the breakage of the C-C bond between isopropyl and benzene ring,hydroxylation reaction or demethylation reaction.Overall,walnut shell biochar can be used as a pollutant adsorbent and potential microbial immobilization carrier,and strain X（Xenophilus azovorans）and strain BF（Phanerochaetc chrysosporium）as two BPA-degrading bacteria enrich the strain pool of efficient BPA-degrading strains,and immobilization treatment improves the adaptability of the strains to adverse environments,providing a theoretical basis and technical support for the removal of novel pollutants from water bodies.