Preparation Of Bacillus BQ-3 Immobilized In Hydrogel Microspheres And Its Degradation Properties And Pathways To Pyrene

In recent years,polycyclic aromatic hydrocarbons（PAHs）have seriously harmed our living environment due to their extreme toxicity and universality.Pyrene（PYR）with symmetric tetracyclic aromatic hydrocarbons,as the first high molecular weight（HMW）PAHs,has attracted our attention due to its characteristics of being difficult to volatilize,more hydrophobic and not easy to degrade naturally.In this paper,we mainly used the hydrogel immobilized microbial remediation technology which has the advantages of environmental protection,economic,efficient and sustainable degradation to study the degradation characteristics of PYR,and then deduced the PYR degradation pathway of strain BQ-3 through the differential metabolomics method.The main conclusions are as follows:（1）Hydrogel microsphere immobilized carrier was prepared with sodium alginate（ALG）,sodium carboxymethyl cellulose（CMC）,Zeolite P and CaCl₂solution as crosslinker.characterization and performance tests were carried out on the carrier.FT-IR and XRD results showed that ALG formed a stable double cross-linked network structure after hydrogen bonding with CMC and interaction with Ca²⁺,and Zeolite P was enclosed in the hydrogel microspheres.It is known from the SEM results that the uniform dispersion of Zeolite P in microspheres not only makes the inner surface of the microspheres rough and easy to attach to microorganisms but also improves the mechanical strength of the microspheres.Mass transfer efficiency and hydraulic impact performance also indicate that the ALG/CMC/Zeolite P hydrogel microspheres can be used as suitable immobilization carriers.（2）PYR degradation test was carried out on the preserved strains in the laboratory,and it was found that the degradation rates of BQ-3,the dominant degrading bacteria of PYR,reached 62.77%,74.42%and 85.68%in 7 d,14 d and 21d,respectively.BQ-3 was identified as Bacillus by 16S rRNA sequencing.BQ-3 was embedded in ALG/CMC/Zeolite P hydrogel microspheres with PYR degradation rate as the response value.The response surface optimization method was used to infer the optimal degradation conditions of each matrix concentration:ALG concentration:2.5%,Zeolite P concentration:1%,and CMC concentration:1.2%.The degradation rate of PYR by immobilized BQ-3 in hydrogel microspheres reached 84.2%.（3）To explore the PAHs degradation performance of BQ-3 immobilized by hydrogel microspheres,compare the PYR degradation rate of BQ-3 immobilized by free BQ-3,blank hydrogel microspheres and hydrogel microspheres in different cycles,and find that the PYR degradation rate of BQ-3 immobilized by hydrogel microspheres in each cycle is significantly higher than that of free BQ-3.After 7 days,the degradation rate of BQ-3 PYR immobilized by hydrogel microspheres reached70.84%,and the Physical absorption rate of PYR by blank hydrogel microspheres was21%.When different factors were investigated,it was found that hydrogel microspheres immobilized BQ-3 could broaden the p H range of the degradation system,and had the best degradation effect at 100mg/L pollutant concentration.（4）In the results of differential metabolite analysis of PYR and glucose by strain BQ-3,90 differential metabolites were detected and identified,67 of which were up-regulated and 23 of which were down-regulated.KEGG enrichment annotation showed that many substances related to metabolic pathways were found in the PYR degradation group.By summarizing the up-regulated intermediate metabolites,we speculated that the initial ring-opening sites of BQ-3 on PYR are C1,C2 and C4,C5.