Construction Of Immobilized Atrazine-degrading Bacteria-algae System And Study On Removal Of Atrazine In Water

In the actual process of repairing polluted environment by the exogenous free atrazine-degrading bacteria,multiple survival pressures would result in the low survival rate and low atrazine degradation rate of effective degrading bacteria.Microbial immobilized technology could compensate for the above deficiencies.In this study,an immobilized algal-bacterial symbiotic system that could degrade atrazine by sodium alginate embedding method was conducted.Factors affecting atrazine degradation by immobilized cells were investigated.The results were as follows:1.Three atrazine-degrading bacteria were isolated by an enrichment method.Physiological and biochemical identification and 16S rRNA gene sequencing indicated that strains CS3 and 100TPT1,belonged to Arthrobacter ureafaciens,were the same strain.Strain TT3 was identified as Citricoccus sp.To the best of our knowledge,there are no reports of Citricoccus sp.strains that could degrade atrazine.Our work provides a novel candidate for atrazine bioremediation and enriches microbial resources.2.The range for growth and atrazine degradation of TT3 and CS3 was found to be broad,with a preference for alkaline conditions.This indicated that they have potential applications in the remediation of atrazine-contaminated sites in alkaline environments.At 30°C and pH 7.0,strain TT3and CS3 removed 50 mg/L atrazine in 48 h and 66 h respectively.3.Sodium alginate embedding method was used to immobilize mixed cells of strain TT3 and Chlorella vulgaris.The optimal conditions for the preparation of immobilized bacteria-algae microspheres were obtained through orthogonal experiments:sodium alginate 5%,CaCl₂ 4%,and the volume of added bacterial suspension and algal suspension were both 30 mL?bacterial concentration5.0×10⁸ CFU/mL,algae concentration 5.0×10⁶ cells/mL?.Scanning electron microscope showed that the immobilized microspheres prepared under the optimal conditions contained porous network structure.This structure could provide immobilized sites for degrading bacteria and algal cells.It could also provide a large surface area for adsorption of substrates,which was beneficial to the adsorption and degradation of atrazine.4.Factors?such as pH,temperature and heavy metal ions?affecting atrazine degradation by immobilized cells were investigated,and the stability of the immobilized cells was also reported.The results showed that under temperature stress,acid-alkali stress,and heavy metal ion stress,the atrazine degradation rate of immobilized cells was higher 13%-60%than that of free cells after 3 d.In addition,the co-immobilized bacteria-algae treatment was higher at least 5%,up to 24%,than immobilized single bacteria.After being stored at 20°C for 50 days,the immobilized cells still maintained a degradation rate of more than 80%,whereas the free cells decreased to 19.49%.The results indicated that the tolerance of the immobilized cells toward adverse environments and toxic substances were improved.The atrazine degradation effect of co-immobilized bacteria and algae was significantly better than that of immobilized single bacteria.5.Adsorption kinetics studies showed that the adsorption of atrazine by immobilized microspheres conformed to a pseudo-first-order kinetic equation,indicating that the adsorption process was determined by a single factor.The isotherm adsorption of atrazine by immobilized microspheres followed the Langmuir isotherm model better.Therefore,the adsorption process of atrazine by immobilized microspheres could be considered as a single-molecule adsorption model.During biodegradation,the contribution of sorption to the whole atrazine removal mattered in the early reaction stage,and biodegradation was the predominant process after reaching adsorption equilibrium.Investigation on the atrazine biodegradation kinetics by both immobilized and free cells showed that the experimental datas fitted well to the Haldane model.The value of the substrate inhibition constant K_I of the immobilized cells was higher than that of the free cells,indicating that resistance to substrate inhibition for immobilized cells was improved.6.The results of a small simulation experiment for 30 days showed that the immobilized bacteria-algae microspheres had efficient and long-lasting atrazine degradation effect.After 15 days,the ability of atrazine degradation by immobilized bacteria-algae microspheres would not be reduced,and deformed and fractured of microspheres did not appear.This indicated they had a good practical value.