| Heavy metal chromium has high toxicity,carcinogenicity and teratogenicity.It is one of the most difficult to dispose heavy metal pollution.The use of microbes to remediate chromium pollution not only saves costs,but also does not cause secondary pollution.It has more advantages than traditional physical remediation and chemical remediation.In this paper,The endogenous bacteria isolated Enterobacter cloacae G04 from the hyperaccumulator Leersiahexandra Swartz is used as research objects.And discuss the characteristics and mechanism of Cr?VI?removal.1.Single factor test method was used to study the influencing factors of Enterobacter cloacae G04removal of Cr?VI?process.The best reaction conditions for Enterobacter cloacae G04 removal of Cr?VI?were as follows:pH 5.0,temperature of 37°C,15%inoculate quantity,substrate concentration of 100mg·L-1,shaking speed of 120 r·min-1,with fluid volume of 80 mL in 250 mL conical flask and incubation time of 48 hours.Under those condition,the removal rate of Cr?VI?was 83.60%.Cr?VI?removal rate was greater than total chromium removal rate,The results showed that the removal of Cr?VI?by strains was likely to be mainly reduction and adsorption.Kinetic analysis of the reaction process of Enterobacter cloacae G04 removal Cr?VI?showed that Zero-order kinetic model applies to this reaction process.Through the study of apparent activation energy in the reaction process,The apparent activation energy of this reaction is Ea=44.45 kJ/mol.2.Through the cell component reduction test,it showed that the removal of Cr?VI?was strongest in the Enterobacter cloacae.G04 of the culture solution.Cell debris and cell contents also had a certain removal effect on Cr?VI?.Through a grown cell test,it was shown that the culture fluid was the more important place where the reaction took place.By correlation analysis,it was found that the extracellular proteins,extracellular polysaccharides and small organic acids secreted by Enterobacter cloacae G04 are important material bases for the reduction of Cr?VI?.The characterization of the reaction product showed that Cr?VI?could promote the cell to secrete more polymer to protect itself from Cr?VI?toxicity.Cr?VI?and Cr?III?were found on the surface of bacteria.The presence of Enterobacter cloacae G04 had demonstrated the reduction and adsorption of Cr?VI?.3.The study of extracellular polymeric excretion of Enterobacter cloacae.G04 showed that low concentrations of Cr?VI?and can promote the secretion of more extracellular polymers by the cells.Using the exopolysaccharide secreted by the bacteria and extracellular proteins to remove Cr?VI?,it was found that extracellular polysaccharides had a stronger ability to remove Cr?VI?.The analysis of the adsorption process of Enterobacter cloacae G04 extracellular polymer showed that the optimal conditions for the adsorption of Cr?VI?by the extracellular polymer were:pH 1.5,substrate concentration of 150 mg·L-1,EPS dosage 0.05 gand incubation time of 8 hours.Under the condition,the equilibrium adsorption capacity and Cr?VI?removal rate were 70.53 mg/mg and 48.06%.The thermodynamic analysis of the adsorption process of polymer Cr?VI?showed that the Langmuir adsorption model is more suitable for the adsorption process;the kinetic analysis results of the adsorption process showed that the pseudo-secondary kinetic model was more suitable for the adsorption process.4.Study on enzymatic properties of Enterobacter Cloacae G04 Intracellular Reductase,it was found that Cr?VI?had a certain inhibitory effect on intracellular enzyme production and enzyme activity.The best reaction conditions were as follows:temperature of 37°C,pH 7,substrate concentration of 0.1 mmol·L-1,enzyme dosage of 105?L and incubation time of 40 Minute.The enzyme activity of Enterobacter cloacae.G04 intracellular reductase is the highest,which can reach 53.11U. |
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