Studise On Characteristics Of Leucobacter Sp.N-4 For Metal Adsorbtion And Dye Decoloration

In this study, several strains capable of tolerating and adsorbing metals were isolated from heavy metal-contaminated soil by concentration gradient screening technique. Morphology and 16S rDNA sequence analysis were used to identify and classify the strains. Moreover, the basic characteristics of these strains, including the influences of temperature, pH and NaCl concentration on the growth of strains, as well as the adsorption capacity of different metal ions, were also investigated.Among all the strains isolated, a strain named N-4, which exhibited excellent adsorption capacity of Ni2+, was screened and identified as genus Leucobacter. The 16S rDNA sequence of strain N-4 has been deposited in the GenBank database under accession number HM641755. Firstly, the effect of adsorption time on the removal of Ni2+ was investigated and the result showed that the biosorption of Ni2+ by strain N-4 was very rapid, which could reach 80% of the maximum adsorption within 10 min and approach a adsorption balance within 40 min. Secondly, three important factors in the Ni2+ absorption by strain N-4, including pH of initial solution, Ni2+ concentration and inoculation amount, were evaluated and assigned the optimal values by response surface methodology (RSM). The optimal conditions for Ni2+ absorption by strain N-4 were as follows:pH 4.75, inoculation amount of 5.38 g/L and Ni2+ concentration of 53.6 mg/L, where the maximal removal rate of Ni2+ was nearly 99%. Furthermore, the adsorption-equilibrium data fitted Langmuir adsorption isotherm better than Freundlich adsorption isotherm, indicating the monolayer adsorption of Ni2+ by strain N-4. Pseudo first-order, pseudo second-order and intraparticle diffusion models were adopted to describe the adsorption dynamics of Ni2+. As a result, the pseudo second-order kinetic model provided the best correlation with the experimental data. On the other hand, some chemical functional groups (e.g.-NH2,-OH, and COO-M) have been identified as the active binding sites of the biomass for Ni2+ biosorption using infrared spectrometer system.Finally, the capacity of strain N-4 for the decoloration of dyes was also studied. As a result, strain N-4 presented the capacity of decolorizing 10 kinds of dyes. Four key factors in the decoloration process of Reactive Dark Blue K-R were evaluated and optimized by RSM. The maximum decoloration rate of Reactive Dark Blue K-R by strain N-4 can reach about 100% within 10 h under the following conditions:10 g/L strain N-4,222 mg/L dye,1.5 g/L and 3.5 g/L fructose. Meanwhile, the effects of different metal ions on the decoloration process were also investigated. The results indicated that K+, Ca2+, Mg2+, Ba2+, and Mn2+ could improve the decoloration rate, while Ni2+, Cu2+, and Hg2+ could inhibit it obviously. In addition, the decoloration rate can be improved to some extent with the increase of NaCl concentration, which might be due to the common ion effect.