Screening Of Tolerant Microorganism From Lead-zinc Tailing And Its Biosorption Mechanism

The study is to screen lead-zinc tolerant fungus for the bioremediation of heavy metal pollution in Zixing, Hunan. In order to provide basis and guidance for the application of tolerant fungus, the biosorption characteristics and mechanism of growing strain and dry biomass were studied respectively. The main conclusions are as follows:(1) After 3 times continuous enrichment cultivation,19 fungi strains and 5 actinomycetes were isolated from the local tailing of lead-zinc deposit.The fungus J3 was used by comparing their growth and the removal rate. According to the morphological characterization and phylogenetic tree, J3 was preliminarily identified as Verticillium insectorum.(2) The amount of dry biomass affected the removal rate of Pb2+strongly, followed by pH value and time. However, concentration of heavy metal was the most notable factor for Zn2+, next was pH value. Under the optimal conditions, the removal rate of Pb2+ and Zn2+ by dry biomass was 72.6% and 23.8%. Morever, biosorption mechanism was discussed by kinetics simulation, the adsorption of Pb2+ by dry biomass was affected with membrane diffusion and intra-particle diffusion. Meanwhile, the adsorption process of Zn2+ was controlled by membrane diffusion. The results which fitted to the second-order equation can provide the basis and guidance for bioreactor settings.(3) For growing strain, the concentration of heavy metal affected the removal rate of Pb2 +and Zn2+, and pH value, time and inoculation amount were not remarkable. It indicated growing strain had a stable removal efficiency.Under the optimal conditions, the removal rate of Pb2+and Zn2+ by growing strain was 92.2% and 87.7%. The results of kinetics study indicated that the absorption by growing strain was affected by the concentration of Pb2+ and Zn2+, while intra-particle diffusion was the main rate-controlling step for the adsorption of Zn2+.(4)The study on the biosorption mechanisms of the growing strain was carried out through a variety of analytical methods. Firstly, the mycelial pellet with Pb2+ and Zn2+ had denser hyphae on the surface than mycelia pellets in metal-free media, but it was looser and hollow internally. With the increase of the Pb2+ and Zn2+ concentration, hyphae were deformed or even applanated. So morphology modifications of the mycelial pellet and hyphae may played an important role in biosorption process.Secondly, the functional groups on the surface of the growing strain, such as -OH,-NH, —CH2, C=O and C-0 were involved in the biosorption process, of which -OH and C-0 were the preferred adsorption sites. Thirdly, J3 produced alkaline substances, which led to precipitation on the surface of hyphae at high concentrations. Finally, these results and desorption experiments showed intracellular accumulation was the predominant mechanism for Pb2+ in culture with lower metal concentrations (below 75 mg/L), but was overshadowed by extracellular adsorption at higher concentrations. In addition, Zn2+ bioaccumulation play a major role at all concentration assayed.