Study On Screening Of Tolerant-Lead & Zinc Strains And Its Adsorption Capability

With the development of industry,the heavy metals pollution has been a prominent problem in the field of environmental protection.Using microbial treatment technology to remove heavy metals from wastewater has become a new hotspot recently.It not only has the advantages of high speed and high selectivity but also do not create the second pollution as well as be friendly to environment.So it arouses immense hope to ultimately tackle the environmental problems.After 4 times continuous enrichment cultivation,twenty-two strains with ability of Pb²⁺ and Zn²⁺ tolerance,including 12 bacteria and 10 fungi strains,were isolated from the soil collected from Hanyuan county Sichuan province.4 strains of bacteria and 5 strains of fungi have best growth when the concentration of Pb²⁺ and Zn²⁺ was 2500 mg/L.However,bacteria and fungi strains that can tolerant Pb²⁺ and Zn²⁺ at the same time were seldom reported home and abroad.Bacteria strain B6 and fungi strain F1 had high tolerance and adsorb activity of heavy metal,and their adsorption rate of Pb²⁺, Zn²⁺ reached more than 89.31%and 78.72%,and the adsorption quantity were 44.66mg/g and 39.36mg/g respectively;the adsorption rate of Pb²⁺,Zn²⁺ by strain F1 were 92.28%and 93.16%,and the adsorption quantity were 46.14mg/g and 46.58mg/g. The bacterium B6 was identified as Micrococcus lylae and fungus F1 was identified as Fusarium sp.preliminary.Using bacteria strain B6 and fungi strain F1 to remove Pb²⁺,Zn²⁺ explores whether the adsorption is dependent on time,the amount of bacteria,the initial concentration of Pb²⁺ and Zn²⁺ and the temperature or not.The results indicated that pH5.0～6.0 was a feasible range.The biosorption of the two strains on Pb²⁺ and Zn²⁺ is a rapid process which was independent on time that after 10-minite adsorption,the adsorption rate of both bacteria strain B6 and fungi strain F1 have reached 70%of their highest figure.B6 and F1 strains have obvious absorbing effect when initial concentration of Pb²⁺ and Zn²⁺ is 150 mg/L～300 mg/L.When biomass of B6 strain is more than 0.1g,and F1 strains in excess of 0.2g,the biosorption rate tends to slow down.The result of orthogonal test suggested that,the pH affected removal rate of Pb²⁺ and Zn²⁺ strongly,the time and the amount of bacteria also affected the removal ration, and the concentration of heavy metal had no affection to removal ration. Both of the Langmuir and Freundlich adsorption isotherms were studied,which indicated that the Langmuir model well fitted this experimental data and the Pb^2(?) and Zn²⁺ adsorption by strain B6 and F1 was a complex process including not only physical adsorption but also chemical adsorption.The dynamics of the sorption system was better described by the pseudo-second kinetic model.According to the properties of Pb²⁺,Zn²⁺ biosorption by strains B6 and F1,the biosorption mechanism was preliminarily regarded as a physical-chemical process of electrostatic adsorbing and chelation on cell surface.Strains B6 and F1 which was used to remove heavy metals in contaminated waste have high adsorption rate on Pb²⁺,Zn^2- Cd^2- and Ni²⁺,and the concentration of Pb^2(?), Zn²⁺ and Ni²⁺ in treated wastewater achieved the national discharge standards,which showed that strain B6 and F1 could be widely used to adsorb the divalent heavy metal ions and possessed the excellent application potential in environmental engineering.