Isolation Of Aspergillus Niger And Its Role In Heterotrophic Bioleaching Of Heavy Metals-laden Soil

Sulfur–based bioleaching process using autotrophic bacteria （autotrophicbioleaching） is a promising means in removing heavy metals from polluted soils, butheavy metals removal efficiencies are often delayed or deal with unsustainable due topH and the presence of toxic dissolved organic matter （DOM） in soils. In this paper aheterotrophic bacteria （Aspergillus niger A80） which produce small molecular weightorganic acids was isolated from soil. The leaching efficiency of Zn-Cu-Cd frompolluted soil was researched. The paper fouced on the impact of leaching efficiency ofheavy metals by the soil initial pH and the time of soil intervented leaching processing.At last, the paper investigated the complexation efficiency of heavy metal （Cu） byextra-cellular polymers （ECP） which produced by Aspergillus niger A80.（1） Heterotrophic bacteria A80, separated from the soil, which produce smallmolecular organic acid. After the morphological and rDNA-ITS gene sequenceanalysis appraisal, this heterotrophic bacteria belongs to Aspergillus niger. The pHsuitable for the growth of fungus growth range wide, the range is3.0-8.0. In thegrowth of the fungus large numbers of glucose acid （the maximum production is80mM）, citric acid （60mM） and oxalic acid （25mM） are produced.（2） The research on the bioleaching of heavy metals-laden soil by Aspergillusniger A80showed that: The leaching reaction can start at the initial pH of the soil4.0-6.0. When the initial pH is5.8, leaching removal efficiency of the heavy metal isthe best. The removal rate of Zn、Cu、Cd was62.3%、45.9%、50%, respectively. Inaddition, the time of soil intervention leaching processing had small affect on theheavy metal removal, but has a certain effect on the leaching cycle. The leachingcycle was shorten7days when the soil was put into bioleaching after2days culturethan6days and15days.（3） The components of ECP extracted from Aspergillus niger A80werepolysaccharide （45.4%） and protein （10.5%）.The yield of ECP had regular as follows:During0-48h, the number increase slowly, up to2.02g/L,48h-120h increaserapidly, the maxium number was4.5g/L, the number reduced during120h-240h.TheECP produced by Aspergillus niger A80could complexate Cu²⁺strongly. The effectintensity of ECP differ widely at different periods,48h ECP has the largest amountadsorption of Cu²⁺（maximum adsorption is149.3mg/g）. Langmuir model andPseudo-second Order model could describe complexation processes.