Removal And Mechanism Of Ni(Ⅱ) And Cr(Ⅵ) From Aqueous Solutions By Marine Aspergillus Niger Mycelial Pellet

Due to the high water volume, difficulties in treatment and high damage to environment and human beings, heavey metal wastewater pollution has attracted widely attention and become a pressing environmental problem. Biosorption as the most promising method for heavey metal wastewater treatment has been shown to be one of the most potential methods.The Aspergillus niger isolated from the marine sediment samples was used as a starting strain, using its self-immobilization ability to prepare bioadsorbent, which could remove heavy metals from aqueous solutions. This paper mainly studied the performance in Ni(II) and Cr(VI) removal from solutions by this kind of new bioadsorbent and corresponding operation conditions, analyzing relevant mechanisms of biosorption and biodegradation.The surface properties and morphology of pellets were investigated, indicating that large amount of heavy-binding sites on the surface of mycelial pellet, which made it adsorb heavy metal ions. Zeta potentiometer measurement indicated around pH 2.5 the charge of pellet surface was zero, implying that it was in negative zeta potential condition in a wide pH range, which was in good favor of the adsorption of positive heavy metal ions.Different influences on Ni(Ⅱ) adsorption by marine A. niger mycelial pellet were investigated, results showed that Ni(Ⅱ) adsorption capacity increased with the increase of initial Ni(Ⅱ) concentration and decreased with the increase of temperature, adsorption capacity reduced after heat treatment, country to the NaOH treatment, and the adsorption efficiency reached best at pH 4. Kinetic studies indicated that the biosorption behavior followed the pseudo-second-order kinetic model (R2>0.99). The experimental data of A.niger pellet biosorption Ni(Ⅱ) were fitted by four models (Langmuir model, Freundlich model, Tempkin model, D-R model), among this, Freundlich model was best in describing the A.niger pellet biosorption behavior (R2>0.99). Results initially indicated that A.niger pellet biosorption of Ni(Ⅱ) was a surface combination of physical adsorption process.The process of removal of hexavalent chromium ion by marine A niger mycelial pellets was studied and effects of process parameters were investigated, such as pH, initial Cr(Ⅵ) concentration and biomass concentration and so on. To some extent, these parameters above would affect Cr(Ⅵ) removal efficiency and the highest Cr(Ⅵ) removal efficiency was over 99%.Finally, the removal mechanism of Cr(Ⅵ) through a serial of modern analysis methods was analyzed. Although environmental conditions were different, most of Cr(Ⅵ) has been reduced to Cr(Ⅲ) in aqueous solutions. Therefore, Cr(Ⅵ) removal with A. niger pellet was biosorption--bioreduction process, namely, mycelial pellets could both adsorb Cr(Ⅵ) and reduce Cr(Ⅵ) into Cr(Ⅲ), which indicated that it may be considered as an efficient bioadsorbent with the function of biological reduction in the treatment of chromate containing wastewater.