Cr and Zn biosorption by Aspergillus niger

The dead biomass of Aspergillus niger was studied as biosorbent for removing Zn(II) and Cr(VI) from wastewater. The surface characteristics of the biomass were evaluated based on the point of zero charge (PZC), identification of adsorption sites and structure by scanning electron microscopy. The adsorption capacity was determined by kinetic studies and adsorption equilibrium. The results showed that the PZC is between pH 4.4 and 4.6. At pH values below the PZC, the adsorption of anions occurs by electrostatic attraction. For pH values above the PZC, the surface is negatively charged, and cations are removed. The adsorption of metals by the dead biomass fits the pseudo-first and pseudo-second-order models. Moreover, the equilibrium followed the Langmuir and Freundlich models when the adsorbate concentrations were lower than 50 mg/L, whereas it followed only the Freundlich model at concentrations above 50 mg/L. The biosorption process was characterized by the prevalence of chemical forced between the functional groups present on the biomass surface and the metallic ions. Adsorption capacities of Zn(II) and Cr(VI) were 3.833 and 4.997 mg/L, respectively. Therefore, the biomass of A. niger shows potential application as a biosorbent in the removal of these metal ions.