Biosorption performance of the multi-metal tolerant fungus Aspergillus sp. for removal of some metallic nanoparticles from aqueous solutions

Abstract

The wide spread of nanotechnology applications currently carries with it the possibility of polluting the environment with the residues of these nanomaterials, especially those in the metallic form. Therefore, it is necessary to study the possibility of treating and removing various nanoscale metal pollutants in environmentally friendly ways. The present study focused on the isolation of multi-metal tolerant fungi to be applied in the bioremoval of Zn, Fe, Se, and Ag nanoparticles as potential nanoscale metal pollutants. Aspergillus sp. has been isolated as multi-metal tolerant fingus and investigated in the bioremoval of targeted nanometals from their aquoues solutions. The effect of biomass age, pH, and contact time was studied to determine the optimal biosorption conditions for fungal pellets towards metal NPs. The results showed a high percentage of fungal biosorption on the of two-day-old cells, which amounted to 39.3, 52.2, 91.7, and 76.8% of zinc, iron, selenium, and silver, respectively. The pH 7 was recorded the highest percentage of NPs removal for the four studied metals i.e. 38.8, 68.1, 80.4, and 82.0% of Zn-, Fe-, Se- and Ag-NPs, respectively. The contact time required between Aspergillus sp. and the metal nanoparticles to obtain the best adsorption was only 10 min in the case of Zn and Ag, but it was 40 min for both Fe and Se NPs. The efficiency of living fungal pellets in removing the four metallic NPs exceeded that of dead biomass by 1.8, 5.7, 2.5, and 2.5 folds for Zn, Fe, Se and Ag, respectively. However, utilization of dead fungal biomass for metallic NPs removal could be considered more applicable to the actual environmental applications.

Keywords: Aspergillus sp.; Bioremediation; Biosorption; Metallic nanoparticles.

Fig. 1

Flowchart for preparation of metal nanostructures, zinc (A), Iron (B), selenium (C) and silver (D).

Fig. 2

Growth diameter of fungal isolates No. MR1, MR2, MR3, and MR4 on PDA plates containing different metal ions (Zn²⁺, Fe²⁺, Se²⁺ and Ag²⁺) with different concentrations.

Fig. 3

Morphological characteristics of fungal isolate MR3; (A) macroscopic using different media, YPG (a), DOX (b), PDA (c) and Sabouraud's dextrose (d). (B) The microscopic observations at different incubation periods: (1, 2) after incubation for 24 h (conidia formed germ tube), (3, 4, 5, and 6) after 48h of incubation (germ tube grow into hyphal mycelium and forming aerial hyphae), (7) after 72 h (aerial hyphae forming conidiophores forming the vesicle has sterigmata carrying conidia).

Fig. 4

HRTEM characterization of Zn (a), Fe (b), Se (c) and Ag (d) nanoparticles.

Fig. 5

Efficiency capacity (%) of Aspergillus sp. biomass for removing of Zn, Fe, Se and Ag NPs at different biomass age.

Fig. 6

Removal efficiency (%) of Zn, Fe, Se and Ag NPs by Aspergillus sp. biomass under various pH values.

Fig. 7

Biosorption capacity (%) of Aspergillus sp. towards (Zn, Fe, Se and Ag) nanoparticles at different contact time.

Fig. 8

The amount of adsorbed Zn, Fe, Se and Ag-nanoparticles per gram of the dry mass or its equivalent of the wet mass of the fungus Aspergillus sp.

Fig. 9

Effect of the dead biomass of Aspergillus sp. on removal of mixture of (Zn, Fe, Se and Ag) nanoparticles.