Bioremoval of tannins and heavy metals using immobilized tannase and biomass of Aspergillus glaucus

Abstract

Background: The presence of inorganic pollutants and heavy metals in industrial effluents has become a serious threat and environmental issues. Fungi have a remarkable ability to exclude heavy metals from wastewater through biosorption in eco-friendly way. Tannase plays an important role in bioconversion of tannin, a major constituent of tannery effluent, to gallic acid which has great pharmaceutical applications. Therefore, the aim of the current study was to exploit the potential of tannase from Aspergillus glaucus and fungal biomass waste for the bioremediation of heavy metals and tannin.

Results: Tannase from A. glaucus was partially purified 4.8-fold by ammonium sulfate precipitation (80%). The enzyme was optimally active at pH 5.0 and 40 °C and stable at this temperature for 1 h. Tannase showed high stability at different physiological conditions, displayed about 50% of its activity at 60 °C and pH range 5.0-6.0. Immobilization of tannase was carried out using methods such. as entrapment in Na-alginate and covalent binding to chitosan. The effects of Na-alginate concentrations on the beads formation and enzyme immobilization revealed that maximum immobilization efficiency (75%) was obtained with 3% Na-alginate. A potential reusability of the immobilized enzyme was showed through keeping 70% of its relative activity up to the fourth cycle. The best bioconversion efficiency of tannic acid to gallic acid by immobilized tannase was at 40 °C with tannic acid concentration up to 50 g/l. Moreover, bioremediation of heavy metal (Cr³⁺, Pb²⁺, Cu²⁺, Fe³⁺, and Mn²⁺) from aqueous solution using A. glaucus biomass waste was achieved with uptake percentage of (37.20, 60.30, 55.27, 79.03 and 21.13 respectively). The biomass was successfully used repeatedly for removing Cr³⁺ after using desorbing agent (0.1 N HCl) for three cycles.

Conclusion: These results shed the light on the potential use of tannase from locally isolated A. glaucus in the bioremediation of industrial tanneries contained heavy metals and tannin.

Keywords: Aspergillus glaucus; Biosorption; Gallic acid; Heavy metals; Immobilization; Tannase.

Fig. 1

Workflow of tannase enzyme production and biomass production from A. glaucus

Fig. 2

Effect of pH on the enzyme activity (a) and stability (b) of the tannase

Fig. 3

The effect of temperature on the tannase activity

Fig. 4

Thermal stability of tannase enzyme

Fig. 5

SEM micrographs of the surface of 3% Na alginate beads (control) (Upper), SEM micrographs of the surface of 3% Na alginate beads containing tannase enzyme isolated from A. glaucus (Lower)

Fig. 6

FT-IR spectra of 3% Na alginate beads (control) (Upper), FT-IR spectra of 3% Na alginate beads containing tannase enzyme isolated from A. glaucus (Lower)

Fig. 7

Reusability test of the immobilized A. glaucus tannase at repeated enzyme reactions

Fig. 8

Metal ions uptake by A. glaucus biomass

Fig. 9

Cr³⁺uptake by A. glaucus biomass. Living biomass ‘control’ and dead biomass (by boiling and by KOH-treatment