Production and concentration of keratinases and application of fermentation residual in removing hexavalent chromium

The production of keratinases was evaluated in submerged fermentation with Aspergillus niger and by pigs’ swine hair in a batch bioreactor. Experimental planning was performed to assess the interaction between different variables. The enzyme extract produced was characterized at various pH and temperatures and subjected to enzyme concentration using a biphasic aqueous system and salt/solvent precipitation techniques. In addition, the substrate’s potential in reducing hexavalent chromium from synthetic potassium dichromate effluent with an initial concentration of 20 mg L⁻¹ of chromium was evaluated. The resulting enzyme extract showed 89 ± 2 U mL⁻¹ of keratinase. The enzyme concentration resulted in a purification factor of 1.3, while sodium chloride/acetone and ammonium sulfate/acetone resulted in a purification factor of 1.9 and 1.4, respectively. Still using the residual substrate of swine hair from the fermentation, a 94% reduction of hexavalent chromium concentration occurred after 9 h of reaction. Thus, the study proved relevant for producing keratinases, with further environmental applicability and the possibility of concentrating the extract via low-cost processes.