Alkaline Protease Immobilized on Graphene Oxide: Highly Efficient Catalysts for the Proteolysis of Waste-Activated Sludge

This study aims to investigate the enzymatic hydrolysis of waste-activated sludge (WAS) using free and immobilized alkaline protease. Alkaline protease was immobilized on graphene oxide (GO) sheets using glutaraldehyde as cross-linking reagent. The storage stabilities, kinetic parameters, physical properties, and the free amino acid (FAA) profiles of the WAS protein hydrolysates from free and immobilized enzyme were analyzed. The immobilized enzyme showed significantly improved storage stability, whereas kinetic analysis showed that the apparent Km for the immobilized alkaline enzyme was about 1.8-fold higher than that of free protease. Alkaline protease immobilized on GO showed significant activity towards WAS protein hydrolysates, attractive for practical applications. The FAAs formed by free protease and enzyme immobilized on GO were generally similar.