Overview of the Mechanism of Hydrolytic Enzymes and Their Application in Waste Treatment

Hydrolytic enzymes play a crucial role in a wide range of economically important bioconversion processes ranging from the deconstruction of lignocellulosic biomass for generating different bioproducts to the treatment of biowastes. In this chapter, different types of hydrolytic enzymes such as cellulases, cellobiases, chitinases, xylanases, and amylases are described for converting carbohydrates into sugars. Besides these, protease and lipases are also discussed for the hydrolysis of proteins and lipids, respectively. Furthermore, various structural features of the hydrolase enzyme class along with their molecular mechanisms of action, substrate specificities, and hydrolytic activities have been highlighted. Especially, hydrolysis of the glycosidic bonds by the general acid (proton donor), and a nucleophile/base of the glycoside hydrolases, either by overall retention or overall inversion of the anomeric configuration, are discussed in detail. Finally, the application of these enzymes in treating carbohydrates, proteins, and fats present in waste is considered. For example, the treatment of industrial and municipal sludge, fatty wastewaters, waste-activated sludge, dairy wastewaters, agro-industrial waste, and others are presented. Also, the limitations and challenges of the hydrolases are briefly described. Finally, recent advances in protein engineering for the improvement of the hydrolase activity for waste treatment are summarized.