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3 Immobilized Enzymes for Bioconversion of Waste to Wealth

beads and they can get onto the internal surfaces of beads. Hence, adsorption or

the covalent couplings can also be used for the enzyme immobilization. During

the process of encapsulation or entrapment, the enzymes can be found inside the

beads. However, enzyme molecules cannot have free access during encapsulation

or entrapment due to their presence at the interior of the beads.

3.3.2.3

Reusability and Recovery

Recovery can be distinguished from the reusability and considered as a removal

or separation from the reaction component from reuse. The use of smart carriers

to develop stimuli-sensitive immobilized enzymes made them to separate as

homogeneous catalysts. However, heterogeneous catalysts can be easily separated

out suitably from the reaction mixture. Magnetic stirrers can be used to separate

the enzymes immobilized on the solid supports using magnetic field. Immobilized

enzymes can be reused in many cycles of the reaction due to their stability.

3.4

Bioconversion of Waste to Useful Products

by Immobilized Enzymes

Biodegradable wastes are generally established in municipal solid waste (MSW).

In the urban MSWs, the organic substances are commonly present in the range of

75–85% [10]. The pretreatment methods with the use of dilute acid (H2SO4, 3%) and

alkali (NaOH, 3%) will effectively increase the production of ethanol from the MSW.

The enzymatic hydrolytic process can be carried out with the help of microorganisms

like Aspergillus niger, Aspergillus fumigates, and Trichoderma reesei which produce

various amylolytic, pectinolytic, and proteolytic enzymes those degrade the organic

content of waste into sugars and simple molecules. The final fermentation process

can be carried out with ethanogenic yeasts like Saccharomyces cerevisiae, Pichia stipi-

tis, and Candida shehatae for the production of ethanol. The waste pretreated with

alkali yields more sugar and ethanol compared to the acid pretreatment during enzy-

matic hydrolysis of waste [11].

Generally in food processing industries, the wastes with undesired byproducts will

be separated from target products. Nowadays, enormous research has been made to

produce high-value byproducts while handling the food processing waste. Generally,

food waste streams are rich in carbohydrates, lipids, proteins, etc. Certainly, protein,

fat, and high-sugar food waste streams will become an attractive feedstock for the

enzymatic valorization [3]. The food processing wastes can be produced in solid,

liquid, or semi-solid form. Solid food wastes are commonly cooking wastes and waste

products like spoiled food, grape/apple pomace, potato/tomato waste, etc., will also

form solid waste. Solid wastes generally consist of starch, cellulose, lignin, pectin,

and monosaccharaides (i.e. fructose and glucose).

Liquid food wastes contain nutrients in diluted form. Liquid wastes are generated

due to the use of huge quantities of water for the various purposes like sanitization,

cleaning, temperature regulation, cooking, etc. The resulting effluents will contain

nitrogenous compounds, fats, oils, suspended solids, organic matter, and many