28.4 Techniques for Bioconversion of Food Waste Toward Circular Bioeconomy Approach

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alkalinity and balanced micronutrients [15]. Characteristics of the same type of

food waste obtained from different sources are highly variable due to differences

in sources, handling and processing methods, eating habits, culture, climate, and

seasons. Most of the food waste are acidic in nature, which will negatively impact

the anaerobic digestion process. Thus, in order to increase the efficacy, different

anaerobic digestion processes have to be designed for specific kind of food waste

[15]. Methane potential of food waste is comparatively higher than the other sub-

strates used for anaerobic digestion such as biomass, animal manure, sewage sludge

due to the presence of proteins, carbohydrates, and lipids. Chemical composition of

the food waste is linked with methane yield. Methane production potential of food

wastes rich in fats and lipids is comparatively higher (1.014 m³/kg VS) than that

of proteins (0.74 m³/kg VS) and carbohydrates (0.37 m³/kg VS) [15, 28]. Physical

and biological pretreatments are adopted to accelerate the hydrolysis. Physical

pretreatment includes mechanical and heat treatment. Mechanical pretreatment

and grinding reduce the particle size of the substrate and release the cell compounds

which proliferate the anaerobic bacteria thereby enhancing the anaerobic process.

To promote the hydrolysis of the substrate, biological pretreatments like inoculating

microorganisms and enzymes are carried out.

28.4.2

Microbial Fermentation

Microbial fermentation is the suitable approach to convert the food waste into valu-

able bioproducts. Selection of fermentation method for bioconversion of food waste

is highly dependent on type of feedstock. Solid-state fermentation is suitable for solid

substrate, whereas the submerged fermentation is used for liquid substrates. The

most common bioproducts produced through solid-state fermentation are hydrolytic

enzymes such as cellulase and hemicellulase, and mostly these carbohydrases are

associated with biofuel production. The other bioproducts obtained from solid-state

fermentation are antibiotics from fig residues, aromas from sugarcane bagasse and

sugar beet molasses, biopesticides from brewer’s spent grain, biofuels and bioplas-

tics from food and agro-industry waste, and biosurfactants from sugar beet molasses,

soybean oil refinery waste, and palm oil refinery waste. Among these, biosurfactant

is considered as a potential alternative to chemical surfactants due to their lower tox-

icity and biodegradability and has many applications in agriculture and cosmetics

industry.

Several species of Trichoderma are used as inoculum for cellulase production,

and the yield is induced by cellulose content of the waste substrate. Material

homogeneity is important for higher yield of bioproducts and development of

consistent and continuous operation of solid-state fermentation at large scale. This

method of fermentation utilizes low energy and water; thus, it is eco-friendly to

produce concentrated bioproducts. Submerged fermentation usually implemented

for production of enzymes at industrial scale level due to simplicity in process

control, low processing cost, and high throughput [29]. Value-added products such

as biofuels, enzymes, animal feeds, bio-pulp, compost, biofertilizer, biopesticide,

and secondary metabolites can be obtained by bioconversion of lignocellulose by