28.4 Techniques for Bioconversion of Food Waste Toward Circular Bioeconomy Approach

433

Food waste

Protein

Carbohydrate

Carbohydrase

Glucose

Ethanol

fermentation

Dark

fermentation

Bioethanol

Biohydrogen

Biomethane

Anaerobic

digestion

Protease

Lipase

Lipid

Long-chain fatty acid

Transesterification

Biodiesel

Free amino acid

Figure 28.3

Bioenergy recovery through enzymatic pretreatment process . Source: Zou

et al. [50].

sludge from municipal treatment plant. Initially, authors hydrolyzed the sludge and

food waste by fungal mass (enzymatic treatment). Fungal mash is a potential wide

spectrum carbohydrase which can hydrolyze the complex organic matters into sim-

ple glucose structure through pullulanases, xylanases, cellulases, hemicellulases,

α-glucosidases, β-amylases, and β-glucanases. Enzymatic pretreatment of sludge

and food waste yielded 2.5 times higher in biomethane than the substrates without

enzymatic pretreatment. In a recent study, Taheri et al. [52] introduced another

pretreatment step before enzymatic hydrolysis of food waste. Authors claimed such

pretreatment induces the structural changes of biomass, maximizes the generation

of glucose, improves bioconversion rate, and minimizes the requirement of chem-

icals and energy input. Authors used six different pretreatment methods including:

●Hydrothermolysis:

Autoclave

the

food

waste

sample

for

one hour

at

100–120 kPa;

●Sonolysis: Food waste in water is exposed to ultrasonication for one hour at

20 kHz and 225 W;

●Electrochemical oxidation with boron-doped diamond (BBD) anode:

Electrochemical pretreatment with BBD anode and stainless-steel cathode for

one hour;

●Electrochemical oxidation with graphite anode: Electrochemical pretreat-

ment for one hour with graphite anode and stainless-steel cathode;

●Sono-electrochemical oxidation: Combining ultrasonication and electrochem-

ical oxidation;

●Solid–liquid fat extraction: Fat content in the food waste is leached out by Soxh-

let extraction.

Then, the pretreated samples were hydrolyzed with amylase which breaks down

the starch into glucose and cellulase to break down cellulose into glucose. Pretreat-

ment enhances the residual content of carbohydrates from 9.34% to 13.06% for starch