2.2 Food Waste for the Production of Biodegradable Plastics and Biogas

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2.2.2

Food Waste and Bioenergy

2.2.2.1

Ethanol from Food Waste

Food waste should be pretreated to obtain simple waste since it will have complex

lignocellulosic biomass. Pretreatment can be done by thermal process, enzymatic

process, acid or alkali treatment to improve the digestibility of cellulose, lignocellu-

lose, pectin, and starch present in the food waste. After the hydrolysis, the acquired

mash can be subjected to the ethanol fermentation by inoculating with the yeast.

After the fermentation, distillation process can be carried out for obtaining the pure

ethanol. Food waste treated with amylase enzymes helped to obtain ethanol yields

of 29.1–32.2 g/l [7, 8].

2.2.2.2

Food Waste to Biohydrogen

The dark fermentation is mostly used in biorefineries for the production of H2 due

to low energy requirement for the process. The macromolecules present in the waste

need to be broken down into amino nitrogen and glucose before H2 production by

microbial fermentation. The hydrolysis of food waste can be completed by enzymes

and heat treatment without harming bacteria which result in high H2 production.

The sonification of food waste enhanced H2 production without having additional

inoculum, and this study suggested that pretreatment is essential parameter to

enhance H2 production [7, 9]. The optimum production of H2 was 120 ml/g of

carbohydrate with 35.69 ml/h at controlled chemical oxygen demand (COD) of

200 g/l of food waste, and similar value of H2 yield was also obtained at controlled

moisture content of food waste. For optimal production of H2 the required C : N

ratio is up to 20. Food waste is very suitable feedstock for the production of H2, due

to the presence of high carbon content and indigenous microbial consortium [10].

2.2.2.3

Production of Biogas from Food Waste

The food waste is most promising for the production of biogas, due to its wide avail-

ability and heterogeneous composition with high energy content. The processing

of food waste and a shredded municipal solid waste (MSW) by AD with an opera-

tion period of 20–40 days yielded 0.18 m³ of CH4/kg of volatile solid (VS) added. The

1 m³ of biogas produced via AD is equivalent to about 21 mJ energy that is efficiently

converted to electrical energy (2.04 kWh) at 35% process efficiency. A batch study on

methanization of food waste for 10 and 28 days was conducted and observed the opti-

mum CH4 yield (0.435 m³/kg VS) after 28 days of digestion with VS removal of 81%.

A yield of 0.348 m³/kg VS was observed after 10 days of digestion. Different research

studies related to AD have proved that co-digestion of food waste with MSW has

enhanced biogas yield by 40–50% in comparison to digestion of food waste alone

[11]. Co-digestion batch tests with different combinations of sugar beet leaves and

potato waste were conducted, and highest CH4 yield of 0.68 m³/kg VS added was

observed for mixing at 16% : 24% total solid. The observed CH4 yield from potato

waste alone was 0.42 m³/kg VS [7, 12].