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17 Utilization of Microbial Potential for Bioethanol Production from Lignocellulosic Waste

and its conversion technology. First-generation feedstock involves the practice of

fermentation of sugar-based substrates. In tropical countries like India, Brazil, and

Colombia, sugarcane is used as a substrate, while use of corn is prevalent in other

parts of the world [4]. This generation of feed stock competes directly with avail-

able food resources making it costly and unavailable for bioethanol production. This

gave rise to utilization of second-generation feedstock or non-edible lignocellulosic

biomass (LCB) which are crop residues such as corn stalks and wheat straw or woody

biomass and whole plant biomass such as hardwood, soft wood, and grass [5]. Its

wide availability and cost-effectiveness make it a suitable renewable source for bio-

fuel production. The third-generation feedstock comprises microalgal biomass and

is still an unpopular and less studied substrate [3].

17.1.2

Sources of Lignocellulosic Biomass

The yield of LCB obtained globally in a year is around 1.3 billion tons, making it

the most abundantly available bioresource [6]. It can be obtained from three differ-

ent sources: primary, secondary, and tertiary (Figure 17.1). Primary source includes

either crops or key products such as sugarcane, secondary source comprises residues

of production processes such as rice straw, bagasse, and husks, while tertiary source

involves end products or refuge such as organic fraction of municipal solid waste

(MSW), sewage treatment sludge, and wood trimmings [7]. The commercial applica-

tion of these substrates in biofuel production is dependent on their availability, ease

of transportation, cost of processing, treatment, and final yield of bioethanol [3, 7].

17.1.3

Structure and Composition of Lignocellulose

Lignocellulose is a major component of the cell wall in plants, consisting of a back-

bone that comprises cellulose (C6H10O5)n mixed with hemicellulose (C5H8O4)m,

Lignocellulosic biomass

Whole plant

biomass

Aquatic plant

biomass

e.g.

Eichhornia

crassipes, etc.

Perennial grasses

e.g. Miscanthus,

Phalaris, Panicum,

etc.

Field residues

e.g.

Leaves, stover,

straws, etc.

Processing waste

e.g. Bagasse,

cobs, seed pods,

etc.

Hardwood

e.g.

Polar, willow

oak, etc.

Softwood e.g.

pine, cedar,

spruce, etc.

Cattle manures

Saw dust,

pruning, wood

chips, thinning,

slashes, etc.

Pulp, solid

fractions of

wastewater, etc.

Kitchen refuse,

Organic

fraction of

market waste,

house hold

wastes

including paper,

etc.

Agricultural

residues

Agricultural

waste

Forest

biomass

Forest refuse

Industrial

refuse

Municipal

solid waste

Figure 17.1

The sources of different lignocellulosic biomass.