Page 93 - Lignocellulosic Biomass to Liquid Biofuels

Bioconversion of lignocellulosic biomass to bioethanol and biobutanol 69

offered by seaweeds over terrestrial biomass could be synthetized as fol-
lows: (1) higher biomass production rate per unit area; (2) do not compete
with agricultural plants for land; (3) require no agricultural input such as
fertilizer, pesticides, and water; and (4) easier depolymerization as it does
not contain lignin in their cell wall [8]. So far, bioethanol production
from seaweeds has been mainly confined to a few phycocolloid-yielding
species belonging to the genera of Kappaphycus, Gelidium, Gracilaria,
Sargassum, and Laminaria. This strategy would not only affect the existing
multibillion hydrocolloid industry but also may lead to another new
debate, hydrocolloid versus fuel. Alternatively, the production of bioetha-
nol from cellulosic residue following the extraction of hydrocolloid from
seaweed biomass has been demonstrated by Kumar et al. [9].
Nevertheless, the lower cellulose content of residue may prevent it from
being a viable feedstock option considering the growing demand for
bioethanol. Therefore the selection of seaweed species with higher cellu-
lose content together with higher growth rate is of paramount importance
for sustainable bioethanol production. In this context a green seaweed
Ulva fasciata Delile was selected as a potential feedstock for bioethanol pro-
duction following enzymatic hydrolysis. This species in spite of having
higher polysaccharide content grows luxuriantly and has a worldwide
distribution regardless of geographical barriers. This species is also regarded
as an opportunistic species with potentials to form blooms (green tide)
when there is a sudden outburst of nutrients in the aquatic streams.
The major compositions of lignocellulosic biomass are lignin, cellulose,
hemicelluloses, salt, ash, protein, pectin, etc. But in recent days out of
these compositions, cellulose is essential for bioethanol production.
Lignin, which is a cross-linked three-dimensional polymer, consists of
three monolignols: p-coumaryl alcohol, coniferyl alcohol, and sinapyl
alcohol [10]. Lignin is covalently bound with polysaccharides in lignocel-
luloses. It can be described as higher value-added product as it has several
applications in different aspects. It is not only used in manufacturing of
dispersants, bioplastics, nanoparticles, and composite materials but also for
carbon fiber agriculture and biofuel field [11]. So one of the main objec-
tives is to remove lignin from biomass and use it in various applications
for the recovery of high value product.
Different physical, biological, and chemical pretreatment methods
have been suggested by several researchers to change the structure of lig-
nocellulosic biomass. This includes disruption of the covalent linkage
between lignin structure and cellulose, whereas they also alter the