Alternative fuels such as fuels from highly abundant plant biomass are needed to reduce current human dependency on petroleum. One promising biofuel is ethanol, mainly manufactured from lignocelluloses and especially for use as fuel for automobiles (Holmgren & Sellstedt 2008; Ozturk 2010; Ozturk et al. 2006; Shi et al. 2009). There are several steps in the conversion of lignocellulosics to ethanol. The pretreatment step is for the purpose of breaking down the lignin and to release the crystalline structure of cellulose. The hydrolysis step uses a combination of enzymes to transform cellulose into glucose and the fermentation step uses microbes to ferment glucose into ethanol (Sun & Cheng 2002). Of the three steps, pretreatment continues to be the main recalcitrant factor to achieve an efficient and commercially viable process in treating raw biomass. Besides, pretreatment is often singled out as the culprit in the high cost of ethanol production, costing almost one third of the total production cost (NREL 2000). Therefore, it is important to find new improved ways for the pretreatment step.
In the hydrolysis step, enzymes such as cellulases are often introduced into the pretreated biomass. However, lignin and hemicelluloses presence made it difficult for
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the enzymes to reach cellulose, resulting in a less effective
hydrolysis. Thus, preremoval of lignin and hemicelluloses
in the pretreatment processes is highly desirable and can
significantly increase hydrolysis efficiency (Hakalaa et
al. 2005). Existing pretreatment methods include steam
explosion and the use of dilute acid, alkali and oxidant
(Shi et al. 2009). However, these are chemicals both
environmentally not friendly and costly. A more desirable
option to chemicals is a pretreatment method that uses
microorganisms such as fungi, which possess certain
enzymes that can naturally breakdown lignin found in
lignocellulosic biomass. Because microbes are readily
available and can multiply on its own in simple processes
using fundamental equipment, they provide an attractive
alternative over the much sought physicochemical
methods, which are more costly (Shi et al. 2009).
Microorganisms such as the brown, white and
soft-rot fungi have been used to breakdown lignin and
hemicellulose in waste materials such as agricultural
residues and even for cleaning of chemically uploaded
textile waters (Schurz 1978; Seker et al. 2006). Brown
rots mainly attack cellulose, while white and soft rots
attack both cellulose and lignin (Fan et al. 1987). These
basidiomycetes fungi have developed specialization in
consuming organic materials. White rot fungi are known
to degrade lignin to a great extent and at a fast pace when
compared to any other group of organisms (de Koker
et al. 2000). Lignin degradation by white rot fungi is
thought to involve in delignifying enzymes including
lignin peroxidase (LiP), manganese peroxidase (MnP) and
laccase (Eriksson et al. 1990). Previous work has indicated
that using white rot fungi as a delignification agent in
pretreating plant materials could reduce lignocellulose
defiance to enzymatic hydrolysis (Zhang et al. 2007).
Several white rot fungi have been investigated on different
lignocellulosic biomass to evaluate their delignification
efficiencies (Shi et al. 2009). This could improve present
technology in energy production from plant-based
materials.
Biological pretreatment using natural organisms has
been gaining attention, reason being more emphasis has
been placed on natural properties and environmentally
friendly methods. There are many species and types of
organisms and their capabilities are yet to be discovered.
Consequently, more studies are awaited to be done on
various species for understanding their degrading ability.
In this paper, growth and degrading ability of four different
fungi species on kenaf biomass has been compared.