Page 65 - Lignocellulosic Biomass to Liquid Biofuels

44 Lignocellulosic Biomass to Liquid Biofuels

deactivated. Therefore improving the enzyme stability and activity is cru-
cial to this integrated process.
Application of ILs for biomass pretreatment has provided a new path
for effective utilization of biomass. However, there are still many chal-
lenges for industrialization of IL-based pretreatment. The most important
challenge is the high cost of ILs, and thus to find economical solutions for
the reuse and recycle of ILs is of great importance. How to eliminate the
toxicity of the residual ILs to cellulases and microorganisms is also
important.

2.4 Biological pretreatment
Biological pretreatment refers to using microorganisms or enzymes to pre-
treat various lignocellulosic materials prior to enzymatic hydrolysis of
polysaccharide [1]. The primary microorganisms used mainly include
white- (e.g., Phanerochaete chrysosporium and Ceriporia lacerata), brown-
(e.g., Serpula lacrymans and Coniophora puteana), and soft-rot (e.g.,
Paecilomyces sp. and Cadophora spp.) fungi as well as bacteria (e.g., Bacillus
circulans and Sphingomonas paucimobilis) to degrade lignin, partially hydro-
lyze hemicelluloses, and reduce DP of cellulose [4]. It was reported that
white-rot fungi are the most widely used and effective for biological pre-
treatment [7]. The advantages of biological pretreatment are low energy
requirement, no or little chemicals requirement, mild pretreatment condi-
tions, and little environmental pollution. However, the primary disadvan-
tage of biological pretreatment is the low efficiency [7]. Different fungi or
bacteria secrete different enzyme systems and have different effects on pre-
treatment. White- and soft-rot fungi secrete enzyme systems comprising
xylanase, lignin peroxidases, polyphenol oxidases, manganese-dependent
peroxidases, and laccases as the main compositions and can catalyze the
degradation of lignin and hemicellulose [4].
Sindhu et al. investigated biological pretreatment of paddy straw with
white-fungus (Trametes hirsuta) and compared with SE pretreatment at
121°C. The results indicated that biological pretreatment had higher lig-
nin removal than SE. The highest saccharification efficiency observed after
24 h for biological pretreatment (76.5%) was also somewhat higher than
that of steam pretreatment (74.1%), with a maximum production of sugar
(52.91 g/L) observed for biologically pretreated biomass at 10% glucan
loading after 24 h enzymatic hydrolysis [2]. Gao et al. compared Trametes
versicolor 52J (TV52J), T. versicolor m4D (TVm4D), and P. chrysosporium to