Page 43 - Lignocellulosic Biomass to Liquid Biofuels

22 Lignocellulosic Biomass to Liquid Biofuels

(HMF), furfural and acetic acid, and so on, which are toxic to yeast or
other microorganisms.

2.2.1.2 Irradiation pretreatment
As shown in Fig. 2.1, irradiations including gamma ray, ultrasound,
microwave, and EB have been used for biomass pretreatment to improve
the cellulose digestibility [4]. Gamma irradiation can deconstruct the cell
wall structure with depolymerization of cellulose and lignin thus improv-
ing the biodegradability of the pretreated materials [17]. Yin et al. found
that gamma irradiation combined with alkaline pretreatment of wheat
straw could well enhance the accessible surface area for enzymes [18].
Xiang et al. applied cobalt-60 gamma-ray irradiation for pretreatment of
hybrid poplar sawdust (with 300 kGy irradiation pretreatment) and the
enzymatic saccharification (reducing sugar yield) at the first 12 h increased
by 16.7% (from 71.2 to 83.1 mg/g) with 20 FPU/g enzyme loading at
45°C [19]. Gamma irradiation also can be used to assist the fungal degra-
dation of the polypropylene/biomass composites [20]. Wang et al. com-
pared gamma irradiation and SE pretreatment for ethanol production
from agricultural residues. For the irradiation-pretreated rice straw, the
cellulose, hemicellulose, and lignin were much more easily degraded, and
the glucose yield was enhanced from 6.58% to 47.44%, being better than
SE pretreated results [21].
Ultrasound can disrupt the structure of cell wall, increase the specific
surface area, and reduce the DP of cell wall components [22]. Yu et al.
employed ultrasound-assisted ionic liquid (IL) pretreatment to enhance
the enzymatic and acid hydrolysis of sugarcane bagasse and wheat straw
[23]. The results showed that the enzymatic hydrolysis of bagasse and
wheat straw pretreated with IL resulted in the maximal glucose yield at
ultrasound of 20 kHz (40.32% and 53.17%), and the maximal glucose
yields of acid hydrolysis were 33.32% and 48.07% when pretreated at
ultrasound of 40 kHz [24]. Ultrasound pretreatment also has an influence

Figure 2.1 Actions of irradiation-based physical treatment for biomass.