(587af) Effect of Different Pretreatment Methods of Corncob On Bioethanol Production and Enzyme Recovery

With the continuous fossil fuel consumption,
and various kinds of environmental problems caused by the use of nonrenewable
resources, people have come to realize the importance of looking for renewable
energy (Hahn-Hägerdal et al ,2006). Corncob has higher bulk density and can be easy to collect and
transport, which is considered as one of the most potential lignocellulosic
feedstocks compared to the others. Pretreatment is extremely significant in the
process of bioconversion of lignocellulose to bioethanol, aiming to remove
lignin and hemicellulose, to disrupt the crystalline structure of cellulose, to
increase the porosity of the materials, so as to make the raw materials more
accessible to enzyme attack (Chen et al ,
2008). Furthermore, high cost of
enzymes required for cellulose conversion to fermentable sugar is major
limitation hindering the commercialization of lignocellulose bioconversion to
bioethanol. Efficient pretreatment and reuse of cellulase are effective methods
to promote the cellulosic bioethanol commercialization.

In this work, corncob was used as substrate.
The effects of pretreatment methods(Fig. 1a) including dilute acid, sodium hydroxide, aqueous ammonia soaking
and coupling acid-base (dilute sulfuric acid-aqueous ammonia) on glucose and
ethanol concentration were analyzed during pre-hydrolysis and the simultaneous
saccharification and fermentation (SSF) process(Fig. 1b). The influence
of each pretreatment on the adsorption and desorption of cellulase (Fig. 1c) and on the
recycling effect of cellulase after re-adsorption by fresh substrate were also
discussed. The results showed that acid-base coupling pretreatment could
effectively removed hemicelluloses (83.46%) and lignin (78.53%) together from
the lignocellulose with a final cellulose content of 73.84% and a cellulose
recovery of 85.40%; the desorption percent and recycling percent of cellulase
after 96h of SSF and re-adsorption one time was 57.7% and 62.4% respectively;
ethanol concentration amounted to 62.0% of the first time in the second round
of SSF after the enzyme re-adsorption.

This work was supported by the NSF of China
(51173128, 31071509, 21276192), the Ministry of Science and Technology of China
(Nos. 2012YQ090194, 2013AA102204, 2012BAD29B05), the Program for New Century
Excellent Talents in Chinese University (NCET-08-0386; NCET-11-0372), and
Beiyang Young Scholar Program (2012).

References

[1]     Chen
H., Han Y., Xu J., Simultaneous saccharification and fermentation of steam
exploded wheat straw pretreated with alkaline peroxide, Process Biochemistry,
2008, 43(12): 1462~1466

[2]    
Hahn-Hägerdal B., Galbe M., Gorwa-Grauslund
M.F., et al., Bio-ethanol-the fuel of tomorrow from the residues of today, Trends
in Biotechnology, 2006; 24(12): 549~556.

Figure 1 a) Procedures of different pretreatment methods; b) Schematic
diagram of a cellulase recycling process; c) Free enzyme protein percentage of
initial in solution during pre-hydrolysis, SSF and re-adsorption process for
corncobs after different pretreatments.