Biomedical Engineering Reference
In-Depth Information
by which the maximum efficacy and benefit of process can be achieved due to the
production of many high-value co-products simultaneously with ethanol. The major
difficulties for the production of ethanol from lignocellulose focus on the technical
and economic issues [
32
]:
•
It is difficult to realize the completive utilization of cellulose, hemicellulose,
and lignin with a single technology. Emphasis on the use of cellulose and the
ignorance of other components will undoubtedly cause environmental pollution
and a waste of resources.
•
The research on the key breakthroughs of technology is insufficient in the lig-
nocellulose conversion process. For example, application of traditional acid pre-
treatment results in high costs and serious environmental pollution. In addition,
indiscriminate application of technology and equipment of ethanol fermentation
from starch results in the high cost of ethanol because of the high dosage of
cellulase and low ethanol conversion efficiency.
•
There are difficulties in technology integration and research. The economical
and highly efficient conversion of straw is a systematic engineering problem
because of the highly complicated structure of raw material and the shortage
of appropriate techniques.
To achieve an economical ethanol production system, Chen and Wang proposed
the concept of composition classification and oriented conversion. Each compo-
nent of raw materials can be converted efficiently to realize the simultaneous
conversion to ethanol and other high-value coproducts from agricultural residues
[
33
,
34
].
Based on these ideas, a demonstration project with annual straw ethanol output
of 3,000 t has been successfully established at Shandong Province in China. This
demonstration project achieves the high-efficiency and environmentally friendly
production of ethanol by integrating the following technologies: steam explosion
technology, gas double dynamic solid-state fermentation (GDD-SSF) of cellulase,
solid-state enzymatic hydrolysis coupled with liquid ethanol fermentation and
CO
2
gas stripping, and organic fertilizer production technology using fermentation
residue [
32
].
As Fig.
10.17
shows, ethanol, organic fertilizer, and xylooligosaccharides would
be produced simultaneously. In this process, hemicellulose in straw is extracted
after corncobs are pretreated by steam explosion and can be used to produce
xylooligosaccharide. A small portion of straw residues can be utilized for the
production of cellulase, and a majority of residues are hydrolyzed by the crude
enzyme preparation. Then, the hydrolysate is converted into ethanol, and the
unhydrolyzed residues enriched in lignin are used for the preparation of organic
fertilizers. In this process, hemicellulose is separated from straw and converted
into high-value products instead of low-value or low-yield fuel ethanol. Meanwhile,
fermented residues enriched in lignin are further used for bioconversion for organic
fertilizers. Lignin mainly acts as an inert carrier with a characteristic of slow release
to further enhance the practical application of bioorganic fertilizer.
