Page 269 - Advances in Eco-Fuels for a Sustainable Environment

232 Advances in Eco-Fuels for a Sustainable Environment

and economic issues associated with cellulosic ethanol production that need to be
addressed for further improvement.
l Lignocellulosic pretreatment: Because of the recalcitrant nature of the lignocellulosic feed-
stocks, they require harsh pretreatment to deconstruct the feedstock. However, these pre-
treatment techniques are energy and cost-intensive as some of the chemicals are very
difficult to recycle. Moreover, some chemicals used in the pretreatment have environmental
and health hazards. So far, some improvements have been made in recent years; however,
extensive research is required for the development of a cost-effective pretreatment method to
enhance the overall process efficiency [60].
l Enzymatic inhibition: During the pretreatment of lignocellulosic biomass, there is a possi-
bility of formation of various inhibitory products, for example, phenols, furans, and carbox-
ylic acids [61, 62]. These inhibitory compounds can suppress the hydrolysis or fermentation
efficiency. Integration of a detoxification method to the bioethanol production process can
be a cheap and easy option to selectively remove the inhibitors [63]. However, cost-effective
and efficient process integration is a challenging task that needs further attention.
Enzyme and microorganism: Selection of the enzyme for efficient hydrolysis and microor-
l
ganisms for efficient fermentation is another technical challenge. The development and
choice of the enzyme for hydrolysis must be based on the activity, stability, and production
costs [64]. During the pretreatment, lignocellulosic biomass produces a significant amount
of pentose. However, the widely selected microorganism S. cerevisiae is not able to profi-
ciently ferment pentose [65]. Recently, Madhavan et al. developed a genetically manipulated
microorganism that exhibited a promising fermentation result [66]. However, more improve-
ments are still necessary for efficient process development.
l Sugar concentration and separation: Sufficient sugar concentration in hydrolysate is
required for the low-cost distillation process as separation of the ethanol-water mixture is
a very challenging task. In some cases, lignocellulosic biomass can produce a low concen-
tration of sugar in the hydrolysate. Therefore, blending of first-generation and second-
generation feedstocks in an appropriate ratio can resolve the issues associated with sugar
concentration as well as inhibitor formation. However, research focus should be given on
the mixing behavior and conversion efficiency.

8.7 Conclusion

The study concluded that bioethanol production has been increased significantly to
meet the increasing energy demand throughout the world. It has been used as an alter-
native fuel to overcome the drawbacks of fossil fuels. Currently, it has been
implemented commercially for large-scale bioethanol production from cellulosic
feedstocks due to its wide range of benefits. However, this category of the industry
is still facing some challenges (such as hurdles of lignocellulosic biomass pre-
treatment, bacterial contamination during fermentation, separation of ethanol, etc.)
to increase productivity to meet the market demand. Therefore, the study rec-
ommended extensive research and development of new technologies for addressing
the issues with cellulosic ethanol production and enhancing production efficiency.
The study also recommended further extensive research for the development of tech-
nology for third- and fourth-generation bioethanol technology before being rec-
ommended to commercial applications.