Page 68 - Refining Biomass Residues for Sustainable Energy and Bioproducts

42 Refining Biomass Residues for Sustainable Energy and Bioproducts

Synthesis and production of FFA by naturally isolated bacterial strains is rare.
Significant development has been observed during the last few decades relating to
genetic modification of E. coli as well as cyanobacteria to enhance the production
and secretion of FFAs. In spite of all this, the attainable yields are still not compara-
ble with the natural lipid producers, so this process requires significant improve-
ment. At present, FAME is mainly produced by methanol derived from fossil
resources; ethanol has also been used as an alternative to produce FAEE that is having
better fuel properties than FAME (Ro ¨ttig et al., 2010). Still the production of branched
FAEE needs some improvements. Alternatively, bacterial strains, which naturally accu-
mulate branched chain fatty acids into TAGs, could be a promising approach for the
production of biodiesel having both residues of straight and branched chain fatty acid.
Biodiesel is produced by transesterification reaction in which triglyceride and alcohol
react in the presence of a catalyst. Among all the existing processes, transesterification
process is relatively simple and preferable as the physiochemical characteristics of the
produced biodiesel are similar to the traditional diesel fuel. Generally, methanol, ethanol,
propanol, butanol, and amyl alcohol are used in the transesterification reaction. As com-
pared to methanol, ethanol is much more preferable because it is produced from the
agricultural wastes, which is environmental friendly and green in nature (Demirbas,
2005). The catalyst used in the transesterification could be an alkali, acid, or an enzyme
with each one having its own advantages and disadvantages. These days biocatalyst
(enzymatic) based transesterification is gaining attention, but in order to apply enzymatic
transesterification at an industrial level, the basic characteristics of enzymes, such as sol-
vent tolerance, working temperature, pH, source of enzyme, need optimization.
Nevertheless, the yield as well as efficiency of enzymatic transesterification is not much
effective as compared to the alkali-catalyzed transesterification (Schuchardt et al., 1998).
But considering the ease in handling and its green nature, this method could be har-
nessed in future for enzymatic transesterification and production of biodiesel.

2.6 Conclusion

Increasing population load and an altered lifestyle attitude are exerting extra pres-
sure on the production market, to satisfy the demands and desire of society. The
recently developed production and consumption models largely rely on fossil-based
resources, which are affecting the environment and natural resources adversely. The
cost-effective production of biological materials is an emerging sector with remark-
able future prospects and provides many business opportunities. With time the
research endeavors are gradually shifting toward bacterial lipids-derived biofuel
production, which is more suitable and compatible for an industrial application. The
major challenge in the overall process of the production of lipids-derived fuels from
microbes is the involved carbon source as it contributes to more than half of the
production cost. Therefore the production of lipids and biodiesel from bacteria
using different waste materials as carbon source involving the application of
advanced biotechnological tools, and modified transesterification reactions will
make the biodiesel production cost effective.