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216 Advances in Eco-Fuels for a Sustainable Environment

0.6

0.5
0.5
0.48
0.46
0.44 0.4
Potential yield (L/kg) 0.3 0.31 0.29 0.26 0.28 0.27 0.29 0.28
0.41
0.41
0.4

0.2

0.1

0.0
Barley Corn Corn stove Oat Oat straw Rice Rice straw Sorghum Wheat Sugarcane Bagasse
Wheatstraw
Barley straw
Sorghum straw

Fig. 8.3 Bioethanol yield of different feedstocks.
(Prepared using data from reference Kim S, Dale BE. Global potential bioethanol production
from wasted crops and crop residues. Biomass and Bioenergy 2004;26:361–75. doi:10.1016/J.
BIOMBIOE.2003.08.002).

and fertilizer and no direct competition with food crops [30]. Fig. 8.3 shows the bio-
ethanol production potential of major first- and second-generation feedstocks. How-
ever, it can be seen from the figure that the first-generation feedstocks have a higher
sugar concentration for producing ethanol compared to second-generation feedstocks.
Although second-generation bioethanol feedstocks have addressed some of the issues
associated with first-generation feedstocks, they still have some drawbacks. For exam-
ple, second-generation bioethanol production requires more capital cost due to the
sophisticated processing equipment and lower energy density compared to first-
generation bioethanol [31]. However, second-generation bioethanol has lower green-
house gas (CO 2 2.85kg/kg) emissions compared to the other feedstocks.
With the aim of addressing the issues associated with first- and second-generation
bioethanol, researchers have explored an alternative feedstock for bioethanol produc-
tion. Typically, bioethanol produced from algal biomass (i.e., microalgae, microbes)
is considered third-generation bioethanol [32]. Third-generation bioethanol feed-
stocks represent a promising feedstock due to the number of remarkable advantages
over first- and second-generation feedstocks [33]. For instance, microalgae can be cul-
tivated on marginal land with a water environment, a low cost of cultivation, a high
conversion efficiency, and a high energy density. However, the bioethanol produced
from algae is less stable compared to the bioethanol produced from other sources. Bio-
ethanol produced from captured carbon dioxide by using advanced technologies such