Page 15 - Biofuels for a More Sustainable Future

8 Biofuels for a More Sustainable Future

to high costs of second generation biofuels by introducing microbial or fun-
gal systems facilitating more effective and faster cellulose breakdown and fer-
mentation process (Bhatia et al., 2017; Ziolkowska, 2014). However,
research and development in this field is ongoing and no wide-scale com-
mercial solution has been introduced, which again, will depend on the
respective feedstocks and their cellulose and lignin contents.
An advantage of advanced biofuels is that feedstocks used for their pro-
duction generally generate greater greenhouse gas emissions savings, and
thus are more sustainable and desirable from the environmental point of
view. For this reason, in the United States, with the 2007 Energy Indepen-
dence and Security Act, the Renewable Fuel Standards (RFS) were intro-
duced as a mandate to expand the quantity of renewable fuels blended into
transport fuel from 9 billion gallons (34.07 billion liters) in 2008 up to 36 bil-
lion gallons (136.27 billion liters) in 2022 (Ziolkowska, 2018; Ziolkowska
et al., 2010). Within these totals, starting in 2015, only 15 billion gallons
(56.78 billion liters) can be provided on the market from conventional eth-
anol, while the remaining annual mandated quantity needs to be supplied
from advanced feedstocks. In April 2010, the RFS2 was enacted by the
EPA as an extension of the original mandate specifying minimum quantities
from different feedstocks or biofuel types needed to be blended toward the
total mandate (FAPRI, 2010; Ziolkowska et al., 2010). Accordingly, the cel-
lulosic ethanol production was mandated to increase each consecutive year
with the goal of 16 billion gallons (60.5 billion liters) in 2022 (US EPA,
2010). Furthermore, cellulosic ethanol was assigned a Life Cycle Assessment
requirement to be effective with reducing GHG emissions by at least 60%
compared to the emission levels generated from combustion of traditional
gasoline (i.e., fossil fuels used in transportation) (Table 1.1). Due to the
2007 Energy Independence and Security Act and renewable fuel standards
established as mandates, production of cellulosic ethanol and compliance
with its supply for blending has been mainly discussed in the United States.
In Europe, where biofuels policy is based on voluntary targets rather than
mandates, cellulosic ethanol production took off at a later time and has
gained less attention in general.
It needs to be mentioned that in addition to bioethanol production from
the second generation feedstocks, also other advanced biofuels (isopropanol,
butanol, isobutanol, and farnesol) have been gaining on importance due to
their high energy density as well as lower hygroscopic properties and lower
corrosity to pipelines during transportation than other fuels (Chen et al.,
2013; Yua et al., 2011). In addition, metabolic engineering of biosynthetic
fuels can lead to even greater productivity of these alcohols.