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R. Abdulla et al.
the world. Renewable energy is a form of alternative energy that can be replenished
for continuous utilization. One of the examples of this alternative energy is biofuels,
which are the fuels derived from biomass (renewable sources) and can be divided
into three common types including biodiesel, bioethanol and biogas (Forssberg 2010;
Salar 2013). Quite a number of promising research have been done on the efficiency
of substituting bioethanol with gasoline. The compatibility of bioethanol especially
with gasoline fuels is undeniable as it can be used as a mixture or in its pure form.
So far, United States and Brazil are the world’s leading bioethanol producers with
about 45 Mt and 24 Mt, respectively (Proskurina et al. 2018).
Varieties of feedstocks can be used up as the starting materials for bioethanol
production and the choice of feedstock is dependent on numerous factors such as
geography, economy and industry (Harun et al. 2010). Based on the feedstocks used,
bioethanol can be divided into three generations. First-generation bioethanol is a fuel
that is extracted from food crops such as sugarcane, corn, soybean and others (Naik
et al. 2010). However, the first-generation bioethanol has created food-versus fuel
debates and some food security issues (Mohr and Raman 2013; Ho et al. 2014). Due
to this debate, second-generation bioethanol has been developed which is derived
from lignocellulosic feedstocks including agricultural forestry residues, energy crops
and short rotation forests (SRFs). Generally, second-generation bioethanol had successfully counteracted the conflicts and competition with food industry (Jambo et al.
2016). Yet, the production of second-generation bioethanol is still not commercially
viable as extensive processing and pretreatment stages are required, thus it is cost
inefficient (Guo et al. 2013). Third-generation bioethanol refers to algae (microand macro-algae)-based fuel. Recently, the promising features of microalgae have
attracted the continuous attention of the world’s researchers to focus on its full utilization for the production of bioethanol. Even though the production of third-generation
bioethanol is still under developmental stages, microalgal-based fuel is expected to
be the benchmark for a better commercialization in the future (Klein et al. 2018).
Microalgae are known to have numerous advantages over other feedstocks. It is
able to provide a high content of carbohydrates which are 50–70% per unit of dry
weight. These contents then can be used as the fermentation substrate or carbon
source for bioethanol production (Ho et al. 2014). The carbohydrates components
are glucose, mannose, ribose, xylose, rhamnose and fucose (Harun and Danquah
2011a). Its high growth rates and a very short harvesting cycle make it a viable
choice as a sustainable feedstock to meet the demands of continuous bioethanol production (Chia et al. 2018). Compared to lignocellulosic feedstock, microalgae is less
resistant to conversion into simple sugars due to its lignin-free composition, thus
no delignification process needs to be performed (Guo et al. 2013). Therefore, it is
more cost-efficient in the aspect of bioethanol conversion processes. The impacts
of microalgal-based bioethanol on the environment are also more beneficial as it
is known to have associated with CO 2 emissions mitigation. Microalgae are efficient in CO 2 fixation since they are able to capture atmospheric CO 2 together with
solar energy from the sun and convert them into biomass through photosynthesis.
Microalgae such as Chlorella vulgaris and Chlamydomonas sp. exhibit this property,
which enables them to emerge as one of the most effective channels to reduce the
R. Abdulla et al.
the world. Renewable energy is a form of alternative energy that can be replenished
for continuous utilization. One of the examples of this alternative energy is biofuels,
which are the fuels derived from biomass (renewable sources) and can be divided
into three common types including biodiesel, bioethanol and biogas (Forssberg 2010;
Salar 2013). Quite a number of promising research have been done on the efficiency
of substituting bioethanol with gasoline. The compatibility of bioethanol especially
with gasoline fuels is undeniable as it can be used as a mixture or in its pure form.
So far, United States and Brazil are the world’s leading bioethanol producers with
about 45 Mt and 24 Mt, respectively (Proskurina et al. 2018).
Varieties of feedstocks can be used up as the starting materials for bioethanol
production and the choice of feedstock is dependent on numerous factors such as
geography, economy and industry (Harun et al. 2010). Based on the feedstocks used,
bioethanol can be divided into three generations. First-generation bioethanol is a fuel
that is extracted from food crops such as sugarcane, corn, soybean and others (Naik
et al. 2010). However, the first-generation bioethanol has created food-versus fuel
debates and some food security issues (Mohr and Raman 2013; Ho et al. 2014). Due
to this debate, second-generation bioethanol has been developed which is derived
from lignocellulosic feedstocks including agricultural forestry residues, energy crops
and short rotation forests (SRFs). Generally, second-generation bioethanol had successfully counteracted the conflicts and competition with food industry (Jambo et al.
2016). Yet, the production of second-generation bioethanol is still not commercially
viable as extensive processing and pretreatment stages are required, thus it is cost
inefficient (Guo et al. 2013). Third-generation bioethanol refers to algae (microand macro-algae)-based fuel. Recently, the promising features of microalgae have
attracted the continuous attention of the world’s researchers to focus on its full utilization for the production of bioethanol. Even though the production of third-generation
bioethanol is still under developmental stages, microalgal-based fuel is expected to
be the benchmark for a better commercialization in the future (Klein et al. 2018).
Microalgae are known to have numerous advantages over other feedstocks. It is
able to provide a high content of carbohydrates which are 50–70% per unit of dry
weight. These contents then can be used as the fermentation substrate or carbon
source for bioethanol production (Ho et al. 2014). The carbohydrates components
are glucose, mannose, ribose, xylose, rhamnose and fucose (Harun and Danquah
2011a). Its high growth rates and a very short harvesting cycle make it a viable
choice as a sustainable feedstock to meet the demands of continuous bioethanol production (Chia et al. 2018). Compared to lignocellulosic feedstock, microalgae is less
resistant to conversion into simple sugars due to its lignin-free composition, thus
no delignification process needs to be performed (Guo et al. 2013). Therefore, it is
more cost-efficient in the aspect of bioethanol conversion processes. The impacts
of microalgal-based bioethanol on the environment are also more beneficial as it
is known to have associated with CO 2 emissions mitigation. Microalgae are efficient in CO 2 fixation since they are able to capture atmospheric CO 2 together with
solar energy from the sun and convert them into biomass through photosynthesis.
Microalgae such as Chlorella vulgaris and Chlamydomonas sp. exhibit this property,
which enables them to emerge as one of the most effective channels to reduce the