Ecofriendly Approach for Bioethanol Production …
303
2 Bioethanol from Microalgae
Bioethanol emerged as a green and sustainable transportation fuel, as burning this
fuel emitted less GHGs than conventional gasoline (RFA 2016; USDOE 2016).
However, using sugarcane, coarse grains, wheat and molasses as the main feedstock for bioethanol production could attributed to the two major controversy issues
(OECD-FAO 2016): (i) the imbalance of worldwide food markets due to the “food
versus fuel” scenario (Lim and Teong 2010); (ii) the use of large agricultural land
(Kirkels 2016). Therefore, microalgae with simple cell structure and those that can
grow rapidly are potentially employed for sustainable bioethanol production. Furthermore, from the environmental perspectives, cultivation of microalgae coupled with
CO 2 fixation and bio-treatment of wastewater, evolved to be a potential green energy
producer (Maity et al. 2014).
Microalgae are unicellular with size ranging from a few to hundred micrometers
(μm). They are commonly found in freshwater or marine water, exists either in the
form of individual or groups and chains (Suganya et al. 2016). They are photosynthetic microorganisms that utilized CO 2 as carbon source and simultaneously release
O 2 into the atmosphere (Andersen 2013). The photoautotrophical process (or lightdriven redox reaction) convert the absorbed CO 2 into carbohydrates and lipid within
the microalgae cells (Masojídek et al. 2013).
2.1 Effect of Cultivation Conditions to Improve
Carbohydrates Production
Besides screening and choosing carbohydrate, rich microalgae species, inducing
specific cultivation conditions is an alternative way to further enhance carbohydrate productivity in the microalgae. In fact, this strategy is also applicable to low
carbohydrate content microalgae species, but grows easily and able to withstand
extreme environment. The following sections discussed several cultivation strategies
to increase the carbohydrate content in microalgae cells.
2.2 Effect of Sulfur
Sulfur is an important element is all living cells, as it is needed to synthesis amino
acids (methionine and cysteine), vitamins and sulfolipids (Becker 1994). The strategy
to deprive sulfur concentration in microalgae cultivation was previously initiated to
produce biohydrogen from Chlamydomonas reinhardtii through direct biophotolysis
(Melis et al. 2000). When microalgae are cultivated under limited sulfur source,
synthesis of the PS II D1 polypeptide chain (32 kDa) is impeded and thus, interfere
the repair of PS II from photooxidative damage (Melis 2007 and Wykoff et al. 1998).
303
2 Bioethanol from Microalgae
Bioethanol emerged as a green and sustainable transportation fuel, as burning this
fuel emitted less GHGs than conventional gasoline (RFA 2016; USDOE 2016).
However, using sugarcane, coarse grains, wheat and molasses as the main feedstock for bioethanol production could attributed to the two major controversy issues
(OECD-FAO 2016): (i) the imbalance of worldwide food markets due to the “food
versus fuel” scenario (Lim and Teong 2010); (ii) the use of large agricultural land
(Kirkels 2016). Therefore, microalgae with simple cell structure and those that can
grow rapidly are potentially employed for sustainable bioethanol production. Furthermore, from the environmental perspectives, cultivation of microalgae coupled with
CO 2 fixation and bio-treatment of wastewater, evolved to be a potential green energy
producer (Maity et al. 2014).
Microalgae are unicellular with size ranging from a few to hundred micrometers
(μm). They are commonly found in freshwater or marine water, exists either in the
form of individual or groups and chains (Suganya et al. 2016). They are photosynthetic microorganisms that utilized CO 2 as carbon source and simultaneously release
O 2 into the atmosphere (Andersen 2013). The photoautotrophical process (or lightdriven redox reaction) convert the absorbed CO 2 into carbohydrates and lipid within
the microalgae cells (Masojídek et al. 2013).
2.1 Effect of Cultivation Conditions to Improve
Carbohydrates Production
Besides screening and choosing carbohydrate, rich microalgae species, inducing
specific cultivation conditions is an alternative way to further enhance carbohydrate productivity in the microalgae. In fact, this strategy is also applicable to low
carbohydrate content microalgae species, but grows easily and able to withstand
extreme environment. The following sections discussed several cultivation strategies
to increase the carbohydrate content in microalgae cells.
2.2 Effect of Sulfur
Sulfur is an important element is all living cells, as it is needed to synthesis amino
acids (methionine and cysteine), vitamins and sulfolipids (Becker 1994). The strategy
to deprive sulfur concentration in microalgae cultivation was previously initiated to
produce biohydrogen from Chlamydomonas reinhardtii through direct biophotolysis
(Melis et al. 2000). When microalgae are cultivated under limited sulfur source,
synthesis of the PS II D1 polypeptide chain (32 kDa) is impeded and thus, interfere
the repair of PS II from photooxidative damage (Melis 2007 and Wykoff et al. 1998).