results in the organic phase containing the neutral lipids, while the aqueous phase
contains the water and solvent–carbohydrate or solvent–protein complexes. The
biofuel is further produced after the separation of organic phase and subsequent
transesterification of the crude lipids (Suali and Sabartly 2012; Bahadar and Khan
2013). Use of solvent extraction on a larger scale is associated with various
disadvantages such as the high-energy consumption and possible contamination of the
algal solids which delimits its use at a commercial scale. Further, serious health issues
can result from contact between a solvent and body surface or exposure to vapors,
thereby restricting the use of this method for oil extraction (Bahadar and Khan 2013).
8.4.3 Supercritical Fluid Extraction (SCFE)
The traditional solvent extraction process is replaced by the SCFE method as the
latter is less toxic and supports the mass transfer equilibrium favorably (Patel et al.
2017). It relies on the principle that a fluid behaves both as a gas and a liquid when
subjected to above critical point temperature and pressure conditions. This green
technology is efficient for lipid extraction as solvent-free crude lipid products are
obtained; higher yield of lipid is achieved owing to the rapid penetration of the
solvent in the algal cells. The fluid density determines the solvent power, and the
former can be adjusted by changing the temperature–pressure conditions, thereby
facilitating the production of neutral lipids. Various features of SCFEs are lower
toxicity, inert nature, and non-corrosiveness, and inflammable characteristic
promotes its wide usability (Sahena et al. 2009; Bahadar and Khan 2013).
8.4.4 Other Methods Employed for Oil Extraction via Algal Biomass
Other methods which have been effectively used for oil extraction via algal biomass
are as follows:
8.4.4.1 Osmotic Shock
The oil is extracted using osmotic shocks where pressure is developed across the cell
wall that results in disruption of the microalgal cells (Kim et al. 2013; Rashid et al.
2014). Hyper-osmotic stress is developed on the cell wall due to higher concentration of salt in the liquid medium and causes the microalgal cells to bulge in the
outward direction. A higher salt concentration inside the cells relative to the outside
medium also results in cell disruption (Rashid et al. 2014; Kumar et al. 2015).
8.4.4.2 Enzymes
The most commonly employed enzymes for extraction are cellulase, pectinase, and
neutrase. Sporopollenin layer is destroyed by the enzyme without causing any harm
to the structure of the whole cell. As opposed to the chemical methods, enzymes are
inexpensive, serve as a highly efficient extraction method, and do not hinder with the
fatty acids in the cell (Taher et al. 2014; Rashid et al. 2014).
8 Algal Biomass: Potential Renewable Feedstock for Biofuels Production – Part I
217
contains the water and solvent–carbohydrate or solvent–protein complexes. The
biofuel is further produced after the separation of organic phase and subsequent
transesterification of the crude lipids (Suali and Sabartly 2012; Bahadar and Khan
2013). Use of solvent extraction on a larger scale is associated with various
disadvantages such as the high-energy consumption and possible contamination of the
algal solids which delimits its use at a commercial scale. Further, serious health issues
can result from contact between a solvent and body surface or exposure to vapors,
thereby restricting the use of this method for oil extraction (Bahadar and Khan 2013).
8.4.3 Supercritical Fluid Extraction (SCFE)
The traditional solvent extraction process is replaced by the SCFE method as the
latter is less toxic and supports the mass transfer equilibrium favorably (Patel et al.
2017). It relies on the principle that a fluid behaves both as a gas and a liquid when
subjected to above critical point temperature and pressure conditions. This green
technology is efficient for lipid extraction as solvent-free crude lipid products are
obtained; higher yield of lipid is achieved owing to the rapid penetration of the
solvent in the algal cells. The fluid density determines the solvent power, and the
former can be adjusted by changing the temperature–pressure conditions, thereby
facilitating the production of neutral lipids. Various features of SCFEs are lower
toxicity, inert nature, and non-corrosiveness, and inflammable characteristic
promotes its wide usability (Sahena et al. 2009; Bahadar and Khan 2013).
8.4.4 Other Methods Employed for Oil Extraction via Algal Biomass
Other methods which have been effectively used for oil extraction via algal biomass
are as follows:
8.4.4.1 Osmotic Shock
The oil is extracted using osmotic shocks where pressure is developed across the cell
wall that results in disruption of the microalgal cells (Kim et al. 2013; Rashid et al.
2014). Hyper-osmotic stress is developed on the cell wall due to higher concentration of salt in the liquid medium and causes the microalgal cells to bulge in the
outward direction. A higher salt concentration inside the cells relative to the outside
medium also results in cell disruption (Rashid et al. 2014; Kumar et al. 2015).
8.4.4.2 Enzymes
The most commonly employed enzymes for extraction are cellulase, pectinase, and
neutrase. Sporopollenin layer is destroyed by the enzyme without causing any harm
to the structure of the whole cell. As opposed to the chemical methods, enzymes are
inexpensive, serve as a highly efficient extraction method, and do not hinder with the
fatty acids in the cell (Taher et al. 2014; Rashid et al. 2014).
8 Algal Biomass: Potential Renewable Feedstock for Biofuels Production – Part I
217