8.3.5 Electrolytic Separation of Algal Biomass
Microalgal biomass are extracted from the culture medium using electric fields. In
the process, hydrogen ions produced by water electrolysis get attached to the algal
flocks that make the biomass move toward the surface. This method is highly
efficient, economically feasible, and environment friendly (Chen et al. 2011; Patel
et al. 2017). Electrolysis can be categorized as electrolytic flocculation and
electrolytic coagulation. The positively charged coagulants at the sacrificial
anode get complexed with the hydroxide ions and react with the microalgal
cells (Lee et al. 2012).
8.3.6 The Use of Ultrasound for Harvesting Algal Biomass
In this process, the microalgal biomass is harvested at low amplitude and low
frequency using ultrasonication. The microalgal cells are disrupted upon sonication,
and their buoyancy is decreased; thus, they become stable and settle down, resulting
in increased efficiency of harvesting process. Cases of high-frequency and highamplitude sonification lead to disruption of the microalgal cells and subsequent lipid
release in the aqueous medium (Adam et al. 2012; Rashid et al. 2014). As
sonification is deleterious, it is not employed for the harvesting process, and commercialization has not been feasible due to large input of energy and high cost
(Milledge and Heaven 2012; Rashid et al. 2014).
8.4
Extraction of Algal Oil for Production of Biofuel
The production of biofuels from the algal biomass involves the removal of water
from the biomass, and lipid is extracted from the cells, and further its recovery or
lipid concentration constitutes the process of extraction (Patel et al. 2017). The oil
extraction acts as a bottleneck for the production of biofuel from potential microalgal
species due to the high demand of effort and cost (Shuba and Kifle 2018). Hence, an
appropriate balance between the cost involved and drying efficiency is vital to obtain
the maximum possible energy output from biofuels (Li et al. 2008; Brennan and
Owende 2010). Several methods used for the extraction of oil from biomass include
physical, chemical (with organic solvents), and supercritical methods (Fig. 8.5);
among them, organic solvent extraction is the most widely employed method
(Borowitzka and Moheimani 2013; Milano et al. 2016).
8.4.1 Extraction of Algal Oil by Physical Method
In the physical method, cells are disrupted using methods such as bed mills,
ultrasound (Hosikian et al. 2010), and cell homogenizers and autoclaved to release
intracellular lipids from microalgal cells (Patel et al. 2017). In this method, oil is
8 Algal Biomass: Potential Renewable Feedstock for Biofuels Production – Part I
215
Microalgal biomass are extracted from the culture medium using electric fields. In
the process, hydrogen ions produced by water electrolysis get attached to the algal
flocks that make the biomass move toward the surface. This method is highly
efficient, economically feasible, and environment friendly (Chen et al. 2011; Patel
et al. 2017). Electrolysis can be categorized as electrolytic flocculation and
electrolytic coagulation. The positively charged coagulants at the sacrificial
anode get complexed with the hydroxide ions and react with the microalgal
cells (Lee et al. 2012).
8.3.6 The Use of Ultrasound for Harvesting Algal Biomass
In this process, the microalgal biomass is harvested at low amplitude and low
frequency using ultrasonication. The microalgal cells are disrupted upon sonication,
and their buoyancy is decreased; thus, they become stable and settle down, resulting
in increased efficiency of harvesting process. Cases of high-frequency and highamplitude sonification lead to disruption of the microalgal cells and subsequent lipid
release in the aqueous medium (Adam et al. 2012; Rashid et al. 2014). As
sonification is deleterious, it is not employed for the harvesting process, and commercialization has not been feasible due to large input of energy and high cost
(Milledge and Heaven 2012; Rashid et al. 2014).
8.4
Extraction of Algal Oil for Production of Biofuel
The production of biofuels from the algal biomass involves the removal of water
from the biomass, and lipid is extracted from the cells, and further its recovery or
lipid concentration constitutes the process of extraction (Patel et al. 2017). The oil
extraction acts as a bottleneck for the production of biofuel from potential microalgal
species due to the high demand of effort and cost (Shuba and Kifle 2018). Hence, an
appropriate balance between the cost involved and drying efficiency is vital to obtain
the maximum possible energy output from biofuels (Li et al. 2008; Brennan and
Owende 2010). Several methods used for the extraction of oil from biomass include
physical, chemical (with organic solvents), and supercritical methods (Fig. 8.5);
among them, organic solvent extraction is the most widely employed method
(Borowitzka and Moheimani 2013; Milano et al. 2016).
8.4.1 Extraction of Algal Oil by Physical Method
In the physical method, cells are disrupted using methods such as bed mills,
ultrasound (Hosikian et al. 2010), and cell homogenizers and autoclaved to release
intracellular lipids from microalgal cells (Patel et al. 2017). In this method, oil is
8 Algal Biomass: Potential Renewable Feedstock for Biofuels Production – Part I
215