mixture and the culture medium are introduced at the bottom of the bioreactor
(Morita et al. 2001; Singh and Sharma 2012).
8.2.1.2.8 Stirred Tank Photobioreactors (STPBRs)
STPBRs involve mechanical agitation provided by various kinds of impellers and
help algae to obtain the carbon needed for its growth from the carbon dioxideenriched air which is bubbled in the system from the bottom of the reactor. This type
of PBR employs optical fibers or fluorescent lamps for illumination in the system
(Singh and Sharma 2012).
8.2.1.2.9 Airlift Photobioreactors (ALPBRs)
These photobioreactors are comprised of two distinct interconnected zones, namely,
the riser and the downcomer. The gas mixture is sparged in the riser, while no gas is
received by the downcomer. Two main forms of airlift bioreactors consist of the
internal loop and the external loop structure. A draft tube/split cylinder separates the
riser and the downcomer in the internal loop ALPBR. Moreover, the external loop
ALPBR consists of two tubes that physically separate the riser and downcomer
(Singh and Sharma 2012).
8.2.1.3 Hybrid Two-Stage Cultivation System (HTSCS)
HTSCS combines CPBRS and OPCS. The first stage comprises of CPBRS in which
the contamination and pollution risks are significantly reduced owing to the stringently controlled culture conditions, and continuous cell division is favored by the
CPBRS. The second production stage is focused at enhancing the synthesis of the
desired lipid product which is achieved by subjecting the microalgal cells to nutrient
stresses (Rodolfi et al. 2009; Brennan and Owende 2010). OPCS are convenient for
the second stage as transfer of microalgal cultures from the CPBRS to the OPCS
results in the generation of environmental stresses that enhance production (Brennan
and Owende 2010). On the basis of the comparative analysis of natural and artificial
algal cultivation system, various advantages and disadvantages are associated which
have been represented in Table 8.2.
8.2.2 Heterotrophic Cultivation System of Microalgae
This method is extensively used for the production of algal biomass and metabolites
(Miao and Wu 2006; Brennan and Owende 2010). This type of method employs
fermenters or stirred tank bioreactors for the cultivation of microalgae on organic
carbon substrates such as glucose glycerol and sweet sorghum. The type and
concentrations of the source of carbon determine the content of lipid obtained and
the yield of biomass (Suali and Sarbatly 2012). The scale-up of the systems is easy as
the algal growth is lightly independent, thereby allowing smaller surface area-tovolume ratios (Eriksen 2008). Advantages of these systems include higher biomass
productivities and high degree of control over the growth of microalgal cells (Chen
and Chen 2006; Brennan and Owende 2010). One limitation of the heterotrophic
210
K. Agrawal et al.
(Morita et al. 2001; Singh and Sharma 2012).
8.2.1.2.8 Stirred Tank Photobioreactors (STPBRs)
STPBRs involve mechanical agitation provided by various kinds of impellers and
help algae to obtain the carbon needed for its growth from the carbon dioxideenriched air which is bubbled in the system from the bottom of the reactor. This type
of PBR employs optical fibers or fluorescent lamps for illumination in the system
(Singh and Sharma 2012).
8.2.1.2.9 Airlift Photobioreactors (ALPBRs)
These photobioreactors are comprised of two distinct interconnected zones, namely,
the riser and the downcomer. The gas mixture is sparged in the riser, while no gas is
received by the downcomer. Two main forms of airlift bioreactors consist of the
internal loop and the external loop structure. A draft tube/split cylinder separates the
riser and the downcomer in the internal loop ALPBR. Moreover, the external loop
ALPBR consists of two tubes that physically separate the riser and downcomer
(Singh and Sharma 2012).
8.2.1.3 Hybrid Two-Stage Cultivation System (HTSCS)
HTSCS combines CPBRS and OPCS. The first stage comprises of CPBRS in which
the contamination and pollution risks are significantly reduced owing to the stringently controlled culture conditions, and continuous cell division is favored by the
CPBRS. The second production stage is focused at enhancing the synthesis of the
desired lipid product which is achieved by subjecting the microalgal cells to nutrient
stresses (Rodolfi et al. 2009; Brennan and Owende 2010). OPCS are convenient for
the second stage as transfer of microalgal cultures from the CPBRS to the OPCS
results in the generation of environmental stresses that enhance production (Brennan
and Owende 2010). On the basis of the comparative analysis of natural and artificial
algal cultivation system, various advantages and disadvantages are associated which
have been represented in Table 8.2.
8.2.2 Heterotrophic Cultivation System of Microalgae
This method is extensively used for the production of algal biomass and metabolites
(Miao and Wu 2006; Brennan and Owende 2010). This type of method employs
fermenters or stirred tank bioreactors for the cultivation of microalgae on organic
carbon substrates such as glucose glycerol and sweet sorghum. The type and
concentrations of the source of carbon determine the content of lipid obtained and
the yield of biomass (Suali and Sarbatly 2012). The scale-up of the systems is easy as
the algal growth is lightly independent, thereby allowing smaller surface area-tovolume ratios (Eriksen 2008). Advantages of these systems include higher biomass
productivities and high degree of control over the growth of microalgal cells (Chen
and Chen 2006; Brennan and Owende 2010). One limitation of the heterotrophic
210
K. Agrawal et al.