In open ponds, it’s almost impossible to control essential growth parameters like
temperature, pH, concentration of dissolved oxygen, and light intensity. Predator
contamination is another issue associated with open ponds. So far many studies have
evaluated the potential of cultivating microalgae in open pond. In a study, it was
reported that barely few microalgae (Chlorella, Spirulina, Dunaliella) can withstand
the strict culture environment (high salinity, high alkalinity) [15]. Chlorella and
Spirulina are cultivated for their protein content, whereas Dunaliella is well known
for carotenoid production. In a study, Chlorophyta sp. and Chlorella sp. was effectively cultivated in raceway ponds with steady photosynthetic efficiency [16]. In
another study, Muriellopsis sp. was grown in open paddle wheel ponds for the
production of lutein [17]. Open ponds are very difficult to operate because there
are high chances of it getting contaminated by photosynthetic microorganisms which
may appear via rain or air. Recently Sapphire Energy Inc. tried mass cultivation of
algae (100 acres) in open ponds, but they couldn’t able to accomplish owing to
problems like invasion of species and broth evaporation [18]. Therefore there has
been great challenge still exists in successful cultivation of microalgae in open
ponds.
3.2 Closed Cultivation System
Closed system provides more options than open systems in control and optimization
of microalgal growth, thus enabling them to produce high yield of biomass. Product
standardization can be attained since each factor associated with production like
light exposure, pH, CO 2 , temperature, water supply, mixing regime, and culture
density can be controlled. Photobioreactors, which are usually used for cultivation in
closed systems, provides fine control of CO 2 transfer and also minimizes the
evaporation loss of culture medium.
3.2.1 Photobioreactors
Photobioreactors are closed systems in which almost all factors correlated with
microalgal growth can be controlled to achieve high productivity [3]. Plate type
and tubular photobioreactors are normally used. The tubular reactor comprises tubes
arranged in coils and straight line configurations. In tubular vertical, helical, external
loop (Fig. 3b), and horizontal (Fig. 3c) arrangements are stated to be used in
numerous studies [19]. However, there exist some limitations associated with the
utilization of photobioreactors due to their very high specificity to microalgae
strain, high start-up and operating cost, and difficulty in scale-up [14, 20]. Some
authors have carried out detailed investigations to build cost-effective, simple, and
effortlessly scalable PBR [21–23]. Some very good practices like intensive mixing,
use of genetically improved strain, and light dilution by employing different
methods were performed earlier to maximize yield and productivity [24–26].
Algal Biomass for Biofuels and Bioproducts
145
temperature, pH, concentration of dissolved oxygen, and light intensity. Predator
contamination is another issue associated with open ponds. So far many studies have
evaluated the potential of cultivating microalgae in open pond. In a study, it was
reported that barely few microalgae (Chlorella, Spirulina, Dunaliella) can withstand
the strict culture environment (high salinity, high alkalinity) [15]. Chlorella and
Spirulina are cultivated for their protein content, whereas Dunaliella is well known
for carotenoid production. In a study, Chlorophyta sp. and Chlorella sp. was effectively cultivated in raceway ponds with steady photosynthetic efficiency [16]. In
another study, Muriellopsis sp. was grown in open paddle wheel ponds for the
production of lutein [17]. Open ponds are very difficult to operate because there
are high chances of it getting contaminated by photosynthetic microorganisms which
may appear via rain or air. Recently Sapphire Energy Inc. tried mass cultivation of
algae (100 acres) in open ponds, but they couldn’t able to accomplish owing to
problems like invasion of species and broth evaporation [18]. Therefore there has
been great challenge still exists in successful cultivation of microalgae in open
ponds.
3.2 Closed Cultivation System
Closed system provides more options than open systems in control and optimization
of microalgal growth, thus enabling them to produce high yield of biomass. Product
standardization can be attained since each factor associated with production like
light exposure, pH, CO 2 , temperature, water supply, mixing regime, and culture
density can be controlled. Photobioreactors, which are usually used for cultivation in
closed systems, provides fine control of CO 2 transfer and also minimizes the
evaporation loss of culture medium.
3.2.1 Photobioreactors
Photobioreactors are closed systems in which almost all factors correlated with
microalgal growth can be controlled to achieve high productivity [3]. Plate type
and tubular photobioreactors are normally used. The tubular reactor comprises tubes
arranged in coils and straight line configurations. In tubular vertical, helical, external
loop (Fig. 3b), and horizontal (Fig. 3c) arrangements are stated to be used in
numerous studies [19]. However, there exist some limitations associated with the
utilization of photobioreactors due to their very high specificity to microalgae
strain, high start-up and operating cost, and difficulty in scale-up [14, 20]. Some
authors have carried out detailed investigations to build cost-effective, simple, and
effortlessly scalable PBR [21–23]. Some very good practices like intensive mixing,
use of genetically improved strain, and light dilution by employing different
methods were performed earlier to maximize yield and productivity [24–26].
Algal Biomass for Biofuels and Bioproducts
145