continuous production cycles (Terry and Raymond 1985). Circular ponds, another
type of open pond system, are also used for algal cultivation (Benemann and Oswald
1996). This is more popular for wastewater treatment by using algal culture. These
ponds system contain a centrally located rotating arm to mix the algae culture.
Raceway and circular ponds are mixed open pond systems that keep algae suspended
culture. Open pond systems are also included some unmixed open ponds for algal
culture. Unmixed ponds allow the algae to settle to the bottom of the reactor and
usually used to grow specific species of algae with very low productivities
(Borowitzka 1999). Open ponds systems are cheaper than other systems in use for
large-scale algal production (Chisti 2008). These are not competing for land with
existing agricultural crops and can be implemented in areas with marginal crop
production potential. They also require lower energy input requirement. Open ponds
systems are subjected with regular maintenance and cleaning and have the potential
to give large net energy production. In 2008, open pond system was resulted about
€2.55/kg of dry biomass of commonly cultivated algae strain, Dunaliella salina,
which was considered to be too high for biofuel production.
Major Issues of Open Pond Systems In open ponds, major issue is the temperature
control that usually fluctuates in a diurnal cycle and very difficult to control due to
seasonal based fluctuation in a diurnal cycle (Mata et al. 2010). Other significant
issue is evaporative water loss from open pond system due to which CO 2 utilization
by algae is much less effective than other systems (Oyler 2009; Narala et al. 2016).
This potential CO 2 deficiency may result in reduced biomass productivity. There is a
poor mixing of algal culture through inefficient stirring that can result in poor mass
CO 2 transfer rate (Chisti 2007). Minimum light intensity due to top layer thickness
may also result in low algal biomass production. Due to significant contamination by
native species, this system is subjected for only a small number of algae species that
can tolerate extreme saline and alkaline environments of systems (Laws et al. 1988).
For example, the species Chlorella, D. salina and Spirulina are adaptable to thrive
under nutrient-rich, very high salinity, and high alkalinity condition of systems
(Borowitzka 1999; Brennan and Owende 2010).
1.3.1.2 Closed Systems
The major issues associated with open pond cultures such as low cell densities,
contamination issues, evaporation, environment regulation, and high land
requirements have been overcome after the establishment of closed photobioreactors
(PBRs) (Narala et al. 2016). Closed systems are facilitated by indoors with artificial
light and outdoors with natural light. PBR’s require higher capital investments and
have issues with scalability. Unlike the open pond systems, closed systems allow the
single algal species cultivation for long duration with low risk of contamination. The
closed configuration of these systems makes the control of potential contamination
easier. Closed systems are consisting of tubular, flat plate, and column
photobioreactors type systems. Closed systems attain higher cell mass productivities
and reduced harvesting costs. Photobioreactors are made up of an array of straight
glass or plastic tubes (Narala et al. 2016).
8
N. Maheshwari et al.
type of open pond system, are also used for algal cultivation (Benemann and Oswald
1996). This is more popular for wastewater treatment by using algal culture. These
ponds system contain a centrally located rotating arm to mix the algae culture.
Raceway and circular ponds are mixed open pond systems that keep algae suspended
culture. Open pond systems are also included some unmixed open ponds for algal
culture. Unmixed ponds allow the algae to settle to the bottom of the reactor and
usually used to grow specific species of algae with very low productivities
(Borowitzka 1999). Open ponds systems are cheaper than other systems in use for
large-scale algal production (Chisti 2008). These are not competing for land with
existing agricultural crops and can be implemented in areas with marginal crop
production potential. They also require lower energy input requirement. Open ponds
systems are subjected with regular maintenance and cleaning and have the potential
to give large net energy production. In 2008, open pond system was resulted about
€2.55/kg of dry biomass of commonly cultivated algae strain, Dunaliella salina,
which was considered to be too high for biofuel production.
Major Issues of Open Pond Systems In open ponds, major issue is the temperature
control that usually fluctuates in a diurnal cycle and very difficult to control due to
seasonal based fluctuation in a diurnal cycle (Mata et al. 2010). Other significant
issue is evaporative water loss from open pond system due to which CO 2 utilization
by algae is much less effective than other systems (Oyler 2009; Narala et al. 2016).
This potential CO 2 deficiency may result in reduced biomass productivity. There is a
poor mixing of algal culture through inefficient stirring that can result in poor mass
CO 2 transfer rate (Chisti 2007). Minimum light intensity due to top layer thickness
may also result in low algal biomass production. Due to significant contamination by
native species, this system is subjected for only a small number of algae species that
can tolerate extreme saline and alkaline environments of systems (Laws et al. 1988).
For example, the species Chlorella, D. salina and Spirulina are adaptable to thrive
under nutrient-rich, very high salinity, and high alkalinity condition of systems
(Borowitzka 1999; Brennan and Owende 2010).
1.3.1.2 Closed Systems
The major issues associated with open pond cultures such as low cell densities,
contamination issues, evaporation, environment regulation, and high land
requirements have been overcome after the establishment of closed photobioreactors
(PBRs) (Narala et al. 2016). Closed systems are facilitated by indoors with artificial
light and outdoors with natural light. PBR’s require higher capital investments and
have issues with scalability. Unlike the open pond systems, closed systems allow the
single algal species cultivation for long duration with low risk of contamination. The
closed configuration of these systems makes the control of potential contamination
easier. Closed systems are consisting of tubular, flat plate, and column
photobioreactors type systems. Closed systems attain higher cell mass productivities
and reduced harvesting costs. Photobioreactors are made up of an array of straight
glass or plastic tubes (Narala et al. 2016).
8
N. Maheshwari et al.