Compared with conventional oil seeds, the biofuels produced from microalgae
have several advantages that include the higher productivities, the ability to use
nonarable land for microalgal cultivation and possibility to use wastewater and gas
flue as source of nutrients and carbon to promote growth (Jacob-Lopes et al. 2014;
Collotta et al. 2017). Microalgae also can produce different types of biofuels, such
as biodiesel, bioethanol, biohydrogen, syngas, biobutanol, and bioelectricity
(Chang et al. 2017; Su et al. 2017a, b). Unfortunately, until now, the majority of
economic analyses conclude that microalgae biofuels cannot compete with conventional fuels (Lundquist et al. 2010; Sun et al. 2011). On the other hand, the
concept of biorefinery can be explored with the aim to improve economic aspects.
This is possible because of the wide variety of high-value compounds that
microalgae can produce, such as carotenoids, proteins, long-chain polyunsaturated
fatty acids, vitamins, and phycobilins (Chew et al. 2017).
Industrialization of microalgae products requires large-scale culture systems,
which generally are raceway ponds, closed photobioreactors (PBRs), or heterotrophic bioreactors. Open systems are much cheaper and easier to operate than
closed systems, however, have many operational problems, such as contamination,
evaporation, susceptibility to weather conditions, and extensive land requirements.
On the other hand, closed systems can eliminate these limitations, but with a high
capital cost, difficulty in scaling-up, and high shear stress. However, due to the high
operational control and the high productivity provided by the PBRs, researchers
have been invested heavily in the development of new photobioreactors designs, in
order to reduce these limitations, and thus make microalgae-based processes viable
(Chang et al. 2017).
This chapter discusses the systems of microalgae production in large-scale
(raceway ponds, horizontal tubular photobioreactors, and heterotrophic bioreactors)
and small-scale (vertical tubular photobioreactors and flat-plate photobioreactors),
with emphasis on major factors that influence their efficiency, biomass productivities, costs of biomass production, scaling-up, and commercial applications.
Moreover, recent developments in microalgae cultivation systems are presented.
Finally, the advantages and disadvantages of all microalgae production systems
discussed are compared, and the criteria for selecting an appropriate PBR are
presented.
2 Large-Scale Microalgae Biomass Production
2.1 Raceway Ponds
The raceway ponds were first developed in the 1950s for treating wastewater and,
since the 1960s, outdoor open raceways have been used in commercial production
of microalgae and cyanobacteria (Chisti 2016). Currently, it is the most utilized
system for commercial microalgae production, accounting for more than 95% of
6
M. M. Maroneze and M. I. Queiroz
have several advantages that include the higher productivities, the ability to use
nonarable land for microalgal cultivation and possibility to use wastewater and gas
flue as source of nutrients and carbon to promote growth (Jacob-Lopes et al. 2014;
Collotta et al. 2017). Microalgae also can produce different types of biofuels, such
as biodiesel, bioethanol, biohydrogen, syngas, biobutanol, and bioelectricity
(Chang et al. 2017; Su et al. 2017a, b). Unfortunately, until now, the majority of
economic analyses conclude that microalgae biofuels cannot compete with conventional fuels (Lundquist et al. 2010; Sun et al. 2011). On the other hand, the
concept of biorefinery can be explored with the aim to improve economic aspects.
This is possible because of the wide variety of high-value compounds that
microalgae can produce, such as carotenoids, proteins, long-chain polyunsaturated
fatty acids, vitamins, and phycobilins (Chew et al. 2017).
Industrialization of microalgae products requires large-scale culture systems,
which generally are raceway ponds, closed photobioreactors (PBRs), or heterotrophic bioreactors. Open systems are much cheaper and easier to operate than
closed systems, however, have many operational problems, such as contamination,
evaporation, susceptibility to weather conditions, and extensive land requirements.
On the other hand, closed systems can eliminate these limitations, but with a high
capital cost, difficulty in scaling-up, and high shear stress. However, due to the high
operational control and the high productivity provided by the PBRs, researchers
have been invested heavily in the development of new photobioreactors designs, in
order to reduce these limitations, and thus make microalgae-based processes viable
(Chang et al. 2017).
This chapter discusses the systems of microalgae production in large-scale
(raceway ponds, horizontal tubular photobioreactors, and heterotrophic bioreactors)
and small-scale (vertical tubular photobioreactors and flat-plate photobioreactors),
with emphasis on major factors that influence their efficiency, biomass productivities, costs of biomass production, scaling-up, and commercial applications.
Moreover, recent developments in microalgae cultivation systems are presented.
Finally, the advantages and disadvantages of all microalgae production systems
discussed are compared, and the criteria for selecting an appropriate PBR are
presented.
2 Large-Scale Microalgae Biomass Production
2.1 Raceway Ponds
The raceway ponds were first developed in the 1950s for treating wastewater and,
since the 1960s, outdoor open raceways have been used in commercial production
of microalgae and cyanobacteria (Chisti 2016). Currently, it is the most utilized
system for commercial microalgae production, accounting for more than 95% of
6
M. M. Maroneze and M. I. Queiroz