organic matter from solar energy, carbon dioxide, water and nutrients (e.g. nitrogen
and phosphorus) through photosynthesis. In addition, they also produce the oxygen
required for metabolism of consumer organisms.
Microalgae are an extremely diverse group of organisms. For example, they
contain a significant amount of lipids in the form of fatty acids, which can be
extracted for subsequent production of biodiesel (Lam et al. 2017).
2.1 Cellular Metabolism
The algae are able to grow with different cellular metabolisms, focusing on the main
forms of nutrition, including autotrophy and heterotrophy (Richmond 2004).
Therefore, microalgae may grow based on four types of cell metabolisms:
autotrophy, heterotrophy, mixotrophy and photoheterotrophy.
Autotrophic organisms obtain energy and electrons (necessary for CO 2 reduction) through the absorption of solar energy and substrates oxidation (mostly water),
respectively (Richmond 2004). On the other hand, the heterotrophic organisms use
only organic compounds as carbon and energy source (Abreu et al. 2012). With
regard to growth under mixotrophy, it is equivalent to grow under autotrophic and
heterotrophic conditions, since both organic compounds and CO 2 can be assimilated by microalgae depending on the growing conditions (Richmond 2004). Thus,
mixotrophic microorganisms synthesize compounds characteristic of both types of
metabolisms, showing high production rates (Cerón Garcı ́ a et al. 2005). Concerning
photoheterotrophic metabolism, organisms require light energy as a source of
energy and organic compounds as carbon source (Richmond 2004).
2.2 Microalgal Growth Conditions
The growth of the culture as well as the biochemical composition of biomass is not
only determined by the microalgae species in cultivation (Rocha 2012). The
medium composition, pH, temperature and light intensity are some of the parameters that can influence the growth and biochemical composition of microalgae.
2.2.1 Nutrients
According to Chisti (2007), the molecular formula of the microalgal biomass is
CO 0.48 H 1.83 N 0.11 P 0.01 . Thus, the most important nutrients for autotrophic growth
(known as macronutrients) are the carbon (C), nitrogen (N) and phosphorus
(P) (Richmond 2004).
Carbon is the macronutrient needed in high concentrations, since it is the main
constituent of all organic substances synthesized by the cells, such as proteins,
3 Process Integration Applied to Microalgal Biofuels Production
37
and phosphorus) through photosynthesis. In addition, they also produce the oxygen
required for metabolism of consumer organisms.
Microalgae are an extremely diverse group of organisms. For example, they
contain a significant amount of lipids in the form of fatty acids, which can be
extracted for subsequent production of biodiesel (Lam et al. 2017).
2.1 Cellular Metabolism
The algae are able to grow with different cellular metabolisms, focusing on the main
forms of nutrition, including autotrophy and heterotrophy (Richmond 2004).
Therefore, microalgae may grow based on four types of cell metabolisms:
autotrophy, heterotrophy, mixotrophy and photoheterotrophy.
Autotrophic organisms obtain energy and electrons (necessary for CO 2 reduction) through the absorption of solar energy and substrates oxidation (mostly water),
respectively (Richmond 2004). On the other hand, the heterotrophic organisms use
only organic compounds as carbon and energy source (Abreu et al. 2012). With
regard to growth under mixotrophy, it is equivalent to grow under autotrophic and
heterotrophic conditions, since both organic compounds and CO 2 can be assimilated by microalgae depending on the growing conditions (Richmond 2004). Thus,
mixotrophic microorganisms synthesize compounds characteristic of both types of
metabolisms, showing high production rates (Cerón Garcı ́ a et al. 2005). Concerning
photoheterotrophic metabolism, organisms require light energy as a source of
energy and organic compounds as carbon source (Richmond 2004).
2.2 Microalgal Growth Conditions
The growth of the culture as well as the biochemical composition of biomass is not
only determined by the microalgae species in cultivation (Rocha 2012). The
medium composition, pH, temperature and light intensity are some of the parameters that can influence the growth and biochemical composition of microalgae.
2.2.1 Nutrients
According to Chisti (2007), the molecular formula of the microalgal biomass is
CO 0.48 H 1.83 N 0.11 P 0.01 . Thus, the most important nutrients for autotrophic growth
(known as macronutrients) are the carbon (C), nitrogen (N) and phosphorus
(P) (Richmond 2004).
Carbon is the macronutrient needed in high concentrations, since it is the main
constituent of all organic substances synthesized by the cells, such as proteins,
3 Process Integration Applied to Microalgal Biofuels Production
37