258 Marine Macro- and Microalgae: An Overview
such as Chlorella, Dunaliella, Isochrysis, Nannochloris, Nannochloropsis, Neochloris, Nitzschia,
Tetraselmis sp., Tetraselmis sp. CTP4, and Phaeodactylum sp. with oil content in the range of 20–50%
biomass dry weight is another advantage for their choice as a potential biomass (Huerlimann et al. 2010;
Gangadhar et al. 2016a; Pereira et al. 2016). Chlorella appears indeed a particularly good option for
biodiesel. The biochemical composition of the microalgae biomass can be altered by varying growth
conditions, and thus significantly stimulating oil yield (Qin 2005; Schüler et al. 2017 and references are
therein). Eukaryotic microalgae are preferred to prokaryotes as they have been shown to produce more
lipids (Williams and Laurens 2010). Microalgal biomass is attracting interest not only as a possible
source of biodiesel (Amaro et al. 2011), but also as a source of other types of biofuels: bioethanol,
biomethane, biohydrogen, and biobutanol (Brennan and Owende 2010; Jasvinder and Gu 2010; Parmar
et al. 2011; Varfolomeev and Wasserman 2011). In addition, microalgae can also produce value-added
co-products such as proteins and residual biomass after oil extraction, which may be used as feed or
fertilizers (Spolaore et al. 2006) and fermented to produce bioethanol or biomethane (Hirano et al. 1997).
Moreover, a few microalgae are capable of photo-biological production of biohydrogen (Ghirardi et al.
2000).
Oil extraction
Storage of lipids in microalgae differs from strain to strain and even within a single culture under different
growth conditions (Huerlimann et al. 2010). Lipid identification is essential as its composition determines
the properties of the biodiesel produced. Lipid qualification and quantification are be determined by
several methods such as Nile red fluorescence microscopy, Nile red spectrofluorometric, and BODIPY
staining (Medina et al. 1998; Mutanda et al. 2011; Pereira et al. 2011; Pereira et al. 2016). These methods
have primarily been employed to identify the presence of lipid bodies within cells as an initial screen for
lipid accumulation and as a semi-quantitative method for lipid storage.
Various methods for extraction of lipids from microalgae have been reported in literature, but most
common methods are expeller/oil press, ultrasound, microwave, osmotic, solvent extraction, supercritical
fluid extraction, and enzymatic extractions. The extraction of microalgal lipids from microalgal biomass
is generally more expensive and technologically more challenging than that of terrestrial plant seeds.
However, commercial scale microalgae biodiesel production is restricted by unfavourable downstream
costs of lipid extraction and availability of water, CO 2 , and nutrients (Pate et al. 2011). A possible solution
would be to integrate microalgal cultivation with existing biogas plants, where algae could be cultivated
using discharges of CO 2 and digestate as nutrient input, and then the attained biomass could be converted
directly to biomethane by existing infrastructures. The downstream processes of biomass drying and lipid
extraction would take up 50–90% of the overall energy consumption (Lardon et al. 2009; Stephenson
et al. 2010). It is therefore worth to explore simple and robust processes for the energy utilization of
microalgal biomass (Collet et al. 2011).
Mechanical extraction methods minimize the contamination from external sources (Greenwell et
al. 2010), while maintaining the chemicals originally contained within the biomass. These methods are
usually used in combination with some kind of solvent extraction. Expellers are the common method for
extraction of oil from biomass such as oil seeds (Popoola and Yangomodou 2006) and microalgae. To
ensure the efficacy of this process, the microalgae need to be dried first. These methods are able to extract
almost 75% of oil, with no special skill required. However, this conventional method has been reported to
be less effective due to relatively longer extraction times (Popoola and Yangomodou 2006). Microwave
extraction directly affects solvents and biomass, even though trace amount of moisture content in cells
are affected. It had been reported to be a useful method for extraction of oils from renewable materials
(Angelis et al. 2005). Microwave-assisted extraction to recover oil has proved the most efficient
method for Botryococcus sp. (Geciova et al. 2002) and Scenedesmus obliquus (Balasubramanian et al.
2010). Microwave-assisted hexane extractions were found to result in higher oil yields compared to
conventionally water-heated hexane extraction. It can be easily scaled-up in commercial scale production
(Sahena et al. 2009). However, microwave-assisted extraction presents some drawbacks, as it has the
potential for causing oxidative damage to value-added products (Sahena et al. 2009).
such as Chlorella, Dunaliella, Isochrysis, Nannochloris, Nannochloropsis, Neochloris, Nitzschia,
Tetraselmis sp., Tetraselmis sp. CTP4, and Phaeodactylum sp. with oil content in the range of 20–50%
biomass dry weight is another advantage for their choice as a potential biomass (Huerlimann et al. 2010;
Gangadhar et al. 2016a; Pereira et al. 2016). Chlorella appears indeed a particularly good option for
biodiesel. The biochemical composition of the microalgae biomass can be altered by varying growth
conditions, and thus significantly stimulating oil yield (Qin 2005; Schüler et al. 2017 and references are
therein). Eukaryotic microalgae are preferred to prokaryotes as they have been shown to produce more
lipids (Williams and Laurens 2010). Microalgal biomass is attracting interest not only as a possible
source of biodiesel (Amaro et al. 2011), but also as a source of other types of biofuels: bioethanol,
biomethane, biohydrogen, and biobutanol (Brennan and Owende 2010; Jasvinder and Gu 2010; Parmar
et al. 2011; Varfolomeev and Wasserman 2011). In addition, microalgae can also produce value-added
co-products such as proteins and residual biomass after oil extraction, which may be used as feed or
fertilizers (Spolaore et al. 2006) and fermented to produce bioethanol or biomethane (Hirano et al. 1997).
Moreover, a few microalgae are capable of photo-biological production of biohydrogen (Ghirardi et al.
2000).
Oil extraction
Storage of lipids in microalgae differs from strain to strain and even within a single culture under different
growth conditions (Huerlimann et al. 2010). Lipid identification is essential as its composition determines
the properties of the biodiesel produced. Lipid qualification and quantification are be determined by
several methods such as Nile red fluorescence microscopy, Nile red spectrofluorometric, and BODIPY
staining (Medina et al. 1998; Mutanda et al. 2011; Pereira et al. 2011; Pereira et al. 2016). These methods
have primarily been employed to identify the presence of lipid bodies within cells as an initial screen for
lipid accumulation and as a semi-quantitative method for lipid storage.
Various methods for extraction of lipids from microalgae have been reported in literature, but most
common methods are expeller/oil press, ultrasound, microwave, osmotic, solvent extraction, supercritical
fluid extraction, and enzymatic extractions. The extraction of microalgal lipids from microalgal biomass
is generally more expensive and technologically more challenging than that of terrestrial plant seeds.
However, commercial scale microalgae biodiesel production is restricted by unfavourable downstream
costs of lipid extraction and availability of water, CO 2 , and nutrients (Pate et al. 2011). A possible solution
would be to integrate microalgal cultivation with existing biogas plants, where algae could be cultivated
using discharges of CO 2 and digestate as nutrient input, and then the attained biomass could be converted
directly to biomethane by existing infrastructures. The downstream processes of biomass drying and lipid
extraction would take up 50–90% of the overall energy consumption (Lardon et al. 2009; Stephenson
et al. 2010). It is therefore worth to explore simple and robust processes for the energy utilization of
microalgal biomass (Collet et al. 2011).
Mechanical extraction methods minimize the contamination from external sources (Greenwell et
al. 2010), while maintaining the chemicals originally contained within the biomass. These methods are
usually used in combination with some kind of solvent extraction. Expellers are the common method for
extraction of oil from biomass such as oil seeds (Popoola and Yangomodou 2006) and microalgae. To
ensure the efficacy of this process, the microalgae need to be dried first. These methods are able to extract
almost 75% of oil, with no special skill required. However, this conventional method has been reported to
be less effective due to relatively longer extraction times (Popoola and Yangomodou 2006). Microwave
extraction directly affects solvents and biomass, even though trace amount of moisture content in cells
are affected. It had been reported to be a useful method for extraction of oils from renewable materials
(Angelis et al. 2005). Microwave-assisted extraction to recover oil has proved the most efficient
method for Botryococcus sp. (Geciova et al. 2002) and Scenedesmus obliquus (Balasubramanian et al.
2010). Microwave-assisted hexane extractions were found to result in higher oil yields compared to
conventionally water-heated hexane extraction. It can be easily scaled-up in commercial scale production
(Sahena et al. 2009). However, microwave-assisted extraction presents some drawbacks, as it has the
potential for causing oxidative damage to value-added products (Sahena et al. 2009).