100 Marine Macro- and Microalgae: An Overview
P. tricornutum with a pH adjusted to 12.2 to 12.5 prior to separation. This separation took place within the
first 5 minutes of filtration and that implied that most of the magnetized cells were captured by the filter
during their first passage after the external magnetic field had been switched on. Separation efficiencies
of 40 and 60% were achieved within 5 min for N. salina at pH 8 and 12, respectively.
Whereas filtration can be more cost-effective than centrifugation for small volumes, costs of filtration
processes are generally considered too expensive for large scale production and centrifugation may be
a more economic method (Molina Grima et al. 2003). However, a recent study suggested a two-step
approach where ultrafiltration is carried out prior to centrifugation. This approach resulted in a 45%
reduction in energy consumption (Monte et al. 2018).
Drying methods
The biomass moisture content can be responsible for an increase in transportation costs as well as it can
impact the downstream processes. For instance, the lipid recovery can be reduced by as much as 50%
when the biomass moisture content increases from 4.5 to 85.4% (Balasubramanian et al. 2013). Therefore,
drying of the harvested biomass can be an important step in algal processing when the components to
be extracted are not thermolabile. A recent study (Balasubramanian et al. 2013) compared three drying
methods on the recovery yield of lipids. The harvested biomass of Nannochloropsis sp. was subjected to
oven drying (60ºC, 3 h), freeze drying (16 h), and solar drying (30–34ºC, 8 h). The lipid content from the
three drying treatments did not show any significant differences in yield. However, when looking at the
composition of lipids (free fatty acids, neutral lipids, and polar lipids), it appeared that while freeze and
oven drying did not differ significantly, solar drying was responsible for a reduction of neutral and polar
lipids and consequently, an increase of free fatty acids. This same alga was also dried under an air flow as
well as freeze-dried and the yield of lipids extracted by SC-CO 2 was investigated (Crampon et al. 2013).
The results showed that the air-dried microalgae required lower CO 2 /microalgae mass ratio and led to
faster extraction kinetic. This phenomenon could be explained by the fact that the freeze-drying preserves
the microalgal cells and thus limits the diffusion of the lipids out of the cells.
However, drying of algal biomass is an energy intensive process which can account for as much
as 30% of the total production costs (Chen et al. 2009) and consequently, may not be appropriate for
industrial applications.
Cell disruption methods
Cell disruption is often required in order to efficiently extract materials from inside the algal cells. Cell
disruption is usually performed on concentrated cell preparations (50–200 kg/m
3
dry weight) in order to
reduce cost and energy consumption (Greenwell et al. 2013). The most important factor for that processing
step is the maximization of the value material to be extracted, which implies a rapid disruption method.
Several disruption techniques can be used to perform cell disruption. These are reviewed in a recent
article (Lee et al. 2012). However, only techniques which have been assessed on marine microalgae will
be described here.
The main disruptive techniques are ultrasounds, hydrodynamic cavitation, and bead milling.
However, other less commonly used techniques can be applied such as temperature treatment and laser
treatment.
Temperature treatment
N. oculata cells subjected to a water bath treatment (90ºC for 20 min) led to 87.72% cell disruption as
quantified by direct optical microscopy techniques (McMillan et al. 2013). Cell disruption due to heat
treatment is caused by cells bursting as they fail to contain their elevated internal pressure leading to large
debris, which is an advantage for further handling and separating steps. However, this technique is not
suitable for thermolabile compounds.
P. tricornutum with a pH adjusted to 12.2 to 12.5 prior to separation. This separation took place within the
first 5 minutes of filtration and that implied that most of the magnetized cells were captured by the filter
during their first passage after the external magnetic field had been switched on. Separation efficiencies
of 40 and 60% were achieved within 5 min for N. salina at pH 8 and 12, respectively.
Whereas filtration can be more cost-effective than centrifugation for small volumes, costs of filtration
processes are generally considered too expensive for large scale production and centrifugation may be
a more economic method (Molina Grima et al. 2003). However, a recent study suggested a two-step
approach where ultrafiltration is carried out prior to centrifugation. This approach resulted in a 45%
reduction in energy consumption (Monte et al. 2018).
Drying methods
The biomass moisture content can be responsible for an increase in transportation costs as well as it can
impact the downstream processes. For instance, the lipid recovery can be reduced by as much as 50%
when the biomass moisture content increases from 4.5 to 85.4% (Balasubramanian et al. 2013). Therefore,
drying of the harvested biomass can be an important step in algal processing when the components to
be extracted are not thermolabile. A recent study (Balasubramanian et al. 2013) compared three drying
methods on the recovery yield of lipids. The harvested biomass of Nannochloropsis sp. was subjected to
oven drying (60ºC, 3 h), freeze drying (16 h), and solar drying (30–34ºC, 8 h). The lipid content from the
three drying treatments did not show any significant differences in yield. However, when looking at the
composition of lipids (free fatty acids, neutral lipids, and polar lipids), it appeared that while freeze and
oven drying did not differ significantly, solar drying was responsible for a reduction of neutral and polar
lipids and consequently, an increase of free fatty acids. This same alga was also dried under an air flow as
well as freeze-dried and the yield of lipids extracted by SC-CO 2 was investigated (Crampon et al. 2013).
The results showed that the air-dried microalgae required lower CO 2 /microalgae mass ratio and led to
faster extraction kinetic. This phenomenon could be explained by the fact that the freeze-drying preserves
the microalgal cells and thus limits the diffusion of the lipids out of the cells.
However, drying of algal biomass is an energy intensive process which can account for as much
as 30% of the total production costs (Chen et al. 2009) and consequently, may not be appropriate for
industrial applications.
Cell disruption methods
Cell disruption is often required in order to efficiently extract materials from inside the algal cells. Cell
disruption is usually performed on concentrated cell preparations (50–200 kg/m
3
dry weight) in order to
reduce cost and energy consumption (Greenwell et al. 2013). The most important factor for that processing
step is the maximization of the value material to be extracted, which implies a rapid disruption method.
Several disruption techniques can be used to perform cell disruption. These are reviewed in a recent
article (Lee et al. 2012). However, only techniques which have been assessed on marine microalgae will
be described here.
The main disruptive techniques are ultrasounds, hydrodynamic cavitation, and bead milling.
However, other less commonly used techniques can be applied such as temperature treatment and laser
treatment.
Temperature treatment
N. oculata cells subjected to a water bath treatment (90ºC for 20 min) led to 87.72% cell disruption as
quantified by direct optical microscopy techniques (McMillan et al. 2013). Cell disruption due to heat
treatment is caused by cells bursting as they fail to contain their elevated internal pressure leading to large
debris, which is an advantage for further handling and separating steps. However, this technique is not
suitable for thermolabile compounds.