3.1.3 Flotation
The flotation technique consists in making that the microalgae float up in the water
surface through air bubbles. These bubbles catch the cells making they float up with
the aim to be recollected in the surface (Sharma et al. 2013). This technology has
the advantage to separate low-density microalgae cultures. In some cases, it is
necessary the addition of a flocculating agent to perform an effective flotation
(Edzwald 1993). It has been found that for a flotation system like dissolved air
flotation, the energy demand is high due to the high pressure required for the
bubbles’ formation (Hanotu et al. 2012).
3.1.4 Ultrasound
This method consists in the cell concentration or flocculation due to acoustic forces,
without generating shear strength in the microalgae, and then the cells are recollected by methods using gravity forces like centrifugation or sedimentation. As
disadvantages, the low concentration factor in comparison with other methods, and
operative costs make this method unsuitable yet (Bosma et al. 2003).
3.2 Chemical Methods
3.2.1 Chemical Flocculation
Due to the negative charge present in microalgae, it does not permit the aggregation
of suspended cells. These superficial charges can be neutralized adding flocculating
agents, allowing the increment in particle size due to cell aggregation, increasing
the sedimentation or flotation rate (Mata et al. 2010). The ideal flocculating agent
must have some characteristics like non-toxic, inexpensive, and effective in low
concentration compound (Molina Grima et al. 2003). For this reason, inorganic
flocculating agents like FeCl 3 and Al 2 (SO 4 ) 3 that are very effective are not ideal for
an environmental suitable process (Lee et al. 2014). Another disadvantage for
chemical flocculation is the possibility of cell alterations generated by flocculating
agents that can interfere in the final processing of biomass like lipid extraction
(Uduman et al. 2010).
4 Process of Oil Extraction
Lipid extraction from microalgae and its efficiency are an important factor in the
biodiesel production process (Adam et al. 2012). Two options for lipid recovery are
available, dry algal biomass and wet algal biomass extractions. In the dry algal
186
D. L. Restrepo-Serna et al.
The flotation technique consists in making that the microalgae float up in the water
surface through air bubbles. These bubbles catch the cells making they float up with
the aim to be recollected in the surface (Sharma et al. 2013). This technology has
the advantage to separate low-density microalgae cultures. In some cases, it is
necessary the addition of a flocculating agent to perform an effective flotation
(Edzwald 1993). It has been found that for a flotation system like dissolved air
flotation, the energy demand is high due to the high pressure required for the
bubbles’ formation (Hanotu et al. 2012).
3.1.4 Ultrasound
This method consists in the cell concentration or flocculation due to acoustic forces,
without generating shear strength in the microalgae, and then the cells are recollected by methods using gravity forces like centrifugation or sedimentation. As
disadvantages, the low concentration factor in comparison with other methods, and
operative costs make this method unsuitable yet (Bosma et al. 2003).
3.2 Chemical Methods
3.2.1 Chemical Flocculation
Due to the negative charge present in microalgae, it does not permit the aggregation
of suspended cells. These superficial charges can be neutralized adding flocculating
agents, allowing the increment in particle size due to cell aggregation, increasing
the sedimentation or flotation rate (Mata et al. 2010). The ideal flocculating agent
must have some characteristics like non-toxic, inexpensive, and effective in low
concentration compound (Molina Grima et al. 2003). For this reason, inorganic
flocculating agents like FeCl 3 and Al 2 (SO 4 ) 3 that are very effective are not ideal for
an environmental suitable process (Lee et al. 2014). Another disadvantage for
chemical flocculation is the possibility of cell alterations generated by flocculating
agents that can interfere in the final processing of biomass like lipid extraction
(Uduman et al. 2010).
4 Process of Oil Extraction
Lipid extraction from microalgae and its efficiency are an important factor in the
biodiesel production process (Adam et al. 2012). Two options for lipid recovery are
available, dry algal biomass and wet algal biomass extractions. In the dry algal
186
D. L. Restrepo-Serna et al.