The selection of the best method depends on several factors like the final products’
characteristics (Molina Grima et al. 2003), the deformation–destruction level of the
algae after harvesting process thinking in posterior procedures and the economic
and energetic costs (Barros et al. 2015).
3.1 Physical Methods
3.1.1 Filtration
Filtration is a dehydration method in which a pressure drop is required along the
system with the object to force the fluid through a membrane (Barros et al. 2015).
Certain types of filters have been used for the microalgae harvesting, depending on
the cell or colonies size. Usually, a high recovery is reached if they are used in big
cells, but it fails in the recovery of organisms near to bacterial size (Mohn 1980).
Systems like microfiltration can be used for microalgae recovery of common
microalgae with a size order of 5–6 µm (Edzwald 1993). Process like macrofiltration can be used if a previous process of flocculation is performed (Milledge
and Heaven 2013). In this type of process, microalgae have the tendency to deposit
in the filtrate medium, growing its thickness and flux resistance (Show and Lee
2014). Micro- and ultra-filtration processes are possible alternatives to conventional
filtration, but these methods are not usually used at large-scale (Molina Grima et al.
2003).
Methods like dead-end filtration have been evaluated giving as a result that this
type of processes can be energetically competitive in comparison with other harvesting methods like flocculation or vacuum filtration (Bila et al. 2012).
Cross-flow filtration methods have demonstrated to be an alternative for
microalgae concentration (being concentrated at about 150 times) using less energy
that required for other methods like flocculation, centrifugation, or vacuum filtration
(Drexler and Yeh 2014).
3.1.2 Centrifugation
In centrifugation, forces higher than gravity are generated with the aim of performing the cell separation, allowing the separation of almost all types of
microalgae (Mohn 1980). Disk stack centrifuge are the most common centrifugation systems applied in the commercial plants for the production of high-cost
derived products and in the production of pilot-scale biodiesel (Molina Grima et al.
2003). The centrifugation methods are very expensive and energetically no viable if
used for low-cost products like biofuels due to the volume to be processed. An
alternative for the energetic consumption diminution is the application of flocculation process before decreasing the volume to be treated for centrifugation in 65%
(Barros et al. 2015, Wilson 2012).
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characteristics (Molina Grima et al. 2003), the deformation–destruction level of the
algae after harvesting process thinking in posterior procedures and the economic
and energetic costs (Barros et al. 2015).
3.1 Physical Methods
3.1.1 Filtration
Filtration is a dehydration method in which a pressure drop is required along the
system with the object to force the fluid through a membrane (Barros et al. 2015).
Certain types of filters have been used for the microalgae harvesting, depending on
the cell or colonies size. Usually, a high recovery is reached if they are used in big
cells, but it fails in the recovery of organisms near to bacterial size (Mohn 1980).
Systems like microfiltration can be used for microalgae recovery of common
microalgae with a size order of 5–6 µm (Edzwald 1993). Process like macrofiltration can be used if a previous process of flocculation is performed (Milledge
and Heaven 2013). In this type of process, microalgae have the tendency to deposit
in the filtrate medium, growing its thickness and flux resistance (Show and Lee
2014). Micro- and ultra-filtration processes are possible alternatives to conventional
filtration, but these methods are not usually used at large-scale (Molina Grima et al.
2003).
Methods like dead-end filtration have been evaluated giving as a result that this
type of processes can be energetically competitive in comparison with other harvesting methods like flocculation or vacuum filtration (Bila et al. 2012).
Cross-flow filtration methods have demonstrated to be an alternative for
microalgae concentration (being concentrated at about 150 times) using less energy
that required for other methods like flocculation, centrifugation, or vacuum filtration
(Drexler and Yeh 2014).
3.1.2 Centrifugation
In centrifugation, forces higher than gravity are generated with the aim of performing the cell separation, allowing the separation of almost all types of
microalgae (Mohn 1980). Disk stack centrifuge are the most common centrifugation systems applied in the commercial plants for the production of high-cost
derived products and in the production of pilot-scale biodiesel (Molina Grima et al.
2003). The centrifugation methods are very expensive and energetically no viable if
used for low-cost products like biofuels due to the volume to be processed. An
alternative for the energetic consumption diminution is the application of flocculation process before decreasing the volume to be treated for centrifugation in 65%
(Barros et al. 2015, Wilson 2012).
9 Biofuels from Microalgae: Energy and Exergy Analysis for the …
185