(Grima et al. 2003; Patel et al. 2017). The secondary alternatives such as ultrafiltration and membrane filtration techniques can also be employed, but they are expensive due to the presence of many filters along with the primary filter (Patel et al.
2017). The surface charge of the microalgal cells, culture age, size, temperature,
contact angle, hydrophilic or hydrophobic nature of the membrane, and concentration of the microalgal cells are the factors that influence the process of filtration.
Fouling acts as a major bottleneck in the filtration process and demands frequent
membrane replacements and backwashing that increases the production costs
involved. Fouling can be reduced to some extent by application of pressure on the
filter of the system (Rashid et al. 2014).
8.3.4 Harvesting of Microalgae Using Flotation
This method depends on the mechanism of interaction in between the negatively
charged microalgal surfaces that are hydrophilic in nature (Patel et al. 2017). The
size of the bubbles (microbubbles/nanobubbles/fine bubbles) is responsible for the
determination of the efficiency of the harvesting process (Shuba and Kifle 2018).
The technique of flotation offers many benefits (e.g., inexpensive, easy to operate,
and involves less processing time), but it is also associated with various drawbacks
(e.g., difficulties in scale-up operations and higher-energy consumption) (Rashid
et al. 2014); however, various methods for performing flotation were designed which
includes the following:
8.3.4.1 Dissolved Air Flotation
In this method, liquid stream is injected via a nozzle in the microalgal suspension.
This stream saturated with air and the generated air bubbles from the nozzle rise to
the surface after attachment with the microalgal cells (Pragya et al. 2013).
8.3.4.2 Dispersed Air Flotation
The injection of unpressurized air results in the generation of larger bubbles, thereby
resulting in relatively lower efficiency (Laamanen et al. 2016).
8.3.4.3 Ozone Flotation
In this process, the proteins are released after the disruption of cell walls of
microalgae by applying ozone, and this protein further acts as bio-flocculant
(Singh and Patidar 2018).
8.3.4.4 Electro Flotation
In this process, the electrolysis of water leads to production of hydrogen gas bubbles
that further carry the microalgal cells to the surface for skimming (Uduman et al.
2010; Rashid et al. 2014).
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K. Agrawal et al.
2017). The surface charge of the microalgal cells, culture age, size, temperature,
contact angle, hydrophilic or hydrophobic nature of the membrane, and concentration of the microalgal cells are the factors that influence the process of filtration.
Fouling acts as a major bottleneck in the filtration process and demands frequent
membrane replacements and backwashing that increases the production costs
involved. Fouling can be reduced to some extent by application of pressure on the
filter of the system (Rashid et al. 2014).
8.3.4 Harvesting of Microalgae Using Flotation
This method depends on the mechanism of interaction in between the negatively
charged microalgal surfaces that are hydrophilic in nature (Patel et al. 2017). The
size of the bubbles (microbubbles/nanobubbles/fine bubbles) is responsible for the
determination of the efficiency of the harvesting process (Shuba and Kifle 2018).
The technique of flotation offers many benefits (e.g., inexpensive, easy to operate,
and involves less processing time), but it is also associated with various drawbacks
(e.g., difficulties in scale-up operations and higher-energy consumption) (Rashid
et al. 2014); however, various methods for performing flotation were designed which
includes the following:
8.3.4.1 Dissolved Air Flotation
In this method, liquid stream is injected via a nozzle in the microalgal suspension.
This stream saturated with air and the generated air bubbles from the nozzle rise to
the surface after attachment with the microalgal cells (Pragya et al. 2013).
8.3.4.2 Dispersed Air Flotation
The injection of unpressurized air results in the generation of larger bubbles, thereby
resulting in relatively lower efficiency (Laamanen et al. 2016).
8.3.4.3 Ozone Flotation
In this process, the proteins are released after the disruption of cell walls of
microalgae by applying ozone, and this protein further acts as bio-flocculant
(Singh and Patidar 2018).
8.3.4.4 Electro Flotation
In this process, the electrolysis of water leads to production of hydrogen gas bubbles
that further carry the microalgal cells to the surface for skimming (Uduman et al.
2010; Rashid et al. 2014).
214
K. Agrawal et al.