respiration (Anbalagan 2016). These two processes occur simultaneously in
wastewater with nutrient exchange, as shown in Fig. 4.
Sforza et al. (2014) evaluated the effect of the wastewater native microflora on
the growth of microalgae Chlorella protothecoides. The obtained results indicated
that significant differences were not detected in the growth of microalgae, suggesting that the presence of the native microflora in wastewater does not influence
its growth.
4.4 Biomass Harvesting
Despite the numerous advantages of wastewater bioremediation by microalgae,
there are also some obstacles that limit their application on a large scale, such as
harvesting of biomass. Currently, biomass harvesting is quite expensive, since this
step is about 20–30% of the biomass production cost (Molina Grima et al. 2003).
The microalgae separation from effluent remains the main obstacle for the bioremediation of wastewater in WWTPs, in part due to the small size of the microalgae.
The size of eukaryotic unicellular microalgae usually varies between 3 and 30 lm
(Molina Grima et al. 2003), and the size of the cyanobacteria varies between 0.2
and 2 µm (Chorus and Bartram 1999). Moreover, the fact that cultures are relatively
diluted (200–600 mg/L) (Uduman et al. 2010) with densities close to the water also
affects the harvesting process. Finally, the negative charge of microalgae maintains
cells in suspension (Danquah et al. 2009a). Until now, there is no method for
microalgal harvesting that is economically viable and efficient (Barros et al. 2015).
Biomass harvesting techniques applied to microalgae include coagulation/
flocculation, auto and bioflocculation, gravitational sedimentation, flotation, electrical processes, filtration and centrifugation. However, none of these techniques
meets the ideal conditions for use in large scale (cost vs. efficiency) (Christenson
and Sims 2011). Cost reduction of harvesting is therefore considered to be a key
factor for the development of sustainable production in large scale of microalgal
biomass. An ideal process should be effective for most species of microalgae and it
must allow the obtaining of high concentrations of biomass (Danquah et al. 2009b).
In addition, the harvesting process must introduce moderate costs of operation,
maintenance and energy.
4.5 Wastewater Characteristics
The amount and quality of light penetration affect the photosynthetic process of
organisms that use sunlight as an energy source (Butler et al. 2017). Thus, as
photosynthetic organisms, the colour of wastewater, as well as the amount of
particles in suspension should be factors to be used for the cultivation of microalgae
(Yaakob and Fakir 2011). The high content of particulates in wastewaters can affect
3 Process Integration Applied to Microalgal Biofuels Production
49
wastewater with nutrient exchange, as shown in Fig. 4.
Sforza et al. (2014) evaluated the effect of the wastewater native microflora on
the growth of microalgae Chlorella protothecoides. The obtained results indicated
that significant differences were not detected in the growth of microalgae, suggesting that the presence of the native microflora in wastewater does not influence
its growth.
4.4 Biomass Harvesting
Despite the numerous advantages of wastewater bioremediation by microalgae,
there are also some obstacles that limit their application on a large scale, such as
harvesting of biomass. Currently, biomass harvesting is quite expensive, since this
step is about 20–30% of the biomass production cost (Molina Grima et al. 2003).
The microalgae separation from effluent remains the main obstacle for the bioremediation of wastewater in WWTPs, in part due to the small size of the microalgae.
The size of eukaryotic unicellular microalgae usually varies between 3 and 30 lm
(Molina Grima et al. 2003), and the size of the cyanobacteria varies between 0.2
and 2 µm (Chorus and Bartram 1999). Moreover, the fact that cultures are relatively
diluted (200–600 mg/L) (Uduman et al. 2010) with densities close to the water also
affects the harvesting process. Finally, the negative charge of microalgae maintains
cells in suspension (Danquah et al. 2009a). Until now, there is no method for
microalgal harvesting that is economically viable and efficient (Barros et al. 2015).
Biomass harvesting techniques applied to microalgae include coagulation/
flocculation, auto and bioflocculation, gravitational sedimentation, flotation, electrical processes, filtration and centrifugation. However, none of these techniques
meets the ideal conditions for use in large scale (cost vs. efficiency) (Christenson
and Sims 2011). Cost reduction of harvesting is therefore considered to be a key
factor for the development of sustainable production in large scale of microalgal
biomass. An ideal process should be effective for most species of microalgae and it
must allow the obtaining of high concentrations of biomass (Danquah et al. 2009b).
In addition, the harvesting process must introduce moderate costs of operation,
maintenance and energy.
4.5 Wastewater Characteristics
The amount and quality of light penetration affect the photosynthetic process of
organisms that use sunlight as an energy source (Butler et al. 2017). Thus, as
photosynthetic organisms, the colour of wastewater, as well as the amount of
particles in suspension should be factors to be used for the cultivation of microalgae
(Yaakob and Fakir 2011). The high content of particulates in wastewaters can affect
3 Process Integration Applied to Microalgal Biofuels Production
49