54
Most start-ups in the microalgae sector choose to use photobioreactors, preferably because each of these configurations has efficient and robust parameters, providing artificial conditions that give the whole basis for better control and monitoring
of the culture medium. In addition to these requirements, the reasons for selecting
these vessel reactions are also due to the lower propensity to contamination, smaller
hydrodynamic stress, higher surface/volume (S/V) and height/diameter (H/D) ratio,
and CO 2 capture and productivities and, ultimately, closed systems can reduce
losses by evaporation in the exhaust gases, which is very favorable for obtaining
volatile substances (Chauton et al. 2015; Jacob-Lopes et al. 2016; Acién et al. 2017).
The main factors that should be considered to avoid poor cell growth performance in photobioreactors are light, temperature, pH, nutrient supply, and CO 2 /O 2
balance and mixing (Chang et al. 2017). Associated with these issues, the ideal
photobioreactor design for industrial application should take into account the species of microalgae used, process yield, production costs, and product obtained
(Huang et al. 2017).
In terms of costs, however, photobioreactors are probably the most expensive
equipment in microalgae cultivation. This is because its sophistication is related to
high energy consumption and cost with construction materials. The cost of a photobioreactor can range from USD 55 to 150/m
2
, which represents about 50% of the
total cost of the plant. Some companies around the world provide values of commercial photobioreactors ranging from USD 80,000 to 668,000 and can reach
extremely high costs of USD 20 million (AlgaeLink 2019). Although they face
many fluctuations in the sale price, the values of the photobioreactors depend almost
entirely on capital and operational expenditures, and this is because they are still far
from becoming an industrial reality (Christiansen et al. 2012; Tredici et al. 2016). If
all of these aspects were addressed, photobioreactors could be an essential milestone in VOC research. This is a challenging question that depends not only on the
culture conditions but also on various environmental factors.
2.5 Environmental Implications
In addition to the GHG emissions such as CO 2 , methane, fluorinated gases, and
nitrous oxide, substantial quantities of VOCs are also released into the atmosphere
from anthropogenic activities, including sources such as fossil fuel combustion,
industrialization, agriculture, mining, transportation, construction, and wastewater
treatment process, impacting negatively the environment (Franco et al. 2014; EPA
2016; Bonan and Doney 2018). In parallel with the issues mentioned above, they
contribute to photochemical pollution and for being the precursors of tropospheric
ozone (Fu et al. 2019).
It is also useful to highlight that VOCs have a wide range of adverse effects on
human health due to their toxicity. According to the World Health Organization,
problems are generally mutagenic and carcinogenic, causing respiratory damage;
I. A. Severo et al.
Most start-ups in the microalgae sector choose to use photobioreactors, preferably because each of these configurations has efficient and robust parameters, providing artificial conditions that give the whole basis for better control and monitoring
of the culture medium. In addition to these requirements, the reasons for selecting
these vessel reactions are also due to the lower propensity to contamination, smaller
hydrodynamic stress, higher surface/volume (S/V) and height/diameter (H/D) ratio,
and CO 2 capture and productivities and, ultimately, closed systems can reduce
losses by evaporation in the exhaust gases, which is very favorable for obtaining
volatile substances (Chauton et al. 2015; Jacob-Lopes et al. 2016; Acién et al. 2017).
The main factors that should be considered to avoid poor cell growth performance in photobioreactors are light, temperature, pH, nutrient supply, and CO 2 /O 2
balance and mixing (Chang et al. 2017). Associated with these issues, the ideal
photobioreactor design for industrial application should take into account the species of microalgae used, process yield, production costs, and product obtained
(Huang et al. 2017).
In terms of costs, however, photobioreactors are probably the most expensive
equipment in microalgae cultivation. This is because its sophistication is related to
high energy consumption and cost with construction materials. The cost of a photobioreactor can range from USD 55 to 150/m
2
, which represents about 50% of the
total cost of the plant. Some companies around the world provide values of commercial photobioreactors ranging from USD 80,000 to 668,000 and can reach
extremely high costs of USD 20 million (AlgaeLink 2019). Although they face
many fluctuations in the sale price, the values of the photobioreactors depend almost
entirely on capital and operational expenditures, and this is because they are still far
from becoming an industrial reality (Christiansen et al. 2012; Tredici et al. 2016). If
all of these aspects were addressed, photobioreactors could be an essential milestone in VOC research. This is a challenging question that depends not only on the
culture conditions but also on various environmental factors.
2.5 Environmental Implications
In addition to the GHG emissions such as CO 2 , methane, fluorinated gases, and
nitrous oxide, substantial quantities of VOCs are also released into the atmosphere
from anthropogenic activities, including sources such as fossil fuel combustion,
industrialization, agriculture, mining, transportation, construction, and wastewater
treatment process, impacting negatively the environment (Franco et al. 2014; EPA
2016; Bonan and Doney 2018). In parallel with the issues mentioned above, they
contribute to photochemical pollution and for being the precursors of tropospheric
ozone (Fu et al. 2019).
It is also useful to highlight that VOCs have a wide range of adverse effects on
human health due to their toxicity. According to the World Health Organization,
problems are generally mutagenic and carcinogenic, causing respiratory damage;
I. A. Severo et al.