In conclusion, PBR systems allow for better control of the algal cell growth but
are also accompanied with higher energy demands and, therefore, are more costly
than open systems to operate (US20090011492A1). On the other hand, areal productivity of airlift PBRs is higher than that of the tubular PBRs, but their volumetric
productivity is around half of what achieved using tubular PBRs (Tabernero et al.
2013). More detailed information on cultivating microalgae using PBRs
could be found in patents such as US20090130704A, US20140356931A1,
WO2015050775A1, US9045724B2, and US8003379B2.
3.2.2 Production Media and Nutrients Supply
As mentioned earlier, by using PBRs, growth-limiting factors such as light,
CO 2 , nutrients supply, and temperature can be easily controlled. Numerous
patents like US20110092726A, US20110107664A1, US20130023044A1, and
US20110294196A1 are concerned about efficient nutrient supply. More specifically, their aim is the development of nutrient media to increase biomass production
and boost accumulation of valuable compounds. Introduction of novel sources of
essential minerals and CO 2 to enhance the economic aspects of the systems has also
been among the objectives of such patents.
Historically, biochemical engineering, e.g., nutrients management (such as
nitrogen and phosphor starvation), precursor addition as well as design of growth
and/or environmental conditions (like salinity, acidity, and photon flux) in
microalgae have been used as primary forward tools to enhance desired metabolic
productivity (Courchesne et al. 2009). Exploring the respective regulatory mechanisms was the subject of the following patents: GB2501101A, US9295206B2, and
WO2015088127A1.
As it was previously mentioned, the environmental conditions as well as provided nutrients could directly affect the FA profile of oleaginous microalgae.
Heterotrophic culture system is an example of ways to increase FA concentration in
microalgae. Within the heterotrophic culture, the microalgal cells consume an
organic source (e.g., glucose, glycerol) instead of CO 2 . In spite of increased cost
and reduced environmental benefits, several advantages such as an increase in
growth speed and lipid concentration are expected. This has been the subject of
numerous investigations such as the patents WO9107498A1, US20090209014A1,
US5130242A, and US20060094089A1.
Although the mechanisms of wastewater tolerance in microalgal community are
yet to be discovered, strains which are naturally adapted and are capable of efficiently growing in wastewaters/effluents are regarded as successful strains to
achieve economical biofuel production. This is ascribed to the fact that nutrient-rich
municipal, agricultural, and industrial wastewaters could provide an economically
sustainable means of cultivation for different strains of microalgae. In addition, such
systems offer the advantage of combining wastewater treatment (i.e., heavy metal
and nutrients removal) with biofuels production systems (Pittman et al. 2011). Such
combination can potentially reduce unit cost energy by 20–25% in addition to
300
A. F. Talebi et al.
are also accompanied with higher energy demands and, therefore, are more costly
than open systems to operate (US20090011492A1). On the other hand, areal productivity of airlift PBRs is higher than that of the tubular PBRs, but their volumetric
productivity is around half of what achieved using tubular PBRs (Tabernero et al.
2013). More detailed information on cultivating microalgae using PBRs
could be found in patents such as US20090130704A, US20140356931A1,
WO2015050775A1, US9045724B2, and US8003379B2.
3.2.2 Production Media and Nutrients Supply
As mentioned earlier, by using PBRs, growth-limiting factors such as light,
CO 2 , nutrients supply, and temperature can be easily controlled. Numerous
patents like US20110092726A, US20110107664A1, US20130023044A1, and
US20110294196A1 are concerned about efficient nutrient supply. More specifically, their aim is the development of nutrient media to increase biomass production
and boost accumulation of valuable compounds. Introduction of novel sources of
essential minerals and CO 2 to enhance the economic aspects of the systems has also
been among the objectives of such patents.
Historically, biochemical engineering, e.g., nutrients management (such as
nitrogen and phosphor starvation), precursor addition as well as design of growth
and/or environmental conditions (like salinity, acidity, and photon flux) in
microalgae have been used as primary forward tools to enhance desired metabolic
productivity (Courchesne et al. 2009). Exploring the respective regulatory mechanisms was the subject of the following patents: GB2501101A, US9295206B2, and
WO2015088127A1.
As it was previously mentioned, the environmental conditions as well as provided nutrients could directly affect the FA profile of oleaginous microalgae.
Heterotrophic culture system is an example of ways to increase FA concentration in
microalgae. Within the heterotrophic culture, the microalgal cells consume an
organic source (e.g., glucose, glycerol) instead of CO 2 . In spite of increased cost
and reduced environmental benefits, several advantages such as an increase in
growth speed and lipid concentration are expected. This has been the subject of
numerous investigations such as the patents WO9107498A1, US20090209014A1,
US5130242A, and US20060094089A1.
Although the mechanisms of wastewater tolerance in microalgal community are
yet to be discovered, strains which are naturally adapted and are capable of efficiently growing in wastewaters/effluents are regarded as successful strains to
achieve economical biofuel production. This is ascribed to the fact that nutrient-rich
municipal, agricultural, and industrial wastewaters could provide an economically
sustainable means of cultivation for different strains of microalgae. In addition, such
systems offer the advantage of combining wastewater treatment (i.e., heavy metal
and nutrients removal) with biofuels production systems (Pittman et al. 2011). Such
combination can potentially reduce unit cost energy by 20–25% in addition to
300
A. F. Talebi et al.