Microalgae Chlorella as a Sustainable Feedstock …
85
Fig. 2 Microalgae growth
curve for 30 days
According to Fog and Thake (1987), there are five defined growth phases in batch
cultures of microalgae which are lag, exponential, declining growth rate, stationary,
and death phase. However, according to Fig. 1.2, only four growth phases were
observed with no stationary phase. From day 0 to day 6, the microalgae cells were in
their lag phase. Lag phase is the phase where the microalgae cells start to adapt to their
environment including temperature, light intensity, as well as medium composition
and pH. At this stage, the number of viable cells remained nearly stationary (Held
2011). Following lag phase, the microalgae cells entered the exponential phase or
log phase during day 6–day 15. During this phase, the microalgae cells were growing
at a rapid rate as there were plenty of nutrients to be utilized for the cell metabolism.
From day 15 to day 27, the cells entered declining growth rate phase. During this
phase, the cells grew at a slower rate and yet, the number of viable cells was still
increasing. From day 27 to day 30, the cells entered death phase where the number
of viable cells started to decrease (Held 2011; Burlew 1976).
The growth phase determination was important as microalgae cells would be harvested during the exponential phase for the subsequent acid hydrolysis process. This
is due to the maximum growth rate of microalgae cells achieved during exponential
phase. Similar growth curve and growth pattern were reported in previous studies.
Makareviˇ cien˙ e et al. (2011) reported that the exponential phase of microalgae cells
was observed in the period of day 5–day 15. In their study, microalgae Chlorella sp.
was cultivated in medium with different nitrogen concentration and sources, yet similar periods of exponential phase were observed through different cell densities. The
cell density is strongly influenced by dissolved oxygen and carbon dioxide concentration, light intensity, temperature, medium composition and pH as well as salinity
(Ho et al. 2014; Liu et al. 2014a, b). According to Guo et al. (2013), the exponential
phase of growing microalgae cells was reported to be in the period of day 4–day 15.
The length of the exponential phase is dependent on the nature of several factors
and these factors decide when the microalgae cells will enter the declining growth
phase and stationary phase. One of the most important factors is the depletion of
85
Fig. 2 Microalgae growth
curve for 30 days
According to Fog and Thake (1987), there are five defined growth phases in batch
cultures of microalgae which are lag, exponential, declining growth rate, stationary,
and death phase. However, according to Fig. 1.2, only four growth phases were
observed with no stationary phase. From day 0 to day 6, the microalgae cells were in
their lag phase. Lag phase is the phase where the microalgae cells start to adapt to their
environment including temperature, light intensity, as well as medium composition
and pH. At this stage, the number of viable cells remained nearly stationary (Held
2011). Following lag phase, the microalgae cells entered the exponential phase or
log phase during day 6–day 15. During this phase, the microalgae cells were growing
at a rapid rate as there were plenty of nutrients to be utilized for the cell metabolism.
From day 15 to day 27, the cells entered declining growth rate phase. During this
phase, the cells grew at a slower rate and yet, the number of viable cells was still
increasing. From day 27 to day 30, the cells entered death phase where the number
of viable cells started to decrease (Held 2011; Burlew 1976).
The growth phase determination was important as microalgae cells would be harvested during the exponential phase for the subsequent acid hydrolysis process. This
is due to the maximum growth rate of microalgae cells achieved during exponential
phase. Similar growth curve and growth pattern were reported in previous studies.
Makareviˇ cien˙ e et al. (2011) reported that the exponential phase of microalgae cells
was observed in the period of day 5–day 15. In their study, microalgae Chlorella sp.
was cultivated in medium with different nitrogen concentration and sources, yet similar periods of exponential phase were observed through different cell densities. The
cell density is strongly influenced by dissolved oxygen and carbon dioxide concentration, light intensity, temperature, medium composition and pH as well as salinity
(Ho et al. 2014; Liu et al. 2014a, b). According to Guo et al. (2013), the exponential
phase of growing microalgae cells was reported to be in the period of day 4–day 15.
The length of the exponential phase is dependent on the nature of several factors
and these factors decide when the microalgae cells will enter the declining growth
phase and stationary phase. One of the most important factors is the depletion of