We combined in situ extraction with biomass cultivation in a
turbidostat-controlled flat panel photobioreactor. After a growth
phase to obtain high biomass levels, the cells were stressed by
applying a high incident light intensity. As was shown by Lamers
et al. [6] the cells use the first 4 h to adjust to the inflicted stress
by increasing cell size and simultaneously increasing production of
carotenoids.We started the turbidostat after the maximum cell size
and carotenoid content were reached in order to be able to keep cell
numbers of the stressed cells constant (24 h after the switch to high
light). Furthermore, dodecane was applied as an organic phase on
top of the aqueous phase and pumped through the reactor to yield
a high contact area between the organic and the aqueous phase.
-Carotene was continuously extracted from the aqueous
phase to the organic phase with an extraction rate of approximately
2.75mg-carotene Ldod
−1 d−1 (equivalent to 0.7mg-
carotene LRV
−1 d−1) as shown in Fig. 2. This rate is comparable to
values obtained by Hejazi et al. [2] who found extraction rates
varying between 2.5 and 4.1mgLdod
−1 d−1 for comparable sparging
rates of organic phase.
As the reactor was operated as a turbidostat the turbidity was
kept constant by pumping medium into the reactor while keeping
the total aqueous volume constant via an overflow tube. As can be
seen in Fig. 3 this resulted in the first days of the turbidostat period
in a small increase in cell number and a decrease in cell size until
steady state was attained.