Previous studies have shown microalgae would
increase cellular lipid level from 20–30 to 60–70%
through nitrogen deficiency but at the expense of
greatly reduced growth rates, resulting in small
increase of overall lipid productivity (Hsieh and Wu
2009; Xiong et al. 2008). Lipid productivity has been
regarded as the primary concern for microalgal
biodiesel production. To study the potential use
of the crude glycerol as a carbon substrate for
production of biomass and lipid by the microalgae
C. protothecoides batch fermentation experiments
were performed without pH control. Fig. 1(a–c)
shows the time course of biomass, substrate consumption
and pH condition of the microalgal cultures
with 30 g glucose/l, pure glycerol and real glycerol
(SE crude glycerol) being used as substrates in the
medium. As shown in Fig. 1(b, c), the cells grew well
in pure and crude glycerol and the biomass reached
peak levels in 5–6 days. Crude glycerol consumption
was low during first two days (0.85–0.46 g substrate
consumed/g cells), but after that the cells became
acclimated and then the substrate uptake increased to
0.91–1.18 g substrate consumed/g cells during days
three through six. Glucose was completely consumed
in four days which resulted in termination of growth
due to lack of substrate (Fig. 1 a). The results
suggested that microalgae C. protothecoides could
consume glucose much faster than other substrates.
The pH value of both glucose and pure glycerol
cultures decreased after day one, suggesting biosynthesis
and accumulation of organic acids or acidic
wastes in the medium. The pH was stable in the SE
glycerol culture, probably because of the buffering
capacity of this medium.