Lipid contents were 18.1% and 18.7% when the initial cell densities
were 0.45 and 0.75 cm1 respectively, a little higher than 16.5%
at 1 cm1 (Table 1). Initial cell densities had only a little influence
on lipid content, and lipid production (0.167 g/L, 0.182 g/L and
0.189 g/L respectively) did not show significant difference due to
the compensation between lipid content and ultimate biomass
dry weight (Table 1). Higher initial cell incubation density might
decrease the time to reach a high biomass production and affect
the follow-up persistent time of algae cultivation. In the first few
days in cultivation, all the growth conditions and nutrients were
suitable, as a result of which microalgae could rapidly multiply
especially in the condition of high initial incubation density. At
low initial density, the external high nutrient conditions might
inhibit the activity and become pressures for microalgae to accumulate
lipid [35]. Based on the results of the experiments, any of
the three initial cell densities in the culture of Chlorella sp. could
be selected as the optimal initial incubation density because of little
difference among them. High initial cell density might lead to premature
shadow and cell decline with cultivation. Therefore the following
experiments were conducted at the initial cell density of
about 0.45 cm1.