Cell density of Chlorella sp. was estimated by measuring
turbidity at 750 nm with a spectrophotometer. To ensure that
the turbidity represented well the cell density, a relationship
between turbidity and cell density was established. Chlorella
sp. cells grown in control medium to the stationary
phase were concentrated threefold and then gradually
diluted before the turbidity of cells was measured. As shown
in Fig. 1, the value of turbidity (as absorbance at 750 nm)
within the range of 0.028–1.384 was linearly correlated with
the cell density.
The effects of glucose, sodium thiosulphate and the
combination of these two compounds on the growth kinetics
of Chlorella sp. are summarized in Fig. 2. Under all growth
conditions, Chlorella sp. cells growth kinetics displayed a
typical growth S-curve, i.e. there were a lag phase from 0 to
3rd day, an exponential phase from 4th to 13th day and a
stationary phase after 13 days of growth. Initial addition of
glucose to the culture medium resulted in an increase in cell