From the graph you can see that the amount of glycerol is gradually reduced until 4 day in cultivation.
so have no glycerol
Variations of SCOD concentration by time depending on culture type are shown in Fig. 3. SCOD in heterotrophic and mixotrophic conditions were removed at 4.3 g/L and 2.5 g/L, and removal rates were 70% and 65%, respectively. Microalgae cultured in autotrophic conditions do not use organic carbon; thereby the SCOD did not change significantly. Inorganic carbon concentrations by each cultivation type are presented in Fig. 4. Four hundred milligrams of CO2 was consumed in autotrophic conditions, while 200 mg of CO2 was produced in heterotrophic conditions, and mixotrophic microalgae did not present any appreciable change in CO2 during cultivation.
SCOD concentration depending on (●) autotrophic, (▴) heterotrophic, (□) ...