Fig. 1 illustrates the effect of the N source and concentration on the Chlorella sp. biomass growth.As shown in Fig. 1 the initial growth of Chlorella sp. biomass at an early lag phase was very similar to that when the source of N was NaNO3, despite that the concentrations were different (Fig. 1. curves 1 and 2). A sharp increase in concentration was characteristic
of the growth medium with the initial NaNO3 concentrations of 1.5 g l-1 during the lag phase of the cultivation. The biomass growth for the medium with initial NaNO3 of 0.75 g l-1 was not so sharp but noticeable. The critical day of the biomass growth for the both media was identified as day 30, when the biomass concentration started to decrease rapidly until it reached a constant concentration In the case of urea, the sharp growth of biomass concentrations was
noticed in the lag phase period, when the lag phase period of growth was very slight and stable till day 40.