Decrease in NaNO3 concentrations in the medium and increase in algal metabolism products led
to a slight decrease in the biomass amount. But an increase in N source concentration leads to decreasing of lipid content in the cells (Hsieh and Wu 2009; Yeesang 2011). According Hsieh and Wu (2009) the critical urea concentration was observed at 0.1 g l-1 when the biomass grew intensively and had a higher lipid content compared to that cultivated with a sufficient nitrogen amount. Moreover, urea was reported to be the best nitrogen source of culturing
Chlorella (Becker 1994). Consequently, an optimized supply of urea or deficiency of NaNO3 is considered to be a cultivation strategy for microalgae lipid production.