Effects of nitrogen source and concentration on biomass and oil production of a Scenedesmus rubescens like microalga

This investigation examined the effects of nitrogen source and concentration on the ash free dry biomass (AFDB) and oil accumulation and productivity of a Scenedesmus rubescens like alga cultivated in indoor photo-bioreactors and outdoor raceway ponds. Among the nitrogen sources ((NH4)2CO3, urea, NaNO3, urea and NaNO3 mixture), the algae fed with the mixture of urea-N and NaNO3-N had the highest AFDB productivity of 0.539 ± 0.040 g/L/d and the content of fatty acid methyl esters (FAME) (%) fed with (NH4)2CO3-N increased continuously for 17 days and reached 42.94 ± 2.05% in the indoor photo-bioreactors. The content of C18 series (as % of total FAME) was high in all the treatments of nitrogen sources. The algae fed with (NH4)2CO3-N had the highest FAME productivity of 0.133 g/L/d (P < 0.001). The effect of ammonia concentration on the AFDB and FAME productivity was also studied during the 20-day cultivation in the outdoor raceway cultivation system. The mean FAME of the algae cultivated in the ammonia concentration of 1.0–1.5 mg/L were the highest (0.556 ± 0.112 g/m2/d) (P < 0.001). The total Kjeldahl nitrogen (TKN) in the algae and cultivation water decreased but the FAME content (%) of the algae increased during the nitrogen starvation phase.