Cultivation of Spirulina platensis by continuous process using ammonium chloride as nitrogen source

This work is focused on the influence of dilution rate (0.08 D 0.32 d−1) on the kinetics of continuous cultivation of Spirulina platensis at two different concentrations of ammonium chloride (N0=1.0 and 10 mM) as nitrogen source. Cell productivity increased in both series of runs up to D 0.12–0.16 d−1, and then decreased. While at N0=1.0 mM biomass washing was certainly the cause of progressive cell concentration decrease, a combination of this phenomenon with the toxic effect of excess ammonia was responsible, at N0=10 mM and D 0.20 d−1, for quick stop of cell growth just beyond the achievement of maximum cell productivity (92.4 mg l−1 d−1). Similar profile was observed for protein productivity, that achieved a maximum value of 67.0 mg l−1 d−1, because of the very high protein content (72.5%) of biomass produced under these conditions. The yield of nitrogen-to-biomass was much higher at the lower N0, because of the low protein content, and reached a maximum value of 9.7 g g−1 at D=0.08–0.12 d−1. The yield of nitrogen-to-protein showed less marked difference, being most of the nitrogen present in the cell as proteins or free amino-acids.