A multistage gradual nitrogenreduction strategy for increased lipid productivity and nitrogen removal in wastewater using Chlorella vulgaris and Scenedesmus obliquus

Abstract

Chlorella vulgaris and Scenedesmus obliquus were grown in artificial-wastewater using a new nitrogen-limitation strategy aimed at increasing lipid productivity. This strategy consisted in a multi-stage process with sequential reduction of N-NH4 concentration (from 90 to 60, 40, and 20 mg.L1) to promote a balance between cell growth and lipid accumulation. Lipid productivity was compared against a reference process consisting of nitrogen reduction in two stages, where the nitrogen concentration was suddenly reduced from 90 mg.L1 to three different concentrations (10, 20, and 30 mg.L1). In the multi-stage mode, only C. vulgaris exhibited a net lipid-productivity increase. Lipid content of S. obliquus did not present a significant increase, thus decreasing lipid productivity. The highest lipid productivities were observed in the two-stage mode for both S. obliquus and C. vulgaris (194.9 and 133.5 mg.L1.d1, respectively), and these values are among the highest reported in the literature to date.