Abstract— A strain of microalgae was isolated from phytoplankton samples collected from the sea coast of Amsheet, North Lebanon. Molecular diagnosis based on ribosomal RNA genes showed it to be most closely related to Chlorella sp. (GenBank accession KC188335.1) with over 90 % nucleotide identity. It was then evaluated whether N and P amendments of seawater fertilized with Guillard’s f/2 medium would improve algal growth and production. Addition of nitrogen (30 ppm) and/or phosphorus (2 ppm) to microalgae grown under laboratory conditions in 3L bioreactors resulted in improved biomass yield (mg dry matter/ L) by approximately 48%, and increased protein yield by approximately 56%, from 19.5% to 30.6% of DM content. Total protein yield/L of culture medium was therefore increased by approximately 83%. Total lipid content and carotenoid levels of the microalgal culture were not affected by the N+P amendement, whereas chlorophyll content was almost doubled. When lower levels of N+P supplementations, 10 and 20 ppm N, were tried, the biomass yield was also improved. The experiment was repeated in 20 L bioreactors in a plastic greenhouse, under normal environmental conditions, with an average temperature of 28°C and a maximum temperature of 36°C. At these relatively high temperatures, the growth rate was slowed down, but N supplementations at 10 and 20 ppm resulted in improved dry matter yield by 25 and 45% respectively, and protein content by 17 and 35%, respectively. Knowledge of the optimal culturing conditions of this local Chlorella strain is essential for its efficient production and is expected to serve future environmental and biotechnological purposes.
Keywords— Microalgae, nutrient amendment, nitrogen, phosphorus, dry weight, yield, protein yield, chlorophyll.
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