Biomass and oil production by Chlorella vulgaris and four other microalgae - Effects of salinity and other factors

- The nominally freshwater microalga Chlorella vulgaris was grown in seawater.
- Oil productivity in sweater was double the productivity in freshwater.
- Biomass yield on phosphate was ∼27% higher in seawater relative to freshwater.
- Biomass loss in the dark obeyed first-order kinetics.
- The calorific value of the seawater-grown biomass exceeded 25 kJ g−1.

Five nominally freshwater microalgae (Chlorella vulgaris, Choricystis minor, Neochloris sp., Pseudococcomyxa simplex, Scenedesmus sp.) with a known ability to produce high-levels of lipids for possible use as fuel oils were evaluated for their ability to thrive and produce lipids in seawater and brackish water. Only C. vulgaris was found to thrive and produce lipids in full strength seawater. Seawater tolerant strains of C. vulgaris are unusual. Lipid productivity in nutrient sufficient seawater exceeded 37 mg L−1 d−1 and was nearly 2-fold greater than in freshwater. Although other microalgae such as C. minor had higher lipid productivities (e.g. 45 mg L−1 d−1), they did not thrive in seawater. The lipid content of the C. vulgaris biomass was nearly 16% by dry weight. The calorific value of the seawater-grown C. vulgaris biomass exceeded 25 kJ g−1. Compared to continuously illuminated cultures, a 12/12 h light-dark cycle reduced lipid productivity of C. vulgaris by ∼30%, but did not affect the lipid content of the biomass. Biomass yield on phosphate was nearly 27% higher in seawater compared to in freshwater. While C. vulgaris has been extensively studied in freshwater, it has not been examined to any detail in full strength seawater. Studies in seawater are essential for any future large scale production of algal oils for biofuels: seawater is available cheaply and in large amounts whereas there is a global shortage of freshwater.