Strategies to improve oil/lipid production of microalgae in outdoor cultivation using vertical tubular-T ype photobioreactors

The indoor laboratory-scale microalgae culture was elevated to 50 liter in outdoor photobioreactors for the cultivation of an oil-rich microalga, Chlorella vulgaris ESP-31. Under phototrophic and photoheterotrophic conditions using CO2 and acetic acid as carbon source, respectively, the lipid productivity and lipid content obtained were 30-31 mg/L/d and 35-44%, respectively. The effect of inoculum sizes on the performance of biomass and lipid production under phototrophic cultivation was also investigated. The lipid productivity of C. vulgaris ESP-31 was further improved to 47.6 mg/L/d when a higher inoculum size of 0.70 g/L was used. Finally, to avoid severe contamination problem during outdoor cultivation in the summer time, a two-stage lipid accumulation strategy was employed. The results show that the proposed two-stage process was able to avoid the bacterial contamination and enhanced the lipid content and lipid productivity of Chlorella vulgaris ESP-31.