Two phase microalgae growth in the open system for enhanced lipid productivity

Enhancement of the intracellular lipid content of Nannochloropsis sp. was first studied in a two phase culture system i.e. 7 days in photoautotrophic mode followed by 3 days in mixotrophic mode in the presence of either glycerol, glucose and sucrose in small scale closed system. During the first phase of growth, average biomass productivity was approximately 111 mg/l/day, and after 7 days the biomass contained 9.5% lipid as fatty acid methyl esters (FAME). Addition of fixed organic carbon sources to the cultures in the second phase resulted in higher biomass productivity. During the second growth phase (day 8–10), maximum volumetric FAME productivity was 51.7 mg/l/day when grown in the presence of 2 g/l glycerol in mixotrophic culture, an increase of over 72% compared to photoautotrophic culture alone. The strain, Nannochloropsis sp. was able to grow in hyper-saline water; however the biomass yield decreased when the salinity of the culture was over 50 ppt. Taking advantage of the strains ability to grow in hyper-saline water, the lipid productivity of dual culture system, i.e. phototrophic for 8 days followed by next 4 days in presence of glycerol, was then studied in open raceway pond.

► Increased salinity can minimize contamination from unwanted species.
► Nannochloropsis sp. can utilize a range of organic substrates to increase the lipid productivity.
► Microalgal lipid productivity in an open system can be increased by growing the culture initially in phototrophic followed by mixotrophic condition.