Enhancing the production of eicosapentaenoic acid (EPA) from Nannochloropsis oceanica CY2 using innovative photobioreactors with optimal light source arrangements

• Strategies to enhance EPA production from Nannochloropsis oceanica CY2 were studied.
• A binary combination of LED-Blue and LED-Red gave the highest EPA productivity.
• Semi-batch operation (40% medium replacement ratio) further enhanced EPA production.
• A novel PBR with additional immersed LEDs improved the light penetration efficiency.
• Immersed LED at 9 Hz flashing-frequency lowered the energy consumption yield of EPA.

Binary combinations of LEDs with four different colors were used as light sources to identify the effects of multiple wavelengths on the production of eicosapentaenoic acid (EPA) by an isolated microalga Nannochloropsis oceanica CY2. Combining LED-Blue and LED-Red could give the highest EPA productivity of 13.24 mg L−1 d−1, which was further enhanced to 14.4 mg L−1 d−1 when using semi-batch operations at a 40% medium replacement ratio. A novel photobioreactor with additional immersed light sources improved light penetration efficiency and led to an 38% (0.170–0.235 g L−1 d−1) increase in the microalgae biomass productivity and a 9% decrease in electricity consumption yield of EPA (10.15–9.33 kW-h (g EPA)−1) when compared with the control (i.e., without immersed light sources). Operating the immersed LEDs at a flashing-frequency of 9 Hz further lowered the energy consumption yield to 8.87 kW-h (g EPA)−1.