Microalgal TAG production strategies: why batch beats repeated-batch.

Area of Science:

• Biotechnology
• Algal Biotechnology
• Photobiology

Background:

• High triglyceride (TAG) productivities are crucial for commercially viable microalgal biofuel production.
• Operational strategies significantly influence TAG productivity, yet systematic comparisons are lacking.
• This study investigates Nannochloropsis sp. responses to nitrogen (N) starvation and re-supply under continuous light.

Purpose of the Study:

• To systematically compare batch and repeated-batch cultivation strategies for microalgal TAG production.
• To develop a mechanistic model describing physiological responses to N variations.
• To identify optimization potential for both cultivation strategies.

Main Methods:

• Lab-scale batch and repeated-batch cultivations of Nannochloropsis sp. under continuous light.
• Controlled nitrogen starvation and N-rich medium replenishment cycles.
• Development and application of a mechanistic model to analyze physiological responses and predict TAG yields.

Main Results:

• The developed model accurately described both batch and repeated-batch strategies.
• Optimized batch processes showed significantly higher TAG yields on light (up to 0.49 g molph⁻¹) compared to optimized repeated-batch (up to 0.39 g molph⁻¹).
• Base case yields align with current state-of-the-art outdoor TAG production.

Conclusions:

• Optimized batch cultivation consistently yields higher TAG on light than optimized repeated-batch under continuous light.
• Repeated-batch processes suffer from reduced photosynthetic efficiency during the N-starved cell regrowth phase.
• This inefficiency in light utilization leads to lower overall TAG yields in repeated-batch compared to batch processes.