Enhanced CO₂ Fixation Through Continuous Cultivation of Microalgae in a Two-Stage Photobioreactor System

Area of Science:

• Biotechnology and Bioengineering
• Environmental Science and Engineering
• Sustainable Energy and Biomass Production

Background:

• Microalgae cultivation in biorefineries offers a sustainable route for CO2 sequestration and biomass generation.
• Efficient photobioreactor (PBR) design is crucial for optimizing microalgal growth and product accumulation.
• Integrating biogenic CO2 sources enhances the economic viability and environmental benefits of microalgal systems.

Purpose of the Study:

• To evaluate the CO2 fixation performance and biomass productivity of a two-stage PBR system for Haematococcus pluvialis cultivation.
• To compare the efficiency of the two-stage PBR with a single-stage system for CO2 assimilation and biomass yield.
• To investigate the impact of operational parameters on nutrient uptake and carotenoid accumulation.

Main Methods:

• Continuous cultivation of Haematococcus pluvialis in a two-stage PBR system with varying dilution rates.
• Utilizing biogenic CO2 from a heterotrophic culture as the carbon source.
• Employing high-irradiance columns in the second stage for biomass and carotenoid accumulation.
• Analyzing CO2 fixation rates, biomass productivity, nutrient consumption, and pigment content.

Main Results:

• The two-stage PBR achieved a maximum CO2 assimilation capacity of 0.747 g/L/d and 94% CO2 fixation efficiency.
• Overall biomass productivity reached 0.332 g/L/d, with the second stage alone yielding up to 1.18 g/L/d.
• Batch-induced carotenogenesis in the second stage led to high biomass concentration (3.33 g/L) and pigment production.
• Higher dilution rates resulted in increased unconsumed nutrients, indicating potential for optimization.

Conclusions:

• The two-stage PBR system significantly enhances CO2 capture efficiency and biomass productivity compared to single-stage systems.
• This integrated approach provides operational flexibility for both CO2 mitigation and valuable biomass production.
• The findings support the scalability and sustainability of microalgal biorefineries for carbon capture and the circular bioeconomy.