Integrated hybrid Nested-bottled photobioreactor for enhanced mixing, mass transfer, and CO₂ fixation in Arthrospira platensis raceway pond cultivation systems

This study introduces a novel hybrid photobioreactor system that integrates an open raceway pond (ORWP) with a Nested-bottled photobioreactor (NB-PBR) in a closed-loop configuration to enhance microalgal biomass production and CO₂ fixation. The system facilitates continuous culture circulation, improving mass transfer and mixing efficiency while ensuring optimal light exposure and CO₂ dissolution. This design resulted in a 38% increase in dry mass (3.1 g/L) and improved mass transfer and mixing times by 16.6% and 15.3%, respectively. The optimized cultivation conditions led to a 39.9% enhancement in CO₂ fixation and an 8.7% increase in photosynthetic efficiency (Fv/Fm) compared to traditional systems. The strategic movement of poorly illuminated ORWP to the NB-PBR maximized light absorption and nutrient uptake, significantly boosting overall productivity. These findings highlight the potential of hybrid photobioreactor systems in improving microalgal growth efficiency and advancing sustainable algal cultivation for commercial applications.