Performance and feasibility analysis of an integrated airlift microalgae photobioreactor for cultivation and pre-harvesting

Microalgae technology is highly attractive in the realm of wastewater treatment and CO₂ removal. However, during the cultivation of microalgae, the phenomenon of light attenuation intensifies with the increasing cell concentration, resulting in a decrement in microalgal growth rate. To maintain high light transmittance and growth rate of microalgae, this study introduces a two-step pre-harvesting process involving flocculation and filtration within an airlift photobioreactor. In this way, the growth performance of microalgae was bolstered by an improvement in light availability, which was increased 1.59 times by harvesting 30% of the microalgae biomass. Additionally, the microalgae productivity was increased 12.3%. By diluting the cationic starch concentration to 3 g L^-1, the harvesting efficiency approached levels comparable to those achieved through magnetic stirring, while filtration resulted in a 1.9-fold increase in final biomass concentration. Moreover, a comparative life-cycle assessment of three harvesting methods revealed that the flocculation-filtration method exhibited the lowest global warming potential of -0.09 CO₂ eq, positioning it as a viable and low-carbon alternative for microalgae harvesting.