Comparative experiments of two novel tubular photobioreactors with an inner aerated tube for microalgal cultivation: Enhanced mass transfer and improved biomass yield

Abstract The efficient cultivation of microalgae plays an important role in CO2 fixation and the efficient use of bioenergy resources. To enhance mass transfer and improve algal biomass yield, a novel tangent double-tube photobioreactor (TDTP) with an inner aerated tube generating vortices is proposed, which increases the mixing performance to improve the micro-environment in microalgal cultivation with tubular photobioreactors. The tangent double-tube photobioreactor is an improvement on a concentric double-tube photobioreactor (CDTP). Compared to concentric double-tube photobioreactor, tangent double-tube photobioreactor offers a 31.6% increase in mass transfer coefficient and a 22.1% reduction in mixing time. Besides, the gas holdup rate and the shear rate of the tangent double-tube photobioreactor were nearly 18.2% higher and 39.3% lower than those of the concentric double-tube photobioreactor, respectively. A 10-day cultivation experiment showed that as compared to the concentric double-tube photobioreactor and the traditional tube photobioreactor (TTP), the peak CO2 fixation rate for the tangent double-tube photobioreactor was 0.8 g∙L−1∙d−1, which increased by 33.3% and 293%, respectively. Meanwhile, the microalgal biomass yield for the tangent double-tube photobioreactor increased by 51.2% and 124.8%, respectively. In addition, the dissolved oxygen concentration for the tangent double-tube photobioreactor fluctuated between 6.0 and 6.5 mg/L. Therefore, the tangent double-tube photobioreactor holds promise in the cultivation of microalgae.