Pilot-scale semi-continuous cultivation of microalgae Chlorella vulgaris in bubble column photobioreactor (BC-PBR): Hydrodynamics and gas–liquid mass transfer study

Abstract

A 56L compressed-air aerated bubble column photobioreactor (BC-PBR) was used to cultivate Chlorella vulgaris under indoor conditions via semi-continuous cultivation method. The effects of hydrodynamics and gas–liquid mass transfer limitations towards the biomass production of C. vulgaris at different compressed-air aeration rates were studied. The optimum biomass production of microalgae was achieved at compressed-air aeration rate of 0.16VVM, with superficial velocity, UG of 0.185ms−1. The experimental volumetric gas–liquid mass transfer coefficient, kLaL(CO2), was 4.5×10−3s−1 under the optimum growth condition. Besides that, the physical properties such as density, viscosity and surface tension remained constant throughout the semi-continuous cultivation mode. Low biomass production was observed at the highest aeration rate (0.19VVM), which indicated that shear sensitivity has significant effect on microalgae growth in BC-PBR. Apart from that, the effect of shear stress on the growth of C. vulgaris was also reported, especially on the reproduction of microalgae cells. The semi-continuous cultivation system had shown the possibility to partially harvest microalgae biomass during the exponential growth phase and thus, shorten the overall cultivation time in the subsequent cycles (elimination of lag phase) which resulted in higher biomass production.