Developing a water-circulating column photobioreactor for microalgal growth with low energy consumption.

A water-circulating column photobioreactor (WCC-PBR) was developed to decrease bubble generation time and mixing time for growing microalgal biomass at low energy consumption. Bubble generation time was decreased by 60.4% and mixing time was decreased by 41.5% owing to an enhanced solution velocity with a water pump. Bubble residence time was decreased by 31.1% and mass transfer coefficient was decreased by 0.4% owing to a reduced distance between air aerator and solution surface. Microalgal growth rate was decreased by 12.7% from 128.9mg/Lday in an air-lifting column photobioreactor (ALC-PBR) to 112.6mg/Lday in a WCC-PBR because of the decrease in residence time of bubbles and an additional shear of cells in a water pump. However, total energy consumption of a WCC-PBR with an air compressor and a water pump was lower by 21.1% than that of an ALC-PBR with only an air compressor.