Promoting Photochemical Efficiency of Chlorella PY-ZU1 with Enhanced Velocity Field and Turbulent Kinetics in a Novel Tangential Spiral-Flow Column Photobioreactor

A novel tangential spiral-flow column photo-bioreactor (TSCP) was developed to strengthen the velocity field and turbulent kinetics for improving CO2 fixation with microalgae. Microalgal solution was injected into a column photobioreactor from four symmetrically arranged nozzles, whose central axes had 10 degrees-included angles with the radius. The injection solution streamline formed a tangential swirling circle, thereby driving the surrounding solution to spirally flow upward. This flow pattern was determined via computational fluid dynamics simulation and a miniature Doppler velocimeter. The optimal structural and operational parameters were determined as follows: relative diameter of imaginary tangential circle = 0.3, nozzles number = 4, and injection solution velocity = 1.33 m/s. The average turbulent kinetic energy, bubble diameter, and actual photochemical efficiency in TSCP were 15% higher, 47% lower, and 19% higher than those in the bubble column photobioreactor (BCP), respectively. Therefore, the microalgal biomass yield and maximum CO2 fixation rate in TSCP were promoted by 1.4 times and 53%, respectively.