Computational and experimental studies of high depth algal raceway pond photo-bioreactor

Microalgae are promising candidate for biofuels as well as precursors for many high value products like polyunsaturated fatty acids, pigments or polysaccharides. Major cultivation of microalgae is carried out in open raceway ponds. Conventional raceway pond designs with paddle wheels have limitations such as high capital investment, inefficient mixing, lower depth (approximately 0.3 m) and lower productivity. In the present work, a modified high depth (1 m) raceway pond design with side entry axial flow impeller has been studied. The higher depth decreases the land requirement as well as capital cost. The pilot scale (4.5 m3) studies for cultivation of Spirullinaplatensis in nutrient rich Zarrouk's culture media have shown productivity of 21.22 gm/m2/day compared to 11.05 gm/m2/day in convectional raceway ponds. The specific power consumption was found to be 4 W/gm in modified design compared to 6 W/gm in conventional design. Computational Fluid Dynamics (CFD) analysis shows that modified design minimized the excessive turbulence generation and provided higher convective currents keeping biomass in suspension. The simulation results have been validated with ultrasonic velocity profiler (UVP) and particle image velocimetry (PIV) measurements.