Improving flashing light frequency and CO2 fixation rate with vortex movement of algal cells in raceway pond with conic baffles

The inefficiency of the flashing light effect is one of the major obstacles to CO2 fixation by microalgae. To improve the flashing light frequency of Chlorella vulgaris in a raceway pond with alternatively permutated conic baffles (RWP-APCB), the detailed vortex structures of algal cell movement were clarified and optimised. Numerical simulation results showed that the peak vortex intensity occurred in the centre of the APCB, whereas the peak solution velocity occurred in the middle of the baffle spacing. The vortex diameter was mainly affected by the relative spacing of the conic baffles, whereas the vortex centre was mainly affected by their relative height. Optimisation of the relative height and spacing of the RWP-APCB doubled the flashing light frequency of algal cells and increased the light fraction during the light/dark cycle by a factor of 3.1. The CO2 fixation rate of the algal biomass in the RWP-APCB increased by 18.1-3.8 g/L/d. (C) 2020 Elsevier Ltd. All rights reserved.