An integrated growth kinetics and computational fluid dynamics model for the analysis of algal productivity in open raceway ponds

An integrated growth kinetic, light transfer and computational fluid dynamics (CFD) model was developed to simulate the algal growth in open raceway ponds (ORP). C. vulgaris was used as a model algal strain. The coefficients of the growth kinetics were experimentally determined for the prediction of the growth of C. vulgaris as a function of environmental factors of light intensity, temperature and pH value. Experiments were conducted to grow C. vulgaris in lab-scale ORPs with medium depths of 0.20, 0.25 and 0.30 m to validate the mathematical model. The final measured biomass concentration after the 3-week growth were 0.48, 0.41, and 0.35 g/L for the ORPs with the medium depths of 0.20, 0.25, and 0.30 m, respectively. The predicted algal productivities for a 3-week cultivation were 7.3, 7.4, and 7.5 g/m2/day for depths of 0.20, 0.25, and 0.30 m, respectively, which well agreed with the measured values of 6.8, 7.2 and 7.4 g/m2/day, respectively. The biomass productivity decreased with the increase of growth time due to the increase of cell concentration. The model was further used to analyze the effects of different harvesting strategies on the algal productivity in ORPs. The algal productivity for the 3-week cultivation in the ORP with a 0.2 m depth by harvesting 50% algae at the target 0.2 g/L cell density was 10.5 g/m2/day, which was 43.8% higher than 7.3 g/m2/day for the 3-week cultivation under the same condition without harvesting at a final cell density of 0.48 g/L. The average algal productivity decreased with the increase of harvesting cell density.