Hydrodynamic evaluations in high rate algae pond (HRAP) design

Since open ponds are considered to be a proper means to produce microalgae biomass at large scale, the design of these ponds remains a major issue in this field. Besides light intensity, the hydrodynamic characteristics are critical to obtain high microalgae productivity. Hydrodynamic mixing is required to ensure frequent exposure of algae cells to light, to avoid the settling of algae cells, to homogenize the nutrient distribution and to enhance the utilization of CO2 in the pond. However, the current design of algae ponds lacks visual assessment of hydrodynamic characteristics in the pond, resulting in the appearance of dead zones where the flow is stagnant and in the presence of non-uniform velocity throughout the pond, both of which are still major problems because of their negative impact on algae growth. Therefore, this paper describes these characteristics to support current pond design by using Computational Fluid Dynamic (CFD). In order to simulate the hydrodynamic characteristics of the pond, the variation of velocity, ratio of channel length to width (L/W), and depth of culture were performed and power consumption, dead zone volume and shear stress were evaluated. The results showed that a ratio of L/W higher than 10 yields better performance with respect to velocity uniformity and shear stress. However, power consumption increased, as well. The hydrodynamic flow in the modified pond was simulated, providing better understanding for dead zone volume reduction. To implement this modeling evaluation in the design, an experimental validation is, however, still required. (C) 2012 Elsevier B.V. All rights reserved.