Enhancement of vertical mixing in an open raceway pond by installing internal structures

Abstract

Microalgae has recently getting attentions as an alternative energy source and mass production of microalgae is an important issue. Open raceway pond is a most widely used system for microalgae mass cultivation. Light is an essential element in the growth of microalgae. However, the deeper the medium, the weaker the light intensity because of light attenuation by water and microalgae. This limits the depth of the pond and the concentration of the cells in the culture fluid, leading to a decrease in productivity of the whole pond. To prevent this problem, vertical mixing should be promoted in an open raceway pond to better expose microalgae to light. In this study, internal structures were installed to improve vertical mixing in an open raceway pond and to expose more microalgae to sunlight. Numerical simulation of fluid flow was carried out for the flow in an open raceway pond with installed internal structures by computational fluid dynamic (CFD) software, ANSYS CFX 18. In the raceway pond with proposed internal structure, generation of vertical flow was enhanced compared to the conventional ORP. Flow velocity in lab-scale ORP was experimentally measured to demonstrate CFD simulation model. Experimental validation by cultivation was carried out in a laboratory scale open raceway pond. and productivity was doubled when internal structure was installed. This strategy with internal structure will increase microalgae productivity in an open raceway pond.