Flat Plate Airlift Loop Photobioreactor For Microalgae Growth

As the third generation biofuels, microalgae energy is a frontier research topic in the new energy field in the world. The development of photobioreactor for highly density of microalgae growth is a hot and difficult issue currently. In this paper, a novel flat plate airlift loop photobioreactor was developed for microalgae growth, and the flashing light characteristics and fluid dynamic characteristics effects on microal-gae autotrophic growth were studied.Nannochloropsis sp. was chosen as the training algal species in this paper. The optimal air flow rate of0.5L·min-1per liter of culture was obtained through the venti-lation experiment in the flat plate airlift photobioreactor. The attenuation formula which was I=I0·e-(0.4x-0.021)L of microalgae fitting the Lambert-Beer formula was obtained through the light attenuation experiment. The specific growth rate of microalgae during exponential growth time increased with the increased of the light intensity in the range of35μmol·m-2·s-1and95μmol·m-2·s-1,whilst the increase de-gree declined gradually through the experiment of light intensity on microalgae.The flow field in the reactors was simulated through the Fluent fluid numerical simulation software, and the results of gas holdup and liquid were verified by expe-riment. The influence of inner diversion plate length, diversion plate distance and loading liquid level height on flow field in the reactor were studied, and the optimal reactor type was selected which the diversion plate length was25cm, the diversion plate distance was20cm,the liquid level height was35cm. The overall gas holdup increased and the diversion effect was more significant in the rising area with the transverse cross baffles were built in the original reactor. A turbulent flow field with many large eddies that clockwise vortices alternated with anticlockwise vortices was formed in the airlift procedure, which improved gas-liquid mixing and nutrients mass transfer. The horizontal flow velocity of microalgae culture increased to15-22times and light-dark cycle period markedly reduced to1/19compared to those in the photo-bioreactor without cross-diversion transverse baffles. The high-frequence flashing light effect improved microalgae growth and increased biomass yield by25%.The growth curves of microalgae in the reactors were simulated. The microalgae growth dynamics under a constant light source was studied. The growth curve func-tion of microalgae in the reactors has favorable agreement with the Logistic equation, thus laid a basis for the development of industrial photobioreactor for microalgae growth.