PI: Myeongsub (Mike) Kim, Ph.D.Project Summary: For global energy sustainability, cutting-edge biodiesel production technologies have been extensively developed as scavenging methods of nonconventional energy. Despite its importance, the current extremely low-efficiency of microalgae cultivation and harvesting makes this energy resource expensive and non-competitive. The goal of this proposal is to develop an innovative scalable methodology that enables enhanced microalgae cultivation and harvesting for large-scale biodiesel production. The increased growth rate of microalgae permits better cultivation at higher efficiency over the conventional technologies while the higher separation efficiency of solid microalgae from solvents guarantees cost-effective lipid harvesting. In pursuit of this goal, the objectives of this Janke research are to design and fabricate a proof-of-concept microreactor at a smaller scale and test its performance and feasibility for scaling-up of the system. For the high-efficient cultivation of microalgae, the fundamentals of microfluidics will be employed. That is, microbubbles with high CO2 content, therefore having extreme surface-to-volume ratios, will be fed to the algae suspension for the fast algae growth. For the increased microalgae harvesting, the nature of fluid mechanics will play a role: a combination of centrifugal rotation and Dean flow will determine the optimal separation of microalgae from the culturing suspension. The key questions that will be tackled include 1) how is the rate of microalgae cultivation sensitive to the size of microbubbles and input flow conditions?; 2) What type of flow between stationary and dynamic is the best to grow microalgae faster?; 3) What is the optimal curvature radius and angle to reach the critical Dean force?; and 4) How does the separation efficiency depend on the geometry of the microreactor and input flow conditions? To answer these questions, the project team will first create a series of microscale CO2 bubbles in a uniquely-designed microreactor and characterize CO2 dissolution rates in stagnant or flowing conditions. The effect of incident light intensity, nutrients (nitrogen, phosphorus, iron), size of bubbles, and a number of bubbles on the growth rate will be tested. Next, the team will quantify the separation efficiency of microalgae from the suspension in microreactors under the centrifugal and Dean forces. By changing curvature angles and geometries, the microreactors will have the exclusive flow nature that drives algal cell segregation when the centrifugal and Dean forces are dominant. Lastly, the project team will test the feasibility of scaling-up of the small-scale system to the massive production of biodiesel lipid through parallelization of multiple microreactors. By completing these research tasks along with quantitative analyses, this timely project responds to an urgent and strong demand to advance efficient cutting-edge technologies for renewable biofuel production. In addition, the project will fill the current technology gap by providing a fundamental understanding of the physics behind enhancement mechanisms of cultivation and harvesting approaches. The core knowledge and techniques gained from this research will ultimately help us build long-term strategies for large-scale production of biodiesel. Using preliminary data obtained in the Janke project, submissions of grant proposals to various agencies are anticipated as follow-up efforts during and after this project.
