Development of a Continuous Flow Ultrasonic Microalgae Harvesting System
Anthony J. Marchese, Ph.D.
Department of Mechanical Engineering
Colorado State University
Fort Collins, CO 80523-1374
Because of its potential productivity in comparison to any other oil producing, biological feedstock, phototrophic microalgae are arguably the only biofuel feedstock that can hypothetically achieve production at a scale commensurate with global liquid fuel needs. However, numerous technical and environmental challenges must be overcome to realize an economically viable algal biofuels industry. Harvesting and dewatering of microalgae at scale, in particular, is a critical challenge that must be addressed. Because algae are typically cultivated at highly diluted concentrations, algae dewatering represents the most substantial energy sink in the entire microalgae-to-biofuels value chain. Current technologies used for microalgae dewatering such as the decanter-bowl centrifuge have energy requirements on the order of 10 kWh/m3. Accordingly, the development and demonstration of a scalable, low-energy, continuous-flow dewatering system represents a critical need for the nascent algal biofuels industry.
Ultrasonic standing waves have previously been demonstrated as means to manipulate cells in suspension within a liquid media. This technology has already been exploited for concentrating various biological cells at relatively small batch volumes and/or low throughput of less than 1 L/hr. Typically, these designs are operated in batch or semicontinuous mode, wherein the flow is interrupted and the cells are subsequently harvested. These batch techniques are not well-suited for scaling to the throughput levels required for harvesting microalgae from the large scale cultivation operations necessary for a viable algal biofuels industry. In this research, a combined experimental, modeling and acoustic property characterization study is performed with the ultimate goal of developing a scalable, novel continuous flow ultrasonically enhanced inclined settler microalgae harvesting system.
The specific aims of this work are as follows: 1) gain better understanding of the acoustic radiation forces and particle drag forces in the context of a laminar flow device, 2) study the sensitivity of the acoustic radiation force to different microalgae strains, growth conditions and neutral lipid accumulation, 3) develop a finite element model to accurately characterize the particle forces for different harvester configurations and accurately predict dewatering efficiency, 4) design and build a novel inclined acoustic settler by using acoustically transparent membranes to increase the settling area, and 5) design and build an optimized, scalable ultrasonic inclined solution to process 15 L/hr with a specific energy consumption of 1.5 kWh/m3.
To achieve these goals, the following specific tasks will be accomplished:
- Determine the acoustic response of algal cells in the presence of the ultrasonic standing wave.
- Quantify the speed of sound, density and acoustic contrast factor of multiple microalgae strains at various growth stages and carbohydrate/protein/lipid composition.
- Develop a finite element analysis coupling the acoustic radiation force with the particle drag and multiphase settling.
- Assemble a laboratory scale acoustically enhanced inclined settler for experimental validation of the finite element model.
- Identify the resonant modes of the device, maximize transmission through the acoustic transparent membranes and develop and algorithm to track the optimal frequency.
- Design a new acoustic harvesting device by optimizing the balance between drag and acoustic forces and perform experiments to determine separation efficiency and power consumption.
Anthony Marchese, PI
Esteban Hincapie, Grad Student
Last Updated: March 18, 2014