(215e) Evaluation and Comparison of the Scale-up Potential for Autotropic and Heterotrophic Algal Oil Production

Authors: 
Kreft, J., University of North Dakota
Seames, W. S., University of North Dakota
Significant research has been completed over the past decade to develop technologies to facilitate the production of algal lipids for use as feedstock for next generation renewable fuel facilities. The interest for microalgae is motivated by the substantial increase in yield per land area compared to oilseed crops reducing the pressure to supplant food crops with energy crops. However, the challenges to produce oil from algae at scales approaching crop oil production facilities have been great. One of those barriers is the need to get photons from sunlight or artificial sources to the growing algae as an energy source. It has recently been proposed that growing the algae heterotropically might overcome this scale-up barrier. The transition to heterotrophic halts the photosynthesis process, and requires an organic carbon source to provide energy, as the heterotrophic strain of microalgae is not able to produce energy compared to the autotrophic which produces an energy source though photosynthesis. Additionally, the transition has been proven to increase the lipid content of the microalgae by replacing the chlorophyll cells produced during photosynthesis. If the strain of microalgae used is non-light dependent it will negate the requirement of industrial scale, clear photo bioreactors or open ponds. Additional chemicals and catalysts will be required for the growth and development of the microalgae strains for the growth media.

In this study, a group of senior chemical engineering students developed preliminary designs and then performed an economic analysis for algal oil production utilizing both autotropic and heterotrophic growth strategies. Both proposed systems utilizes the strain of microalgae Chlorella Vulgaris as the raw material. Chlorella Vulgaris has a lipid content ranging between 15-35 wt%.

The study involved the development of Input/output diagrams, block flow diagrams, and process flow diagrams for compete processes starting from lab algae inoculation through to final lipid oil product purification. Preliminary equipment sizing was performed. The capital costs were estimated using a factored broad cost estimation method based on vendor quotes for the largest equipment and cost chart data for the rest of the equipment. Revenues and operating costs for a 20 year project life were also estimated.

The heterotrophic option will yield a higher lipid content which will generate a larger amount of oil when compared to the autotrophic strain but will require a higher quantity of inputs. The production throughput was comparable to a small scale oilseed production facility. Neither option is currently economically competitive with a commercial soybean oil processing facility. However, the heterotrophic option had significant advantages over the autotropic design. The key barriers to commercialization were identified so that future R&D activities can focus in these areas.