Washington State University (WSU) researchers have developed a unique biofilm reactor that recycles gasses and uses less water and lower light than typical reactors. The new reactor grows algae more efficiently—in days instead of weeks—and makes the algae more viable for several industries, including biofuels.
The main fatty acids produced were C18:1, C18:2 and C16:0, and there was a low saturated fatty acid content of 23.37%. The biofilm growth mode affected algae metabolism such that the cell met its CO2 requirements internally (i.e., no exogenous CO2) and a high oil yield was obtained without nitrogen starvation. A paper on the work is published in the journal Algal Research.
Microalgal biomass cultivation is commonly done using raceway ponds in planktonic growth mode. Biofilm reactors provide an alternative technology to the existing planktonic algae production because biofilms in these reactors can achieve high algal densities with low volumes of culture medium. The biomass production capacities reported so far for biofilm reactors are in the range of 2 to 6 g m−2 d−1. The dry weight of the algal biofilms fluctuates between 100 and 200 g dry weight kg−1 wet biofilm. Furthermore, microalgal bio-film production reduces harvesting costs with more efficient water utilization and a smaller areal footprint. However, to increase the general use of biofilm reactors for algae production, further biofilm reactor development and a better understanding of microalgal biofilm processes are needed.
… In a biofilm reactor, microalgae grow on a surface while receiving nutrients and light. The light is usually delivered from the top of the biofilm, whereas nutrients are delivered either from the top or from the bottom.—Rincon et al.
Researchers would like to produce algae efficiently because of its potential environmental benefits. Its use in industry hasn’t caught on primarily because it requires a lot of time and water to grow. Generally, large ponds are required, and harvesting is labor intensive. Researchers have begun developing biofilm reactors to grow the algae, but the reactors aren’t efficient because of pH or temperature variations or a limited supply of carbon dioxide gas.
The WSU team set out to develop a mixotrophic algal biofilm reactor using glycerol and urea as carbon and nitrogen sources.The system allows the algae simultaneously to do photosynthesis like a plant while also “eating” carbon and respiring like an animal, said Haluk Beyenal, professor in the Gene and Linda Voiland School of Chemical Engineering and Bioengineering. The system recycles carbon dioxide and oxygen.
The researchers have filed a patent application on the technology and are working to optimize the process.
Sandra Milena Rincon, Hernan Mauricio Romero, Wrya Moh Aframehr, Haluk Beyenal (2017) “Biomass production in Chlorella vulgaris biofilm cultivated under mixotrophic growth conditions,” Algal Research, Volume 26, Pages 153-160 doi: 10.1016/j.algal.2017.07.014