Investigating alakli-tolerant microalgal monocultures and polycultures for industrial cultivation

Abstract

The use of algae to create high value products from the biomass grown is not a novel idea. However, problems with culture stability, productivity, and resource costs have limited the large-scale production of algae. The ability for growth in alkaline conditions allows for stability of the culture's pH and a more efficient capture of atmospheric CO 2. This thesis explores the use of high pH and high alkalinity tolerant algal strains both as monocultures and in polyculture combinations to produce lipids and other high value products. The algae used were a green alga (strain ALgE), a cyanobacterium (blue-green 'alga', strain SLcyaH) and a diatom (strain SLdC) that were obtained from a Soda Lake chain near Spokane, WA. The monocultures, two-member cocultures, and the three-member polyculture were compared for their product spectrum and productivities. While not as productive as monocultures, in every combination, algal polycultures incorporating the diatom SLdC produced similar amounts of lipids (4.23*10 -2 + or - 1.84*10 -2 grams of lipids per liter per day) and biomass (0.357 + or - 3.85*10 -2 grams of biomass per liter per day) as the monoculture of the diatom, while having lower input costs due to the lower amount of silica used in the media. Moreover, because the different organisms produce different lipids, the choice of strain or strain combination has the potential to affect the type of lipids produced. The diatom for instance produces high value polyunsaturated lipids while the green alga produces lipids more suitable for use in fuels, biodiesel, and foam production. The cyanobacterium does not produce many lipids but rather carbohydrates (sugars, starches, etc.). hence, the potential benefits of using polycultures are their culture stability and ability to affect lipid speciation with little to no loss in productivity.