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Development of an Algae-based System for CO2 Mitigation
C.L. Crofcheck, M.D. Montross
Department of Biosystems and Agricultural Engineering
Atmospheric carbon dioxide levels have risen since the industrial revolution due to the increase in fossil fuel combustion. These elevated levels of CO2 have been cited as a significant cause of climate change. Hence, there is a well motivated need to find ways of curbing CO2 emissions to the atmosphere, such that even when burning fossil fuels such as coal, the process is closer to being carbon neutral.
One avenue for controlling the CO2 concentration in the atmosphere involves CO2 capture and long term storage underground. Another avenue involves using plant based organisms to utilize CO2 by conversion to biomass. Microalgae, microscopic photosynthetic organisms that grow in salt or fresh water, are fast growing autotrophic plants that require CO2 as a nutrient. Hence, it may be possible to use waste CO2 to grow algae, before the CO2 is released to the atmosphere.
In addition, there is a possibility that the resulting algae can be further processed into valuable co-products, such as biofuels or animal feeds. Such a CO2 mitigation strategy is an attractive option for Kentucky, considering the number of coal fire plants in the Commonwealth.
2010 Project Description
We currently have several potential set-ups for running algae studies. In our environmental chambers we have the ability to run with constant temperature and consistent lighting (16 h days, 8 h nights). This set-up is used for media development, strain selection, and inoculum preparation with cultures up to 400 mL and capacity of 123 flasks. We also have a varying temperature chamber, where the temperature of the cultures is varied using a circulating water bath through the metal base of the chamber. This system has consistent lighting (16 h days, 8 h nights) and uses cultures up to 400 mL with a capacity of up to 27 flasks. We also have a ventilated and constantly stirred system for use with lower flow rates, which also requires stirring. This set-up is also used with simulated flue gas experiments that need to be properly ventilated. This system utilizes cultures up to 400 mL with a capacity of up to 27 flasks. We also have a pilot-scale, continuously harvested system, which is currently under renovation. This system will be able to run a 60 L culture.
We have found a promising strain of Scenedesmus, which has a high growth rate at a pH less than 7. Chlorella vulgaris and Scenedesmus have been tested with varying amounts of sulfuric acid. Small amounts (6 ppm) appear to have little effect on the culture growth. Intermediate amounts (60 ppm) inhibit growth, but the algae appear to have the ability to recover. Higher amounts (90 ppm) will kill the culture. The influence of strain selection and media components are also currently under way.