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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.
2011 Project Description
We have completed a temperature study to determine the relationship between the culture temperature and the expected growth rate of the algae. In addition, a model was developed to determine the expected temperature of the photobioreactor tubes in the greenhouse based on the outside temperature and solar radiation, so that energy management strategies could be used to optimize the growth of the algae.
We have also completed studies looking at the effect of various coal fire ashes on the growth of algae. Interestingly, a small amount of ash can actually increase the growth of the algae by supplying additional carbon.
In addition to the studies done last year to show the influence of sulfuric acid on the growth of algae, this year we have added a buffer (NaHCO3) showing at what levels the system needs to be buffered in order to maintain optimum pH with the addition of the highly acidic flue gas.
We have also continued our media studies and taken a closer look at the need for micronutrients, vitamins, and EDTA.
Today we have a better media formula then we started with. We have been able to increase the growth rate by adding micronutrients and save on media cost by not adding ingredients that are not necessary (vitamin B and EDTA).
We also have a model that will allow for us to make decisions about what kinds of heating and heat recovery will need to be done to operate the algae greenhouse in such a manner that the temperature of the PBR tubes doesn't adversely affect the growth.
Cassidy, K. 2011. Evaluating Algal Growth at Different Temperatures, M.S. Thesis, University of Kentucky.