Algae To Soak Up Our Carbon

Well we know that much of the human carbon dioxide (CO2) emissions result from the combustion of fossil fuels for energy production. For instance, in the United States stationary combustion sources, particularly electric utility plants represent 35% of the carbon dioxide emissions from end-use of energy.  

Photosynthesis has long been recognized as a means, to sequester human made CO2. Plants and indeed forests uptake significant amounts of CO2 everyday and it is one of the reasons why we need to replant forests and stop the broad acre clearing around the world. However aquatic microalgae have also been identified as fast growing species whose carbon fixing rates are higher than those of land-based plants by one order of magnitude. 

So the concept which is in the early stages of development is to use the stinking flue gases from coal fired power stations to feed algae farms. In this process, CO2is separated and captured from the exhaust gas stream. The CO2 is then passed through colonies of algae, which use the CO2in photosynthesis, effectively storing the carbon.  

For algae to keep soaking up the CO2 and to maintain high algal production rates, the biomass needs to be harvested each day. If the algae are not harvested, production peaks and then declines as concentrations of algae increase. This is because less light is available to the algae for photosynthesis coupled with a depletion of nutrient levels. 

Harvesting algae daily and using the biomass to sequester CO2 also has the potential to produce useful byproducts.  We know that some microalgae species, such as Chlorella, Spirulina and Dunaliella have commercial values. Biofuels, fertilizers and a host of other products (see here) can be made from the harvested algae.  

It appears that algae farms tethered to fossil-fuelled power stations could in principle sequester much of the carbon they emit. In this case, not only would the products cover the cost of capturing and sequestrating the CO2 but the enterprise would also make a profit. 

A report on a pilot project by the US Department of Energy confirmed that, “The results of this project have verified the potential applicability of using microalgae biofixation to sequester carbon dioxide from flue gas at coal-fired power plants. The results indicate that an algae based system is feasible without the need for technological breakthroughs, but key design criteria need to be further developed, including CO2 mass transfer, algal growth rates, and developing strategies to produce a revenue stream from the harvested algae." 

DOE, SUBTASK 2.3 – CARBON DIOXIDE SEQUESTERING USING MICROALGAL SYSTEMS http://www.osti.gov/bridge/purl.cover.jsp?purl=/882000-St23VC/