Microalgae Potential - AWMA

28 em march 2015 awma.org

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Microalgae Potentialfor Carbon Utilization

Microscopic algae this page: ©iStock.com/annedde; page right: ©iStock.com/NNehring; page 30: Paweł Burgiel/iStock/Thinkstock

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by Worrarat Thiansathit and Tim Keener

Worrarat Thiansathit is a Ph.D. candidate and Tim Keener is a professor, both in the Department of Biomedical, Chemical, and Environmental Engineering at the University of Cincinnati, Ohio. E-mail: [email protected].

A brief overview ofthe development of microalgae production for renewable energy.

Climate change has been a growing global concern for the past several decades. A recent Intergovernmental Panel on Climate Change (IPCC) report indicated increases

in the atmospheric concentration of the greenhouse gases (GHGs) carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) over pre-Indus-trial levels of 40%, 250%, and 20% respectively. Annual average worldwide CO2 emissions from fossil fuel combustion and cement production in 2002–2011 were 8.3 Gt of C12, which is equivalent to 30.4 Gt of CO2 with an average growth rate of 3.2%/yr -1.1 CO2 emissions from energy consump-tion continue to rise. If the trend continues in the same trajectory, energy use will increase by more than two-thirds (based on 2011 levels) by 2050; an average global temperature will rise approximately 6°C in the long term (by 2100).2,3 Low-carbon energy technologies are required to signifi cantly reduce CO2 emissions. Carbon capture, utilization, and storage is one of the important measures to curb global CO2 emission.

Carbon Capture, Utilization, and StorageThe term carbon capture and storage (CCS) is widely recognized as referring to the technology to reduce carbon emission by capturing CO2

from major CO2 emission point sources, such as power plants and industrial facilities, compressing and transferring, and then injecting into geo-logical formation to permanently store it deep underground.4,5 CCS evolved to carbon capture, utilization, and storage (CCUS) in 2012 by the U.S. Department of Energy to strategically drive the research and development to economically utilize CO2 for commercial processes.4 Accord-ing to the 2012 United States Carbon Utilization and Storage Atlas—Fourth Edition (Atlas IV), there are at least 2,400 Gt of possible CO2 storage resources in the United States. Current estima-tions of CO2 emissions from power plants and industrial sources are 33% and 22%, respectively; the application of CCUS technologies at these facilities will greatly benefi t the U.S. environment



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and economy in both preventing CO2 release to the atmosphere and utilizing capture CO2 in the industrial processes.5

CO2 UtilizationCO2 utilization has been introduced as a possible alternative and/or complement to the geological storage of CO2 that could increase the economic value for captured CO2. Current estimates of CO2 sold annually for commercial application are 80–120 Mt.2 Example applications include use as chemical solvents, soft drinks carbonation, and fer-tilizer manufacture. Tertiary recovery (or enhanced oil recovery, EOR) is largest CO2 consumption industry, mostly from natural sources. EOR tech-niques can ultimately increase 30–60% more pro-duction than the reservoir original oil. Gas-injection EOR currently accounts for nearly 60% of EOR production in the United States.6

As of 2014, there were 113 CO2 EOR projects in the United States, injecting 3.1 billion cubic feet per day (Bcfd) or 60 Mt per year of natural and industrial CO2 for EOR. The EOR-associated crude oil production was 282,000 barrels per day in 2012. However, the growth of CO2 EOR oil pro-duction has been limited in the past few years due to restrictions in accessibility to affordable supplies of CO2.7 The current cost of utilizing captured CO2 is 5–10 times higher than naturally occur-ring CO2 from underground reservoirs.8 Other emerging applications, such as plastics production or enhanced algae cultivation for chemicals and fuels, are still in the developmental stages.2

Microalgae ProductionIn the past decade, there has been increased interest in the development of microalgae pro-duction for renewable energy supply. Microalgae are photosynthetic microorganisms that can grow rapidly. With abundant solar energy, during pho-tosynthetic activities, microalgae consume CO2 to reproduce their cells and store energy in the form of oils, carbohydrates, and proteins. Advantages of microalgae biofuels are greater production yields per land area compared with terrestrial crops, such as corn and soybean. Microalgae production does not require arable land, hence it does not compete with food crops.

Algae biomass production is estimated to produce 2–10 times more biomass per unit area than the best terrestrial systems. The main reason for this is greater photosynthetic efficiency. Under ideal growth conditions, algae use most of their energy in cell division allowing for rapid biomass accumu-lation.9 Approximately 1.8 tons of CO2 is required to produce 1 ton of algae. By contrast, some esti-mates have shown that 0.63 Gt of CO2 is required to produce 1 million barrels of gasoline.10

Pilot ProjectA pilot renewable energy project has been designed and constructed at the University of Cincinnati to study the production of microalgae utilizing the CO2 from biogas content. The biogas is derived from an anaerobic digester designed to convert food wastes from the University of Cincinnati’s caf-eterias into usable energy. The microalgae produc-tion system was designed as closed system using continuous flow stirred tank reactor (CFSTR) with bubble column to transfer CO2 into growth media. The system will demonstrate the economical setup

With abundant

solar energy,

during

photosynthetic

activities,

microalgae

consume CO2

to reproduce

their cells and

store energy in

the form of oils,

carbohydrates,

and proteins.



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of microalgae production in pilot scale, as shown in Figure 1. This setup can also be used with other CO2 source such as captured CO2 or can be constructed with any CO2 source with small area requirement.

ConclusionIn 2013, biofuels such as ethanol and biodiesels contributed to only about 5% of total energy used by the U.S. transportation sector.11 Large-scale

production of microalgae as a source of biofuel will potentially be another technology utilized car-bon captured from CCUS. However, many chal-lenges remain in the research and development of microalgae production, including identifying fast growing and tolerance strains, enhancing photo-synthetic effi ciency, contamination control, recycle growth media and nutrients, lowering harvesting, and conversion cost. em

Figure 1. Pilot-scale microalgae system at the University of Cincinnati (left) biogas storage and bubble column (right).

References1. Climate Change 2013: The Physical Science Basis; Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental

Panel on Climate Change, 2013.2. Technology Roadmap Carbon Capture and Storage; International Energy Agency, 2013. See http://www.iea.org/publications/freepublications/

publication/technologyroadmapcarboncaptureandstorage.pdf.3. Schaeffer, M; van Vuuren, D. Evaluation of IEA ETP 2012 emission scenarios; Climate Analytics Working Paper 2012-1. See http://www.

climateanalytics.org/sites/default/fi les/attachments/publications/Climate-projections%20evaluation%20of%20IEA%20ETP%202012%20emission%20scenarios%20-%20Climate%20Analytics%20Working%20Paper%202012-1%2020120507.pdf.

4. Adding “Utilization” to Carbon Capture and Storage; U.S. Department of Energy, 2014. See http://energy.gov/articles/adding-utilization-carbon-capture-and-storage.

5. Carbon Utilization and Storage Atlas (Atlas IV); Offi ce of Fossil Energy, 2012.6. Enhance Oil Recovery; Offi ce of Fossil Energy. See http://energy.gov/fe/science-innovation/oil-gas-research/enhanced-oil-recovery.7. Near-Term Projections of CO2 Utilization for Enhanced Oil Recovery; DOE/NETL-2014/1648; U.S. Department of Energy, 2014.8. Deich, N. The Good, The Bad, and the Ugly of CO2 Utilization. See http://theenergycollective.com/noahdeich/2155311/good-bad-and-ugly-

co2-utilization.9. Sayre, R. Microalgae: The Potential for Carbon Capture; BioScience 2010, 12 (60), 9.10. Algae Biofuel: A Category of its Own; Algae Biomass Organization, 2014. See http://www.algaebiomass.org/blog/7483/algae-biofuel-a-

category-of-its-own/.11. Use of Energy in the United States; U.S. Energy Information Administration, 2014. See http://www.eia.gov/EnergyExplained/?page=us_

energy_transportation.



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Microalgae Potential - AWMA