Biodiesel from Algae Oil

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Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.

By Allison Vela-Mendoza

Algae are eukaryotes and conduct photosynthesis within membrane-bound organelles called chloroplasts. Chloroplasts contain circular DNA that is similar in structure to cyanobacteria. Algae are prominent in bodies of water, common in terrestrial environments.

Algal organisms are photosynthetic macro-algae or microalgae growing in aquatic environments. Macro-algae or “seaweeds” are multicellular plants growing in salt or fresh water. They are classified into three broad groups based on their pigmentation: (1) brown seaweed (Phaeophyceae), (2) red seaweed (Rhodophyceae) and (3) green seaweed (Chlorophyceae) (Demirbas & Demirbas, 2010).

Microalgae are unicellular photosynthetic microorganisms, living in saline or fresh water environments that convert sunlight, water and carbon dioxide to algal biomass. Microalgae can be used for bioenergy generation (biodiesel, biomethane, biohydrogen). The three most important classes of microalgae in terms of abundance are the diatoms (Bacillariophyceae), the green algae (Chlorophyceae), and the golden algae (Chrysophyceae) (Demirbas & Demirbas, 2010).

Among the eukaryotic, green microalgae of the class Chlorophyceae, those most widely utilized belong to the genera Chlamydomonas, Chlorella, Haematococcus, and Dunaliella. As aquatic relatives of plants, microalgae thrive in aerated, liquid cultures where the cells have sufficient access to light, carbon dioxide, and other nutrients. Algae are primarily grown photoautotrophically; yet, some species are able to survive heterotrophically by degrading organic substances like sugars. Unlike terrestrial plants, microalgae do not require fertile land or irrigation. Because algae consume carbon dioxide, large-scale cultivation can be used to remediate the combustion exhaust of power plants (Rosenberg et al., 2008).

Algae biomass can play an important role in solving the problem between the production of food and that of biofuels in the near future. Microalgae appear to be the only source of renewable biodiesel that is capable of meeting the global demand for transport fuels.

The potential of algae oil as a fuel source

Over 80% of the energy we use comes from three fossil fuels: petroleum, coal, and natural gas. About 98%of carbon emissions result from fossil fuel combustion. About 98% of carbon emissions result from fossil fuel combustion. Reducing the use of fossil fuels would considerably reduce the amount of carbon dioxide and other pollutants produced. This can be achieved by either using less energy altogether or by replacing fossil fuel by renewable fuels. Renewable energy is a promising alternative solution because it is clean and environmentally safe. They also produce lower or negligible levels of greenhouse gases and other pollutants when compared with the fossil energy sources they replace. Algae, like corn, soybeans, sugar cane, wood, and other plants, use photosynthesis to convert solar energy into chemical energy. They store this energy in the form of oils, carbohydrates, and proteins. The plant oil can be converted to biodiesel; hence biodiesel is a form of solar energy. The more efficient a particular plant is at converting that solar energy into chemical energy, the better it is from a biodiesel perspective, and algae are among the most photosynthetically efficient plants on earth.

Biodiesel derived from seed oils, such as rapeseed or soybean produces, 39.5 MJ/kg, while biomass derived from algae yields 41 MJ/kg. Although the lower energy biodiesels based on seed oils are the most common, they have enough energy density to make the, a viable alternative to petroleum diesel (Demirbas & Demirbas, 2010).

The algae used in biodiesel production are usually aquatic unicellular green algae. This type of algae is a photosynthetic eukaryote characterized by high growth rates and high population densities. Under good conditions, green algae can double its biomass in less than 24 hours. Green algae can also have high lipid contents, usually over 50%. This high yield is ideal for intensive agriculture and can be an excellent source for biodiesel production (Demirbas & Demirbas, 2010).

The annual productivity and oil content of algae is far greater than seed crops. Soybean can only produce about 450 l of oil per hectare. Canola can produce 1200 l per hectare, and palm can produce 6000 l. Algae, on the other hand, can yield 90,000 l per hectare (Demirbas & Demirbas, 2010).

Microalgae contain lipids and fatty acids as membrane components, storage products, metabolites and sources of energy. Algae contain anywhere between 2% and 40% of lipids/oils by weight (table 1). Algae can grow anywhere there is enough sunshine. Some algae can grow in saline water. All algae contain proteins, carbohydrates, lipids and nucleic acids in varying proportions. Microalgae can complete an entire growing cycle every few days. Although the percentages may vary, there are types of algae that are comprised up to 40% of their overall fatty acids. Microalgae are very efficient solar energy converters and they can produce a great variety of metabolites (table 2). The culture of algae can yield 30-50% oil. Oil supply is based on claims that 47,000-308,000 l/hectare/year of oil could be produced using algae. Like all plants, algae require large quantities of nitrogen fertilizer and water, plus significant fossil energy inputs for the functioning system. Harvesting the algae from tanks and separating the oil from the algae are difficult and energy intensive processes (Demirbas & Demirbas, 2010).

Manipulation of metabolic pathways can redirect cellular function toward the synthesis of preferred products and even expand the processing capabilities of microalgae (figure 1). For microalgae that are able to survive heterotrophically, exogenous carbon sources offer prefabricated chemical energy, which the cells often store as lipid droplets. Heterotrophically cultivated Chlorella protothecoides as been shown to accumulate as much as 55% of its dry weigh as oil, compared to only 14% in cells grown photoautotrohpically. Another natural mechanism through which microalgae can alter lipid metabolism is the stress response owing to a lack of bioavailable nitrogen. Although nitrogen deficiency appears to inhibit the cell cycle and the production of almost all cellular components, the rate of lipid synthesis remains higher, which leads to the accumulation of oil in starved cells (Rosenberg et al., 2008).

The properties of various fatty esters that comprise biodiesel determine the overall fuel properties of the biodiesel fuel. There is no one strain or species of algae that can be said to be the best in terms of oil yield for biodiesel. But, diatoms and green algae are the most promising. Scenedesmus dimorphus is a unicellular algae in the class Chlorophyceae (green algae). While this is one preferred species for oil yield for biodiesel, one of the problems with Scenedesmus is that it is heavy, and forms thick sediments if not kept in constant agitation. The strain called Dunaliella tertiolecta has oil yield of about 37%. It is a fast growing strain and that means it has a high CO2 rate as well (table 4 shows the yields of various plant oils) (Demirbas & Demirbas, 2010).

Highest-yielding algae

Chlorella is a single-celled green algae belonging to the class of Chlorophyceae. It is spherical in shape, about 2 to 10 μm in diameter, and does not have a flagella. Chlorella has green photosynthetic pigments, chlorophyll-a and chlorophyll-b, in its chloroplast. Using photosynthesis, it multiplies rapidly requiring only carbon dioxide, water, sunlight, and a small amount of minerals to reproduce. Chlorella is believed to be capable in serving as a potential food and energy source because of its photosynthetic efficiency to reach 8% comparable to other highly efficient crops such as sugar cane.

Dunaliella is a unicellular green algae also belonging to the class of Chlorophyceae. It is rod to oval shaped and about 9 to 11 μm in diameter. The organisms are simple to cultivate and do not clump or form chains. Dunalliela tertiolecta is a marine green flagellate with a size of 10 to 12 μm in diameter. This strain is said to have an oil yield of about 37%. D. tertiolecta is a fast growing strain, therefore allowing it to have a high carbon dioxide sequestration rate ( Wikipedia-Dunaliella).

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Introduce the topic of your paper. What microorganisms are of interest? Habitat? Applications for medicine and/or environment?

Section 1

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Section 2

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[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by student of Joan Slonczewski for BIOL 238 Microbiology, 2011, Kenyon College.