Algal Biofuel Production
Algae offer a promising alternative to terrestrially grown vascular plants as a future source of biofuel (feedstock)
Large-scale biofuel production may require the use of algae instead of land plants:
The alternative energy industry is poised for rapid global growth as attempts to reduce greenhouse gas emissions and dependence on nonrenewable fossil fuels gain traction. These efforts will be particularly intense in the transportation sector, where alternatives for car, truck, train, marine, and aviation fuels may still be decades away. Companies are therefore investing substantially in the conversion of plant products into renewable biofuels. The early diesel engine that inventor Rudolf Diesel demonstrated at the 1900 World’s Fair was powered by pure peanut oil, and it was soon discovered that plant oils can be modified to create better-performing fuels using simple chemical reactions (transesterification) that transform them into biodiesel. Diesel fuel already has a dominant position in the refined petroleum market, even in countries where standard gasoline is the primary liquid fuel, and diesel-powered vehicles dominate commerce and transportation worldwide.
Although conventional biofuel production relies primarily on land plants as a feedstock, many researchers believe that biofuel production on the scale needed to compete with petroleum-based fuels on the open market will require the use of microscopic algae, which grow abundantly and naturally in the world’s surface waters and can be converted into multiple kinds of biofuel. Algae have the potential to produce sufficient quantities of biofuel to satisfy the world’s growing energy demands, even considering predicted limitations on the availability of land and water resources.
Algae require less water and can produce more fuel than land plants:
Algae are tiny, plantlike organisms that include the green alga Pediastrum . The algae used in biofuel production are freshwater algae, comprising both prokaryotic and eukaryotic species, that grow naturally in every freshwater creek, river, pond, lake, and reservoir on the Earth’s surface. Algae are also aquatic biomass production systems that have both a higher fuel yield potential and lower water demand than terrestrial plants, and they generate cellular products such as oils, starch, protein, and other marketable compounds. Like land plants, microalgae derive their energy from the biochemical process of photosynthesis, which captures the sun’s radiant energy and converts atmospheric carbon dioxide (CO2) into new cellular biomass. When measured in standard calorie units, the energy content of algae per unit weight does not differ significantly from that of land plants. In addition, although there can be considerable variation in their cellular oil content, all species of algae contain oil that can be extracted for use in biofuel production. To date, more than $1 billion in private sector funding has been committed to the development of algae-based fuels.
Algae can be used to produce a variety of renewable energy resources:
The idea of using algae as a feedstock for biofuel production dates back at least 50 years, to when William J. Oswald and Clarence G. Golueke first proposed the use of “raceway ponds” to cultivate large quantities of algal biomass for fermentation to create methane gas.In such ponds, growing algae are moved along with paddles and then removed at the downstream end. Soon after the proposed use of raceway ponds, research in algae-derived bioenergy focused on the production of liquid fuels that can be combusted directly in standard internal combustion and jet engines, and large oil companies and research institutions have recently joined forces in commercial ventures to produce biodiesel from algae. However, algae can also be used to produce other renewable energy products, such as biohydrogen, hydrocarbons, and bioethanol; in addition, as noted above, the algal biomass itself can be processed to generate biogas.
Alternatively, dried algae can be combusted directly, much like the burning of crop residues, wood, coal, or peat. This use of algae is important because the direct combustion of plant biomass is a sector of bioenergy already in development that takes advantage of existing commodity supply chains. Just like any energy commodity that can used for direct combustion, however, algal biomass would need to consistently meet several key criteria with respect to its energy, moisture, and undesirable pollutant content.
Algae offer numerous significant benefits relative to their soil-grown counterparts:
- Algal cells can exhibit extremely rapid growth rates, doubling one to three times per day, and they can be grown abundantly in waters of widely varying chemical composition.
- Algal cells can synthesize and accumulate large quantities of bioproducts (e.g., oil), that can be harvested and marketed to offset the costs of biofuel production.
- Cultivating algae rather than land plants, such as corn, for bioenergy could reduce the diversion of agricultural crops away from vitally needed food production.
- The land “footprint” needed to produce a given amount of bioenergy is much smaller for algae than for terrestrial biofuel crops.
- Algae can be grown using effluents from domestic wastewater treatment plants and other sources of nontoxic liquid waste, which provide an abundant source of water and mineral nutrients that are required for algal growth.
- If grown in wastewater streams, the water “footprint” needed to produce a given amount of bioenergy is much smaller for algae than for terrestrial biofuel crops.
- Algae can provide an important ecosystem service by removing nitrogen, phosphorus, and other contaminants from wastewater feeds.
- Algae can also be used to remove carbon dioxide from high-CO2 gas streams, such as flue gases and flaring gases, that can be piped to algal biofuel production facilities from nearby energy generation plants.
- Algal biomass yields can be optimally maintained by modifying harvesting rates.
- The ability of algae to grow continuously in many climates may help reduce the strong seasonality of biomass yields currently seen with terrestrial biofuel crops.