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The following traits make certain vascular plants good for potential development as biofuels, but it is important to note that they have overlap with traits known to contribute to invasiveness (indicated with a *). The decision to use plants as biofuels should carefully consider the pros and cons of each candidate species and anticipate any potential for the threat it poses as an invasive species.
*C4 photosynthesis. This refers to the use of a 4-carbon rather than a 3-carbon compound in photosynthesis. C4 plants are better adapted to arid conditions because they use water more efficiently.
*Long canopy duration
*No known pests or diseases
*Rapid growth in spring (to outcompete weeds)
*Partitions nutrients to below-ground components in the fall
The United States Geological Survey (USGS) is developing renewable energy technology along with other public and private agencies and institutions. Scientists in the USGS Microbiology Program are working on several projects that use microorganisms for biofuel technology development, such as bacterial formation of nano-scaled materials, biogenic methane generation from coal and other geopolymers, microbial fuel cells, and production of nanomaterials of Group 15 and 16 elements.
Grain harvesting for biomass energy. [Photo: US Department of Energy]
Biofuels are a form of renewable energy derived from organic material, or biomass. Biofuels are also referred to as biofuel energy, biomass energy, bioenergy, biogas, or biodiesel. There are many sources of biofuels ranging in scale from microbes to traditional crops such as corn
, giant Miscanthus
(Miscanthus x giganteus)
, and rapeseed
, to name a few. Plant crops grown on land as well as in water are primary producers of biomass for the production of biofuel, and in the United States corn ethanol is the most common. Other sources of biofuel energy include agricultural and forestry residues which are the unharvested and traditionally undesirable parts of a field or forest, such as corn stalks or the limbs and tops of trees left on the ground.
Advantages: widespread distribution and diverse use
As a renewable energy resource, biofuels are advantageous because their potential for production is more evenly distributed over the Earth's surface than that of other non-renewable energy sources. Plant or animal matter used as biofuels can be produced most places across the Earth's surface, unlike petroleum, which can only be found in pockets deep within the Earth. Biofuels also have diverse uses such as transportation fuels, electricity generation, and heating, making them flexible energy sources. Like other renewables, biofuels also provide a means toward energy independence because they can be produced within the country's boundaries.
Disadvantages: land competition, energy inputs, and water use
The use and production of biofuel, especially corn ethanol, is controversial. The energy inputs (fertilizers used, harvesting and processing with machinery, greenhouse gases emitted) versus the energy outputs, and the food or fuel debate, are at the forefront of the controversy. The food or fuel debate is centered around the question of whether or not we should be using crops as fuel rather than using them for food purposes. An example of this is corn, which is used not only for human food products, but also feed for livestock. If enough of the corn produced was used for fuel purposes, theoretically the price of food and feed could increase. In addition, biofuel power plants use water resources and may degrade water quality through increased temperature and pollutants.
Microorganisms as Biofuels
Biofuels can be derived from more sources than animal and vascular plant residues or crops. Microorganisms, especially algae, are playing a growing role in the biofuel industry.
Microbial fuel cells (MFCs) use bacteria or cultures of several species of bacteria as catalysts to oxidize matter, which in turn creates an electric current. Many types and combinations of bacteria microorganism catalysts, and electrodes can be used in MFCs. MFCs can range in size and complexity, and new technologies are constantly emerging in this growing field as it gets closer to commercialization.
Algae is another biofuel source currently in the research and development stages. It can be cultivated nearly anywhere, in containers and water bodies, as long as there is a source of sunlight and a source of water for the algae to use in photosynthesis. Algae can be cultivated to produce ethanol, methanol, biodiesel, or hydrogen through different processes.
Logan, B..E. and J.M. Regan. 2006. Electricity-producing bacterial communities in microbial fuel cells. Trends in Microbiology: 14(12): 512-518.
World Intellectual Property Organization
Biomass power plants emit nitrogen oxides and a small amount of sulfur dioxide. The amounts emitted depend on the type of biomass that is burned and the type of generator used. Although the burning of biomass also produces carbon dioxide, the primary greenhouse gas, it is considered to be part of the natural carbon cycle of the earth. The plants take up carbon dioxide from the air while they are growing and then return it to the air when they are burned, thereby causing no net increase.
Biomass contains much less sulfur and nitrogen than coal; therefore, when biomass is co-fired with coal, sulfur dioxide and nitrogen oxides emissions are lower than when coal is burned alone. When the role of renewable biomass in the carbon cycle is considered, the carbon dioxide emissions that result from co-firing biomass with coal are lower than those from burning coal alone.
Water Resource Use
Biomass power plants require the use of water, because the boilers burning the biomass need water for steam production and for cooling. If this water is used over and over again, the amount of water needed is reduced. Whenever any type of power plant removes water from a lake or river, fish and other aquatic life can be killed, which then affects those animals and people that depend on these aquatic resources.
As is the case with fossil fuel power plants, biomass power plants have pollutant build-up in the water used in the boiler and cooling system. The water used for cooling is much warmer when it is returned to the lake or river than when it was removed. Pollutants in the water and the higher temperature of the water can harm fish and plants in the lake or river where the power plant water is discharged. This discharge usually requires a permit and is monitored. For more information about these regulations, visit EPA's Office of Water Web site. In general, crops grown for biomass fuel require fewer pesticides and fertilizers than crops grown for food, which means that less pesticide and fertilizer runoff will reach local streams and ponds than if food crops are grown.
Solid Waste Generation
The burning of biomass in boilers creates a solid waste called ash that must be disposed of properly. However, the ash from biomass normally contains extremely low levels of hazardous elements.
Land Resource Use
Generating electricity from biomass can affect land resources in different ways. Biomass power plants, much like fossil fuel power plants, require large areas of land for equipment and fuel storage. If these biomass plants burn a waste source such as construction wood waste or agricultural waste, they can provide a benefit by freeing areas of land that might otherwise have been used for landfills or waste piles. Biomass grown for fuel purposes requires large areas of land and, over time, can deplete the soil of nutrients. Fuel crops must be managed so that they stabilize the soil, reduce erosion, provide wildlife habitat, and serve recreational purposes.
Arundo donax as a Biofuel
A flower head of Arundo donax. Photo credit: USDA.
Giant reed (
) is a tall perennial cane that grows in damp soils; it is known by many names including Carrizo, Spanish cane, wild cane giant reed and Arundo. It is native to eastern Asia but can grow in California, the Mediterrean and Caribbean.Arundo can grow up to 10 meters, and consumes large amounts of water.Arundo grows in dense groups crowding out other native plants.Arundo is a potential second generation biofuel, because of its fast growth, it is essentially sterile, and can potentially produce more fuel than first generation biofuels.
The Greenhouse Effect
[Image: NOAA Paleoclimatology]
Gases in the Earth's atmosphere that trap heat are referred to as "greenhouse gases". Some of these greenhouse gases occur naturally in the atmosphere but are augmented by inputs from human activities. Others are unnatural compounds that are only created and emitted into the atmosphere from human activities. The principal greenhouse gases released into the atmosphere from human activities are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases. The U.S. Environmental Protection Agency inventories greenhouse gas emissions and sinks and provides information about greenhouse gases and climate change.
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