Biomass (ecology)



Biomass refers to living and recently dead biological material that can be used as fuel or for industrial production. Most commonly, biomass refers to plant matter grown for use as biofuel, but it also includes plant or animal matter used for production of fibres, chemicals or heat. Biomass may also include biodegradable wastes that can be burnt as fuel. It excludes organic material which has been transformed by geological processes into substances such as coal or petroleum.

Biomass is grown from several plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sugarcane and oil palm (palm oil). The particular plant used is usually not very important to the end products, but it does affect the processing of the raw material. Production of biomass is a growing industry as interest in sustainable fuel sources is growing.

Although fossil fuels have their origin in ancient biomass, they are not considered biomass by the generally accepted definition because they contain carbon that has been "out" of the carbon cycle for a very long time. Their combustion therefore disturbs the carbon dioxide content in the atmosphere.

Plastics from biomass, like some recently developed to dissolve in seawater, are made the same way as petroleum-based plastics, are actually cheaper to manufacture and meet or exceed most performance standards. But they lack the same water resistance or longevity as conventional plastics.

Processing and uses
Biomass which is not simply burned as fuel may be processed in other ways such as corn.

Low tech processes include: More high-tech processes are: Burning biomass, or the fuel products produced from it, may be used for heat or electricity production.
 * composting (to make soil conditioners and fertilizers)
 * anaerobic digestion (decaying biomass to produce methane gas and sludge as a fertilizer)
 * fermentation and distillation (both produce ethyl alcohol)
 * Pyrolysis (heating organic wastes in the absence of air to produce gas and char. Both are combustible.)
 * Hydrogasification (produces methane and ethane)
 * Hydrogenation (converts biomass to oil using carbon monoxide and steam under high pressures and temperatures)
 * Destructive distillation (produces methyl alcohol from high cellulose organic wastes).
 * Acid hydrolysis (treatment of wood wastes to produce sugars, which can be distilled)

Other uses of biomass, besides fuel and compost include:
 * Building materials
 * Biodegradable plastics and paper (using cellulose fibres)

Environmental impact
Biomass is part of the carbon cycle. Carbon from the atmosphere is converted into biological matter by photosynthesis. On death or combustion the carbon goes back into the atmosphere as carbon dioxide (CO2). This happens over a relatively short timescale and plant matter used as a fuel can be constantly replaced by planting for new growth. Therefore a reasonably stable level of atmospheric carbon results from its use as a fuel. It is commonly accepted that the amount of carbon stored in dry wood is approximately 50% by weight.

Though biomass is a renewable fuel, and is sometimes called a "carbon neutral" fuel, its use can still contribute to global warming. This happens when the natural carbon equilibrium is disturbed; for example by deforestation or urbanization of green sites. When biomass is used as a fuel, as a replacement for fossil fuels, it still puts the same amount of CO2 into the atmosphere. However, when biomass is used for energy production it is widely considered carbon neutral, or a net reducer of greenhouse gasses because of the offset of methane that would have otherwise entered the atmosphere. The carbon in biomass material, which makes up approximately fifty percent of its dry-matter content, is already part of the atmospheric carbon cycle. Biomass absorbs CO2 from the atmosphere during its growing lifetime. After its life, the carbon in biomass recycles to the atmosphere as a mixture of CO2 and methane (CH4), depending on the ultimate fate of the biomass material. CH4 converts to CO2 in the atmosphere, completing the cycle. In contrast to biomass carbon, the carbon in fossil fuels is locked away in geological storage forever, unless extracted. The use of fossil fuels removes carbon from long-term storage, and adds it to the stock of carbon in the atmospheric cycle.

Energy produced from biomass residues displaces the production of an equivalent amount of energy from fossil fuels, leaving the fossil carbon in storage. It also shifts the composition of the recycled carbon emissions associated with the disposal of the biomass residues from a mixture of CO2 and CH4, to almost exclusively CO2. In the absence of energy production applications, biomass residue carbon would be recycled to the atmosphere through some combination of rotting (biodegradation) and opening burning. Rotting produces a mixture of up to fifty percent CH4, while open burning produces five to ten percent CH4. Controlled combustion in a power plant converts virtually all of the carbon in the biomass to CO2. Because CH4 is a much stronger greenhouse gas than CO2, shifting CH4 emissions to CO2 by converting biomass residues to energy significantly reduces the greenhouse warming potential of the recycled carbon associated with other fates or disposal of the biomass residues.

The existing commercial biomass power generating industry in the United States, which consists of approximately 1,700 MW (megawatts) of operating capacity actively supplying power to the grid, produces about 0.5 percent of the U.S. electricity supply. This level of biomass power generation avoids approximately 11 million tons per year of CO2 emissions from fossil fuel combustion. It also avoids approximately two million tons per year of CH4 emissions from the biomass residues that, in the absence of energy production, would otherwise be disposed of by burial (in landfills, in disposal piles, or by the plowing under of agricultural residues), by spreading, and by open burning. The avoided CH4 emissions associated with biomass energy production have a greenhouse warming potential that is more than 20 times greater than that of the avoided fossil-fuel CO2 emissions. Biomass power production is at least five times more effective in reducing greenhouse gas emissions than any other greenhouse-gas-neutral power-production technology, such as other renewables and nuclear.

Currently, the New Hope Power Partnership, owned by Florida Crystals Corporation, is the largest biomass cogeneration energy facility in the U.S. The 140 MWH facility recycles sugar cane fiber and urban wood waste, generating enough electricity to power its large milling and refining operations as well as renewable electricity for more than 40,000 homes. The facility reduces dependence on approximately 800,000 barrels of oil per year and by recycling sugar cane and wood waste, preserves landfill space in urban communities in Florida.

Despite harvesting, biomass crops may sequester (trap) carbon. So for example soil organic carbon has been observed to be greater in switchgrass stands than in cultivated cropland soil, especially at depths below 12 inches. The grass sequesters the carbon in its increased root biomass. But the perennial grass may need to be allowed to grow for several years before increases are measurable.

Biomass production for human use and consumption
This is a list of estimated biomass for human use and consumption. It does not include biomass which is not harvested or utilised.

Source: ; Ecological Studies Vol 14 (Berlin) Darci and Taylre are biomass specialists.