1 - Biomass - Mc Graw-Hill

The organic materials produced by plants, such as leaves, roots, seeds, and stalks. In some cases, microbial and animal metabolic wastes are also considered biomass. The term “biomass” is intended to refer to materials that do not directly go into foods or consumer products but may have alternative industrial uses. Common sources of biomass are

(1) agricultural wastes, such as corn stalks, straw, seed hulls, sugarcane leavings, bagasse, nutshells, and manure from cattle, poultry, and hogs;
(2) wood materials, such as wood or bark, sawdust, timber slash, and mill scrap;
(3) municipal waste, such as waste paper and yard clippings; and
(4) energy crops, such as poplars, willows, switchgrass, alfalfa, prairie bluestem, corn (starch), and soybean (oil). See also Biological productivity.

Biomass is a complex mixture of organic materials, such as carbohydrates, fats, and proteins, along with small amounts of minerals, such as sodium, phosphorus, calcium, and iron. The main components of plant biomass are carbohydrates (approximately 75%, dry weight) and lignin (approximately 25%), which can vary with plant type. The carbohydrates are mainly cellulose or hemicellulose fibers, which impart strength to the plant structure, and lignin, which holds the fibers together. Some plants also store starch (another carbohydrate polymer) and fats as sources of energy, mainly in seeds and roots (such as corn, soybeans, and potatoes). See also Cellulose; Lignin.

A major advantage of using biomass as a source of fuels or chemicals is its renewability. Utilizing sunlight energy in photosynthesis, plants metabolize atmospheric carbon dioxide to synthesize biomass. An estimated 140 billion metric tons of biomass are produced annually.

Major limitations of solid biomass fuels are difficulty of handling and lack of portability for mobile engines. To address these issues, research is being conducted to convert solid biomass into liquid and gaseous fuels. Both biological means (fermentation) and chemical means (pyrolysis, gasification) can be used to produce fluid biomass fuels. For example, methane gas is produced in China for local energy needs by anaerobic microbial digestion of human and animal wastes. Ethanol for automotive fuels is currently produced from starch biomass in a two-step process: starch is enzymatically hydrolyzed into glucose; then yeast is used to convert the glucose into ethanol. About 1.5 billion gallons of ethanol are produced from starch each year in the United States. See also Alcohol fuel; Gasoline.

2 - Biomass

Biomass, in the energy production industry, refers to living and recently dead biological material which 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. It is usually measured by dry weight.

The term biomass is useful for plants, where some internal structures may not always be considered living tissue, such as the wood (secondary xylem) of a tree.

Biofuels include bioethanol, biobutanol, biodiesel & biogas.

Biomass is grown from several plants, including switchgrass, hemp, corn, poplar, willow and sugarcane. 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.[citation needed]

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. These acivities are termed 'carbon leakage'.

Biomass is part of the carbon cycle. Carbon from the atmosphere is converted into biological matter by photosynthesis. On decay or combustion the carbon goes back into the atmosphereor soil. 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 biomass is approxiamtly 50% of the biomass by weight.

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.

Other uses of biomass, besides fuel:

* Building materials
* Biodegradable plastics and paper (using cellulose fibres)

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.