♦ Sugar cane is grown in some areas, and can be fermented to make alcohol, which can be burned to generate power. Alternatively, the cane can be crushed and the pulp (called "bagasse") can be burned, to make steam to drive turbines. ♦ Other solid wastes, can be burned to provide heat, or used to make steam for a power station. ♦ "Bioconversion" uses plant and animal wastes to produce fuels such as methanol, natural gas, and oil. ♦ Wood was once our main fuel. We burned it to heat our homes and cook our food. Wood still provides a small percentage of the energy we use, but its importance as an energy source is dwindling.

Biomass is produced from organic materials, either directly from plants or indirectly from industrial, commercial, domestic or agricultural products. It is often called 'bioenergy' or 'biofuels'. It doesn't include fossil fuels, which have taken millions of years to be created.

♦ Woody biomass includes forest products, untreated wood products, energy crops and short rotation coppice (SRC), which are quick-growing trees like willow. ♦ Non-woody biomass includes animal waste, industrial and biodegradable municipal products from food processing and high energy crops. Examples are rape, sugar cane, maize.

PLANTS PLANTS AGRICULTURAL WASTE INDUSTRIAL WASTE

Plants are the most common source of biomass. They have been used in the form of wood, peat and straw for thousands of years. Plants can either be specially grown for energy production, or they can be harvested from the natural environment. Plants can either be specially grown for energy production, or they can be harvested from the natural environment. Plantations tend to use breeds of plant that are to produce a lot of biomass quickly in a sustainable fashion.These could be trees (e.g. Pine or Eucalyptus) or other high growth rate plants (such as sugar cane, maize or soybean). Plantations tend to use breeds of plant that are to produce a lot of biomass quickly in a sustainable fashion.These could be trees (e.g. Pine or Eucalyptus) or other high growth rate plants (such as sugar cane, maize or soybean).

Waste from agriculture includes: the portions of crop plants discarded (including forestry waste), whether damaged or surplus supplies, and animal dung. When wood is used as a fuel, there are low sulphur and nitrogen oxide emissions, but there is concern about the by- products of using pesticide treated materials (as with straw). Waste from agriculture includes: the portions of crop plants discarded (including forestry waste), whether damaged or surplus supplies, and animal dung. When wood is used as a fuel, there are low sulphur and nitrogen oxide emissions, but there is concern about the by- products of using pesticide treated materials (as with straw). There is some potential to use more wood waste, especially residues arising from forestry operations. This could be collected, dried and used by rural industry. If the residues produced by sugar cane, forestry, and grain manufacture, plus all animal dung were converted to energy this would supply 30% of the world's energy needs.

Industrial waste that contains biomass may be used to produce energy. For example, the sludge left after alcohol is made (known as vinasse) if this is processed it can produce flamable gas. Other useful waste products include waste from food processing and fluff from the cotton and textiles industry Other useful waste products include waste from food processing and fluff from the cotton and textiles industry.

The methods of generating energy can be split into two different groups: ~there are the dry processes and the wet processes~ Combustion The dry processes are: Combustion Pyrolysis Anaerobic digestion The wet processes are: Anaerobic digestion Gasification Gasification Fermentation Fermentation

The most obvious way of extracting energy from biomass, the technology of direct combustion is well understood, straightforward and commercially available.Combustion systems come in a wide range of shapes and sizes burning virtually any kind of fuel, from chicken manure and straw bales to tree trunks, municipal refuse and scrap tyres. Some of the ways in which heat from burning wastes is currently used include space and water heating, industrial processing and electricity generation. Some of the ways in which heat from burning wastes is currently used include space and water heating, industrial processing and electricity generation. One problem with this method is its very low efficiency. With an open fire most of the heat is wasted and is not used to cook or whatever.

A wide range of energy-rich fuels can be produced by roasting dry woody matter like straw and woodchips. The process has been used for centuries to produce charcoal. The material is pulverised or shredded then fed into a reactor vessel and heated in the absence of air. Pyrolysis can also be carried out in the presence of a small quantity of oxygen ('gasification'), water('steam gasification') or hydrogen ('hydrogenation'). One of the most useful products is methane, a suitable fuel for electricity generation using high- efficiency gas turbines.

Biogas is produced when wet sewage sludge, animal dung or green plants are allowed to decompose in a sealed tank under anaerobic (oxygen-free) conditions. Feedstocks like wood shavings, straw and refuse may be used, but digestion takes much longer. Each kilogram of organic material (dry weight) can be expected to yield litres of biogas.The residue left after digestion is a potentially valuable fertilizer or compost. Fermentation: Ethanol (ethyl alcohol) is produced by the fermentation of sugar solution by natural yeasts.

This is done by partially burning and partially heating the biomass (using the heat from the limited burning) in the presence of charcoal (a natural by-product of burning biomass). The gas can be used instead of petrol and reduces the power output of the car by 40%. It is also possible that in the future this fuel could be a major source of energy for power stations. This process, usually using wood produces a flammable gas mixture of hydrogen, carbon monoxide, methane and other non flammable by products.

If the biomass used is (or can be converted into) mostly sugar, then yeast can be added. The fermentation that follows produces alcohol which is a very high energy fuel that makes it very practical for use in cars. This has been tried succesfully in Brasil.

In addition to the many environmental benefits, biomass offers many economic and energy security benefits. By growing our fuels at home, we reduce the need to import oil and reduce our exposure to disruptions in that supply. Farmers and rural areas gain a valuable new outlet for their products. Biomass already supports 66,000 jobs in the United States; if the DOE's (Department of Energy) goal is realized, the industry would support three times as many jobs.

♦ Biomass is very abundant. It can be found on every square meter of the earth as seaweed, trees or dung; ♦ It is easy to convert to a high energy portable fuel such as alcohol or gas; ♦ It is cheap in contrast to the other energy sources; ♦ Biomass production can often mean the restauration of waste land (e.g. deforested areas); ♦ It may also use areas of unused agricultural land and provide jobs in rural communities; ♦ If it is produced on a renewable basis using biomass energy does not result in a net carbon dioxide increase as plants absorb it when they grow; ♦ It is very low in sulphur reducing the production of acid rain.

♦ Expensive to collect, harvest and store raw materials; ♦ We burn the fuel, so it makes greenhouse gases; ♦ Some waste materials are not available all year round; ♦ Extra costs of installing technology to process and recycle wastes; ♦ Large scale crop production will use vast areas of land and water, representing major problems.