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United Nations Environment Programme
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Freshwater Management Series No. 7

Phytotechnologies

A Technical Approach in Environmental Management

III. Examples of Environmental Applications of Phytotechnology >

J. Bio-Energy

Biofuels, such as ethanol and methane are commonly produced from plants grown and harvested for this purpose and from waste plant biomass, including wood or agricultural residues. These sources of energy are renewable and relatively clean, and can be produced in most regions where pla nts can be grown.

chunk of fermented sugarcane

Brazil, for example has produced fuel alcohol for years from fermented sugar cane. Fuel-making factories are built in areas where the cane is grown, minimizing the need for transport. Cane debris left behind after the fermentable juice is squeezed out is used as boiler fuel, supplying steam for stills, sterilization of equipment, and local electrical production. Since no other fuel is required for these operations, the fuel alcohol produced is a net gain.

The biggest part of the carbohydrate content in plants is not in the form of either starch or sugars but in cellulose – the material making up the structural cell walls of stems, leaves, hills, husks, cobs, etc. Lignocellulose (a mixture of cellulose, hemicellulose, and lignin) in wood and paper wastes makes a vast, cheap, widespread and largely untapped renewable source of biomass that can be converted to fuel. However, lignocellulose is very difficult to break down and convert into sugars and alcohol. The breakdown of cellulose alone re leases a mixture of sugars, including glucose, xylose, mannose, galactose and arabinose. Work is now being done to determine the best enzymes for rapidly and efficiently metabolize all of these sugars into ethanol With the right microbes feeding on the sugar residues found in waste paper and other biomass, significant quantities of ethanol could be produced each year.

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