Which forms of biomass do you think are worth using for fuel?

Biomass and Biofuels

Scientifically speaking, biomass is any living material. It is estimated that there is very roughly 560 x 10¹²kg carbon (0.2% or 1 x 10¹²kg carbon of which is in animals) in the total biomass spread over the Earth. Tropical rain forests support approximately 20 kg carbon per square metre, compared to 0.5 kg carbon per square metre for agricultural land and 0.01 kg carbon per square metre in lakes and streams.

In the context of energy production, however, biomass usually means plants grown for fuel use, or biofuels - fuels derived from crop materials. Biofuels include ethanol (made from corn, cotton gin waste, cow manure, maize, grain sorghum, soybeans, sugar cane and wood, for example), methanol (made from wood), biodiesel (rape methyl ester from oilseed rape), methane, and wood (for heating and producing electricity). Another source of fuel is Short rotation coppicing (SRC), where fast-growing woody biomass such as willow or poplar is regularly coppiced and the wood chips used to produce electricity and heat for local use. Rudolf Diesel used a biofuel, peanut oil, in his first working engine.

Biofuels compete with food production for land use, though some of it can be produced on marginal land. The land used for biofuel production is included in Ecological Footprint calculations. The use of pesticides, herbicides and fertilizers and even water used in growing each of the crops has to be taken into account, as does the ratio of energy put into producing them to the amount of useful energy produced for the price. Because of the financial and energy costs of transport, the biomass is best converted fairly near to where it is produced.

Apart from solar energy, a lot of other energy is invested in the things we use to produce our crops - seed, fertilisers (nitrogen, phosphate, potash), insecticides, plant growth regulators, fungicides and machinery fuel, for example. That doesn't count the farmer's labour, which is itself fuelled by food. These things all have to be taken into account when comparing and contrasting uses and sources of energy. We also need to take into account the transportation and processing after the crop has been harvested to turn it into food (e.g. bread) or fuel.

Other biomass can be put to use, for example farm wastes like pug slurry, chicken manure, straw and wood waste from forestry. Some of these can be turned into methane as well as being burnt. Some industrial and domestic waste can also be used, but particularly in the case of domestic waste it can contain a wide range of materials some of which, like plastics, can produce toxic emissions when burnt.

Methane (biogas) can also be collected from landfill sites. As methane is a much more powerful greenhouse gas than carbon dioxide, it is a good idea to collect it and put it to use. Chicken fat and other animal remains can also be converted into fuel oil. Many environmentalists would prefer that we generated much less waste in the first place than treating it as a renewable energy resource. To be considered renewable, biomass has to be sustainably grown; that is, it should be grown at the same rate that it is used. This is particularly important because it stores carbon dioxide (especially trees).

Decaying biomass can be a problem in reservoirs, particularly if the vegetation is left to rot underwater when the reservoir is first filled, when it can produce methane or hydrogen sulphide (toxic to humans) instead of carbon dioxide.

Cow Manure Eyed As Alternate Fuel Source

Texas is looking into cow manure as an alternative fuel source, as oil costs rise. It is to be one of the forms of biomass used to supply an ethanol plant that is due to open in Hereford next year. The plant will also use cotton gin waste. Manure is only a third as full of energy as coal, so it is not economical to transport it far from where it is produced.

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