In almost all developing countries, the
lack of adequate supplies of cheap, convenient and reliable fuel is a major
problem. Rural communities depend largely on kerosene, wood and dung for their
cooking and lighting needs. But kerosene is now priced out of reach of many
people and wood, except in heavily forested areas, is in short supply. The
search for firewood occupies a large part of the working day and has resulted in
widespread deforestation. Dung is in constant supply wherever
there are farm animals and, when dried, it is convenient to store and use. But
burning dung destroys its value as fertilizer, thus depriving the soil of a much
needed source of humus and nitrogen. Rural areas of developing
countries are also plagued by a lack of adequate sanitation. Improper waste
disposal spreads disease, contaminates water sources and provides breeding
grounds for disease-carrying insect. The problems of improving
environmental hygiene, conserving resources and finding alternative sources of
fuel may be unrelated. Their solutions, however, are not, as many countries
experimenting with biogas technology are discovering. Biogas, a mixture of
methane and carbon dioxide, is produced by the fermentation of organic matter.
The process of anaerobic fermentation is a natural one occurring whenever living
matter decomposes. By containing the matter-and the process-in a digester or
biogas plant, the combustible gas can be trapped and used as fuel for household
lighting and cooking. The digested slurry that remains can be used on the land
as a soil conditioner and fertilizer. Biogas plants have
attracted much interest in recent years and they are in use in several Asian
countries: 36,000 are reported in rural areas of India, 27,000 in Korea and more
than 80,000 in China. In most countries the value of the gas has been the prime
factor leading to their adoption: 70 per cent of India's plants, for instance,
were built during the energy and fertilizer crisis of 1975-1976-although their
use in that country dates back to 1951. Similarly in Thailand and Korea, biogas
is being investigated as an alternative to costly charcoal and to save compost
materials from being burned. In Japan and China, reducing
pollution from animal wastes has been an important factor. Privies, hen houses
and pigpens are built in proximity to the fermentation chamber in China.
Examinations of the digested slurry have shown that the total number of parasite
eggs was reduced by 93.6 per cent, hookworms by 99 per cent and no schistosome
flukes were found. The greatest benefits from biogas systems,
however, are probably to be derived from the manurial value of the slurry,
although it is not widely used outside of India and China. Vegetable farmers
near Calcutta found that the digested slurry produced bigger and better tasting
peas than did other fertilizers and the weight of root vegetables increased by
nearly 300 per cent. The production of biogas by fermentation
of animal and vegetable wastes is a technology that has been largely developed
and used in the {{U}} {{U}} 1 {{/U}} {{/U}}countries. Only very
recently have scientists in the industrialized nations begun to show an
interest-presumably because of the "energy {{U}} {{U}} 2
{{/U}} {{/U}}" Family-sized-biogas {{U}} {{U}}
3 {{/U}} {{/U}}first came into widespread use in India in the 1950s in
an effort to make a cleaner and more efficient use of cattle dung. The programme
really expanded in the 1970s, and today there are as many as 100,000 plants
throughout the world. Most are in domestic use to provide fuel for plants, but
some larger units are operated in order to recycle wastes, supply fertilizer,
control pollution and improve {{U}} {{U}} 4 {{/U}} {{/U}}. One
Chinese study has shown that digestion of animal {{U}} {{U}} 5
{{/U}} {{/U}}in the airtight digesters greatly reduces health hazards from
parasitic diseases. One Indian study has estimated that the value of the
fertilizer obtained is in itself greater than the cost of producing the biogas.
Thus, the system is economically sound, in addition to other benefits such as a
cleaner, healthier environment.