Section D This section consists of one passage
followed by a summary. Read the passage carefully and complete the summary below
by choosing no more than three words from the passage for each blank. Remember
to write the answers on the answer sheet. Questions 61 to 65 are based on the following
passage.
Biogas: a Solution to Many Problems
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 ma-nurial 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. Summary The production of
biogas by fermentation of animal and vegetable wastes is a technology that has
been largely developed and used in the (61) countries. Only
very recently have scientists in the industrialized nations begun to show an
interest--presumably because of the "energy (62) ".
Family-sized-biogas (63) 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 (64) . One
Chinese study has shown that digestion of animal (65) 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.