Know how to about Renewable Energy
:
Please visit :
Biogas based on the phenomenon of microbial
decomposition of organic matter in the absence of air
resulting in a gas called biogas. It mainly consists of
methane and carbon dioxide. This biological conversion is
better known as anaerobic digestion. A natural process
termed as microbial methanogenesis takes place during
anaerobic digestion. Methanogenesis has traditionally been
considered a two-step process involving acid-forming
bacteria which hydrolyse and ferment organic compounds
to fermentation. Products such as organic acids, alcohols,
neutral compounds, hydrogen and carbon dioxide, and
methane-forming bacteria convert these fermentation products
to methane and carbon dioxide. The
energy scenario of Bangladesh is dominated by
traditional energy sources. They supply about 64 percent of
the total energy consumption. These are based on
agricultural residues (40.9%), animal dung (14.3%) and
fuel-wood (8.7%). The livestock survey of 1983-1984
estimated that of the total yearly dung production of 11.60
million tons (dry dung), 31 percent was used as fuel
directly in the form of dung cakes and 68 percent was used
as manure applied directly in the field, while the balance
was used for other purposes. Unfortunately, the direct
burning of cow dung causes a total loss of
fertiliser and pollution of the atmosphere, whereas
applying it directly to the field causes a total loss of
fuel and pollution of the atmosphere. On the other hand, the
production of biogas through anaerobic digestion would not
only guarantee reliable and cleaner renewable energy sources
but would also provide treated slurry as fertiliser. The common
factors affecting biogas production are the type of basic
organic materials,
temperature, pH of the media, and solid concentrations.
Material having non-lignin C:N from 20 to 25:1 are good for
biogas production. Cow dung having a C:N ratio of 20:1 is
considered suitable material for biogas production.
Production by anaerobic digestion takes place within the
temperature range of 10-35?C and the optimum temperature is
33-35?C. The optimum pH range is 6.5 to 7.5. The optimum
solid content for biogas production is 8-12%. The 1:1 inputs
of water and cow dung with 18-20% solid content makes the
solid content to 9-10% and is within the range of
recommended value. Slow agitation/mixing of slurry helps in
improving biogas production. Bangladesh
has a great potential for development of biogas technology.
The
cattle population including
buffaloes is about 24.19 million (1996), which yield
about 242 million kg of cattle wastes per day. This waste
has a potential of production of 3.19109 cu m of gas. If
even 50% of the cattle wastes could be used for biogas
production, about 1.36 million biogasdigesters of the
capacity of 3 cu m could be set up. A biogasdigester of 3 cu
m capacity could provide the energy requirements for cooking
and lighting of a family consisting of 7-8 members. Such a
digester would require 60-70 kg cow dung which could be
obtained from 5-6 cattle or 3-4 buffaloes. Apart from the
benefits of energy, the treated slurry could be used as
fertiliser, since it is a bonus from biogas production. Biogas
technology programmes based on adaptive design and
demonstration of family size biogasdigesters were initiated
at
bangladesh agricultural university, Mymensingh, and
Bangladesh Council of Scientific and Industrial Research (BCSIR),
Dhaka, in the early seventies. The first family size design
of biogasdigester of capacity of 3 cu m was installed at
BCSIR in 1976. and was of the floating dome type. The
typical floating dome digester is a brick-lined cylinder
sunk in the earth, with a wall dividing the cylinder into
two, and with inlet and outlet ports leading to the bottom
of the tank. The price of such a biogasdigester was Tk
12,000. Subsequently, a lower cost design of the floating
dome digester of capacity of 3 cu m was installed at BCSIR
in 1981. The price of this came down to Tk 3,000 only. Another
biogas production technology programme to meet the fuel
crisis for cooking was subsequently undertaken and 214
floating dome type biogasdigesters were installed under the
supervision of the Institute of Fuel Research and
Development at BCSIR. Unfortunately, the operating life of
these digesters was 3-5 years because of leakage in the
gas-holder of the digester. Because of this leakage problem,
a fixed dome type family size biogasdigester with a capacity
of 3 cu m was installed at BCSIR in 1991. A digester of this
type varies somewhat in shape, but, unlike the floating
type, everything is below the ground. Because it has a gas
reservoir of fixed volume, the gas pressure varies. The
digester pit is dug into the ground and then lined with
bricks. A biogas
production technology programme was undertaken in 1999 and
led to the installation of 5,000 biogasdigesters in
Bangladesh that year. The most common size of digester is
that for the small farm. A volume of about 3 cu m is
suggested for five to six cattle and it is the smallest
possible size. Bigger digesters are built for bigger farms
and for institutional purposes.
Biogas
Biomass
Gasification ProgrammeElectricity
generation from poultry wasteBiomass
Briquetting Programme in Bangladesh
To assess the investment potential on biogas production, it is essential to examine the economic benefits. The net benefit for a biogasdigester operated on slurry from cows in Bangladesh increases with an increase of the government subsidy. The net benefit is also highly sensitive to the price of fuelwood and the cost of construction of the digester. Thus, any increase in the price of fuelwood will encourage introduction of biogasdigesters. An increase in inflation would obviously make the installation of a biogasdigester more profitable over a period of time, whereas high interest rates would reduce the net present benefit and discourage the introduction of the biogasdigester. Although their cost is low in terms of the economics of a rich population, in terms of the economics of the people for whom they are designed the cost is often high. In some cases, cost is a factor limiting their further spread. However, whatever the economics or other limitations, there is no doubt that small digesters can serve as a major source of energy for single houses or small communities in rural areas of Bangladesh. [BK Bala]
