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system in Bauniabad. For the
trial, two small septic tanks,
each for about 6 families, and
another big one, for about 60
families, were installed. Two
latrines were connected to each
of the small septic tanks. Two
separate rows of latrines were
connected to the big septic tank.
Each row consisted of several
latrines installed on the top of
the tank (Photo 2.4). Both the
septic tanks were rectangular
in shape and included two
chambers separated by a baffle
wall. The first chamber was
about two times the size of the
second chamber as the bigger
(first) chamber included scum boards near the inlets and outlets. About 0.8 m 2 area was assumed for every 10
persons when constructing the first chamber of the tanks. The septic tank system allows the waste/wastewater,
once discharged from the latrines, to enter the septic tank from one end and go through the system where it has
a chance to decompose, and once decomposed, the effluents of the tank are then discharged in a nearby ditch.
However, the septic tank system installed and studied in Agargao, was deemed inappropriate due to the nuisance
of insects and bad odors, leading to the system not being adopted in Bauniabad.
A biogas facility is an anaerobic system, and consists of an inlet pipe and tank, an anaerobic reactor (often
referred to as a biogas chamber or a fermentation chamber), and outlet pipe. As an anaerobic reactor, many types
of the digesters have been promoted, such as the floating drum digester known as the Indian type, the fixed
dome digester known as the Chinese type, the Deenbandhu model, the bag digester, the plug flow digester, the
anaerobic filter, and the up-flow anaerobic sludge blanket .
The anaerobic digestion, which is the main reaction of the biogas facility, is summarized in the three stages,
namely Stage 1: hydrolysis, Stage 2: acidification and Stage 3: methanation. Human waste mainly consists of
carbohydrates, lipids, proteins and inorganic materials. In Stage 1, large molecular complex substances are
solubilized into simpler ones with the help of extra cellular enzymes released by bacteria. This stage is also known
as the polymer breakdown stage. In Stage 2, the monomer, such as the glucose which is produced in Stage 1, is
fermented under anaerobic conditions into various acids with the help of enzymes produced by acid forming
bacteria. During this stage, the acid-forming bacterium breaks down molecules containing six atoms of carbon
(glucose) into molecules containing less atoms of carbon (acids), which are in a more reduced state than glucose.
The principal acids produced in this process are acetic acid, propionic acid, butyric acid and ethanol. In Stage 3, the
principle acids produced in Stage 2 are processed by methanogen to produce methane. It is reported that the gas
production potential of human waste is 0.020-0.028 m 3 /kg (United Nations, 1984).
Biogas facilities for producing renewable gas from animal waste has been promoted for over a decade by
more than one government department in Bangladesh; various designs were promoted. Recently it has been
encouraged through a subsidized programme to install and use on-site batch type biogas facilities for energy
production and treatment of combined animal and human waste. As the main objective is energy production, the
subsidy is only allowed for families that have at least two cows or enough numbers of other animals to produce
the gas. However, most of the people could not afford to have the required number of animals.
From 1997-1999 the research and development of biogas based sewerage system was simultaneously done
under two conditions: (1) community latrine, and (2) household latrine connections. Three biogas based sewerage
systems were studied for community latrines; one in a rural school hostel for about 300 residential students in
Singair of Manikganj District, and two in the Agargao for about 80 families. It included a few community latrines
that were connected to collection pipelines of various dimensions, a connection pit, a fixed dome shaped digester
(biogas chamber), a joint hydraulic chamber, and a soak pit. The biogas based sewerage system connected to
poor households in Bauniabad using the small-bore sewerage system under the household condition, was
also connected, and had components, similar to that of the communal system; this type of connection to
individual households is a pioneering project. The two types of biogas based sewerage systems were observed
and compared with the other options for about 3 years during 1997-1999. It was found to be performing highly
satisfactory compared to the studied different types of pit latrines and septic tanks. However, there were limited
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