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Waste Management
One of the most common
problems facing rural
communities around the
world is that of waste
disposal. The incorrect
disposal of animal and
human waste can lead to
the poisoning of
waterways, render land
un-farmable and cause
numerous fatal diseases
such as Cholera, Typhoid
and Diphtheria. CART
needed a way to not only
dispose of its waste but
also to find a way of
actually making this
waste useful. After much
research it was decided
that a Bio-Digester
could provide the
solution to this
problem, however no
design existed that
could be cheaply
replicated in rural
areas – so CART made
one. Conventional
Bio-digesters cost in
the region of US$30,000,
CART’s costs about
US$500.
The simple design
consists of a hole 7m x
1.5m x 1.5m into which a
reinforced PVC
cylindrical black bag is
placed. At one end is
the "inlet" situated at
the bottom of the bag, a
pipe from the toilet
block brings all human
waste into the bag
together with a hatch
for animal and kitchen
waste. Two outlet pipes
are situated at the
other end of the bag,
one at the top for gas
removal the other is 1/3
of the way up for liquid
removal. The design
incorporates a black
colour so as to attract
solar heat to accelerate
decomposition. The
placement of the outlet
pipe is important as it
is necessary to maintain
1/3 liquids : 2/3 gas.
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Due to the sealed nature
of the bag all this
waste begins to
decompose anaerobically
releasing methane gas,
water and sludge waste
whilst also killing
harmful pathogens such
as E-Coli. The methane
gas is released and
captured using the valve
at the top of the outlet
end of the bag, this gas
can be used for cooking,
lighting and heating
(although CART currently
intend to use the gas
solely for cooking.) The
water is released
through the outlet pipe,
this water is known as
‘High nutrient’ or
‘Black’ water. Less than
10% of the products are
solids and therefore
only need removing from
the bag every few years,
these solids can be used
as a high nutrient
fertiliser for fruit
trees or for plants
where the fertiliser
does not come into
direct contact with the
crop. The black water is
mixed with grey waters,
such as shower or
washing water (CART only
uses organic,
Bio-degradable washing
products to ensure no
toxins are introduced to
the cycle.) This water
is filtered through sand
and charcoal and used to
irrigate the food
gardens. Excess water,
together with runoff
from the gardens is
collected in the Dam,
from which it can be
used to water gardens in
the dry season or
filtered further making
it safe for drinking
(See water cycle) |
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