Managing organic municipal waste
Practical Action
Compost - technical data
The ideal moisture level of raw materials for compost is 40%. If they are much drier,
microorganisms cannot access nutrients and composting will slow or stop. If it is wetter
anaerobic microorganisms will prevail.
The centre of a compost heap should reach temperatures of around 65°C. Turning
compost, although not always necessary, can help ensure that all organic matter has been
exposed to high temperatures during production.
The carbon: nitrogen (C:N) ratio is important for microorganisms to thrive. Generally
'brown materials' such as wood chips and sawdust are high in carbon, while 'green
materials' such as leaves and grass are high in nitrogen. The ideal ratio is between 25:1
and 40:1. This can often be achieved by a 50:50 mixture of green and brown materials,
though this differs according to the exact types of waste.
There are many methods of making compost, ranging from small-scale home composting
techniques to large-scale industrial plants requiring significant capital investment. The
following box presents some of those most commonly used. Technologies may be selected
according to a number of criteria, including the volume of raw materials available, budget,
land availability, the cost and availability of water and electricity, and costs of labour. The
nature of the market for compost may also affect technology choice.
Methods of making compost
Barrel composting (Dhaka, Bangladesh)
This barrel is installed in a low-income area in
Dhaka, Bangladesh. It receives organic waste from
around four families. High-quality compost is
made because the waste is uncontaminated. It is
sold to a local NGO.
Each barrel can produce around 160 kg of
compost before requiring emptying, from around
600 kg of organic waste. Compost is sold at Tk2/
Kg (around US$0:03). In view of generation rates,
this could generate an income of around Tk30/
family/ month.
Barrels cost around Tk2000, meaning relatively
long payback periods.
Vermi composting (Bais City, Philippines)
Vermi composting predominantly uses worms to
digests the waste, rather than microorganisms.
Raw materials are spread daily in thin layers and
cannot be piled very high, so the technique
requires much more space than other methods.
Worms are also more vulnerable to extreme
temperature and contamination than
microorganisms. One of the advantages of vermi-
composting is the high nutrient content of the
product.
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