Managing organic municipal waste
Practical Action
for human and animal waste, but there are examples of their successful use with organic
waste.
Innovative small-scale biogas plant in India
The Appropriate Rural Technology Institute (ARTI) in
Pune, India recently won an Ashden Award for its
design of a biogas digester which can be fed with
household organic waste. It can also accept spoiled
grain, fruit, oil cake and so on. Costing around
$350, the plant is made using two plastic water
containers. One contains the digesting materials, the
other is inverted to capture the gas.
Users apply 1Kg of organic waste daily and add 10
litres of water. In return the plant will produce
around 250 g of methane per day, enough to cook a
full meal for a family of five. This is an impressive
input: output ratio. The gas could also be fed into a
generator to provide around 1 kWh of electricity.
One of the main advantages of using organic waste as the feedstock compared with dung or
excreta, is that its calorific value is considerably higher. After all, it has not already been
digested using microorganisms in a cow’s intestine!
See www.arti-india.org
Biogas is a source of energy with one of the lowest relative carbon footprints of all. Methane
can be burnt cleanly on simple stoves, producing mainly carbon dioxide and water, making it
a very clean household fuel. As with all organic waste processing techniques, one of the most
significant challenges of using digesters is ensuring the quality of raw materials.
Contamination from plastic, sand and soil can reduce the effectiveness of the plant, and
chemical contamination could compromise the microorganisms, as well as contaminate the
resultant compost.
Compost and composting
Compost is a stable, dark brown, soil-like material which can hold moisture, air and nutrients.
Contrary to popular belief compost does not smell rotten: often it will smell as fresh as a
forest floor (which is, of course, naturally-made compost).
Compost contains some plant nutrients including nitrogen, phosphorus and potassium (NPK),
though not as much as animal manure or chemical fertilisers. Compost can also contain a
range of minerals and microorganisms beneficial to plant growth. However, its main benefit
is as a soil conditioner. Soil is made up of sand and 'humus’: stable organic matter which
retains nutrients and water. Adding compost to soil can lessen the need for chemical
fertilisers because it holds nutrients in the soil, it can also help reduce soil erosion, and
improve the structure of the soil thus benefiting drainage and plant roots.
Compost is a product of controlled aerobic decomposition of organic matter made using
aerobic microorganisms, insects and worms. Microorganisms thrive in a moist, warm
environment with an abundance of organic matter and air. If conditions are too hot, cold, wet
or dry, the composting process will be compromised. The activity of the microorganisms
generates heat which can act to kill pathogens and denature seeds. The composting process
can take as little as two months. Ideally compost is matured for 3 – 4 months before use. In
cold weather, high altitudes or very dry conditions, the composting process may slow or even
stop.
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