Managing organic municipal waste
Practical Action
disposal facilities. The products of decomposition are corrosive, and containers and vehicles
need to be designed with this in mind, and cleaned frequently to reduce this problem.
In industrialised countries much organic waste is disposed of in landfills where it decomposes
anaerobically, producing methane. It also produces leachate: the liquid which filters down
through the layers of waste picking up soluble chemicals and metals on its way. It can be
highly toxic and poses a serious environmental and health risk unless carefully confined and
treated. In developing countries, organic waste is often left to rot on streets where it is eaten
by animals and birds, blocks drains, and generally causes a public nuisance and health
hazard.
In view of the quantities of organic waste produced and the problems associated with
transporting and disposing of it, finding alternative solutions is a high priority.
Dealing with organic waste
There are three main ways of dealing with the organic portion of municipal waste:
Feed for animals;
Feedstock for anaerobic digestions (i.e. biogas plants);
Aerobic composting.
This technical brief focuses primarily on composting, which is often the most straightforward
and lowest-cost option. However we will briefly discuss the first two options.
Feed for animals
Using organic waste as animal feed is outlawed in many industrialised countries because of
concerns of disease transmission, and the risk of introducing toxic chemicals into the human
food chain. However, some countries do allow this, and it may be a suitable solution, for
example, for using waste from a food processing factory or a vegetable market where quality is
relatively easy to control. Check with national regulations. The following box presents an
example of the use of organic waste to feed pigs in the Philippines.
Pig-feeding in Metro Manila
In the outlying urban areas of Manila, backyard pig- rearing has long been a traditional
source of income. Commercially produced feed for this activity is expensive and pig
raisers often turn to organic scraps to supplement or replace the commercial product. A
network of collectors collects organic waste from restaurants in the city centre, and then
distributes it among backyard farmers. The farmers can purchase the waste at about half
the price of the commercial feed. A cost comparison showed that profit was more than
doubled by feeding the pigs on organic scraps, even after all other costs, such as veterinary
costs, transport, fuel, etc., are taken into consideration. Animal feeding happens in many
other countries such as Egypt, Turkey, India and Pakistan.
Such ventures are beneficial not only to the pig raisers, but also to the municipality who
would otherwise have to dispose of the waste in a landfill.
Anaerobic digestion
Anaerobic microorganisms thrive in environments with no oxygen. Many such microorganisms
occur naturally; in the absence of air these will prevail and decompose the organic material.
Anaerobic decomposition gives rise to methane. Methane is a potent greenhouse gas which
over a period of 100 years is thought to be 23 times more harmful to the environment than
carbon dioxide (CO2). Therefore, where anaerobic digestion is employed as a treatment
method, it is vital that the methane is captured and used. One such example of a controlled
anaerobic digestion system for organic waste is biogas digester. These are most often used
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