Recycling of organic waste
Practical Action
in domestic waste. From Figure 1 we can see that up to 60% (or more in some cases) of all
municipal waste is organic matter, much higher than the figure for an industrialised country. It is
therefore well worth intercepting this supply of useful material where it can be used effectively.
Developing
60 countries - front
50
Industrialised
40 countries - back
30
20
10
0
Figure 1: Composition of municipal waste in a typical developing and industrialised country (actual
figures vary significantly – this figure is only an example).
Commercially produced organic waste.
By this, we mean waste generated at institutional buildings, such as schools, hotels and restaurants.
The quantities of waste here are much higher and the potential for use in conjunction with small-
scale enterprise is good (see box 2).
Animal and human waste.
It is worth mentioning at the start of this section that there are serious health risks involved with
handling sewage. Raw sewage contains bacteria and pathogens that cause serious illness and
disease. It should be stressed that health and safety procedures should be followed when dealing
with sewage and that people involved with its handling should have a clear understanding of the
health risks involved. Raw sewage should never be applied to crops which are for consumption by
humans or animals.
Human faecal residue is produced in large quantities in urban areas and is dealt with in a
variety of ways. In the worst cases, little is done to remove or treat the waste and it can
present enormous health risks. This is often the case in the slum districts or poor areas of
some large cities. Sewage is often dealt with crudely and is pumped into the nearest water
body with little or no treatment. There are methods for large-scale treatment and use of
sewage as a fertiliser and a source of energy. The most commonly used method is anaerobic
digestion to produce biogas and liquid fertiliser. Composting toilets (see later section)
facilitate the conversion of human faecal waste into rich compost.
Animal residue is rarely wasted. This fertile residue is commonly used as a source of
fertiliser, being applied directly to the land, or as a source of energy, either through direct
combustion (after drying) or through digestion to produce methane gas.
Agricultural residue
This is the ‘waste’ which remains after the processing of crops (e.g. maize stalks, rice husks,
foliage, etc.). There are a wide variety of applications for this residue, ranging from simple
2