How to Start Composting
Composting is simply the method of breaking down organic materials in a large container or heap. The decomposition occurs because of the action of naturally occurring micro-organisms such as bacteria and fungi. Small invertebrates, such as earthworms and millipedes, help to complete the process. Composting can convert organic waste into rich, dark coloured compost, or humus, in a matter of a few weeks or months. There is nothing mysterious or complicated about composting. Natural composting, or decomposition, occurs all the time in the natural world. Organic material, the remains of dead animals and plants, is broken down and consumed by micro-organisms and eaten by small invertebrates. Under controlled conditions, however, the process can be speeded up.
Composting has many benefits;
- It provides a useful way of reclaiming nutrients from organic refuse
- Saves valuable landfill space and possible contamination of land and water due to landfill ‘leachate’
- Can be used as fertiliser on farmland or in the garden
- Improves the condition of soils
In composting, provided the right conditions are present, the natural process of decay is speeded up. This involves controlling the composting environment and obtaining the following conditions:
- The correct ratio of carbon to nitrogen. The correct ratio is in the range of 25 to 30 parts carbon to 1 part nitrogen (25:1 to 30:1). This is because the bacteria which carry out the composting process digest carbon twenty five to thirty times faster than they digest nitrogen. This is often seen as being a roughly equal amounts of "greens" and "browns". Carbon to nitrogen ratio will be referred to hereafter as the C:N ratio. The C:N ratio can be adjusted by mixing together organic materials with suitable contents.
- The correct amount of water. Plants have a liquid rather than a solid diet and therefore the compost pile should be kept moist at all times. On the other hand, a wet compost pile will produce only a soggy, smelly mess.
- Sufficient oxygen. A compost pile should be turned often to allow all parts of the pile to receive oxygen.
- The optimum pH level of the compost is between 5.5 and 8.
In these conditions, bacteria and fungi feed and multiply, giving off a great deal of heat. In well managed heaps, this temperature can reach as high as 60 C, which is sufficient to kill weed seeds and organisms that cause disease in plants and animals. While the temperature remains high, invertebrates are not present in compost heaps, but when the temperature drops, the invertebrates enter the heap from the surrounding soil and complete the process of decomposition.
Forms of decomposition
- Anaerobic. In anaerobic decomposition, the breakdown of the organic material is caused by bacteria and fungi that thrive in low or no-oxygen conditions. It is the type of decomposition that takes place in closed containers. This type of system is more complex and difficult to control and requires complex equipment for larger scale composting (see Box 4).
- Aerobic. In aerobic decomposition, bacteria and fungi which thrive in high oxygen conditions are responsible for the decomposition. This form of decomposition occurs in open heaps and containers that allow air to enter. With open heaps and more ventilated containers, compost can be formed in a matter of a few months, and even faster if the organic material is turned regularly. In heaps or bins where aerobic decomposition is occurring, there should be no unpleasant odours.
Some methods of composting
Composting systems can be opened or closed, that is the organic matter will either be placed in open piles or rows or in a closed container or reactor. The open system is rarely used in low-income countries due to its technical complexity, so we look at some of the open systems in use.
- Backyard composting at the household level is a simple technique. It requires only suitable organic waste, space to construct the heap and time to carry out the necessary work. The waste can be placed in a pit (say 2m x 2m x 1m deep) and left to decompose for 2 - 3 months. Alternatively, the waste can be piled up within an enclosure of 4 poles and surrounded by boards or chicken wire and left for a similar period. This produces a rich compost which can be used as a fertiliser on fields or gardens.
- Neighbourhood composting. A commonly used technique for neighbourhood composting is the use of windrows. Here waste is simply laid out in long rows and turned occasionally. Another method is the rotating bin method which uses a series of closed, aerated bins (see Lardinois3).
- Co-composting is technique whereby organic food waste is mixed with human or animal excreta and composted Similar techniques are used to those described above. There are many examples of successful co-composting systems throughout the world (see Lardinois3).
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