Composting

Composting is the controlled breakdown of organic matter by microbes in the presence of air. The process produces carbon dioxide, water, heat and compost.

The biology of composting

Most organic materials can be represented as a mixture of three groups of chemicals.

1. Lipids and carbohydrates
2. Proteins and amino acids
3. Ash, lignin and cellulose

In the presence of air and water a wide range of microbes break down the material. The lipids, carbohydrates, proteins and amino acids are broken down via a number of intermediates into carbon dioxide and water. At the same time energy is released in the form of heat. It is this biologically produced heat that raises the temperature of the material being composted. The more resistant components of the organic material - the ash, lignin and cellulose contribute to the organic matter content of the final compost.

As the temperature of the compost changes there is a change in the types of microbes in it. Pathogens are sterilised at the high temperatures found during the composting process and the microbial species change between low temperature (mesospheric) and heat loving (thermophilic). Most of these microbes die as the temperature changes and become part of the organic material being broken down. Once the temperature has stabilised, it enters the maturing phase. This is where the easily broken down organic matter has been used up and the product becomes useful as compost.