© 2007 IWA Publishing. Organic Waste Recycling: Technology and Management. Authored by
Chongrak Polprasert. ISBN: 9781843391210. Published by IWA Publishing, London, UK.
3 Composting
Haug (1980) defined composting as the biological decomposition and
stabilization of organic substrates under conditions which allow development of
thermophilic temperatures as a result of biologically produced heat, with a final
product sufficiently stable for storage and application to land without adverse
environmental effects. Another definition refers composting to a controlled
aerobic process carried out by successive microbial populations combining both
mesophilic and thermophilic activities, leading to the production of carbon
dioxide, water, minerals, and stabilized organic matter (Pereira-Neta, 1987).
Generally, composting is applied to solid and semi-solid organic wastes such as
nightsoil, sludge, animal manures, agricultural residues, and municipal refuse,
whose solid contents are usually higher than 5 %.
Aerobic composting is the decomposition of organic wastes in the presence
of oxygen (air); the end-products of biological metabolism are carbon dioxide
(CO 2 ), NH3, water and heat (similar to Equation 2.1). Anaerobic composting is
the decomposition of organic wastes in the absence of oxygen; the end-products
are methane (CH 4 ), CO 2 , NH 3 and trace amounts of other gases, and other low-