Abstract
Due to environmental concerns about waste management and global warming, composting has become an increasingly popular method for handling organic waste,
manure and other organic materials as it is an inexpensive, simple and environmentally
friendly process. However, due to the lack of a fundamental understanding of the
self-heating processes inside a compost heap, there have been many fire accidents in
composting facilities such as those storing industrial waste products like municipal
solid waste and landfills. In most cases, these incidents have been manageable and
not destructive enough to attract outside attention. However, over the years, there
have been several notably devastating fires at such facilities which have created
financial losses in addition to damage to lives, facilities, the environment, etc.
The models in this thesis incorporate terms that account for both the biological
and chemical heating processes which occur within compost piles. To date, only
the latter mechanism has been analysed using models for internal heating in bulk
solids such as coal, grain, hay, etc. However, the main decomposition and stabilisa-
tion processes of organic materials within a compost pile are due to the biological
reaction which is both a heat-generating and dehydrating process. The biological
decomposition process works effectively within the elevated temperature range of
323 - 363 K but, above this temperature, the chemical or oxidative reaction "kicks
in" which sometimes generates too much heat and triggers spontaneous ignition
within compost piles.
In this thesis, detailed investigations of several mathematical models for the self-
heating of a compost heap are presented. Firstly, the generic solution behaviour
of the self-heating process within a compost pile and then the mechanisms which
maximise the composting process whilst minimising the chance of spontaneous igni-
tion within a compost heap are examined. To improve composting performance, we
determine compost pile behaviour as a function of several important factors, such
as the compost pile size, air-flow rate, ambient temperature and water content.
These studies give us a better understanding of the composting process so that, in industrial composting facilities, we are able to monitor and adjust these factors to
achieve optimum outcomes.