Mathematical Modelling of Self-Heating in Compost Piles

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 environmentallyfriendly process. However, due to the lack of a fundamental understanding of theself-heating processes inside a compost heap, there have been many fire accidents incomposting facilities such as those storing industrial waste products like municipalsolid waste and landfills. In most cases, these incidents have been manageable andnot destructive enough to attract outside attention. However, over the years, therehave been several notably devastating fires at such facilities which have createdfinancial losses in addition to damage to lives, facilities, the environment, etc.The models in this thesis incorporate terms that account for both the biologicaland chemical heating processes which occur within compost piles. To date, onlythe latter mechanism has been analysed using models for internal heating in bulksolids 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 biologicalreaction which is both a heat-generating and dehydrating process. The biologicaldecomposition process works effectively within the elevated temperature range of323 - 363 K but, above this temperature, the chemical or oxidative reaction "kicksin" which sometimes generates too much heat and triggers spontaneous ignitionwithin 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 behaviourof the self-heating process within a compost pile and then the mechanisms whichmaximise the composting process whilst minimising the chance of spontaneous igni-tion within a compost heap are examined. To improve composting performance, wedetermine compost pile behaviour as a function of several important factors, suchas 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 toachieve optimum outcomes