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Published on June 4th, 2013 | by Jo


The mathematics of fire: self-heating in compost piles

By A/Prof Harvinder Sidhu, Applied and Industrial Mathematics Research Group

Composting is a natural process that transforms organic material into a stabilised form that can be used for agriculture. The key elements that transform the organic helotes_blogmaterials are invertebrates, such as insects and earthworms, and micro-organisms, such as bacteria and fungi. The biological activity involved in the breakdown of organic materials by micro-organisms creates heat. Appropriate ranges for moisture, aeration and temperature (50—80oC) is required to provide ideal conditions for the composting process, whereby bio-degradation is enhanced.

With a rapidly increasing world population, there are many concerns about a sustainable future for humans; two of the most important being food production and waste recycling and management. These concerns have caused composting to become an increasingly popular method for handling organic waste, manure and other organic materials, as it is an inexpensive, simple and environmentally friendly process. Actually, there are many developed countries which mandate the use of composting methods for controlling and recycling organic waste.  Due to the rapid increase in biological waste over the last two decades, there has been a concerted effort to build more composting facilities around the world. However with this increase in compost facilities, the incidence of unexpected fires has also increased significantly. These are due mainly to the spontaneous combustion of organic materials at composting facilities.  Some claim that fires at these facilities are very common and most are managed in-house, with some notable exceptions that are reported in the media. Overall, there is still a lack of knowledge of the cause of spontaneous ignitions of compost piles at these facilities.

Our group, working in collaboration with researchers from University of Wollongong and Monash University, are developing mathematical models for the self-heating processes in compost heaps. Some of our models, which have been experimentally validated by other international researchers, can be used to:-

  • investigate the overall generic self-heating behavior of compost piles;
  • improve composting performance by determining optimal compost pile size, air flow rate, ambient temperature and moisture content;
  • investigate the mechanisms and factors which minimise the chance of spontaneous ignition within a compost heap.

The Applied and Industrial Mathematics (AIM) Research Group in the School of Physical, Environmental and Mathematical Sciences at UNSW Canberra continues to use mathematics and statistics to study complex real-world problems. We believe that models similar to those used for composting can be used to study the occurrence of unexplained fires at landfill sites.  Watch this space for more work in this area!

The Applied and Industrial Mathematics Research Group

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