Abstract

Self-heating in compost piles results in unsuitable doors, smoke production and fires, having strong negative environmental impacts. Field, laboratory and numerical studies were accomplished trying to reproduce and understand the conditions where self-heating and combustion may take place. Inside a compost pile, built from solid obtained after municipal waste water treatment, oxygen, methane, carbon monoxide and carbon dioxide concentrations and temperature change with time and in depth. Electrical conductivity and pH showed only sligth changes. In field piles temperature increased with time until get a maximum about 90°C. While no spontaneous combustion was observed after 6 months in field experiments, in laboratory studies carried out in a closed bottom cylinder, self-ignition was observed and a maximun temperature of about 400 °C was reached. Numerical simulations describe the field piles internal heat generation, concluding that a minimum of 1.8 m height is required to reach a self-ignition condition.