Composting is a microbiological process for the degradation and stabilisation of organic waste. It is characterized by an important self-heating of the composted material, reaching temperatures up to 80'C. These high temperatures are generally considered sufficient for the elimination of pathogenic niicroorganisrm that occur in organic waste. Measurerments have shown, though, that an important temperature gradient exists in a compost heap, and that the outer or lower zones can have temperatures up to 3O0C below the core temperature. In these temperate zones (30-55'C), Aspergillus fumigatus can proliferate.In a three-year study in collaboration with several composting industries that employ different processes, we monitored microbial and physico-chernical parameters in the compost material and in the air. The aim was to identify parameters that would allow a) fast self-heating, b) homogenous temperature distribution in the whole composting material, c) good stabilization, to avoid recolonisation during the maturation phase.Depending on the specificity of each installation (open-air window composting, box composting in roofed or completely closed structures, composting in bioreactors), the influence of different parameters, such as turning (type of machine, frequency), aeration (type, force and interval) and starting material (CIN ratio, structure, premethanization) were analyzed.From our experiments, the following conclusions were drawn: Daily or weekly turnings of open-air windrows effected a faster temperature rise in the compost heap, compared to turnings carried out only once a month. Also, degradation of organic matter was favored by an intensive treatment. Due to the frequent mixing of the composting material, Aspergillus fumigatus counts were low in the center as well as at the surface of the compost heaps. Whereas for the extensively treated material, a strong proliferation of Aspergillus fumigatus was observed in the colder surface layers. The lower Aspergillus fiimigatus counts in the intensively treated compost were reflected in lower concentrations of mold propagates in the air during turning. For box composting, aeration showed to be indispensable for a correct process. However, care has to he taken to mix the compost regularly with water, in order to avoid excessive drying.Conclusively, health risks for the personnel working on the composting sites can be diminished by an intensive treatment of the compost.
Full conference title:
13th Congress of the International Society for Human and Animal Mycology
- ISHAM 13th (1997)