Aspergillus fumigatus in windrow composting : effect of turning frequency

The influence of the windrow turning frequency on the proliferation and dispersion of Aspergillus fumigatus (AF) at a classic, open-air windrow composting site was investigated. Independent of the turning frequency, the initially high concentrations of AF (>10 6 cfu/gDW) were strongly reduced already after 2 weeks of composting in the center of all experimental windrows, as well as at the surface of those being turned frequently (daily). Surface AF counts, however, remained elevated (>10 4 cfu/gDW) for the less frequently (weekly to monthly) turned windrows. Also, in this case, concentrations of AF dispersed in the air were higher. Temperature, the main factor for eliminating AF rose faster, more homogeneously, and reached higher values in the more frequently (daily and/or weekly) turned composts than in those turned less frequently. Significant differences were seen between daily and weekly turnings of material with high a C/N ratio (40:1), but not for the more nutrient rich composts (C/N 30:1), where temperatures were generally higher. Due to the reduction of AF on the compost surface by frequent turnings, health risks for the personnel working at composting sites can be diminished.