Occurrence of Aspergillus fumigatus during composting of sewage sludge

Abstract

Aspergillus fumigatus, a medicaRly important fungal opportunist and respiratory allergen, was isolated from woodchips and sewage sludge used in the production of compost at the U.S. Department of Agriculture's composting research facility in Beltsville, Md. It was also regularly isolated as a dominant fungus during forced aeration composting and after 30 days in an unaerated stationary curing pile; in both cases, the fungus was found in pile zones with temperatures less than 60°C. Compost stored outdoors in stationary unaerated piles from 1 to 4 months after screening out of woodchips contained easily detectable amounts of A. fumigatus in the exterior pile zones (0to 25-cm depths). Semiquantitative studies of the airspora at the composting site revealed that A. fumigatus constituted 75% of the total viable mycoflora captured. At locations 320 m to 8 km from the compost site, the fungus constituted only 2% of the total viable mycoflora in the air. Of 21 samples of commercially available potting soil, one had levels of A. fumigatus nearly equivalent to those of 1month-old storage compost; 15 others had lower but detectable levels. Sewage sludge disposal is an immediate and growing problem for many U.S. municipalities. Composting, one of the altemative disposal/utilization options available, has been investigated from engineering, economic, bacteriological, and viral aspects (6, 11, 20, 48). The agronomic characteristics of the compost have also been evaluated (19). One aspect which has not been investigated thoroughly and evaluated with a view toward health safety is the fungal flora which develops during composting. Aspergillus fumigatus Fres. is one of the relatively few fungi which are known to infect hulmans. Records of its ecological distribution and pathogenicity, which follow below, suggested that the fungus might proliferate during composting and thereby pose a health problem for certain individuals.

Physico-Chemical and Microbial Quality of Locally Composted and Imported Green Waste Composts in Oman

“…Most of the fungi involved in the slow degradation of the screened composts belong to the thermophilic genus and moisture tolerant Aspergillus. In the present study ( Table 4), A. niger was the predominant species recovered from all compost types (100%) at the later stage as reported by many authors [1,48,49]. This fungus was followed by A. fumigatus (75%), A. sparsus (50%), yeasts (50%), A. flavus (37.5%), where the remaining fungi such as A. restrictus, A. versicolor, Cladosporium spp., and Penicillium spp.…”

Fungal succession in an in-vessel composting system characterized using 454 pyrosequencing

“…These results would suggest that the composting process seems to be effective at reducing the levels of these pathogens. Another opportunistic pathogen of interest is Aspergillus fumigatus , which has been previously highlighted by culture‐based studies as one of the most abundant fungi in composting systems (Finstein & Morris, ; Beffa et al ., ), sometimes accounting for more than 50% of the viable mycoflora (Millner et al ., ). In our culture‐independent survey, this fungus was detected in the compost materials at the start of the process and during the maturation stage, although its relative abundance was low in comparison with other fungi throughout the whole process (0.25 ± 0.07%).…”

Aspergillus fumigatus, a saprotrophic pathogenic fungus

“…In its natural habitat, this species is found in high concentrations in compost. Surrounding compost plants, conidial concentrations higher than 10 6 conidia/m 3 are often encountered, with similar conidial concentrations often found in material arriving at the composting plant and in the resulting commercial product (Beffa et al, 1998 ;Millner et al, 1977). This may represent a biological hazard for the general population, as A. fumigatus is known to produce polypeptide allergens responsible for asthma and rhinitis, mycotoxins and ß1,3 glucans that are known modulators of the immune system (Heederik et al, 2000;Fisher et al, 2000;Rylander, 1999, Sigsgeard et al, 2000.…”