Green job bio-aerosol exposure during anaerobic digestion for biomass energetic valorisation

• Green job expansion introduces a new occupational risk profile.
• Anaerobic digestion of biomasses is one of the most widespread green technologies.
• The bioaerosol, PM10 fractions and endotoxin exposure were evaluated in 2 plants.
• Biological risk is not negligible, intermediate or high contamination is observed.
• PM10 and endotoxin exposure was not valuable as risk factor at such sampling sites.

The continued expansion of the green economy increases the risk profile for green occupational jobs. One of the broadest green sectors in terms of growth is the anaerobic digestion of biomasses. In recent years, this development has also interested Italian regions. The management of biomass includes biological risk and the risk of particulate and endotoxin exposure. In the present study, we evaluated airborne exposure for anaerobic digestion workers at two real-scale plants. Digested biomass has different origins, ranging from cattle sludge and manure to poultry manure to agricultural harvesting or processing residues, particularly from maize and fruits. Two sampling points were chosen: at the first, the input biomasses were stored, and the hopper was loaded; at the second, the digested sludge exited the digester. The microbiological parameters, assessed using an active sampler and cultural method, were the total bacteria counts (at 22, 37, and 55 °C), yeasts, fungi, Pseudomonaceae, Clostridia spp., Enterobacteriaceae and Actinomycetes. Moreover, at the same sampling points, we evaluated six PM10 fraction levels (10.0–7.2, 7.2–3.0, 3.0–1.5, 1.5–0.95, 0.95–0.49, and <0.49 µm) and the endotoxin content of each fraction. In this investigation, the microbe contamination of the air varied from low to high levels, while the PM10 and endotoxin levels were limited, reaching rural environmental levels (61.40 µg/m3 and 18.88 EU/m3, respectively). However, contamination and occupational risk must be evaluated individually for each plant because numerous variables influence the risk magnitude, particularly digested sludge treatments, such as input biomass nature, storage, movement conditions, building configuration and technological processes.

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