Biogas, or rather methane, is produced in biogas plants by a complex microbial community from biomass in closed fermentation systems under oxygen-free conditions. In Germany, this form of renewable power generation is being used increasingly frequently, with 40,000 jobs having been created in biogas plants. Until recently, the exposition by airborne biological agents at these workplaces was unknown.
To determine this, airborne biological agents were collected by filtration at different workplaces in seven biogas plants. The samples were analysed for their endotoxin content using the Limulus amebocyte lysate test. Furthermore, moulds were quantified and identified, as well as the total cell count determined by microscopy. The bacterial diversity was described with the use of gene analyses. These values were set in relation to outdoor air samples on the windward side of the facility.
The results showed a slight elevation in the measured parameters in biogas plants compared with the outdoor air by a factor of 5 to 10. On the basis of the endotoxin determination, every fifth sample was assigned to the lowest exposure level, "increased", according to TRBA 400. In 40% of the samples, the quantification of the airborne moulds also showed values for the lowest exposure level. A total of 15% of the samples were assigned to the next higher exposure level of "high". The highest concentrations were found for activities in delivery and cleaning. Regarding the analysis of moulds, the composition of the mould community, which differed considerably between the outdoor air and the burdened workplaces, is worthy of particular mention. The analysis of the bacterial composition exhibited an exceptionally complex composition, mainly of bacteria of the order Bacillales or Lactobacillales. Despite this, it did not prove possible to assign many of the detected bacterial genes to any previously known bacterial species.
Considering the duration and frequency of the examined activities at the workplaces and the determined exposure levels, this results in the lowest hazard level according to TRBA 400. If the protective measures in TRBA 214 are taken into account, the results of this project can be considered to pose little concern.
Unit 4.7 "Biological Agents"
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