Microorganism and odor emissions from composting plants often lead to acceptance problems, especially for people living close to such plants. Both parameters were studied in a systematic approach under specific local climate conditions at nine different composting plants in Germany with emphasis on microorganisms. Selected results from four samplings are presented. Both emission and immission measurements were performed under "normal case" and "real worst case" conditions, i.e. conditions which weretypical for the specific locations (local climatic conditions, and working activities at the plants), or during which obvious spread of bioaerosols from the composting facility into the surrounding environment could be documented. Airborne microorganismswere sampled using filitration and impingement. Subsequent cultivation on four different culture media allowed quantification and also partial identification of the microflora. It was determinated that a general statement about the emission of microorganisms from composting plants is not a realistic option. The site specific meteorological situations must be considered carefully in any samplingprotocol and, hence, any siting strategy. Air inversions in particular can lead to high microorganism concentrations (>104-105 cfu m~(-3) of thermophilic actinomycetes and thermophilic fungi) in the surroundings of composting plants. Finally, it was determinated that thermophilic fungi and actinomycetes can serve as indicator organism groups.
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