Sludge Watch ==> Aerosolized bacteria dispersed by composting sites - study

[Maureen Reilly]

The assessment of airborne bacterial contamination in three composting 
plants revealed site-related biological hazard and seasonal variations.

Fracchia L,
Pietronave S,
Rinaldi M,
Martinotti MG.

Department of Chemical, Food, Pharmaceutical and Pharmacological Sciences 
(DiSCAFF), University of Eastern Piedmont Amedeo Avogadro, Novara, Italy. 
letizia.fracchia at pharm.unipmn.it

AIMS: The purpose of this study was to evaluate the degree of bacterial 
contamination generated by three Italian composting plants (1, 2 and 3) in 
two different seasons and to assess the health risk for the employees.

METHODS AND RESULTS: Aerosols samples were collected with an agar impact 
sampler. Several plant sites and external upwind and downwind controls were 
examined. Total colony-forming counts of mesophilic and thermophilic 
bacteria, actinomycetes and streptomycetes, Gram-negatives, coliforms and 
sulfite-reducers were determined. Selective media were used in order to 
isolate pathogenic bacteria. The levels of total mesophilic and thermophilic 
micro-organisms ranged between 33 and >40,000 CFU m(-3) in plant 1, 39 and 
18,700 CFU m(-3) in plant 2 and 261 and 6278 CFU m(-3) in plant 3. Strains 
of Escherichia coli, Staphylococcus aureus and Clostridium perfringens were 
also found.

CONCLUSIONS: The plants monitored in this study have proved to be sources of 
aerosolized bacteria. The activities involving mechanical movement of the 
composting mass and the indoor activities were of greatest potential risk. 
In all the studied plants, a statistically significant dependence was found 
between the bacterial contamination and the season for some or almost all 
the analysed parameters, but a clear seasonal trend could not be observed.

SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides broad evidence of 
bacterial aerosol dispersion and site-related biological hazards that may be 
useful to the regional government to implement regulations on worker safety 
in composting plants.