Measurement and Modelling of
Emissions from Three Composting Sites
The focus of this project is on improving regulatory risk assessments.
Ongoing research has improved the quality of source term data used in
regulatory risk assessments and this study aimed to improve modelling
of bioaerosols downwind of composting facilities, by examining the
influences on variability of emissions.
Objectives of research
In order to achieve these objectives, three different composting
facilities were chosen as case studies, each representing different a
- Examine bioaerosol and odour emissions from in-vessel and
open windrow composting facilities.
- Examine the seasonal differences in bioaerosol emissions
- Examine the bioaerosol emissions from different input
- Examine the downwind dispersal of bioaerosols and odour
- Place the results of this study within the context of other
published studies on bioaerosols and health impacts
Bioaerosol samples were collected using a SKC personal air filter
sampler. The bioaerosols examined were Aspergillus fumigatus and
actinomycetes. The sampling locations at each facility were determined
depending on facility layout and activities taking place during each
site visit. Each site was visited on three different days during three
different seasons to capture any seasonal variation, with a total of
nine sampling days.
- Site A: Open windrow composting system (Green waste)
- Site B: Vertical, continuous flow silo cage composting
system (Animal by-products waste)
- Site C: Thermally insulated in-vessel composting system
(Municipal solid waste)
The odour sampling was carried out for all three composting sites
during the summer, as it was estimated that odour concentrations would
be highest during warmer conditions. A sampling hood was used for the
windrow and silo cage composting systems to estimate the odour
concentrations from static emissions, and ‘stack’
sampling was used for the municipal solid waste in-vessel composting
system as these represent point source emissions only.
Key findings and recommendations
Keywords: bioaerosols, composting, risk assessment, dispersion modeling.
The two in-vessel composting
facilities had higher measured odour concentrations than the open
windrow site. However, as they are both in-vessel, their impact on the
surrounding communities might be minimised. The sampling at site C was
carried out straight from the in-vessel units, before the biofilter
that should control odour and bioaerosol emissions. Likewise planned
installation of an exhaust management system at site B will help to
control emissions at this site.
The seasonal variation of
Aspergillus fumigatus at all the three sites was up to 1-log10.
For all sites, the
concentrations of both A. fumigatus and actinomycetes in the autumn
were higher than the concentrations detected in the summer and winter.
For all sites and all
seasons, the results indicated that background concentrations (such as
upwind or downwind) of actinomycetes were lower than the concentrations
from on-site activities and sources. For A. fumigatus, the results were
less conclusive, with some of the on-site concentrations being lower
than the background concentrations.
Site C had the highest
concentrations of actinomycetes during the summer and winter. Site A
had the highest concentrations of actinomycetes during the autumn.
The compost agar performed
better as a growth media for actinomycetes compared to the half
strength nutrient agar. The actinomycetes growth when using half
strength nutrient agar was masked by other species of bacteria.
In general, there was no
link between the age of compost grab samples, their moisture content
and the concentrations of micro-organisms detected in the compost grab
The concentration of
micro-organisms in the compost grab samples was always higher than in
the equivalent air sample.
The results do not
conclusively show which composting technology and which input material
will consistently produce the highest bioaerosols emissions.
Dispersion modelling of the
static emissions shows that both dispersion models underestimate the
downwind concentrations (in comparison to sampled concentrations) by 1-
to 3-log10. For the agitation activities, the model predictions of
downwind concentrations were within the same order of magnitude as the
sampled concentrations, suggesting that the major contribution to
downwind emissions was from agitation activities, as shown by other
A comparison of the best and
worst case emission scenarios revealed that sealing the leakage areas
of the buildings at Site B may lower the downwind bioaerosol
concentrations by up to 3-log10.
The majority of the sampled
concentrations reduce to below the suggested threshold limit value of
Wheeler et al. (2001) of 1000 cfu/m3 by 250 m downwind of the sites.
The sampled concentrations
are within the same range as previously reported at source measurements
(e.g. Taha et al., 2006; 2007a)
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£25.00, less 20% to FWR members.
N.B. The report is available for download from the SNIFFER Website