14 research outputs found
Use of dispersion modelling for Environmental Impact Assessment of biological air pollution from composting: Progress, problems and prospects
© 2017 The Authors With the increase in composting as a sustainable waste management option, biological air pollution (bioaerosols) from composting facilities have become a cause of increasing concern due to their potential health impacts. Estimating community exposure to bioaerosols is problematic due to limitations in current monitoring methods. Atmospheric dispersion modelling can be used to estimate exposure concentrations, however several issues arise from the lack of appropriate bioaerosol data to use as inputs into models, and the complexity of the emission sources at composting facilities. This paper analyses current progress in using dispersion models for bioaerosols, examines the remaining problems and provides recommendations for future prospects in this area. A key finding is the urgent need for guidance for model users to ensure consistent bioaerosol modelling practices
Size fractionation of bioaerosol emissions from green-waste composting
Particle size is a significant factor in determining the dispersal and inhalation risk from bioaerosols. Green-waste composting is a significant source of bioaerosols (including pathogens), but little is known about the distribution of specific taxa across size fractions. To characterise size fractionated bioaerosol emissions from a compost facility, we used a Spectral Intensity Bioaerosol Sensor (SIBS) to quantify total bioaerosols and qPCR and metabarcoding to quantify microbial bioaerosols. Overall, sub-micron bioaerosols predominated, but molecular analysis showed that most (>75%) of the airborne microorganisms were associated with the larger size fractions (>3.3 µm da). The microbial taxa varied significantly by size, with Bacilli dominating the larger, and Actinobacteria the smaller, size fractions. The human pathogen Aspergillus fumigatus dominated the intermediate size fractions (>50% da 1.1–4.7 µm), indicating that it has the potential to disperse widely and once inhaled may penetrate deep into the respiratory system. The abundance of Actinobacteria (>60% at da < 2.1 µm) and other sub-micron bioaerosols suggest that the main health effects from composting bioaerosols may come from allergenic respiratory sensitisation rather than directly via infection. These results emphasise the need to better understand the size distributions of bioaerosols across all taxa in order to model their dispersal and to inform risk assessments of human health related to composting facilities
Characterisation and disersal of bioaerosols emitted from composting facilities
The role of sustainable and natural waste management processes such as composting
are increasingly becoming more important in tackling the current environmental
challenge of the amount of waste that is being produced. However a potential risk of
composting facilities is the release and dispersal of bioaerosols that might result in
adverse health effects in sensitive receptors. Therefore, environmental regulators
request regulatory risk assessments from composting facilities that are within 250m of
sensitive receptors to assess the risk posed by bioaerosols.
The prior art in compost related bioaerosol release and dispersal assessment is not
extensive and gaps in the understanding of bioaerosols at source, on release from
composting facilities and at receptor remain. Therefore, this research was undertaken to
address some of these gaps in the current knowledge and to improve the understanding
of the characterisation and dispersal of bioaerosols emitted from compost.
Therefore firstly two studies were completed in regards to the characterisation of
bioaerosols emitted from compost, in particular in improving the understanding of their
aggregation and size distribution. In this context, a novel methodology (the compost
tumbler) was developed to release and measure bioaerosols in experimental conditions.
Data was generated using a combination of culturing and scanning electron microscopy
methods to characterise the aggregation and size distribution of bioaerosols emitted
from compost. Secondly, site work was conducted to validate the results of these
controlled experiments and characterise the aggregation and size distribution of
bioaerosols emitted from composting facilities. These controlled experiments and site
work showed evidence of aggregation in bioaerosols released from compost. However,
the majority of these bioaerosols were in single cell units hence they are more likely to
be dispersed for longer distances.
Following this, other studies were conducted in regards to the dispersal of bioaerosols
emitted from compost, in particular in improving the understanding of bioaerosol
concentration prediction by air dispersion modelling. Firstly preliminary air dispersion
modelling was completed to assess the ability of a commercial air dispersion model,ADMS 3.3, to predict bioaerosol emissions from composting facilities compared to
bioaerosol concentrations measured by on-site downwind bioaerosol sampling.
Folowing this, the sensitivities of ADMS 3.3 were analysed and the effect of different
modelling parameters on predicted bioaerosol concentrations were assessed. Finally, a
final assessment of the potential of ADMS 3.3 to predict bioaerosol emissions from
composting facilities was conducted. The overall results from the modelling studies
indicated that ADMS 3.3 was not able to consistently predict absolute downwind
bioaerosol concentrations at composting facilities. However it was also concluded that
ADMS 3.3 can be a useful tool for the initial screening and assessing relative changes
of bioaerosols at a compost facility, provided that the detailed assessment of absolute
bioaerosol emissions are made in conjunction with measurement of downwind
bioaerosol concentrations.
The research presented in this thesis makes a significant contribution to knowledge in
terms of improving the understanding of the characterisation and dispersal of
bioaerosols emitted from composting facilities
Morphological classification of bioaerosols from composting using scanning electron microscopy
This research classifies the physical morphology (form and structure) of bioaerosols emitted from open windrow composting. Aggregation state, shape and size of the particles captured are reported alongside the implications for bioaerosol dispersal after release. Bioaerosol sampling took place at a composting facility using personal air filter samplers. Samples were analysed using scanning electron microscopy. Particles were released mainly as small (1 μm) single cells, with aggregates occurring in smaller proportions. Most aggregates consisted of clusters of 2-3 particles as opposed to chains, and were <10 μm in size. No cells were attached to soil debris or wood particles. These small single cells or small aggregates are more likely to disperse further downwind from source, and cell viability may be reduced due to increased exposure to environmental factors
Enumerating actinomycetes in compost bioaerosols at source—Use of soil compost agar to address plate ‘mask
Actinomycetes are the dominant bacteria isolated from bioaerosols sampled at
composting facilities. Here, a novel method for the isolation of actinomycetes
is reported, overcoming masking of conventional agar plates, as well as reducing
analysis time and costs. Repeatable and reliable actinomycetes growth was best
achieved using a soil compost media at an incubation temperature of 44 °C and 7
days’ incubation. The results are of particular value to waste management
operators and their advisors undertaking regulatory risk assessments that
support environmental approvals for compost facilit
Dispersion of bioaerosols from composting facilities.
The promotion of composting as an option for sustainable waste management has
raised concerns regarding public health impacts of exposures to potentially
hazardous bioaerosols. Recent source term experiments show that bioaerosol
emissions are episodic and that peak emissions are related to compost agitation.
The Environment Agency requires risk assessments for facilities that have
sensitive receptors within 250m of their boundary. In order to improve current
risk assessment methodologies, improved predictions of bioaerosol dispersal are
required. Dispersion modelling has been successfully used to determine
dispersion of odours from waste management. In this paper, bioaerosol
concentration data measured at a composting facility is analysed in an ongoing
series of model experiments, using the ADMS air dispersion model. Initial
modelling results reveal that the concentrations of bioaerosols decrease rapidly
with distance from the site, although under certain circumstances, it is
possible that higher concentrations may still be present at 200m from the site
boundary. However, dispersion models are not yet able to take into account all
the properties of bioaerosols, in particular, their viability and their ability
to aggregate and form clumps, which will affect the rate of dispersal. A series
of experiments were designed to examine how the options within dispersion model
affect the dispersion of bioaerosols and under which circumstances high
concentrations may disperse to sensitive receptors. The results will be compared
with bioaerosol measurements taken downwind of a composting facility, to
determine the accuracy of the model predictions. This is the first stage in an
attempt to design a best practice method for modelling bioaerosols
Improving bioaerosol exposure assessments 1 - comparative modelling of 2 emissions from different compost ages and activities.
We present bioaerosol source term concentrations from passive and active
composting sources and compare emissions from green waste compost aged 1, 2, 4,
6, 8, 12 and 16 weeks. Results reveal that the age of compost has little effect
on the bioaerosol concentrations emitted for passive windrow sources. However
emissions from turning compost during the early stages may be higher than during
the later stages of the composting process. The bioaerosol emissions from
passive sources were in the range of 103–104 cfu m−3, with releases from active
sources typically 1-log higher. We propose improvements to current risk
assessment methodologies by examining emission rates and the differences between
two air dispersion models for the prediction of downwind bioaerosol
concentrations at off-site points of exposure. The SCREEN3 model provides a more
precautionary estimate of the source depletion curves of bioaerosol emissions in
comparison to ADMS 3.3. The results from both models predict that bioaerosol
concentrations decrease to below typical background concentrations before 250 m,
the distance at which the regulator in England and Wales may require a risk
assessment to be compl
Progress towards a best practice method for modelling dispersion of bioaerosols from composting facilities
The promotion of composting in the UK as a sustainable waste management option has led to concerns regarding exposure of the public to potentially harmful emissions of airborne micro-organisms or bioaerosols. In response to public concerns, the Environment Agency in England and Wales requires a risk assessment for any licensed composting facility that has a sensitive receptor within 250m of the site boundary. An ongoing programme of studies in association with the Environment Agency has begun to explore methods to improve exposure assessments for bioaerosols. Our results have shown that is is possible to use air dispersion models for estimating downwind concentrations of bioaerosols, and the more advanced modelling options, such as the use of intermittent emission rates, result in lower downwind concentrations. Current risk assessments may be over-estimating the exposure of receptors to bioaerosols from composting, however further studies are needed to validate the results presented here. 1. INTRODUCTION The promotion of composting in the UK as a more sustainable waste management option has led to concerns regarding exposure of the public to potentially harmful emissions of airborne microorganisms or bioaerosols. The composting process is reliant on various micro-organisms, such as bacteria and fungi, to break down the organic matter. However, if as a result of composting operations these micro-organisms become airborne, may be breathed in, and due to their small size, can penetrate deep into the human respiratory system. Conditions such as farmer's lung disease and aspergillosis (Latgé, 1999) have been linked to high concentrations of bioaerosols, although dose-response relationships are not well defined. In response to public concerns, the Environment Agency in England and Wales requires a risk assessment for any licensed composting facility that has a sensitive receptor within 250m of th