A novel tool for estimating the odour emissions of composting plants in air pollution management

Odour emissions are a major environmental issue in sanitary environmental engineering
plants, due to the increasing number of complaints being made by the exposed population.
The particular and complex nature of the substances considered to be the cause of the odour
impact, their variability in time and the climatic conditions, as well as the subjectivity of the
odour perception, are the elements that have delayed their regulation. For this reason there
are few international laws that set the limits of odour emissions from industrial sources and/or
define the criteria of quality related to the smell. In particular, there are currently no
regulations that deal with this problem in Italy.
Analytical techniques such as the use of surrogate chemical markers (i.e. H2S or NH3) as well
as the chemical analysis of odorous mixtures by chromatographic techniques (i.e. GC-MS)
can be used for continuous assessment, but are limited, due to usually being compound
specific, which may not always relate to olfactory perception. Whereas olfactory assessment
offers an accurate measurement of olfactory annoyance. However, the cost, potential
subjectivity and time restrictions (due to being laboratory based) make them unsuitable for
continuous assessment in terms of air quality monitoring.
In this study, a novel tool based on a highly innovative on-site analytical instrument (Portable
GC-MS Hapsite, Inficon) was used to identify and characterize the volatile substances that
cause odour annoyance and the main sources in a composting plant. At the same time, this
work identified odours key compounds and investigated the relationship between their
concentration measured by GC-MS analysis and the performances of the plant. The main
chemical substances responsible for the olfactory annoyances were also identified. In
conclusion, odour abatement system (static biofilter) efficiency was tested in terms of
reduction of both key compounds and quality of the clean gas composition.
The results highlight the applicability of this tool in directly monitoring odour emissions in
terms of air pollution management. 38 different substances are detected, with almost half
being smell relevant components as well as responsible for the typical smell of composting
plants. Limonene and 2-Butanone are identified as key compounds connected to the specific
production process.