Pollutant-specific performance of a stack-level deodorisation system for ammonia, hydrogen sulfide and odour emissions from a non-hazardous waste mechanical treatment and drying plant: an emission and dispersion-modelling assessment

Introduction. Air emissions, particularly odour, ammonia (NH₃) and hydrogen sulfide (H₂S), are key constraints on the social acceptance and permitting of waste-treatment facilities located near sensitive receptors. Although odour-abatement technologies are widely available, their real-world effectiveness is pollutant-specific and condition-dependent, and reductions achieved at the source do not necessarily translate into proportional improvements in ground-level concentrations. This study evaluates a stack-level deodorisation system installed on a non-hazardous solid-waste mechanical treatment and drying plant (approximately 30 t·h⁻¹) in Romania.

Methods. Directed emissions were characterised during a measurement campaign across three exhaust stacks under two operational scenarios: operation without and operation with injection of a vaporised concentrated neutralising reagent. Odour concentration was quantified by dynamic olfactometry (SR EN 13725:2022); NH₃ and H₂S were measured with portable electrochemical and infrared analysers, respectively. Pollutant mass emission rates and odour emission rates were derived from measured concentrations and normalised volumetric flow rates, and used as inputs for AERMOD atmospheric dispersion modelling to estimate maximum ground-level concentrations.

Results. Performance was pollutant-specific. With the system operating, maximum modelled ground-level H₂S decreased from approximately 469 to 429 µg·m⁻³ and odour from approximately 175 to 139 ouE·m⁻³, whereas NH₃ increased from approximately 55 to 98 µg·m⁻³, likely reflecting an ammonium-based reagent composition. The spatial dispersion patterns and the extent of the impacted areas for odour and H₂S remained largely unchanged. Exhaust temperature and relative humidity arising from waste drying strongly influenced the release and transport of odour-active compounds.

Conclusions. Source-level treatment produced only modest, pollutant-dependent changes at ground level and even increased the NH₃ impact. Effective odour management therefore requires an integrated assessment combining control technologies, standardised olfactometry and dispersion modelling, rather than reliance on a small set of chemical indicators.