Odour emission management in composting plants and facilities treating the organic fraction of municipal solid waste (OFMSW) is one of the most critical challenges in the sector, from environmental, operational and community-relations perspectives.
The complexity does not arise from a single source. Each stage of the process, from material reception to maturation cells, generates emissions with different characteristics in terms of compound composition, intensity, temporal variability and containment potential. Adopting a single standardised control system almost always results in an inadequate response to all critical issues, rather than effectively addressing each individual source.
Facilities subject to Integrated Environmental Authorisation operate under the requirements of Commission Implementing Decision (EU) 2018/1147 of 10 August 2018, which establishes conclusions on Best Available Techniques (BAT) for waste treatment pursuant to Directive 2010/75/EU of the European Parliament and of the Council (including a BAT-AEL ranging from 200 to 1,000 OUE/m³ for biological waste treatment plants). In addition, all facilities are subject to the provisions of MASE Decree No. 309/2023, which requires the submission of an odour impact assessment study during the authorisation process or in the event of complaints from local residents.
Compliance cannot be demonstrated through generic control systems: it requires solutions that are correctly sized according to the actual operating conditions of the site.
This article examines the four main emission sources in these facilities and the criteria that guide the selection of the most suitable technology for each of them.
Odour emissions in composting and OFMSW treatment facilities have a direct biological origin: they result from the degradation of organic matter under conditions that continuously change throughout the various stages of the process.
The main emitted compounds are:
What distinguishes these facilities from other industrial sources is the dual variability of their emissions: they vary over time according to the biological stage, operating conditions and seasonal factors, and they vary spatially because different sources generate different emission profiles. This dual variability is the reason why there is no single engineering solution suitable for the entire facility.
The key design distinction is between channelled emissions and diffuse emissions. The former, originating from localised extraction systems or enclosed areas, are captured and can therefore be treated using dedicated filtration systems. The latter, typical of receiving areas, buildings with frequently opened doors and maturation areas, cannot be channelled by their very nature and require perimeter containment systems. The choice of the most appropriate control measure, even before selecting the specific technology, depends on this classification.
The following sections describe four solutions for four typical emission sources found in composting and organic waste treatment facilities. Each case illustrates a different intervention strategy based on the specific characteristics of the area involved.
Waste reception and unloading areas represent the first emission source. Incoming waste, characterised by high organic loads and varying stages of fermentation, releases sulphur compounds and VOCs even during transport and unloading operations. The situation worsens when building doors are opened, interrupting the enclosure of the facility and allowing accumulated emissions to disperse into the surrounding environment.
The main critical issues in this area are:
The most cost-effective solution is an osmogenic barrier synchronised with operating cycles, acting only during periods of actual criticality without requiring continuous full-capacity operation.
At a composting facility, we installed an HPS midi var system with 450 metres of distribution line along the building doors and in areas affected by diffuse, non-channelled emissions. The project included:
In sorting, shredding and material transfer areas, odour emissions are generated directly by mechanical operations on conveyor belts: they are concentrated at the working points and vary in intensity depending on the type and condition of the material being handled. These are not diffuse emissions spread across large areas, but localised and continuous releases associated with the most intensive operating phases.
The main critical issues in this area are:
This localisation is both the challenge and the key design consideration. An extensive system sized to cover large areas would be oversized for the actual requirements, resulting in unnecessary consumption and operating costs. The appropriate solution is a compact and targeted system installed directly in the areas with the highest emission levels, with nozzle distribution calibrated according to the actual release points.
The solution we implemented in a mechanical treatment section involved the installation of an HPS midi fresh system with 50 metres of distribution line and 10 nozzles positioned directly above the conveyor belts. The project included:
The system eliminated odour nuisance complaints in the affected operational areas, achieving a significant reduction in localised odour concentrations.
In bio-oxidation and maturation cells, the constant presence of organic material undergoing biological degradation generates odour emissions with two distinctive characteristics: high concentrations of sulphur compounds and ammonia during periods of intense microbial activity, and strong, unpredictable emission peaks during material turning operations. These two characteristics—continuous background emissions and operational peaks—define the requirements of the control system.
The main critical issues in this area are:
It is not always possible to address emissions in this area through localised extraction systems (the optimal solution from both a technical and operational standpoint). In such cases, the issue can be mitigated using a perimeter barrier providing uniform coverage and continuous operation, sized to maintain effective containment even during peak emission conditions.
For a composting facility located adjacent to a residential area, we designed and installed an HPS EVO system with 200 metres of distribution line and 56 nozzles positioned around the perimeter of the maturation cells. The project included:
Ammonia-containing emissions in composting plants are concentrated in sections with higher fermentative activity and have a characteristic that distinguishes them from the sources described in the previous sections: they are channelled emissions, captured at specific points, with concentrations that can vary significantly depending on operational phases but that nonetheless require a chemically specific abatement system.
The main critical issues in this area are:
Ammonia does not respond effectively to generic filtration systems. The appropriate technological choice is a dry treatment system based on selective chemical adsorption, which ensures high removal efficiency even in the presence of variable emission loads and avoids the operational complexity of wet scrubbers. Under the most demanding operating conditions, however, treating channelled emissions alone is not sufficient: residual dispersion in operational areas requires an odour polishing system to complete the abatement cycle without overloading the primary system.
For this type of issue, we designed and installed an extraction and treatment system with a DKFil dry filter, sized for a flow rate of 4,000 Nm³/h, integrated with an additional odour polishing stage using an ultrasonic osmogenic barrier. The project included:
The four examples described show technically different solutions applied to emission sources within the same facility.
In three out of four cases, the chosen control system belongs to the same technological family—osmogenic barriers—but with radically different configurations and sizing logics. In the fourth case, the channelled nature of the emissions led to a primary abatement system integrated with an odour polishing stage.
This variability is not random: it is the direct result of an analysis of emission characteristics that always precedes the selection of the engineering solution.
The variables that determine technology selection are:
None of these variables can be properly assessed without on-site emission characterisation. Sizing based on literature values or similar case histories is a starting point, not a substitute for measurement.
For this reason, our interventions include a preliminary chemical and olfactometric analysis phase, carried out in collaboration with the Gesteco Analysis Laboratory and the LOD Olfactometric Laboratory, both part of Gruppo Luci.
This phase allows emissions to be characterised with precision, identifies the compounds responsible for odour nuisance, and quantifies the odour load to be abated in order to comply with the limits set by authorisations.
The same approach is also applied to existing plants with already installed systems. In many cases, composting facilities are equipped with outdated or undersized systems compared to current operating conditions.
Our revamping service starts with an assessment of the existing situation, identifies the causes of inefficiencies, and proposes targeted interventions that restore performance without necessarily replacing the entire system.
A preliminary assessment is also available through our consultancy service.
Every composting and organic waste treatment facility presents a unique combination of emission sources that is not replicated elsewhere. The four examples described show how different sources, even within the same site, require distinct intervention strategies. It is this variability that makes a preliminary assessment of the actual emission characteristics essential before any engineering solution is selected.
If you manage a composting or OFMSW treatment facility and are evaluating a new control system or assessing the efficiency of an existing one, contact us for a technical site inspection. We analyse the critical issues of your plant and propose the most suitable solution.