Growing attention to environmental quality and quality of life has led to the recognition of unpleasant odours as a form of air pollution in their own right. Odour pollution from commercial kitchens and restaurants can significantly affect neighbours’ comfort and trigger complaints, even when conventional pollutant limits are respected.
From a technical point of view, an odour can be described as any gaseous emission detectable by the sense of smell, while an odorous substance is the chemical responsible for generating that sensation. Odours are characterised by several properties:
- Hedonic tone: how pleasant or unpleasant an odour is perceived to be.
- Quality: the type of odour (for example “oily”, “fatty” or “pungent”).
- Concentration: the amount of odour present in an air sample; in sensory analysis this is often expressed in odour units per cubic metre (OU/m3).
- Intensity: the perceived strength of the odour, from detection threshold up to irritation.
Odour is a complex phenomenon not only because of the wide range of potential odorants, but also because the ability of a compound to be perceived (its “odour potential”) depends on objective properties (volatility, solubility, etc.), on subjective aspects (physiology and psychology of the observer) and on environmental conditions (temperature, humidity, wind, dilution in the atmosphere). The same emission can be perceived very differently by different people and at different distances from the source.
Odorous compounds are not necessarily associated with a real toxic risk for human health, especially at the low concentrations usually involved. Nevertheless, odour emissions with no specific toxicological relevance can still be a major source of tension between food businesses and the surrounding community, because odours spread over wide areas and can have a strong impact on perceived quality of life.
Odour pollution from commercial kitchens
The nuisance caused by odours from cooking is increasingly common, especially in urban environments. Emissions from commercial kitchens and restaurants typically contain fatty acids, aliphatic and aromatic hydrocarbons, aromatic amines and aldehydes. The type and quantity of pollutants emitted depend mainly on:
- the foods being cooked,
- the cooking methods (frying, grilling, baking, etc.),
- the energy source and the characteristics of the extraction system.
Regulation of odour emissions is not uniform. In many countries and regions, odour is recognised as a form of air pollution and general principles apply, but specific odour limits and criteria are often defined at regional or local level and may target certain categories of activities. In practice, complaints from residents are often the real “trigger” for investigations and mitigation measures.
For operators in the food service sector (restaurants, takeaways, rotisseries, bakeries, etc.), this means that a purely reactive approach is no longer sufficient. Preventive measures are increasingly important: properly designed extraction systems, effective odour abatement and regular maintenance can greatly reduce the risk of complaints and disputes.
From problem to solution: designing filtration for commercial kitchens
Before choosing a filtration system, it is essential to analyse in detail the specific cooking process and installation:
- type of cuisine and typical dishes,
- prevalent cooking methods (e.g. intensive frying or grilling),
- operating hours and peak loads,
- location of the kitchen in relation to sensitive receptors (neighbours, residential areas, hotels, schools, etc.),
- current extraction and ductwork configuration.
Because the range of odorous substances is wide and their properties differ, a single filtration mechanism is rarely sufficient. In most cases, an effective solution combines:
- particulate pre-filtration, to remove grease and aerosols;
- odour filtration, typically based on adsorption media such as activated carbon.
Particulate filters: the first line of defence
Particulate filters form the first stage of filtration in commercial kitchen extraction systems. Their main task is to intercept the coarse particles and grease droplets carried by the exhaust air, in order to:
- protect downstream components (fans, ducts, odour filters),
- avoid fouling of odour filters, which would quickly become a source of rancid smells themselves,
- reduce fire risk linked to grease accumulation.
Two main categories can be distinguished:
Mechanical filters
These are typically metallic or synthetic-fibre media crossed by the contaminated air stream, where particles are captured through interception and impaction. Since frequent cleaning is essential, they must be easy to access, remove and wash. Their dimensions should ideally allow cleaning in standard professional dishwashers.
Electrostatic filters
In electrostatic precipitators, air passes through ionising sections and collecting plates at different potentials. Particles are charged and then captured by the electric field. These filters can be very effective, but they also soil quickly and require regular maintenance, sometimes more complex than for mechanical filters. Newer designs aim to simplify cleaning by making the collecting plates easier to remove and wash.
Odour filters: activated carbon and beyond
Odour filters are mainly based on three mechanisms: adsorption, dry scrubbing and absorption. The most widely used approach in commercial kitchens is adsorption on porous media.
In adsorption, odorous substances in the gas phase are captured on the surface of a solid medium, reducing their concentration below perception thresholds. Typical adsorbents include granular activated carbon, activated alumina and silica gel. These materials retain odorous molecules within their internal pore structure through physical forces.
The performance of an adsorption system depends on:
- the nature and concentration of the odorous compounds,
- contact time between air and medium,
- air temperature,
- relative humidity of the air.
Activated carbon is the most common choice thanks to its favourable cost–effectiveness ratio. However, its adsorption capacity decreases markedly in very humid conditions: when relative humidity is high, water competes with organic compounds for the same adsorption sites. In such cases, alternatives like silica gel, pre-dehumidification or over-dimensioning of the carbon bed may be required.
The sizing of an activated carbon cell is always a compromise between removal efficiency and pressure drop. Smaller granules offer higher surface area and better performance, but also higher pressure losses. Activated carbon can also be impregnated with specific chemicals to enhance removal of certain target substances.
Once all available pores are occupied by odorous molecules, the adsorption medium is exhausted and must be replaced or regenerated. For a given source, the service life of the filter depends mainly on the thickness (and thus the mass) of the adsorbent layer and on the incoming load of pollutants.
Adsorption works best at relatively low temperatures (typically below 60 °C). Above certain humidity levels the filter may need to be oversized, or air should be cooled and dehumidified upstream to preserve efficiency.
Design and maintenance: key to long-term performance
Whatever technologies are chosen, the filtration system must be properly designed, installed and maintained to deliver stable performance over time. This includes:
- matching the layout of hoods, ducts and filters to the real airflows and grease loads,
- choosing adequate pre-filtration stages for particulate and grease,
- dimensioning activated carbon filters with suitable contact time and media volume,
- planning regular cleaning and replacement of filters based on monitored pressure drops and operating hours.
In practice, kitchens with intensive frying or grilling require more robust and often multi-stage filtration systems than those where boiling or baking prevail. Retrofitting an existing system may involve combining improved local capture (hoods and canopies), better duct design and a dedicated odour abatement module based on activated carbon or hybrid solutions.
Ultimately, odour management in commercial kitchens is not just a matter of comfort, but a key factor in community relations and regulatory compliance. Proper design and maintenance of particulate and activated carbon filters are essential to control odours in commercial kitchens and restaurants, protecting both the surrounding environment and the long-term operation of the business.