How to approach odour abatement measures in the food industry and the different odour abatement techniques currently available for the food industry.
Odour emissions are regulated in many countries. In some jurisdictions there are quantified odour limits that can be related to the magnitude of odour emissions, or alternatively to the maximum concentration of a component or group of components known as odour emissions. The internationally accepted unit of measurement is the "Odour Unit per cubic metre" (ouE/m3), but there are other methodologies. The most common techniques for measuring odours are the following:
- Dynamic olfactometry
- Psychometry
- Field inspections
- Dynamic olfactometry
- Field olfactometry
- Physico-chemical methods
- Colorimetric methods
- Electronic detectors
- Gas chromatography
- Electronic noses
The most widely used technique in Europe for odour measurement is Olfactometry coupled with the application of a dispersion model.
In Germany the legislation for odour generating processes focuses on ensuring that the concentration at the stack outlet is limited with respect to the process taking place and the efficiency of an abatement plan. The basic legislation is the TA Luft, which contains a general reference on odour emissions and describes the need for abatement plans to achieve a 99% odour reduction for emissions above 100000 OU/m3.
In the Netherlands, the Air Emission Guideline (InfoMil), mentioned the objective of odour nuisance prevention or abatement. This guideline set an upper limit of 5 OU/m3 p98 for existing installations and suggested a limit of 0.5 OU/m3 99.5% percentile for new installations (although the latter is not a limit).
BEST AVAILABLE TECHNIQUES
In the case of the food industry, there are several guides or reference documents on best available techniques, although the reference guide is the Best Available Techniques Reference Document on Food, Drink and Milk. For each production process, there are countless guides published by the IPTS, or by other national public and private organisations. For example, for the sugar industry, the main reference for this sub-sector is the Guide to Establish Best Available Techniques in the European Sugar Industry, Comite European des Fabricants de Sucre; although there are also other guides such as the "BATNEEC Guidance Note For The Manufacture of Sugar" or the Best Available Technology in the Danish Sugar Industry.
Existing or possible measures to prevent, reduce and control odour emissions in the food industry range from relatively simple containment measures to sophisticated end-of-pipe and recovery technologies and include:
- Load minimisation
- Containment
- Recovery/recycling
- Emission reduction
- Wastewater treatment and management
The technical applicability of the above measures has been demonstrated by various sources. Used individually or in combination, the measures represent the solutions when applied in the appropriate circumstances. These circumstances depend on the scale of the plant, the number of different products used, etc.
The most relevant techniques will be briefly mentioned. For further information it is necessary to consult the documents cited at the end of this report in the bibliography.
- Technologies for load minimisation:
Sulphur reduction using gas boiler for direct drying.
Optimisation of water use
Dry cleaning equipment and vacuum drying systems.
Separation of cooling and process water from effluents of different origin to enable appropriate treatment options.
- Emission prevention.
Covering of materials.
storage, handling, processing and transfer to a suitable building.
Enclosed storage and transfer systems for ground material, raw material, etc.
Insulation of tanks
Use of covered conveyor belts for dusty materials.
System checks to prevent receipt of unsuitable materials to ensure FIFO (First In First Out).
Spill protection of storage tanks.
Condensers in all appropriate processes, e.g. evaporators, vacuum devices.
- Technologies for recovery and recycling
Reuse of process and waste water
Water vapour recovery for reuse
- Technologies to treat air emissions
Condensation
Filtration
Cyclones
Scrubbers
- Technologies to treat wastewater
Primary treatment
pH correction/neutralisation
Sedimentation/filtration/flotation
Coagulation/flocculation/precipitation
Secondary treatments
Biofilters
Anaerobic treatment
Active sludge
Nitrification/denitrification
Tertiary treatments
- Technologies for wastewater treatment and disposal.
Sludge treatment
Gravity
Filtration
Centrifugation
Digestion
Drying
Section 4.4* of the Best Available Techniques Reference Document on Food, Drink and Milk "odour emission control" describes numerous techniques to reduce odours in the food industry. The techniques mentioned and the headings involved are listed below**.
4.4.3.1 Optimisation of the odour abatement equipment
4.4.3.2 Source air emission ducting - local ventilation stack
4.4.3.3 Dynamic separation techniques 4.4.3.8 Absorption of odour emissions
4.4.3.8 Absorption
4.4.3.9 Adsorption
4.4.3.10 Biological treatment
4.4.3.11 Thermal waste gas treatment 4.4.3.12 Waste gas treatment
4.4.3.12 Non-thermal plasma treatment 4.4.3.13 Dissolution of waste gases
4.4.3.13 Physical dispersion of odour/vOC emissions
For each of the headings there are further sub-sections describing the techniques under each heading, e.g. for heading 4.4.3.8 "Absorption", we have sub-section 4.4.3.8.2 Plate absorber, 4.4.3.8.3 Spray chamber or 4.4.3.8.1 Packed bed absorber.
However, one of the most important sources of odour in the food industry are the process water treatment plants or the ponds where this water is deposited. In this case, the accumulation of organic matter and its subsequent degradation is a frequent cause of odour emissions.
In this case, section 4.5. Wastewater treatment at the end-of-pipe (discharge point) and in particular 4.5.7 Wastewater treatment by sector are very informative. For example section 4.5.7.2 which examines the techniques available for the treatment of waste water from the fish and shellfish industry.
These techniques go beyond the simple covering of a basin or the installation of walls or screens against the prevailing wind direction and include aspects such as further anaerobic treatment or the installation of bio-towers, fluidised bed reactors, hybrid processes, etc.
In any case, an odour abatement system installed on odorous emission sources should have an odour abatement efficiency of not less than 95%, determined by sampling and analysis by dynamic olfactometry according to UNE-EN 13725.
To prolong the "reasonable operational life" of odour abatement equipment, it should be properly maintained and repaired. The physical condition of the odour abatement technique (potential for leakage, availability of spare parts, increased frequency of malfunction or failure) and the odour abatement efficiency (that the technique is not able after some time to reach the initial odour abatement efficiency) should be considered as key indicators of whether the equipment is reaching the end of its operational life.
