Odor Control Methods
The methods and techniques set out in this Guide are intended to serve to provide insight to those who wish to follow them and are not legally binding. The information mentioned is analyzed according to the technological level of the period in which they were drafted. Along with ever-changing conditions and developing technology, the practice of these techniques may change, and new practices and technologies may also be on the agenda.
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Undesired odors may occur due to the processes used in the activities they originate from, or they may arise from problems in the operation of the facility and from operational inadequacy. Odor control methods can be discussed under two separate categories:
- By facility type
- By precaution structure
By facility type:
When examining the facilities and activities that cause bad odors, it is seen that the source and structure of the odors that occur, as well as the methods that can be applied to prevent them, may vary depending on the type of these activities. The activities that cause the most odor formation and the precautionary methods that can be applied in these areas are listed below:
Food Industry
- Process Control: Raw materials used in production, their processing, closed or open processes, working temperatures and times, ventilation conditions, etc.,
- Storage: Storage duration and temperatures of organic substances, raw materials, and products, warehouse structure, etc.,
- Absorption: Purification of odorous gases and liquids by absorption,
- Bio-filter: Purification of the resulting odorous gases and liquids by breaking them down by bacteria in a biological environment,
- Oxidation: Oxidation and breakdown of the resulting odorous gases and liquids and purification in this way.
Animal Farms
The working method and physical structure of these facilities greatly affect the formation of odors. In this respect, the most appropriate way to prevent odor formation is to establish and operate these facilities according to certain standards. There are guides prepared by various institutions and organizations for such facilities that give great importance to odor formation.
- VDI (Association of German Engineers) 3471, 3472,
- EC Directive 2001/88/EC (Related to pig health),
- Suitable stable/pen conditions and ventilation (DIN 18910),
- Keeping stables clean and dry,
- The use of moisture-proof floor coverings,
- The design of the manure storage buildings must have a storage capacity of at least 6 months and leak-proof concrete floors,
- Implementation of safety distance: as a last resort, maintaining certain distances between certain facilities and surrounding residential and commercial activities (Germany, Ireland, Spain, etc.),
- Dutch practice: Capacity limitation based on the distance between the facility and surrounding units,
- Research in progress: Reducing odor emissions by changing animal feeding regime.
Slaughterhouse and Animal By-Products
- Rapid processing of substances,
- Storage of by-products for short periods of time and at low temperatures,
- Burning of non-condensable steam and gases,
- Separation of process water from non-process water,
- Collecting process/plant air and burning it in the incineration plant,
- Odor-trapping backup systems (Activated carbon, etc.).
Slaughterhouse and Animal By-Products – Rendering
- Condensation of cooking steam,
- Incineration or biofiltration of non-condensable vapors and gases,
- Thermal oxidation and/or biofiltration of steam and gases,
- Shutting down the entire process line,
- Removal of water from blood before rendering (by vapor coagulation).
Fish Meal and Oil
- Use of fresh raw materials,
- Collecting and burning process air.
Wastewater Treatment Plants
- Closed systems: Units such as pre-sedimentation basins and anaerobic treatment pools that cause odor but cannot be prevented due to the process, should be covered to prevent the spread of odorous gases into the environment, then collected and purified.
- Passing all organic process gases through the biofilter.
- Flare in Chimneys: Burning of the odorous gases formed in various cases with a flare chimney. In this context, the ground flare system should be prevented.
Tanneries
- Closed systems,
- Convenient storage,
- Stock flow control,
- Purification of odorous gases with wet washing systems,
- Adsorption,
- Biofiltering,
- Exhaust gas incineration: collection and burning of odorous gases.
Iron and Steel Plants
- Purification of gases exhausted from furnaces,
- Preventing smoke from forming during casting,
- Cleaning and reuse of washing water,
- Condensation of smoke from granulation.
By Precautionary Structure
When odor pollution control and elimination is approached according to the principles of cleaner production and prevention of pollution at source, it is seen that preventing odor from occurring is more effective and preferable than methods such as treatment or safety distancing. When approached from this perspective, odor prevention methods are specified as follows in decreasing order of preference according to the structure of the precaution:
- Prevention at the source,
- Treatment,
- Dilution,
- Reducing its effectiveness / Masking.
Prevention at the source
Preventing odor before it occurs would be a more economical and effective method. This can be done by improving the production structure and operating conditions of the facility.
- Use of appropriate raw materials: Among the alternatives, raw materials that will not cause odor formation should be preferred. The possible cost difference should be evaluated by taking into account the treatment cost.
- Proper raw material and waste storage: The construction of warehouses and storage conditions in accordance with certain standards is one of the methods that most affect odor formation. It is especially important in the food and livestock industry.
- Process control.
- Prevention of leakages: Carrying out the processes in closed environments as much as possible, preventing leaks in pipes and boilers, and collecting and purifying odorous process gases. (Good Housekeeping).
Treatment: Purification of odorous gases and liquids from odor-forming compounds. For this purpose, in addition to general purification techniques, specific techniques are also used.
- Steam condensation
- Adsorption
- Absorption
- Biofilter
- Wet filtration
- Incineration
- Thermal oxidation
- Catalytic oxidation
- Electrostatic filtering
Condensation
Condensation is a technique for removing solvent vapors or other odorous gases from waste gas by lowering their temperature below their dew point. In odorous gases, water, which is usually separated from water-saturated gas by condensation, acts as an absorber in odorous gases and in this way, the odorous gas is purified. The application limit for odorous gases is 100,000 odor units/Nm3.
Adsorption
Adsorption is a heterogeneous reaction in which gas molecules adhere to solid surfaces with a preference for certain compounds over others and are thus separated from the liquid.
Biofiltration
Here, the odorous gas is passed through a bacterial environment, and the bacteria break down various substances in the gas as nutrients. In the effectiveness of such facilities, the provision and maintenance of operating conditions are as important as the design criteria. For example, the humidity and temperature of the filter medium and the duration of the gas in the environment significantly affect the efficiency.
Bio-Washing
Bio-washing combines wet washing with biodegradation. Here the washing water contains bacterial populations that can oxidize odorous gas components. This requires that the waste gas content be washable and the washed components be biodegradable under aerobic conditions.
Bio-Trickling
Bio-trickling works under the same conditions as bio-washing. Unlike bio-washing, the bacterial population is attached to the support elements, i.e. a bed material. Here, the liquid is circulated through a bed of inert materials.
Thermal Oxidation
Thermal oxidation is the process of oxidizing odorous gases in the waste gas stream by heating the mixture with air or oxygen in a furnace to a temperature above the flash point and maintaining the high temperature for a sufficient time to ensure complete combustion of carbon dioxide and water.
Catalytic Oxidation
Catalytic oxidizers operate in a manner very similar to thermal oxidizers. The major difference is that the gas passing through the flame zone also passes through a bed of catalysts. The catalyst increases the rate of the oxidation reaction, allowing it to occur at lower temperatures. This allows the use of less oxidizer.
Comparison of the Efficiency of Various Purification Techniques
| Technique | Odor Prevention Efficiency (%) |
| Condensation | 60-90 |
| Adsorption | 80-95 |
| Bio-filtration | 75-95 |
| Bio-washing | 70-80 |
| Bio-trickling | 70-97 |
| Thermal Oxidation | 80-95 |
| Catalytic Oxidation | 80-95 |