• Physical
  • Dilution
  • Physic adsorption
  • Coverage
  • Masking
• Chemical
  • Scrubbing
  • Oxidation
  • Incineration
• Biological
  • Biofiltration
• Combined
  • Bioscrubbers

Besides of the above mentioned bad odour control measures, some other technologies may be used to reduce the odour generation, for example:

• Replace the raw material to control of the generation of less odorous emissions
• Change the production process to reduce the generation of odorous compounds
• Diet optimization for animals to limit odour produced from livestock

Adsorbers commonly used empty activated carbon or alumina pellets impregnated with permanganate. These materials are highly porous and consequently there is a large surface area upon which adsorption of odorous compounds may occur.

Activated carbon is generally considered for organic gases and vapours, some inorganic gases and some metallic vapours. The mechanism which attracts and attaches the molesules to the surface of the pores known as Van der Waals forces.

It is generally accepted that compounds with a molecular weight af at least 45 or with a boiling point over 0^oC will be well absorbed on activated carbon.

The odorous stream needs to be pretreated before it passes through activated carbon when its temperature is high, moisture content is high or it contains dusts. The odorous stream should be free of dust in order not to clog the surface of activated carbon.

Activated carbon needs to be replaced before it is saturated. The used activated carbon can be regenerated, otherwise it should be disposed.

Liquid scrubbing

Liquid scrubbing of gases for the removal of odours can involve either adsorption in a suitable solvent or chemical treatment with a suitable reagent. Liquid scrubbing becomes ecnomically attractive compared with incineration and adsortion on activated carbon when the volume of odorous gas to be treated is great than 5000 cubic metres per hour.

Liquid scrubbeing of gases involves bringing the odorous gas stream into intiate contact with the scrubbing liquid. Liquid scrubber needs to be well designed to ensure adequate contact between the gas and liquid phases. The treatment ability should be sufficient enough to treat the odorous gases generated.

The principal types of gas absorption equipments include packed towers, plate or tray towers, spray towers, venturi and fluidised-bed scrubbers.

It is important that hot moist vapour streams be cooled before contacting scrubbing solutions. Direct or indirect condenser can be used to condense the moisture from the odorous stream (the indirect condenser is preferred).

The most frequently used absorbing solutions are:

• Sodium hydroxide - ideal for absorb hydrogen sulfide and mercaptans
• Amine - used to trap hydrogen sulfide of hydrocarbon gases from petroleum refinery
• chlorine, sodium hypochlorite, potassium permanganate, ozone or hydrogen peroxide - effective to absorb unsaturated organic compounds
• Diluted sulfuric acid - used to absorb ammonia

For biological odour control, the odour is removed by biological processes - bacterial action. The bacteria grow on inert supports, allowing intimate contact between the odorous gases and the bacteria. The process is self-sustaining.

Biofiliters require careful attention to ensure continured operation. The bed may have to be replaced regularly because of mechanical failure.

Bioscrubbers

Bioscrubbers use teh combined principles of liquid scrubbing and the biofiltration in order to remove vapours pollutions from waste gases. Bioscrubbers can only be used successfully if the contaminants can be removed from teh waste gas by absorption in a water water/activated sludge mixture. Furthermore the contaminants must be biologically degradable.

Confirmation of odour removal efficiency

Different odour control measures may be combined to achieve high removal efficiency. The odour control technologies being used will depend on the characristics of odorous gases and the quantity of the production.