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Odours arising from Meat Processing and Rendering Plants

Abattoirs and Meat Processing plants are systems that generate odour right from the kill room right through to the render plant. The work conditions in all meat processing plants are such that the indoor air quality requires that the building be ventilated. There is an inherent odour load generated from the air ventilation from the buildings and careful assessment is required to determine whether this air requires treatment. The volumes are enormous and the odour strength is low and therefore Biofilters have been traditionally used for this process treatment.

A section of the process most prone to the release of strong odours is the Rendering Plant. In the Rendering process, off-cut material not able to be used in the finished products are crushed and then cooked over an extensive period of time to recover the tallow and meat meal protein present. The cooker process generates a significant release of odour with volatile compounds released with the water vapour. Although the water vapour is cooled and condensed and some volatiles are captured in this process, a significant portion are able to make their way through to the air extraction system. The process of separating tallow and meat meal generates odour around screen areas and the waste streams from the rejects water off the centrifuges are highly odorous.

Wastewater streams in Meat Processing Plants

Waste streams in meat processing plants tend to contain sulphide and high concentrations of ammonia and are carried in open channels that permit significant quantities to be released. The waste streams generated in meat processing plant are:

• Red Stream - Hot Water and diluted blood with fines meat offcuts. Normally this is fresh from the plant but can become septic in any storage basin. The quantity of steriliser water carried in this stream will have the water temperature at around 65C/150F. This accelerates the generation of sulphides and ammonia.
• Green Stream - Wash water, paunch (semi-digested grass matter found in the stomachs of livestock) and stomach liners
• Manure Stream - Digested grass mater containing high levels of sulphides and ammonia
• Render process vapours and gases including cooker vapours, mostly ammonia, tallow (volatile fatty acids) and animal protein dust.
• Render wastewater containing high levels of tallow and animal protein.

Most abattoirs are based around regional centres and are able to utilities lagoon treatment systems for processing wastewater. It is commonplace now to cover the anaerobic lagoons. This contains the odour, it also allows the biogas to be collected for use either in the Boiler or for generating power in the Combined Heat and Power (CHP) system. The level of Hydrogen Sulphide present in the Biogas can be upwards towards 1500 - 5000 ppm where most engines can only tolerate 100 ppm. Therefore desulphurisation is required prior to use.

Odour generated from Render Plants

The area that is the main cause of odour on meat work sites is the Render Plant. The process of producing Tallow and Protein Solids causes significant volumes of odorous air to be produced. The majority of the odour is from the cooker. The main odour is Ammonia. There will be some Hydrogen Sulphide and Volatile Fatty Acid vapours. Major factor for consideration is the age and origin of the render material. Material that exceeds 48 hours significantly increases the volume of Ammonia released. Also materials high in Keratin such as feathers and fur that are subject to hydrolysis will release a large volume of Ammonia. Any odour treatment process must take this into account. Dust from meat meal milling process must be filtered from the air stream to prevent blockage within the odour control system.

Odour Control for Rendering Plants

The odour control system options for the treatment of air from Render Plants is preferably Biofilters and depending on the degree of clean air required, Activated Carbon polishing. The level of Ammonia coming into the process would generally be too much for the Biofilter to handle and we would recommend pretreatment upfront using a chemical scrubber. Meat Meal dust can be removed by way of an inline air washer system.

Biofilters will manage a wide range of volatile organic compounds. It is essential that the air before entering the Biofilter has its temperature reduced to less that 35C (95F) to optimise the performance of the Biological System.

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