Meat and dairy processing activities
Meat and dairy products are processed in dairy factories, meat works, tanneries, and factories.
Processing in slaughterhouses, leather tanneries, and dairy factories requires the use of large volumes of water that ends up as wastewater. The strength and composition of pollutants in the wastewater depends on the nature of the processes involved.
Meat processing
The processing of meat and meat by-products requires large quantities of water, and after use, nearly all of the wastewater contains high amounts of nutrients (nitrogen and phosphorus), fat, and infectious substances from blood and animal tissue.
Find out more about nutrient overloading
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Leather tanning
The leather tanning process involves a complex chemical process which transforms decomposable dead animal skins into leather, but not without producing some dangerous chemical contaminants like tannins and chromium. Other minor components include sodium, potassium, calcium, and chloride.
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Dairy processing
Dairy wastewater contains considerable amounts of organic milk products, such as milk fat, protein, lactose and lactic acid, nutrients, and minerals. Cleaning of the plant uses chemical contaminants that produce caustic wastewater.
Find out more about nutrient overloading
Find out more about chemical contamination
Wastewater treatment
Most processing plants now have extensive treatment facilities before wastewater is discharged to surface waters (stream or river) or alternatively discharged/applied to land. Wastewater treatment usually involves a series of chemical, mechanical, and biological processes.
The dairy industry uses two main methods of treating wastewater: (1) biological treatment using extended aeration systems, e.g., an aerated lagoon system; and (2) by spray irrigation to pasture. Pre-treatment systems are often used to maximise the removal of solid material first and reduce the organic loading on a system. Land treatment systems are used extensively in the Aotearoa dairy industry.
Wastewater treatment systems for the meat industry may comprise of any combination of aerobic/anaerobic ponds, bioreactors, constructed wetlands, and UV disinfection and filters before the water is discharged into the environment. Any system used needs to be designed to the appropriate criteria to ensure efficient operation.
Find out more about discharging wastewater to waterways and the effects on water quality and mahinga kai.