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Rendering
This method of waste disposal has been around in various forms for over a hundred years. It is a means of processing waste animal tissue and bones into a product which can be used in a number of markets.
It is typically used to process animal by products from slaughterhouses but can also include waste from butchers and restaurants.
There are a number of different ways to render waste of this type. Both batch and continuous processes are options depending on the type of operation the rendering company operates. The different types of rendering relate to the end product produced, with some being edible, and some not.
Edible products come from animals that have been carved to remove the cuts of meat the remaining carcasses, fatty tissue and bones are transported to a rendering plant where it is processed to produce lard for use in the production of food products. This method uses a low temperature to heat the chopped animal by products before a series of separation processed are carried out. During the first stage the liquid and fatty mixture is separated from the solids. The second stage separates the water from the fatty mixture leaving a by product which can be used in food production or in pet foods.
Inedible product rendering is normally carried out by independent rendering companies. They normally use a dry rendering process which is when the waste is processed within a sealed vessel which is heated from the outside in order to remove the moisture from the by products and release the fat contained within the fat cells. Again the waste is ground prior to entering the vessel and then it is percolated to remove the separated fat, before being pressed to remove additional fats contained within the solids.
Although suitable for processing animal by products in various forms rendering does have a number of short falls. Because the process involves heating the waste in its natural form it will produce a strong odour meaning rendering plants are normally located far away from residential areas. This adds additional transport costs to using this method as the waste often has to be transported long distances prior to processing.
Until relatively recently rendering was the only method available for processing animal by products aside from incineration. This has resulting in companies being able to drive the price of rendering waste to levels far higher than it realistically should be. With no alternatives available this led many companies to use this method and thus experience high costs for disposing of their waste.
Other downsides to the process relate to the methods of transportation used. The waste will be collected in trucks before being taken to the plant. The problem this causes is the risk of cross contamination between sites. Although the trucks will be cleaned prior to visiting different sites the risk of contamination is far higher than other methods. Bio security has increased in importance over the past decade due to the BSE and Avian Flu outbreaks within the UK.