Slaughterhouse wastewater usually has a rust-red to brown colour because fats and other suspended matter mix with blood and faeces. When the meat is further processed, oils and fats mix into the wastewater, giving it a shimmering yellow colour. In both cases, the COD (chemical oxygen demand), BOD5 (biological oxygen demand) and TSS (total suspended solids) are particularly high. In addition, slaughterhouse wastewater usually contains insoluble solids such as feathers or bristles.
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Characteristics of wastewater from the meat processing industry
Overview of the meat processing industry
The meat processing industry produces a variety of products, from raw, ready-to-sell meat to sausages and finished products with meat content. The slaughtering and cutting of the animals are separated from further processing. In all areas of the meat industry, a lot of wastewaters with characteristic features is produced.
This page gives an overview of the wastewater produced in slaughtering, cutting, and processing plants. It also discusses the individual categories as well as of the types of slaughterhouse products and their specific wastewater characteristics.
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The demand for meat remains high. While the average per capita consumption in Europe was still 41.5 kg in 2010, it rose to 43.2 kg in 2019. Above all, the number of poultry kept has risen by over 130 percent in the past 20 years. Therefore, the amount of wastewater generated during slaughtering, cutting and further processing is also increasing. It is important to fully understand the characteristics of the wastewater to find the best possible treatment solution for it.
Wastewater generation in slaughterhouses
Water plays a crucial role in the meat processing industry, especially in cleaning the equipment and surfaces. Around 950 litres of wastewater are produced when slaughtering a cow, around 200 litres when slaughtering a pig and around eight litres when slaughtering a chicken. The amounts of wastewater and the resulting pollution loads vary greatly due to the different slaughter processes.
Most of the slaughterhouse wastewater is produced during production cleaning, slaughtering including knife disinfection and processing of offal. Especially in areas where more faeces and urine are produced, the hot water content is higher. When cleaning surfaces, the share of cold water – due to the use of high-pressure cleaners – is somewhat higher.
Slaughterhouse wastewater categories
CIP process (Clean in Place)
The CIP process is a closed circuit in which the wash water circulates. Detergents are added to it in storage tanks, pumped through pipes and placed in the machine. In the process, the water has a pre-set temperature and is discharged at a set pressure. This has the advantage that the machine does not have to be disassembled for this. To close the water circuit, a treatment can be used after cleaning. This means that the water loss is very low (around five percent).
Alluvial water is usually used to remove solids such as feathers, bristles, or litter. Therefore, it should not be mixed with other slaughterhouse wastewater at the beginning. After extensive, usually multi-stage screening, it can be treated with another wastewater.
Transport purification takes place in two steps: First, mechanical cleaning takes place to remove faeces, straw, feathers, and litter. Afterwards, a high-pressure cleaning removes the adhering residues. It is important to separate the solids from the liquids via mechanical screening.
Scalding water after cutting
There are two main scalding methods for processing meat: One is scalding in a water bath, the other is the vertical scalding process. While in the water-bath scalding process the carcasses are pulled through 59° to 60°C hot water, in the vertical scalding process the animals hang in chambers and are sprayed with hot water. The resulting wastewater contains salts and fats – foam cleaners with low alcohols are used for daily cleaning.
Wastewater from smoking processes
In the smoking chamber, resins settle on the chamber walls, which are washed once a week. Alkaline surfactant solutions, so-called smoke resin removers, are used for this purpose. Around 40 litres of highly contaminated wastewater are produced per smoking chamber. The table opposite gives an overview of the parameters of cleaning wastewater from smoking systems.
Types of slaughter products
The range of meats is wide – but the most common slaughter products are pork, beef, and poultry. While the consumption of pork predominates in Europe, poultry meat takes precedence in the USA. Here, the cutting into the individual components plays a decisive role: in the case of pork and beef into topside, bottomside, rump and neck – in the case of poultry into breast meat, leg and wing. Below you will find an overview of the special features of slaughter processes and the characteristics of slaughterhouse wastewater.
Around 250 million pigs are slaughtered in Europe every year. This makes it by far the most consumed type of meat. The wastewater produced when pigs are slaughtered therefore mainly contains blood, fat, urine, solids, and disinfectants.
After the hygienic bleeding of the pig, the following processing steps follow: Scalding at around 60°C, mechanical dehairing, removal of the remaining hair by heat, polishing and cleaning of the carcass surface.
The table opposite provides an overview of the process steps, by-products, dirt loads and treatment solution.
The European annual demand for slaughtered cattle without calves is around 14.5 million animals with a slaughter weight between 200 and 450 kg. Here, the wastewater quantities mainly occur during cleaning.
Once the animal has been bled hygienically, the rendering process begins. After opening, the organs are divided into edible and non-edible offal. The decisive factor is the removal of the spinal cord, which is collected in a container for “specified risk material”. The companies collect the fat produced in specially designated containers, which is sent for fat recycling.
The table opposite shows the dissolved and non-dissolved substances in the wastewater during and after the slaughter of a cow.
The European annual production of poultry meat is around 13.4 million tonnes. Slaughtering and further carcass processing usually take place in one plant. Plucking and cutting are highly automated, so that cleaning mainly takes place according to the CIP process. In addition, sponging water is produced for the removal of the feathers.
Poultry is usually transported in containers. These containers must undergo a washing process. Specially constructed facilities flush faeces, urine and feathers out of the containers before they are allowed to leave the abattoir. After the animals have been stunned, they are bled by circular knives. Wastewater is produced during the cleaning of the knives, the transport systems, and the blood gutters.
The table opposite shows the sources and characteristics of wastewater from poultry slaughtering.
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Slaughterhouse wastewater and rendering plants varies greatly. Therefore, individual consultation and treatment are necessary. The above data is taken from our clients’ projects, which are mainly located in Europe.
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Wastewater treatment in the meat processing industry is a very complex issue. Each specific processing step generates wastewater with different characteristics.
Therefore, it is particularly important to know the exact composition of the slaughterhouse wastewater to choose the right treatment technology.
Would you like to learn more about the different treatment options for wastewater from slaughter processes? Please read on here.
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