2. SLAUGHTERHOUSES
2.1. Red meat slaughter
2.1.1. Description of the slaughter
process.SlaughteringIn slaughterhouses animals are received and kept around in
stockyards and pens for 1 day. The animals are watered, but in most cases not
fed unless they are kept more than 1 day.The animals are then driven from the holding pens to the
slaughtering area where the following activities take place:- S- Suspension from an overhead r- Sticking and bleeding over a collecting trough. The
collected blood may be - Hide removal (cattle) or scalding and dehairing
(hogs);In some plants hogs are skinned to
eliminate scalding and dehairing. Scalding is a method to loosen hair before
removal. For several minutes the hogs are held in a scalding tank at
45°C to 65°C. After scalding, the hogs are
mechanically dehaired by abrasion and singed in a gas flame to complete the hair
removal process.- D- Opening of th- Inspe- Evisceration (removal of intestines and internal
organs);- Splitting and cu and- Chilling or freezing.MeatpackingMany large scale plants ship whole graded carcasses to retail
markets, others perform some on-site processing to produce retail cuts. The
processes are the following:- C and- Meat processing. This includes a variety of operations
amongst which grinding, mixing with additives, curing, pickling, smoking,
cooking and canning.RenderingRendering is a heating process for meat industry waste
products through which fats are separated from water and protein residues for
the production of edible lards and dried protein residues. Commonly it includes
the production of a range of products of meat meal, meat-cum-bone meal, bone
meal and fat from animal tissues. It does not include processes where no fat is
recovered.There are basically two different rendering
processes:- High temperature rendering: through cooking or
steam application (5 systems are known: (1) (2) open pan
(3) (4) and (5) dry
rendering.)- Low temperature rendering (around 80°C).
This process requires finely ground material and temperatures slightly above the
fat melting point. It results in a better quality lard. The rendering at low
temperatures is a highly sophisticated process requiring large throughputs and
trained personnel. For many developing countries the system is not suitable.
(Kumar, undated).Handling of viscera, paunch and
intestinesViscera can be recovered as edible products (e.g.
heart, liver). They can also be separated for inedible rendering or processing
(e.g. lungs).The paunch contents, ‘paunch manure’
(partially digested feed), is estimated to range from 27 to 40 kg. The paunch
can be handled in four ways:1: Total dumping. All of the paunch contents is
flushed away into the sewer.2: Wet dumping. The paunch contents are washed out and the wet
slurry is screened on the presence of gross solids, which are subsequently
removed.3: Dry dumping. The paunch contents are dumped for subsequent
rendering or for disposal as solid waste without needless water
flushing.4: Whole paunch handling. The entire paunch may be removed,
intact, for rendering or for disposal as solid waste.Intestines may be rendered directly, or hashed and
washed prior to rendering. For the processing of intestines de-sliming prior to
thorough washing is necessary.Categories of slaughter-plantsPlants for red meat slaughtering may be categorized on the
basis of the final products. A plant that processes meat into products such as
canned, smoked and cured meats is significantly different from a plant with
facilities for slaughtering without further processing.Slaughterhouses and packinghouses (slaughtering and meat
processing) may each be divided into two categories on the basis of the quantity
of waste produced (EPA 1974).Slaugtherhouses:- Simple slaughterhouse:A plant that slaughters animals and does
a very limited amount of by-product processing. Its main products are fresh meat
in the form of whole, half or quarter carcasses or in smaller meat
cuts.- Complex slaughterhouse:A plant that slaughters and does
extensive processing of by-products. Usually at least three of the following
operations take place: rendering, paunch and viscera handling, blood processing,
and hide and hair processing.Packinghouses- Low-processing packinghouse:A plant that both slaughters and
processes fresh meat into cured, smoked, canned and other meat products. Only
the meat from animals slaughtered at the plant is processed. Carcasses may also
be sold.- High-processing packinghouse:A plant that also processes meat
purchased from outside. Sometimes, a high-process packinghouse has facilities
for tanning operations.There are also plants that do not slaughter themselves but
restrict their activities to the processing of meat (meatpacking). These plants
have a waste production comparable to that of a simple slaughterhouse. 2.1.2. Quantities of
by-productsThe products resulting from slaughtering of cattle are
carcasses and by-products. The quantity of animal by-products often exceeds 50%
of the LWK. The weight of the carcass, expressed as a LWK-percentage is the so
called “dressing percentage” (carcass weight/live weight
*100).Table 1 gives dressing percentages for a few different types
of cattle in the U.S.; Table 2 shows dressing percentages for cattle in France.
As shown in these tables, a wide variation in dressing percentages exists,
mainly related to factors like breed, age and feeding. In many developing
countries low dressing percentages (i.e. less then 50%) are common as animals
receive less feed and/or feed that is of lower quality than the feed offered in
developed countries and because the animals are slaughtered at a higher age than
is done in developed countries.Carcasses still contain quantities of fat and bones (see table
2), most of which will be removed if the carcasses are processed further. This
further processing leads to increased amounts of by-products.
U.S. cattle grades
Dressing percentages
Commercial
Young bulls
Carcass (% LWK)
Musle (%):
Fatty tissue (%):
*: Breeds: F: Dutch/Holstein Friesian LI: Limousin
CH: CharolaisKumar (undated) gives a list of waste products in
slaughterhouses in developing countries:hides, skins, blood, rumen contents, bones, horns,
hoofs, urinary bladder, gall bladder, uturus, rectum, udder, foetes, snout, ear,
penis, meat trimmings, hide and skin trimmings, condemned meat, condemned
carcass, oesophagus, hair and poultry offals (feathers, head).Only few of these products can be used directly. Figure 2
gives the division of cattle into various product categories. It shows in
principle that by-products may be used in full (which would result in low waste
production).Whether complete utilization of all by-products can be
realized depends on a number of factors. Ockerman and Hansen (1988) give several
conditions that must be met for an effective use of animal
by-products:- there must be a commercial process for
converting the animal by-product into a usable commodity.- there must be an actual or potential market for the
commodity that has been produced.- there must be a large enough volume in one location of
economically priced animal by-product material for processing.- there must be a facility for storage of the perishable
product before it is processed and for storage of the manufactured product after
the processing.- there should be a critical mass of highly trained technical
operators.The percentages of by-products in some western countries are
presented in Table 3.
Carcass and edible products
Carcass, meat and bone
Retail cuts (bone in)
Retail cuts (boneless)
Edible fats
White offal
Inedible raw material
Hide and/or hair
Hide (cured weight)
Paunch and manure
*: different sources 2.2. Poultry slaughtering
2.2.1. DescriptionReceiving areasThe inlet to the plant is normally designed in such a way that
fluctuations in bird deliveries can be dealt with adequately. This is necessary
since the processing capacity has a fixed maximum. At regular intervals birds
are unloaded onto the holding areas and attached by their feet to a conveyor
belt, transported to the slaughter area.Slaughtering and packingThe birds are suspended from the conveyor after which the
following actions take place:- S- Killing and bleeding by cutti- Collection of blood. The conveyor travels through a blood
collection tunnel at a preselec- Scalding. To loosen the feathers, the birds are held in
water of temperatures ranging from 50°C to
60°C;- Defeathering. Feathers are mechanically abraded from the
scalded birds, usually by rotating rubber fingers. Removed feathers drop in
- Washing. The defeathered carcasses receive a spray wash
p- Opening of the carcass- Inspe- Evisceration, removal of head,- Sorting of the viscera to recover heart, liver and
- Final washing to remove blood and to loosen
- Chilling of the carc- D- Grading,
and- Chilling and freezing. 2.2.2. Quantities of
by-productsTable 4 gives dressing percentages for poultry in the
U.S. grades
Dressing percentages
Chicken, broilers
Chicken, capon
Turkey, broiler
Duck, Peking
The various components of the raw offal can be summarized as
follows (El Boushy and van der Poel, 1994):
- total offal (heads, feet, intestine):
- feathers:
- moisture:
2.3. Emissions
2.3.1. Solid wasteTable 5 shows the estimated solid waste of slaughterhouses and
the meat processing industry in The Netherlands (RIVM, 1994). All the solid
waste mentioned in Table 5 has a potential use as fertilizer (manure) or animal
feed (fat).
Slaughter process:
5.5 kg/ton carcass weight
fat (pretreatment wastewater)
1.7 kg/ton carcass weight
Meatpacking:
fat (pretreatment wastewater)
2.0 kg/ton product
Intestine handling:
fat (pretreatment wastewater)
2.3 kg/ton product
paunch manure
100 kg/ton product
It would appear that rumen contents and the manure of the
stockyards has not been included in the value of manure. 2.3.2. Wastewater
Kumar (undated) remarks that effluents of slaughterhouses
constitute one of the most serious causes of environmental pollution, bad odours
and health hazards in almost all of the developing countries.Table 6 presents some values of the quality of the wastewater
in the Netherlands, as recently estimated by the RIVM (1994), while in Table 7
international but older values of wastewater characteristics of the various
types of red meat slaughterhouses (see chapter 2.1.1) are presented.
4.4 kg/ton carcass weight
1.1 kg/ton carcass weight
Slaughterhouses (1)
Slaughterhouse (2)
Typical Range
0.23 - 1.4
0.6 - 12.9
0.014 - 0.09
0.014 - 0.086
0.05 - 1.2
Packinghouse (1)
Packinghouses (2)
low-processing
high-processing
Typical Range
5.4 - 18.8
0.13 - 2.1
0.04 - 1.3
2.8 - 20.5
0.05 - 1.2
0.05 - 1.2
Values are estimated from data given by:(1): Taiganides (1987), probably based on
EPA (1974)(2): EPA (1974)It has been observed that with a reduction of the water use
also the waste load decreases.Heinen (1994) compared data of water consumption and effluent
quality of large scale slaughterhouses in Poland with Dutch data (Table
Consumption in m3/ton “throughput”:
Netherlands
(4 plants)
(11 plants)
Cutting and deboning
Processing
COD (mg/l)
COD (kg/ton “throughput”); recalculated
Clearly the Polish industry uses much more water for its
processes than the Dutch industry. The difference is enormous, especially as far
as slaughtering is concerned (6 times as much). The chemical oxygen demand per
m3 of wastewater after pre-treatment is approximately the same as in
the Netherlands. The total waste production in slaughterprocess in Poland is
much higher (over 7 times) than in the Netherlands.Comparison of the Polish COD-production figures (Table 8) to
the figures of Table 6, shows that the Polish figures are not extreme, while the
Dutch figures mentioned in Table 8 are low.The Polish non-industrial-scale private slaughterhouses have
in recent years increased the market share of slaughter from 10% (1988) to 60%
in 1993 (Heinen, 1994).According to Heinen, the water use in
non-industrial-scale private slaughterhouses in Poland is considerably lower
than the water use of industrial-scale plants. This implies that the total waste
load per ton LWK in the water will probably be lower than the values given in
Table 8. 2.3.2.1. Wastewater by red meat
slaughteringMajor contribution to the total waste
load.Production of blood: Of all waste products, the waste in the
form of blood has the highest polluting value. Blood itself has a high BOD:
150,000 - 200,000 mg/l, the extreme value being 405,000 mg/l. (Domestic
wastewater has a BOD of 300 mg/l). In the killing, bleeding and skinning phases,
blood is produced which, when completely sewered, leads to a total waste load of
10 kg BOD per ton of LWK. A waste load of up to 3.0 kg BOD per ton of LWK may
occur in wastewater flowing out of the killing-area and the
hide-removal-area.In order to reduce the waste load, attempts should be made to
collect and process blood (= drying). Drying of blood can be done by direct
heating which produces large quantities of bloodwater (corresponding waste load
approximately 1.3 kg BODper ton of LWK) but preferably it is done by indirect
(external) heating (corresponding waste load approximately 0.3 kg BOD per ton of
LWK).Paunch: Paunch manure is the second most important source of
pollution. It may substantially contribute to the total waste load if not
properly handled. Dumping (sewering) of the entire paunch content gives a BOD of
2.5 kg per ton of LWK. There are several ways to handle paunch (see
2.1.1)Minor contributions to the total waste load.Stockyards and pens: Waste results from manure and urine,
feed, livestock dirt, sanitizers and cleaning agents. The waste will reach the
sewer by means of water overflowing from water troughs, by rain and snowwater
and pen washdown water. The sewered raw waste, assuming that solid contaminants
have been removed, has been estimated at 0.25 kg BOD per ton of LWK.Slaughtering: During the slaughtering the following wastes are
produced (Edible offals are excluded because these are considered as meat
(by-products)):- Blood and tissue produced during hide removal
fall on the floor. External contamination of the hide with dirt and manure is a
secondary source of pollutants. The waste load is also increased as a result of
cleaning-up operations in this area.- Wastewater is produced from intentional overflow from
scalding tanks that contain blood, dirt, manure and hair (0.15 kg BOD per ton of
LWK). The fluming of the mechanically removed hair also results in wastewater
containing residual hair, blood and dirt after recovery of the bulk of the hair
(0.4 kg BOD per ton of LWK). Recovered hog hair may be be dumped as solid waste,
washed and baled for marketing (0.7 kg BOD per ton of LWK) or it may be
hydrolysed by pressure cooking (1 kg BOD per of LWK).- Slime and casings from intestines. De-sliming and casing
washing add 0.6 kg BOD per ton of LWK t- Inedible offals that are produced are hair, recovered from
fluming water, heads and carcass trimmings, lungs and paunch. They also
contribute to the amount of wastewater.Meatpacking: Cutting and deboning operations produce
trimmings, blood, bones and bone dust. The total of raw waste loads for meat
processing plants (including cutting and deboning) has been estimated at 5.7 -
6.7 kg BOD per ton of product. Meatprocessing operations produce a raw waste
load from:- Blood, tissues and fat that reach the sewer
during- The curing of solutions containing sugar and salt. Pickling
can cause a high chloride waste, only 25% of the curing brine remains in the
product.- Baking, smoking etc. and energy use (contributing to air
pollution).Edible Rendering: Both wet-rendering and continuous rendering
at low temperatures produce polluted tank water containing residues of fat and
protein (2 kg BOD per ton of LWK).Table 9 summarizes the potential wastewater emissions of red
meat slaughterhouses (no water prevention).
kg BOD/ton LWK
1 stockyards and pens
solid contaminants are removed
all blood sewered
3 cleanup hide removal
depends on cleanup practices
4 scalding, dehairing
overflow scalding tank
flume water
washing of recovered hair
in case of total dumping sewer
in case of wet dumping
in case of dry dumping
in case of whole paunch handling
6 intestine handling
7 rendering
8 general cleanup
depends strongly on cleanup practices
Potential emission:
24.9 - 25.8
9 meat packing
kg BOD/ton product!!
*: authors’ estimate (not mentioned by
Barnes). 2.3.2.2. Wastewater by poultry
slaughteringTable 10 shows characteristic values of waste flows of a
poultry slaughterhouse.Major contribution to the total waste loadEvisceration: For medium-to-high capacity poultry plants, it
has been estimated that offal flume-water from continuous flowaway fluming
contributes a raw waste load of approximately one-third of the total plant load
(presented in Table 10). Values of 1.7 - 13.2 kg BOD per ton of LWK with a
common average of 3.4 kg BOD have been reported (Barnes et al.,
1984).Production of blood: Because of the high BOD of blood, the
same observation with respect to the contribution of blood to the total waste
load applies to poultry plants. Chicken blood contributes 4.5 kg BOD per ton of
LWK if completely sewered.Minor contributions to the total waste loadReceiving areas: Waste load values of the receiving area vary
widely since they are derived from the quantity of dirt, manure and feather
deposits which vary with the length of holding time.
Poultry slaughterhouses
Poultry slaughterhouses
0.15 - 12.2
0.6 - 10.9
0.054 - 2.5
0.034 - 0.2
Values are estimated from data given by:(1): EPA (1974)(2): Taiganides (1987)Slaughtering and packing:Waste water:- Scalding tanks containing settleable residues
and feathers. Approximately 8 litres of wastewater per bird are produced as a
result of overflow (0.6 - 3.1 kg BOD per ton of LWK).- Chilling. Chiller overflow is high to prevent bacterial
contamination (0.4-2.5 kg BOD per ton of LWK);- The final wash water contains blood and tissue (0.7 kg BOD
per ton of LWK);- Whole bird washing after defeathering (0.06 kg BOD per ton
of LWK)- D The underlying troughs are flumed to collect
the feathers.- General plant clean- up to 50% of the BOD can come from
cleaning operations.Solid waste:- Feathers recovered from the flume water of the
- Head, feet and viscera. 2.3.3. Air pollutionSlaughtering is an activity that requires great amounts of hot
water and steam for sterilisation and cleaning purposes. In the process of
generating the energy for heating, gasses are emitted (CO2, CO,
NOx and SO2).Emissions of CFC’s and NH3 into the air are
the result of evaporation of chilling liquids and of the stripping of chilling
and freezing-machines, when out of use.The smoking of meat products and the singing of hogs in a gas
flame to complete the hair removal lead to the production of mainly
CO2, CO and NOx and obnoxious smells.The overall energy used in Dutch slaughterhouses and the meat
processing industry is estimated at 137 kWh/ton of carcass and about 28.7
m3 gas/ton of carcass (RIVM, 1994). The degree of air pollution
caused by the generation of energy depends on the type of process for which the
energy is needed. The processes of “dehairing”, “water
heating” or “production of electricity” each lead to different
levels of emission.Based on estimates of the RIVM (1994), emissions of
CO2, CO and NOx resulting from the burning of gas for
heating and steam production are for the dutch situation as indicated in table
Air emission:
Heating by burning gas:
0.02 kg/ton carcass weight
28 kg/ton carcass weight
0.01 kg/ton carcass weight
Dehairing pigs: (using gas)
0.06 kg/ton carcass weight
6.5 kg/ton carcass weight
0.015 kg/ton carcass weight
Table 12 shows the energy use of Polish large scale
slaughterhouses and comparable figures for the dutch situation. According to
Heinen (1994) Polish meat plants are highly inefficient in their
energy-consumption.The energy-use in non-industrial scale private slaughterhouses
in Poland seems to be considerably lower than that of industrial scale plants,
probably because of a lower level of process-automation. The amount of energy
needed for non-industrial cutting and deboning is considerably lower than that
required in large scale plants, but the energy needed for non-industrial
processing is more than twice as high, probably a matter of economies of scale
(Heinen, 1994).
Steam (GJ)
Electricity (kWh)
Slaugther (per ton carcass)
Cut and debone (per ton carcass)
Processing (per ton product)
Rendering (per ton input)
Other (per ton overall)
2.4. Prevention of waste
productionPractices as discussed in this section are generally called
‘housekeeping practices’. The quality of overall cleaning-up practices
determines to a large extent the total waste load produced. It has been
established that the waste load decreases with a decrease of the water being
used(see e.g. the comparision in Table 8).With reference to the process outline in figure 1, the
following actions may contribute to waste(water) reduction. BOD data are from
several slaughterhouses and from literature reported by Barnes et. al
(1984). BOD values are values of the untreated final wastewater.Red meat:- As much blood as possible should be
collected and processed. Indirect heating can reduce the amount of wastewater
(and thus the waste load), compared with direct heating from 1.3 to 0.3 kg BOD
per ton of LWK.- Paunch can be handled in different ways (Barnes et
al, 1984):1. dumping in full into the sewer,
which leads to a waste load of 2.5 kg BOD per ton of LWK2. wet dumping (washing out and screening the wet
slurry on gross solids); estimated waste load of 1.5 - 2 kg BOD per ton of
LWK3. dry dumping (dumping for subsequent rendering or
disposal as solid waste without needless water flushing): estimated waste load
of 0.2 kg BOD per ton of LWK;4. whole paunch handling (removal of the entire paunch,
intact, for rendering or disposal as solid waste):a: after washing, an estimated waste load
is produced of 0.6 kg BOD per ton of LWK (paunches are marketable as pet
food);b: washing and bleaching lead to an estimated waste load of 1
kg BOD per ton of LWK (paunches are marketable as tripe).- Dry animal pen clean-up reduces the amount of wastewater. If
the pens are covered, no rain or snowwater can enter, which reduces the amount
of of wastewater- Hog hair, recovered from the dehairing process, can be
disposed as solid waste, washed and baled for direct marketing, or hydrolysed by
pressure cooking for marketing as a feed supplement.- Heads and lung- Intestines may be rendered directly, hashed and washed prior
to rendering, or processed for further use (in the case of hog intestines).
Large hog intestines may be used as sausage casings or as surgical
sutures.- Tankwater (from the rendering process) can be evaporated.
This will reduce the waste load from 2 to 0.5 - 1 kg BOD per ton of LWK.
Evaporation on the other hand consumes energy which will lead to CO2
production.Poultry:- Flow-away systems have resulted in quick and
efficient processing in modern plants. However, the costs of flowaway systems
and of wastewater treatment may be such that the development and use of
automated dry viscera handling methods are encouraged.- Stunning before killing reduces the overall loss of blood.
Without prior stunning, blood will be splashed over a wide area and may also
contaminate feathers.- Dry cleaning before washin- Use of chiller overflow water as make up water in scalding
- Recovered feathers may be disposed of as solid waste or
pressure cooked to hydrolyse the otherwise low nutritional value protein,
keratin.- Use of screened water from defeathering operations in
- Head, feet and remaining inedible viscera may be collected
for disposal or inedible rendering.- Re-use of final evisceration wash waters in other
subprocesses and use of special nozzles tha- Potential re-use of screened chiller water overflown
elsewhere in the plant.RIVM (1994) reported also some possibilities for waste
prevention: Table 13.
Waste-prevention
Slaughterprocess:
- mainly energy saving
- dry animal pen clean-up- dry transport (poultry-slaughterhouse)- less loss of blood- more dry cleaning- fast separation of meat and water- improve defatting-process waste water
Solid Waste:
- increases when waste water prevention increases (manure,
Meatpacking:
- mainly energy saving
- separate meat and water as much as possible- more dry cleaning- improve defatting-process waste water- application of steam-tunnels or high pressure-systems for
cooking meat
Solid Waste:
- increases when waste water prevention increases
Intestine handling:
- energy-saving
- application of dry rendering- keep paunch manure separated as much as possible
Solid Waste:
- increases when waste water prevention increases (manure,
Utility-processes*:
- improve efficiency chilling-machines and chilling practices
(keep doors close, repair leakages)
- use as less (warm) water as possible during
cleaning-up
*: e.g. waste water purification, chilling,
cleaning-upOne of the conclusions of an investigation of waste prevention
in ten slaughterhouses in the Netherlands is that in modern western
slaughterhouses good results can be achieved by using simple means (Provinces
Gelderland and Overijssel, 1994). Possible reason for this is that environmental
aspects have received little attention compared to the attention for the
efficiency of the slaughter process.