1.2. General environmental impact
1.3. Overall waste production
1.4. The Key-indicator
The study describes and analyses the relationship between the production of waste in animal product processing industries on the one hand and the prevention and treatment of the waste on the other. The industries discussed are slaughterhouses, tanneries and the dairy industry. The report offers a summary of the knowledge on production, prevention and treatment of waste in these three animal products processing industries. Because of the limited time available for this study, the problems that occur in the mentioned industries have not been treated in full detail.
Important questions related to the subject are those regarding: (1) the differences between various product processing methods; (2) the reduction of the production of waste; and (3) the methods of waste treatment.
Chapter 1 provides a general introduction to the subject, the different types of waste produced, the variables by which to measure pollution and the definition of the Key Indicator (quantity of industrially processed product) of the environmental impact of the processing of animal products.
Chapters 2, 3 and 4 describe the waste production in the three main animal products processing industries and a number of methods by which waste production might be reduced. Chapter 5 describes the handling of by-products and the treatment of waste products.
The conclusions and recommendations in chapter 6 summarize the technological and policy options that may help reduce waste production and the negative impact on the environment from the processing of animal products.
1.2.2. Solid waste
1.2.3. Air pollution
The manufacturing of animal products for human consumption (meat and dairy products) or for other human needs (leather), leads inevitably to the production of waste. Under traditional conditions, the quantities of products processed in a certain area used to be small and by-products were better utilized. This resulted in the production of smaller quantities of waste than at present.
Nature is able to cope with certain amounts of waste via a variety of natural cleaning mechanisms. However, if the concentration of waste products increases, natures mechanisms become overburdened and pollution problems start to occur. Usually, small-scale home processing activities produce relatively small amounts of waste and waste water. Nature can cope with these. Yet as a consequence of the increasing emphasis on large scale production (e.g. for reasons of efficiency, increase in scale of production and hygiene) considerably greater amounts of waste will be produced and steps will have to be taken to keep this production at acceptable levels.
Also methods will have to be found or developed for a more efficient use of by-products and for improved treatment of waste products. Because large scale processes are not easy to survey, the checking of waste production is a problematic undertaking and special efforts are needed to find out where in the production process waste is produced.
An example that illustrates the relationship between the scale of production and the production of waste is that of the production of hard cheese. Before large scale production of cheese came into existence, whey was considered as a valuable by-product that could be used as animal feed. In the Netherlands, about 50 percent of all the milk produced is used for the production of cheese. The whey which is produced in the process could lead to enormous environmental problems partly because the costs of transport of this whey to the farm for use as animal feed is a costly affair.
Only after environmental considerations had become more important, efforts were made to solve this problem. Eventually this has resulted in the establishment of a production line of whey-powder which is now-a-days considered a valuable product.
The example also shows that the borderline between a waste product and a useful product is sometimes hard to draw.
In the present study major attention will be given to the impact on the environment of: (1) the slaughter processes at slaughterhouses; (2) the storage, preservation and processing of hides; and (3) the processing of milk, all at industrial levels. For the discussion concerning the waste production within each of these animal-product-processing industries, it is worth looking at operations that precede and follow the industrial waste producing processes.
* In slaughterhouses: the animals are reared, fattened and transported to the slaughterhouses. After processing, the meat is stored before it is transported to retail outlets. The preceding activities produce manure etc. while for storage and transport (follow activities) cooling facilities are needed. This puts a heavy claim on energy sources.
* In tanneries: hides produced at slaughterhouses must be stored. To prevent spoilage, they should be pickled and preservatives should be added. The methods used to process hides will to some extent determine the durability of the produced leather. The production of more durable leather leads to smaller quantities of leather waste. Chrome tanned leather and leather products contain about 2-3% of dry weight chromium. Worn out leather products, such as shoes and jackets, are frequently dumped at municipal dumping places.
* Before its collection and transportation to a processing plant, milk is produced and stored at the farm. This requires energy and leads to spoilage of milk and production of wastewater (tank cleaning). After the processing at the plants, dairy products are packed and stored and transported to retailers. At the end of its lifeline, packing material finishes in the form of solid waste. The repeated use of milk bottles produces waste water (after cleansing). At the site of the consumer, storage makes a demand on energy and incorrect storage or usage may lead to spilling. It has been estimated that 2-10% of all dairy products are wasted by the consumer as a result of spoilage.
In general terms, waste products may occur as waste water, solid material, volatile compounds or gasses that are discharged into the air.
An important environmental impact of the animal processing industry results from the discharge of wastewater. Most processes in slaughterhouses, tanneries and dairy plants require the use of water. This water and water used for general cleaning purposes will produce wastewater. The strength and composition of pollutants in the wastewater evidently depend on the nature of the processes involved. Discharge of wastewater to surface waters affects the water quality in three ways:
1: The discharge of biodegradable organic compounds (BOCs) may cause a strong reduction of the amount of dissolved oxygen, which in turn may lead to reduced levels of activity or even death of aquatic life.
2: Macro-nutrients (N, P) may cause eutrophication of the receiving water bodies. Excessive algae growth and subsequent dying off and mineralisation of these algae, may lead to the death of aquatic life because of oxygen depletion.
3: Agro-industrial effluents may contain compounds that are directly toxic to aquatic life (e.g. tannins and chromium in tannery effluents; un-ionized ammonia).
Ad 1: Biodegradable organic compounds
Parameters for the amount of BOCs are the Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and the concentration of Suspended Solids (SS). The BOD and COD are overall parameters that give an indication of the concentration of organic compounds in wastewater. The concentration of suspended solids represents the amount of insoluble organic and inorganic particles in the wastewater.
- Biochemical Oxygen Demand (BOD)
Agro-industrial wastewater generally contains fat, oil, meat, proteins, carbohydrates, etc., which are generally referred to as bio-degradable organic compounds (BOC). This term is a denominator for all organic substances used and degraded by micro-organisms. For most common organisms present in the aquatic environment, degradation requires oxygen. The BOD is the amount of oxygen required by micro-organisms to oxidize the organic material in the wastewater. The BOD-value is generally measured after a five day incubation period at 20°C. Officially this is expressed as BOD520. In this report the term BOD will be used for the BOD520.
- Chemical Oxygen Demand (COD)
The COD represents the oxygen consumption for chemical oxidation of organic material under strongly acid conditions. The COD test yields results within a period of a few hours and therefore provides direct information. In this test biodegradable as well as non-biodegradable compounds are oxidized. The COD therefore only provides an indirect indication of the potential oxygen depletion that may occur from the discharge of organic material in surface waters. Use of the BOD is preferred to that of the COD because it provides a more reliable indication of the degree of pollution of wastewater in terms of bio-degradable matter. Nevertheless, the COD is still a widely used parameter for wastewater in general because of the short period of time within which it can be determined.
For slaughterhouse wastewater the COD/BOD ratio varies between 1.5 and 2.2 with an average value of 1.8. (Luppens, 1994).
For dairy industries the COD/BOD ratio of the wastewater is 2.63 for low BOD values (< 450 mg/l). For high BOD values (> 450 mg/l) the ratio is 1.25 (EPA, 1971).
- Suspended Solids (SS)
Suspended solids are insoluble organic and inorganic particles present in wastewater. SS is mainly material that is too small to be collected as solid waste. It does not settle in a clarifier either. Discharge of SS increases the turbidity of water and causes a long term demand for oxygen because of the slow hydrolysis rate of the organic fraction of the material. This organic material may consist of fat, proteins and carbohydrates. The natural biodegradation of proteins (from for instance meat and milk), will eventually lead to the discharge of ammonium. Ammonium oxidation into nitrite and nitrate by nitrifying bacteria, leads to an extra consumption of oxygen.
Problems resulting from the discharge of biodegradable organic compounds may be addressed by means of biological wastewater systems, either of the aerobic or of the anaerobic type.
In aerobic systems the organic compounds are oxidized by aerobic micro-organisms (oxygen required) into CO2, H2O and new bacterial biomass.
Anaerobic systems are based on the capacity of anaerobic bacteria (no oxygen required) to degrade the organic material into CO2, CH4 and small quantities of biomass.
ad 2: Eutrophication
- Nitrogen (N)
In wastewater Nitrogen is usually present as fixed in organic material or as ammonium. Occasionally also nitrate may be present (this may be the case in dairy industries where HNO3 is used for cleaning operations). Kjeldahl developed a test to measure the nitrogen content of wastewater. The Kjeldahl - nitrogen (NKj) is the sum total of organic and ammonia-nitrogen.
- Phosphorus (P)
The presence of Phosphorus (P) is determined photometrically. It concerns inorganic phosphate (mostly ortho-phosphate) and organically fixed phosphate.
Nitrogen and phosphorus removal can be achieved through special wastewater purification systems, which are based on either biological or physic-chemical processes.
ad 3: Toxic compounds
Ammonia particularly in un-ionized form is directly toxic to fish and other aquatic life (NH3 is 300-400 times more toxic than NH4+; Barnes et. al., 1984). Chromium and tannins are toxic compounds. At neutral pH only 0.4% of the sum total of ammonia and ammonium is present as ammonia.
Detoxification of wastewater may be reached by the use of special wastewater purification systems.
The measurements of the quantity of fat, oil and grease (FOG) and acidity (pH) can only take place in a tedious way and yields inaccurate results. Nowadays, the presence of FOG is hardly mentioned in reports and for this reason this aspect has not been treated in this study (Barnes et. al., 1984; Metcalf & Eddy, 1991).
European Community directives give values for BOD equal to 25 mg/l, for N of 10-15 mg/l and for P of 1-2 mg/l for urban wastewater discharge (EEC, 1991). In the Netherlands target values for water quality of large resp. small surface waters are set at 2.2 resp. 1.5 mg/l for N and 0.15 resp. 0.08 mg/l for P (RIVM, 1991).
By-products that are not used in any way will be referred to as solid waste. They must be dumped.
The following types of solid waste may be distinguished:
- toxic compounds. These compounds require special attention, e.g. special dumping grounds.
- organic compounds. These compounds may require attention under certain conditions because of hygienic reasons or because during decomposition ill odour or leaching problems may arise.
- non degradable compounds. These may be dumped at regular dumping grounds.
Air pollution may cause problems of various kinds:
1: global warming, as a result of emissions of CO2;
2: changes in the ozone-layer, as a result of emissions of NOx, CH4, N2O and CFCs;
3: acid rain, as a result of emissions of SO2 and NH3;
4: health conditions
5: dust (for instance as a result of emission of milkpowder) and/or bad odour, as a result of emissions of VOC;
The use of energy leads to the discharge of gasses such as CO2, CO, NOx and SO2. Chilling and freezing (CFCs and NH3) activities, smoking of meat products and singing/scorching of pigs also lead to emissions into the air.
The discharge of volatile organic compounds (VOC) may occur in dairy plants when cleaning agents are used and in the leather industry when leather finishing substances are used. Dust may be produced in bone cutting and bone processing industries. And the production of milkpowder inevitably leads to the production of dust as well.
1.3.1. Slaughter activities
1.3.2. Tanning processes
1.3.3. Milk processing
In the discussion on slaughter activities, the focus will be on the slaughtering of pigs, cattle and poultry. According to the FAO (1993), these three types of animal make up almost 93% of the total world meat production. For the discussion of the slaughtering process and the waste production, a distinction will be made between red meat (pigs and cattle) and poultry.
In the slaughter process basically the following by-products and waste products become available:
(1) manure, contents of rumen and intestines
(2) edible products such as blood and liver;
(3) inedible products such as hair, bones, feathers;
(4) fat (recovered from the wastewater by means of fat-separators); and
In most developed countries, slaughtering is a centralized activity. The consumer in these countries has a preference for lean meat and a few selected offal only, such as brain, kidney, sweetbread, tongue, etc. For this reason, the carcass is often deboned at the slaughterhouse and cooled before being sent to retail outlets. As a result, large quantities of by-products (bones, lungs spleen, oesophagus etc.) are left behind at the slaughterhouse. They fall in the category of inedible offal. For economic and environmental considerations, these need to be suitably processed and utilized. Clean fatty tissues such as kaul and mesentery fat may be processed into edible fat. Other tissues may be used to produce composite bone-cum-protein meals or individual products like bone-meal, meat-meal and blood-meal. In principle all edible and inedible by-products can be processed and put to further use (e.g. human consumption, pet food, feed industry or fertilizer). Modern abattoirs are well equipped and are in the possession of running water, steam, power, refrigeration, transport and other facilities. These facilities make it also possible that glands are preserved for the production of glandular products.
In developing countries a large variety of slaughter sites exists. Slaughter sites vary from simple slaughter slabs to very modern slaughterhouses. Large scale industrial processing units are imported from developed countries, often without rendering or waste treatment facilities. Many slaughterhouses (of various types) are insanitary and pose threats to health, particularly around rapidly expanding population areas. Often old slaughterhouses discharge blood and untreated wastewater. The elimination of sick animals and subsequent destruction are frequently carried out inappropriately (Kaasschieter, 1991a). Blood may coagulate in drains where it putrefies, causing bad odours and sanitary and environmental problems. Edible and inedible by-products are frequently wasted during the slaughtering and further processing owing to amongst others:
(1) insufficient skills and discipline in slaughtering;
(2) poor quality of slaughtering equipment in the slaughterhouse, slaughtering on the floor, no slaughter line, lack of adequate maintenance and lack of spare parts;
(3) a non-cost-effective processing of by-products either because of the small quantities involved, the high costs of processing or the low value of the end product;
(4) lack of equipment for the processing of by-products; and
(5) lack of regulations on the discharge of wastes or the inability of the authorities to enforce regulations.
Charges for slaughtering in abattoirs are often kept low to prevent illegal slaughtering. Furthermore, slaughter fees constitute a source of income for the municipality. As however these funds are not used for the operation and maintenance of the abattoir, abattoirs have difficulties in maintaining certain standards.
Approximately 80 percent of the population in developing countries lives in rural areas (Kumar, 1989). The great majority of animals is likely to be slaughtered and processed domestically or in small slaughter slabs. The processing and the utilization of offal require a technology and capital lay-out which are completely different from those in developed countries. Huge capital investments in infrastructure of plants and machinery, as is the case in developed countries cannot be justified. In developing countries also most of the soft and fat tissues are used for consumption purposes. This reduces the amount of offal with 10-15% of the liveweight killed (LWK).
The incidence of natural death of livestock in developing countries is relatively high. This rather leads to sanitary problems than to environmental problems as most of the dead animals are scattered over large areas.
According to the FAO (1993), 78% of all processed hides come from cattle and buffalo, 15% comes from sheep and 7% from goats. In the present report, the discussion of the tanning process is restricted to the tanning of the above mentioned hides and skins.
The tanning process can be partitioned in three processes:
- Beamhouse operations;
- The tanning itself; and
- The finishing activities.
Some factories only carry out beamhouse operations, others only finishing activities. A third group of tanneries carries out all three activities. Hides are usually tanned twice. The first tanning is a mineral or vegetable type of tanning. These days mineral tanning is the most popular method for large-scale tanning because it acts quickly and produces a leather with desirable physical and chemical properties. Of the minerals, chromium is the most frequently used chemical (95%). For the retanning, a combination of agents is used, mostly of vegetable compounds. For traditional vegetable tanning, barks and nuts are used instead of chromium. Probably a small portion is oil-tanned, mainly for the production of chamois leather. Of the worlds output of tanned material, 60% is assumed to be tanned with chromium while 10% is tanned by means of vegetables. The remainder is estimated to be treated with aniline or other ingredients (Mattioni, 1994). In the United States, over 20,000 hides are tanned per day of which 23.5% with vegetable tannins and 76.5% with chromium (Hemingway and Karchesy, 1989).
In most developing countries, tannery effluents are discharged into sewers or inland surface waters and/or brought onto the land with irrigation water. The high concentrations of salt and hydrogen sulphide in tannery wastewater affects the quality of water and may cause bad taste and odour. Suspended matter (lime, hair, fleshings, etc.) makes the surface water turbid and settles eventually on the bottom. Both processes create unfavourable conditions for aquatic life. Mineral tannery wastewater that is discharged on land, will affect the soil productivity adversely and may cause land to become infertile. As a result of infiltration, the quality of the ground water is affected adversely also. Discharge of untreated tannery effluents into the sewer system causes deposition of calcium carbonate and choking of the sewer.
In developed countries the tannery effluent is treated intensively before it is discharged into surfacewater. As a result of wastewater purification the chromium and BOD levels of the purified water is relatively low. The sludge in the waste water systems has to be brought to special dumping grounds because of its chromium content.
The sensitivity to chromium of different species of aquatic organisms varies greatly. Hexavalent chromium is a strong oxidizing agent, and therefore more toxic than trivalent chromium. Chromium deactivates cellular proteins. Lethal levels for fish range from 17 to 118 mg/l, 0.05 mg/l for invertebrates, and 0.032 to 6.4 mg/l for algae (Anonymus, 1974). The concentration apparently safe for fish is moderately high, but a recommended maximum concentration of 0.05 mg/l (WHO standard for drinking water) has been selected in order to protect other organisms, in particular Daphnia and certain diatoms which are affected at levels slightly below this concentration.
Inside the tannery, chromium should be handled with care, since exposure to elevated concentrations of chromium in the air (> 0.1 mg/m3) may lead to lung cancer (Anonymus, 1974)
Of the total worldwide production of milk, 87% is cow milk (FAO, 1993). The rest of the production comes from buffalo (9%), sheep (2%) and goat (2%). In Europe, North and Latin America, practically only cow milk is being produced. In Asia the percentages are 58% for cow milk and 40% for buffalo milk.
An important factor with respect to environmental impact is whether the produced milk is processed at home or in a factory. Home processed milk hardly offers any environmental problems as little waste is produced (mainly air pollution from heating and some pollution of cleaning water with milk residuals) and as the concentration of the waste is generally low.
In developed countries, nearly all milk is industrially processed at dairy factories. A negligible proportion is used and processed at home.
In developing countries this situation is completely different. In southern and eastern African countries it is estimated that about 80% - 90% of the milk is used and processed within the pastoral/agropastoral communities and their immediate vicinities. In Latin American countries this figure fluctuates between 10 and 88% with an average of 52% (FAO, 1990b).
There is not a great degree of difference between the industrial methods of milk processing in developed and developing countries. It is, with respect to environmental pollution, therefore not useful to make a distinction between developed and developing countries. As will be mentioned, an important source of environmental pollution are house-keeping practices that vary from country to country as well as within countries. Another important polluting factor is the production of whey during the fabrication of hard cheeses. These kind of cheeses are mainly produced in developed countries. Developing countries hardly produce hard cheeses. Most of the production is in the form of soft cheeses or curd. These products absorb most of the whey.
A key-indicator has been defined to quantify the amount of waste that is produced by the processes as described in the previous paragraph.
Data on small-scale and home processing are almost non-existent. The processes show a great degree of variation and one may assume that by-products are used as efficiently as possible and that waste production is minimized (though still major portions of output may be wasted, especially blood and manure). The low concentration of waste is due to scattered processing and the small quantities of waste processed. Because of the limited environmental impact and poor data availability, small-scale and home-processing activities have been excluded from the overall indicator.
The indirect key-indicator used in this report has been defined as:
The amount of industrially processed product.
For the different types of industries, the industrially processed product are:
- for slaughterhouses: tons of Live Weight Killed (LWK)Sometimes the produced waste can not be expressed per ton of LWK, but has to be expressed per ton of product (e.g. per ton carcass weight, or ton smoked meat).
- for tanneries (tons of Raw Hides: RH):The produced waste can be expressed per ton of raw hides.
- for dairies (tons of Raw Milk: RM):Sometimes the produced waste has to be expressed in tonnes per product (e.g. cheese, butter, milkpowder) because of lack of availability of other data or because these products are produced simultaneously from raw milk.
In those cases that the waste production from the slaughtering process is expressed in quantities per ton slaughter weight, conversion factors can be used: Table 1, 2 and 3.
The indirect key-indicator is to be regarded as a summary indicator of the direct indicators which will be discussed later in this document. These direct indicators are: (1) the amount of solid waste; (2) the BOD for wastewater and to a lesser extent COD, SS, NKj and P; and (3) to some extent CO2, CO and NOx for polluted air. It will be clear, from the rest of the report, that of these indicators the BOD will be the most important and most used one. Solid waste, when properly handled, for which numerous methods exist, does not necessarily lead to environmental problems. Wastewater on the other hand may lead to a decrease of surface water quality if discharged untreated.
Data on air pollution related to animal product processing are not easily obtainable. Air pollution is mainly the result of the use of fossil energy and it appears that there is a wide range in the use of energy for the same process. This wide range is amongst others caused by the price of energy and the efficiency of the process.