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6.1. Waste production and its consequences
6.2. Data availability and reliability
6.3. Waste reduction

6.1. Waste production and its consequences

In the three types of animal-product-processing industries (slaughtering, tanning and milk processing), wastewater problems appear to be the most severe ones. Processing activities inevitably produce wastewater, frequently in large quantities. This wastewater is polluted with biodegradable organic compounds, suspended solids, nutrients and toxic compounds (particularly chromium and tannins from tanneries). Via the reduction of dissolved oxygen this pollution directly or indirectly leads to a decreasing suitability of (surface) water for aquatic life, and drinking, swimming or other purposes.

Typical values of wastewater that have been reported are given in Table 26. Huge variations do occur owing to differences of scale and in house-keeping and management practices of factories or plants. The quantity of water used for the various processes is a major determining factor, high levels of wateruse being related to high emission values.

expressed per:

BOD (kg)

SS (kg)

NKj-N (kg)

P (kg)

Red meat slaughterhouses

ton LWK





Red meat packinghouses

ton LWK





Poultry slaughterhouses

ton LWK






ton raw hide





Dairies (consumption milk)

ton milk





If the density of animal product processing is so low that the concentration of pollutants in the receiving water bodies remains low, the production of wastewater does not necessarily lead to environmental problems. However, when from the comparison of the values of Table 26 with the European target values for urban wastewater discharge (e.g. 25 mg BOD, 10-15 mg N and 1-2 mg P per litre), it becomes clear that, from a wastewater production point of view, that there is a trend towards increasing densities of product processing even at relatively small amounts of processed animal products.

The heavy metal Chromium, occurring in the waste of tanneries, has caused and will in all likelihood continue to cause, serious environmental problems. It is common practice that most of the chromium is released in wastewater. There are no indications of other heavy metals in the waste of the animal processing industry causing environmental problems.

Problems caused by air pollution and solid waste disposal are minor in comparison to those related to wastewater production. The main cause of air pollution is the use of fossil energy, with as major exception the volatile organic compounds in the leather industry.

Particularly in slaughterhouses solid waste disposal may lead to hygienic problems, but in principle these are relatively easy to solve. An exception is the leather waste that contains chromium. This waste must be dumped on special grounds.

For a proper discussion of the environmental impact of slaughtering, tanning, and dairy industry, the effects of related activities such as transportation, spoilage by the consumer, durability of the product etc. also have to be taken into account. These activities are especially important for the discussion concerning the advantages and disadvantages of the various production processes and the scale at which processing is undertaken.

6.2. Data availability and reliability

In Table 26 typical values of wastewater production for several processes are given. They are given for most common parameters to characterize wastewater production. The data originate mainly, though not exclusively, from OECD-countries. Data from developing countries on waste production and its environmental impact are difficult to find. Those data that have been reported can often not be interpreted adequately owing to major shortcomings in the description of the relevant processes or the data collection methods. In some cases waste parameters have been recorded without indications of relationships with other parameters. Examples of these are:

- data on suspended solids without any reference to solid waste;

- solid waste data of 5.5 kg manure per ton carcass weight, obviously referring to minor components of the manure, probably the scrapings, but with no reference to other solid waste production (e.g. rumen content).

Most of the reported values originate from EPA-studies published in the period 1970-1975. Even studies published at the end of the eighties refer mainly to these studies. Moreover, huge variations in waste production per unit of product processed have been found. This variation can be partly explained by looking at the types of products made or processes used, but some variation remains unexplained. But even worse, also in OECD-countries exceptions have been recorded which exceed emission values by manifold, without mention of a possible clue of explanation.

The conclusion that needs to be drawn is clear. There is an urgent demand for proper, well described, reference values on waste production. Monitoring programmes need to be set up to allow for a more reliable environmental impact assessment of animal product processing than is presently the case. These monitoring programmes should result in emission factors per unit of product processed. Because of the diversity in processes and waste production, proper data collection on waste processing will be an expensive and time consuming undertaking.

The obtained reference values on waste production will always need to be translated to locally relevant processing methods and production situations. Thus, monitoring programs must be arranged so as to make it possible to give a correct interpretation of the reference values.

To this end monitoring programmes should:

- cover all important pollutant parameters (particularly solid waste, water consumption, SS, BOD, N, P, heavy metals and energy consumption);

- give a clear description of the production processes to which the data relate, including the quantity and type of product processed;

In addition steps must be made that measurements are taken prior to wastewater treatment and before the water is diluted with other (waste-)water. If a wastewater treatment plant is available, the reactor performance should be determined for the evaluation of the effectiveness of the water treatment. In such cases related parameters should also be measured: precipitation not only results in a reduction of BOD, SS, etc., but also increases the amount of solid waste.

6.3. Waste reduction

There are several ways to reduce the waste load:

- prevention of the production of waste;
- development of new clean processing methods;
- treatment of waste (“end-of-pipe treatment”).

In this study possibilities for waste prevention and end of pipe treatment have been treated. No attention has been given to the development of clean processing methods as these entail specific fundamental technical and economical knowledge.

For a reduction of environmental problems that occur because of discharge of waste, improved housekeeping practises and management practices are of more importance than end-of-pipe waste treatment. Good house-keeping practices are not easy to describe, but it is clear that, as the amount of water used is major factor in all industries (if more water is used, total wastewater production per unit of product processed may increase manifold) proper water management is one of the first aspects deserving attention. A reduction of water consumption without decreasing hygienic standards, is often possible. This reduction may be reached by good-house keeping practices, but also by the introduction of new technics such as dry cleaning prior to washing.

Furthermore, environmental problems may also be reduced by converting as much waste as possible into a solid product instead of washing the waste away into the wastewater. In general solid waste is fairly easy to control, requires less energy and is cheaper than wastewater treatment.

For tanneries, it is of prime importance to prevent chromium from polluting wastewater. Precipitation of chromium is an easy process. Solid waste containing chromium should be dumped in special dumping grounds where facilities should be available to minimize the amount of percolation water. Precipitation also results in large reductions of SS and BOD emissions.

In slaughterhouses, blood and paunch contribute enormously to the wastewater load. These and other solid by-products should be prevented being washed away. By-products can be used for several purposes and unusable solid waste can be easily handled properly, e.g. via composting. This process and more sophisticated processes for by-product handling may even result in valuable products.

Given the high BOD-load in the wastewater of tanneries, dairies and slaughterhouses, anaerobic systems would seem to be the most suitable wastewater purification systems. Simple anaerobic systems reach 50% BOD-purification, while high-rate anaerobic systems may achieve a 90% BOD-purification rate.

In a few developed countries, environmental problems have led to the formulation of high quality standards for discharged water. To meet these standards, a combination of anaerobic and aerobic is required, often coupled to nutrient removal systems.

As most of the air pollution is related to fossil energy consumption, prevention as a method to reduce environmental pollution is even more important than it is for wastewater. For some components (e.g. VOC, dust) methods exist for the treatment of polluted air, however frequently at high costs.

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