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Technology. Technologies exist to significantly reduce emissions from processing plants. The problem is one of cost and corresponding incentive and regulatory framework. Because of the high BOD-load in the waste water of tanneries, dairies and slaughterhouses, anaerobic systems are the most suitable waste water purification systems. Simple anaerobic systems could cut the BOD contents by half, while more sophisticated anaerobic systems reach 90 percent BOD-purification. Waste water treatment usually first separates solids from the liquid, followed biological treatment under anaerobic conditions (lagoons). Then, nutrients such as phosphorus are removed by chemical or physical processes such as adsorption, stripping or coagulation. The same process serves to remove the remaining BOD as well as pathogens. In a few developed countries environmental problems have already led to high quality standards being required for discharge water. To meet these standards, a combination of anaerobic and aerobic treatment is required, often coupled with nutrient removal systems.
As most of the air pollution is related to fossil energy consumption, prevention to reduce environmental pollution, is even more important for air pollutants than for waste water. There are methods to treat polluted air, although generally at high cost.
Slaughterhouses. In slaughterhouses, the environmental impact can often be greatly reduced by employing simple technology:
• Waste prevention. Dry rendering of offals reduces the amount of waste water produced, and therefore processing costs. Cutting down on water use is probably the most important factor in reducing the environmental burden of slaughterhouses. Wastes should, as far as possible, be collected as solids because blood and paunch, and other solids, contribute enormously to the waste water load and should not be washed away;
• Use of by-products. Slaughterhouse wastes can be composted and used as fertilizer. Anaerobic treatment results in a slurry that can be used as animal feed the liquid part can be used as irrigation water, or for fish or algae production, although more recently and following the mad cow disease outbreaks in the KU, the recycling of animal waste products for animal feed is seriously questioned.
Tanneries. Pollution through waste water can be reduced by cutting down on total water use, for example, by reusing waste water, by introducing new technologies to minimize water use and by reducing the use of chemicals such as lime, salt, sulphide etc. and chromium. Higham (1991) gives more details:
• Water conservation. As with slaughter, reduction of water use leads to a reduction in the total waste load. To a certain extent, waste water can be reused;
• Curing hides and skins. The use of salt for preservation may be reduced and, where possible, be replaced by biodegradable preservatives. Other preservation methods such as chilling or radiation by electron beam or gamma rays may be used;
• Beamhouse processes. Hair saving methods are recommended to prevent degraded keratin from entering waste streams. Unhairing/liming fluids can be recycled after recharging. It is also recommended to separate the unhairing and liming stages. Both liquids can be recharged and hair screened out. The intermediate wash can be re-used as a soak liquid;
• Tanning. Low chrome pretannage, possibly of an aluminum salt, can be used. Alternative mineral salts with less toxicity, such as aluminum, zirconium, titanium and iron, may be used as possible substitutes for chromium salts. Re-use of chromium is another option. In countries where discharge of chromium is strictly prohibited, much effort is put into chrome recovery and re-use. Precipitation of chromium is an easy process which also results in large reductions of SS and BOD emissions. Alternative vegetable tanning methods can replace chrome tanning to a high degree. The "Liritan" process developed in South Africa has a high chemical uptake, low pollution load, uniform penetration of the tan and is a shorter process (Higham, 1991); and
• Finishing. A reduction of volatile organic compounds can be accomplished by using aqueous finishes for base and middle finish coats.
Dairies. Waste can be prevented to a considerable extent by good management practices and use of adequate equipment. While poor management results in waste loads of 3 kg BOD per ton of milk, good management can reduce this to 1 kg. Again, this can be achieved by optimizing the use of water, resulting in lower volumes of waste water, and by recovering solids from the waste water.
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Box 5.11 Regulations induce search for innovative solutions; the case of Tyson Food Inc. IN THE state of Arkansas, USA, Tyson Food Inc. was sued by more and than 100 Green Forest residents who contended that their water supply had been fouled by a lack of adequate sewage treatment from chicken processing plants in 1989. Tyson was ordered to pay for property damage, for overloading of the city's water treatment system and for violating the Clean Water Act. Furthermore, the use of burial pits for dead bird dispose by growers was banned. This resulted in Tyson Fobs investing in research and development to remedy the problem. Tyson Foods subsequently developed a recovery technology that allowed them to recycle proteins, fat and carbohydrates recovered in their water treatment process into nutrients for animal feed. This enabled the company to recycle not only venous solids (primarily proteins, carbohydrates, and fats) from its water treatment plants in Arkansas, Oklahoma and Missouri, but also the inedible animal parts from its poultry treatment and pretreatment centres attached to its processing plants. Further, it also enabled the recycling of dead birds from the forms. In order to facilitate the use of this technique, Tyson Foods distributed some 2,000 custom freezers to its growers to aid them in the disposal of dead birds, which were collected and transposed to the rendering plant. Thus, the refinement of the rendering process resulted in a win-win solution, i.e. an improvement of the environment and a profitable solution for Tyson. The ability to recycle by-products is becoming more of a concern as consumers are demanding more processed meat and pet food companies, among others, purchase the processed protein meal and other products for use as high-quality ingredients in various animal rations. The feathers can also be hydrolyzed into a feather meal that can be used as another high protein animal feed ingredient. |
Source: Narrod, 1994.
Policies. In contrast to many other impacts of livestock production, processing is usually point source pollution and therefore easier to quantify and to control.
Regulations are an essential component in dealing with the environmental impact of processing plants. They may limit or prohibit the use of chromium in tanneries, control the use of CFCs in chilling processes and limit the total BOD output in waste water. In addition, odour and gaseous emission control may be prescribed.
Zoning. For small processing units, a policy of encouraging an even geographical distribution is probably the best approach. Similarly to the industrial livestock production system, specific sites should be identified for industrial processing operations. Because of its bulkiness and perishable nature, milk processing has always been sited close to producers and is less concentrated. A similar trend is starting in the developing countries. However, zoning is dependent on a functioning infrastructure and adequate enforcement of pollution control regulations.
Incentives. Use and processing of by-products depends to a great extent on whether there is a market for a given commodity, on the availability of a practical commercial process for converting the animal byproduct into a usable commodity, and on storage facilities for the perishable product and on whether there will be a sufficiently large volume for it to be financially viable. Also here, win-win situations can be found, as shown in Box 5.11. Increasing the prices for water and energy can make the use of these resources more efficient and thus reduce the waste load and emissions. Incentive policies may help to stimulate a market, creating selective advantages for by-product use and waste recovery but, as with public incentives in general, should be of short duration and well-targeted.
Institutional instruments. Finally, there is an urgent need to strengthen pollution control and enforcement mechanisms and to establish financial independence of slaughterhouses in the developing world which now, frequently, see all their income going back to the public coffers, without re-investment in maintenance and infrastructure improvements.
Processing of Livestock products
