The waste generated by the abattoir contains inedible parts including skin, bones, blood, gastro-intestinal tract, tendon and visceral organs. The ratio of these contents depends on species of animals to be slaughtered (Grosse, 1984; Sielaff, 1996). Table 1 shows the amount of animal-specific waste. To improve the profitability of the meat industry, there is a need to develop some techniques for proper recycling and potential use of meat by-products. A survey estimates that beef and pork share about 11.4% and 7.5% of the total revenue come from the by-products (USDA, 2001).
Table 1
The specific waste index for slaughter houses with respect to the type of animal.
| Animal | Specific waste indexa |
| Cow | 0.56 |
| Calf | 0.87 |
| Pig | 0.2 |
| Sheep | 0.1 |
a Mass of accumulated waste divided by the mass of saleable product.
In early days, meat organs and offal were efficiently used in different food products in Asia, but due to several health-related threats the use of by-products was diverted to non-food utilization including pet foods, animal feed, cosmetics and pharmaceuticals (Rivera, Sebranek, Rust, & Tabatabai, 2000). Health concerns of using meat by-products for food purpose also affect the market. Another factor responsible for disappearance of these markets is low price. These eco-nomic concerns have diverted the focus of scientists towards non-food uses of by-products generated by meat processing units. In addition to health and economic concerns, improper treatment of waste cause solemn environmental threats. However, these losses can be overcome by proper treatment, disposal and utilization of meat by-products. Slaughtering process in the abattoir, processing, preservation and storage conditions of animal skins and poultry feathers have a great influence on the environment. Thus, it is needed to keep an eye on all the sources of waste generation and types of effluents produced during each processing step. Generally, waste materials associated with the meat processing in-dustry include waste water, solid material, gases and volatile compounds that can cause serious environmental threats.
1.1. Wastewater
Water is a very important constituent of any food processing industry. Activities in the slaughterhouse and meat processing plants need plenty of water. Moreover, water is also used for cleaning purposes in the pro-cessing area. Wastewater is generated and discharge of this wastewater has an important environmental impact. This discharge also results in flagging the quality of surface water. Nature of the processes involved in the processing industry highly influences the type, composition and concentration of pollutants present in the wastewater. Following are the most common ways in which wastewater pollutes the surface water.
Presence of plenteous amount of biodegradable organic materials in the wastewater binds oxygen and reduces its availability which ulti-mately causes death of aquatic animals. Moreover, eutrophication may occur due to certain macronutrients (N, P) and excessive growth and mineralization of algae which results in the mortality of aquatic resi-dents. Additionally, wastewater also contains several toxic compounds including unionized ammonia, chromium and tannins that are directly involved in the deaths of aquatic animals.
Wastewater also contains several suspended solids of organic and inorganic nature that cannot be collected as solid wastes. Presence of these wastes in the water increases its turbidity. These wastes utilize huge amount of dissolved oxygen present in the water. Organic material constitutes fat, carbohydrates and proteins. Protein degradation results in the production of ammonium which eventually leads to the discharge of nitrites and nitrates that result in the higher oxygen consumption. Furthermore, different microbial activities are also involved in the oxidation of organic fraction of suspended solids which ultimately pro-duces CO2, H2O, CH4 and biomass.
Nitrogen is bound with organic material or in the form of ammonium in wastewater. It may also occur in the form of nitrate if HNO3 is used as cleaning agent in the industry. Production of ammonia in the water is toxic to the fish and other aquatic animals (Barnes, Forster, & Hrudey, 1984). Removal of nitrogen can be accomplished through several
wastewater purification systems. Phosphate is present in wastewater as inorganic phosphate and organically fixed phosphate. Phosphorus con-tents in the water can be determined photometrically. Phosphorus con-tamination can also be removed by using various biological or physico-chemical processes.
1.2. Solid waste
By-products of meat industry that cannot be further re-processed are termed as solid waste and must be properly dumped. These include different toxic substances, organic compounds and non-biodegradable material. Viscera of animals and poultry birds have very high microbial load including several types of pathogenic bacteria like Salmonella, Escherichia coli and Shigella. These pathogens produce special types of toxic substances called Shiga toxins that inhibit protein synthesis in the body (Barkocy-Gallagher et al., 2003; Sandvig & van Deurs, 2000). Moreover, ammonia chromium and tannins are also toxic substances which are produced during the processing of fish and other aquatic animals (Metcalf & Eddy, 1991). Special care is needed to dispose-off these compounds. A common practice to discard these toxins is entombing in dumping grounds. Several body parts including skin, feathers, head, feet, hooves, lungs, udder and rectum are also included in the category of solid wastes (Schrieber & Seybold, 1993). Organic com-pounds also require special care while disposing-off due to off-odor and leaching problems. Moreover, spreading of these substances in the atmo-sphere may also cause serious health threats. Non-biodegradable material may also be buried properly in the ground.
1.3. Toxic gases produced by meat processing plants
A number of toxic gases (CO2, CO, NOx and SO2) are discharged in the air due to the use of energy during freezing, chilling, smoking and scorching of meat products. Several volatile compounds are also discharged in the air by using different sanitizing compounds for cleaning purposes. Moreover, dust is also mixed in air from bone cutting and processing industries. Air pollution leads to problems of various kinds including global warming, ozone layer depletion, acid rain, bad odor and health risks (RIVM, 1994). Measures should be taken by meat processing industries to minimize the production of toxic gases.
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Written by .
The authors of this article are
- Syed Mudabbar Hussain Shah from Department of Food Engineering. a
- Syed Shabbar Hussain Shah from Department of Soil Science. a
- Mirtab Ali from Department of Food Science & Technology. a
*a = University of Agriculture, Faisalabad.
