FAO Report on Vegetarianism

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Title: Management of Waste from Animal Product Processing...More details

Management of Waste from Animal Product ProcessingID:62587Language:ENDocument type:OtherDescription:The study describes and analyses the relationship between the production of waste in animal product processing industries on the onehand and the prevention and treatment of the waste on the other. The industries discussed are slaughterhouses, tanneries and thedairy industry. The report offers a summary of the knowledge on production, prevention and treatment of waste in these three animalproducts processing industries. Because of the limited time available for this study, the problems that occur in the mentioned industrieshave not been treated in full detail. Important questions related to the subject are those regarding: (1) the differences between variousproduct processing methods; (2) the reduction of the production of waste; and (3) the methods of waste treatment. Chapter 1 providesa general introduction to the subject, the different types of waste produced, the variables by which to measure pollution and thedefinition of the Key Indicator (quantity of industrially processed product) of the environmental impact of the processing of animalproducts. Chapters 2, 3 and 4 describe the waste production in the three main animal products processing industries and a number ofmethods by which waste production might be reduced. Chapter 5 describes the handling of by-products and the treatment of wasteproducts. The conclusions and recommendations in chapter 6 summarize the technological and policy options that may help reducewaste production and the negative impact on the environment from the processing of animal products.Publication year:1996URL:http://www.fao.org/WAIRDOCS/LEAD/X6114E/X6114E00.HTMJob number:X6114Department:AGDivision:AGA

1. THE ENVIRONMENTAL IMPACT OF THE ANIMAL PRODUCTPROCESSING INDUSTRIES

1.1. Introduction1.2. General environmental impact1.3. Overall waste production1.4. The Key-indicator

1.1. Introduction

The study describes and analyses the relationship between the production of waste in animal productprocessing industries on the one hand and the prevention and treatment of the waste on the other. Theindustries discussed are slaughterhouses, tanneries and the dairy industry. The report offers a summaryof the knowledge on production, prevention and treatment of waste in these three animal productsprocessing industries. Because of the limited time available for this study, the problems that occur in thementioned industries have not been treated in full detail.

Important questions related to the subject are those regarding: (1) the differences between variousproduct processing methods; (2) the reduction of the production of waste; and (3) the methods of wastetreatment.

http://www.fao.org/WAIRDOCS/LEAD/X6114E/X6114E00.HTM

Chapter 1 provides a general introduction to the subject, the different types of waste produced, thevariables by which to measure pollution and the definition of the Key Indicator (quantity of industriallyprocessed 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 processingindustries and a number of methods by which waste production might be reduced. Chapter 5 describesthe handling of by-products and the treatment of waste products.

The conclusions and recommendations in chapter 6 summarize the technological and policy options thatmay help reduce waste production and the negative impact on the environment from the processing ofanimal products.

1.2. General environmental impact

1.2.1. Wastewater1.2.2. Solid waste1.2.3. Air pollution

The manufacturing of animal products for human consumption (meat and dairy products) or for otherhuman needs (leather), leads inevitably to the production of waste. Under traditional conditions, thequantities 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, nature’s mechanisms become overburdenedand pollution problems start to occur. Usually, small-scale home processing activities produce relativelysmall amounts of waste and waste water. Nature can cope with these. Yet as a consequence of theincreasing emphasis on large scale production (e.g. for reasons of efficiency, increase in scale ofproduction and hygiene) considerably greater amounts of waste will be produced and steps will have tobe 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 improvedtreatment of waste products. Because large scale processes are not easy to survey, the checking ofwaste production is a problematic undertaking and special efforts are needed to find out where in theproduction process waste is produced.

An example that illustrates the relationship between the scale of production and the production of waste isthat of the production of hard cheese. Before large scale production of cheese came into existence, wheywas considered as a valuable by-product that could be used as animal feed. In the Netherlands, about 50percent of all the milk produced is used for the production of cheese. The whey which is produced in theprocess could lead to enormous environmental problems partly because the costs of transport of thiswhey 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 thisproblem. Eventually this has resulted in the establishment of a production line of whey-powder which isnow-a-days considered a valuable product.

The example also shows that the borderline between a waste product and a useful product is sometimeshard to draw.

In the present study major attention will be given to the impact on the environment of: (1) the slaughterprocesses at slaughterhouses; (2) the storage, preservation and processing of hides; and (3) theprocessing of milk, all at industrial levels. For the discussion concerning the waste production within eachof these animal-product-processing industries, it is worth looking at operations that precede and follow theindustrial waste producing processes.

* In slaughterhouses: the animals are reared, fattened and transported to the slaughterhouses. Afterprocessing, the meat is stored before it is transported to retail outlets. The “preceding” activities producemanure etc. while for storage and transport (follow activities) cooling facilities are needed. This puts aheavy claim on energy sources.

* In tanneries: hides produced at slaughterhouses must be stored. To prevent spoilage, they should bepickled and preservatives should be added. The methods used to process hides will to some extentdetermine the durability of the produced leather. The production of more durable leather leads to smallerquantities of leather waste. Chrome tanned leather and leather products contain about 2-3% of dry weightchromium. Worn out leather products, such as shoes and jackets, are frequently dumped at municipaldumping 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 theprocessing at the plants, dairy products are packed and stored and transported to retailers. At the end ofits lifeline, packing material finishes in the form of solid waste. The repeated use of milk bottles produceswaste water (after cleansing). At the site of the consumer, storage makes a demand on energy andincorrect storage or usage may lead to spilling. It has been estimated that 2-10% of all dairy products arewasted by the consumer as a result of spoilage.

In general terms, waste products may occur as waste water, solid material, volatile compounds or gassesthat are discharged into the air.

1.2.1. Wastewater

An important environmental impact of the animal processing industry results from the discharge ofwastewater. Most processes in slaughterhouses, tanneries and dairy plants require the use of water. Thiswater and water used for general cleaning purposes will produce wastewater. The strength andcomposition 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 (BOC’s) may cause a strong reduction of theamount of dissolved oxygen, which in turn may lead to reduced levels of activity or even death of aquaticlife.

2: Macro-nutrients (N, P) may cause eutrophication of the receiving water bodies. Excessive algae growthand subsequent dying off and mineralisation of these algae, may lead to the death of aquatic life becauseof oxygen depletion.

3: Agro-industrial effluents may contain compounds that are directly toxic to aquatic life (e.g. tannins andchromium in tannery effluents; un-ionized ammonia).

Ad 1: Biodegradable organic compounds

Parameters for the amount of BOC’s are the Biochemical Oxygen Demand (BOD), Chemical OxygenDemand (COD) and the concentration of Suspended Solids (SS). The BOD and COD are overallparameters that give an indication of the concentration of organic compounds in wastewater. Theconcentration of suspended solids represents the amount of insoluble organic and inorganic particles inthe wastewater.

- Biochemical Oxygen Demand (BOD)

Agro-industrial wastewater generally contains fat, oil, meat, proteins, carbohydrates, etc., which aregenerally referred to as bio-degradable organic compounds (BOC). This term is a denominator for allorganic substances used and degraded by micro-organisms. For most common organisms present in theaquatic 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 BODwill be used for the BOD520.

- Chemical Oxygen Demand (COD)

The COD represents the oxygen consumption for chemical oxidation of organic material under stronglyacid conditions. The COD test yields results within a period of a few hours and therefore provides directinformation. In this test biodegradable as well as non-biodegradable compounds are oxidized. The CODtherefore only provides an indirect indication of the potential oxygen depletion that may occur from thedischarge of organic material in surface waters. Use of the BOD is preferred to that of the COD because itprovides a more reliable indication of the degree of pollution of wastewater in terms of bio-degradablematter. Nevertheless, the COD is still a widely used parameter for wastewater in general because of theshort 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 of1.8. (Luppens, 1994).

For dairy industries the COD/BOD ratio of the wastewater is 2.63 for low BOD values (< 450 mg/l). Forhigh 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 mainlymaterial that is too small to be collected as solid waste. It does not settle in a clarifier either. Discharge ofSS increases the turbidity of water and causes a long term demand for oxygen because of the slowhydrolysis rate of the organic fraction of the material. This organic material may consist of fat, proteinsand carbohydrates. The natural biodegradation of proteins (from for instance meat and milk), willeventually lead to the discharge of ammonium. Ammonium oxidation into nitrite and nitrate by nitrifyingbacteria, leads to an extra consumption of oxygen.

Problems resulting from the discharge of biodegradable organic compounds may be addressed by meansof 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 theorganic 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 alsonitrate may be present (this may be the case in dairy industries where HNO3 is used for cleaningoperations). 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 (mostlyortho-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 300-400times more toxic than NH4+; Barnes et. al., 1984). Chromium and tannins are toxic compounds. Atneutral 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 atedious way and yields inaccurate results. Nowadays, the presence of FOG is hardly mentioned in reportsand 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 1-2mg/l for urban wastewater discharge (EEC, 1991). In the Netherlands target values for water quality oflarge 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).

1.2.2. Solid waste

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 ofhygienic reasons or because during decomposition ill odour or leaching problems may arise.

- non degradable compounds. These may be dumped at regular dumping grounds.

1.2.3. Air pollution

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 CFC’s;

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 ofVOC;

The use of energy leads to the discharge of gasses such as CO2, CO, NOx and SO2. Chilling andfreezing (CFC’s and NH3) activities, smoking of meat products and singing/scorching of pigs also lead toemissions into the air.

The discharge of volatile organic compounds (VOC) may occur in dairy plants when cleaning agents areused and in the leather industry when leather finishing substances are used. Dust may be produced inbone cutting and bone processing industries. And the production of milkpowder inevitably leads to theproduction of dust as well.

1.3. Overall waste production

1.3.1. Slaughter activities1.3.2. Tanning processes1.3.3. Milk processing

1.3.1. Slaughter activities

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 meatproduction. For the discussion of the slaughtering process and the waste production, a distinction will bemade 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(5) wastewater.

In most developed countries, slaughtering is a centralized activity. The consumer in these countries has apreference 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 retailoutlets. As a result, large quantities of by-products (bones, lungs spleen, oesophagus etc.) are left behindat the slaughterhouse. They fall in the category of inedible offal. For economic and environmentalconsiderations, these need to be suitably processed and utilized. Clean fatty tissues such as kaul andmesentery 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 edibleand 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 glandsare preserved for the production of glandular products.

In developing countries a large variety of slaughter sites exists. Slaughter sites vary from simple slaughterslabs to very modern slaughterhouses. Large scale industrial processing units are imported fromdeveloped countries, often without rendering or waste treatment facilities. Many slaughterhouses (ofvarious types) are insanitary and pose threats to health, particularly around rapidly expanding populationareas. Often old slaughterhouses discharge blood and untreated wastewater. The elimination of sickanimals and subsequent destruction are frequently carried out inappropriately (Kaasschieter, 1991a).Blood may coagulate in drains where it putrefies, causing bad odours and sanitary and environmentalproblems. Edible and inedible by-products are frequently wasted during the slaughtering and furtherprocessing 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 slaughterline, 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 highcosts 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 forthe 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 slaughterslabs. The processing and the utilization of offal require a technology and capital lay-out which arecompletely different from those in developed countries. Huge capital investments in infrastructure ofplants and machinery, as is the case in developed countries cannot be justified. In developing countriesalso most of the soft and fat tissues are used for consumption purposes. This reduces the amount of offalwith 10-15% of the liveweight killed (LWK).

The incidence of natural death of livestock in developing countries is relatively high. This rather leads tosanitary problems than to environmental problems as most of the dead animals are scattered over largeareas.

1.3.2. Tanning processes

According to the FAO (1993), 78% of all processed hides come from cattle and buffalo, 15% comes fromsheep and 7% from goats. In the present report, the discussion of the tanning process is restricted to thetanning 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 oftanneries carries out all three activities. Hides are usually tanned twice. The first tanning is a mineral orvegetable type of tanning. These days mineral tanning is the most popular method for large-scale tanningbecause it acts quickly and produces a leather with desirable physical and chemical properties. Of theminerals, chromium is the most frequently used chemical (95%). For the retanning, a combination ofagents is used, mostly of vegetable compounds. For traditional vegetable tanning, barks and nuts areused instead of chromium. Probably a small portion is oil-tanned, mainly for the production of chamoisleather. Of the world’s 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 otheringredients (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 watersand/or brought onto the land with irrigation water. The high concentrations of salt and hydrogen sulphidein 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. Bothprocesses create unfavourable conditions for aquatic life. Mineral tannery wastewater that is dischargedon land, will affect the soil productivity adversely and may cause land to become infertile. As a result ofinfiltration, the quality of the ground water is affected adversely also. Discharge of untreated tanneryeffluents 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 itschromium content.

The sensitivity to chromium of different species of aquatic organisms varies greatly. Hexavalent chromiumis a strong oxidizing agent, and therefore more toxic than trivalent chromium. Chromium deactivatescellular proteins. Lethal levels for fish range from 17 to 118 mg/l, 0.05 mg/l for invertebrates, and 0.032 to6.4 mg/l for algae (Anonymus, 1974). The concentration apparently safe for fish is moderately high, but arecommended maximum concentration of 0.05 mg/l (WHO standard for drinking water) has been selectedin order to protect other organisms, in particular Daphnia and certain diatoms which are affected at levelsslightly below this concentration.

Inside the tannery, chromium should be handled with care, since exposure to elevated concentrations ofchromium in the air (> 0.1 mg/m3) may lead to lung cancer (Anonymus, 1974)

1.3.3. Milk processing

Of the total worldwide production of milk, 87% is cow milk (FAO, 1993). The rest of the production comesfrom buffalo (9%), sheep (2%) and goat (2%). In Europe, North and Latin America, practically only cowmilk 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 athome or in a factory. Home processed milk hardly offers any environmental problems as little waste isproduced (mainly air pollution from heating and some pollution of cleaning water with milk residuals) andas the concentration of the waste is generally low.

In developed countries, nearly all milk is industrially processed at dairy factories. A negligible proportion isused and processed at home.

In developing countries this situation is completely different. In southern and eastern African countries it isestimated that about 80% - 90% of the milk is used and processed within the pastoral/agropastoralcommunities and their immediate vicinities. In Latin American countries this figure fluctuates between 10and 88% with an average of 52% (FAO, 1990b).

There is not a great degree of difference between the industrial methods of milk processing in developedand developing countries. It is, with respect to environmental pollution, therefore not useful to make adistinction between developed and developing countries. As will be mentioned, an important source ofenvironmental pollution are ‘house-keeping’ practices that vary from country to country as well as withincountries. Another important polluting factor is the production of whey during the fabrication of hardcheeses. These kind of cheeses are mainly produced in developed countries. Developing countries hardlyproduce hard cheeses. Most of the production is in the form of soft cheeses or curd. These productsabsorb most of the whey.

1.4. The Key-indicator

A key-indicator has been defined to quantify the amount of waste that is produced by the processes asdescribed in the previous paragraph.

Data on small-scale and home processing are almost non-existent. The processes show a great degreeof variation and one may assume that by-products are used as efficiently as possible and that wasteproduction is minimized (though still major portions of output may be wasted, especially blood andmanure). The low concentration of waste is due to scattered processing and the small quantities of wasteprocessed. 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 ofproduct (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 producedsimultaneously from raw milk.

In those cases that the waste production from the slaughtering process is expressed in quantities per tonslaughter 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 bediscussed later in this document. These ‘direct’ indicators are: (1) the amount of solid waste; (2) the BODfor wastewater and to a lesser extent COD, SS, NKj and P; and (3) to some extent CO2, CO and NOx forpolluted air. It will be clear, from the rest of the report, that of these indicators the BOD will be the mostimportant 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 adecrease of surface water quality if discharged untreated.

Data on air pollution related to animal product processing are not easily obtainable. Air pollution is mainlythe result of the use of fossil energy and it appears that there is a wide range in the use of energy for thesame process. This wide range is amongst others caused by the price of energy and the efficiency of theprocess.

2. SLAUGHTERHOUSES

2.1. Red meat slaughter process2.2. Poultry slaughtering process2.3. Emissions2.4. Prevention of waste production

2.1. Red meat slaughter process

2.1.1. Description of the slaughter process.2.1.2. Quantities of by-products

2.1.1. Description of the slaughter process.

Figure 1 presents a flow diagram of a red meat slaughterhouse.

Slaughtering

In slaughterhouses animals are received and kept around in stockyards and pens for 1 day. The animalsare 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 activitiestake place:

- Stunning;

- Suspension from an overhead rail by the hind legs;

- Sticking and bleeding over a collecting trough. The collected blood may be sewered or processed;

- 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 hairbefore 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 removalprocess.

- Decapitation;

- Opening of the carcass by cutting;

- Inspection of the carcass;

- Evisceration (removal of intestines and internal organs);

- Splitting and cutting of the carcass; and

- Chilling or freezing.

Meatpacking

Many large scale plants ship whole graded carcasses to retail markets, others perform some on-siteprocessing to produce retail cuts. The processes are the following:

- Cutting and deboning; and

- Meat processing. This includes a variety of operations amongst which grinding, mixing with additives,curing, pickling, smoking, cooking and canning.

Rendering

Rendering is a heating process for meat industry waste products through which fats are separated fromwater and protein residues for the production of edible lards and dried protein residues. Commonly itincludes the production of a range of products of meat meal, meat-cum-bone meal, bone meal and fatfrom 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) simplecooking; (2) open pan rendering; (3) kettle rendering; (4) wet rendering; and (5) dry rendering.)

- Low temperature rendering (around 80°C). This process requires finely ground material andtemperatures slightly above the fat melting point. It results in a better quality lard. The rendering at lowtemperatures is a highly sophisticated process requiring large throughputs and trained personnel. Formany developing countries the system is not suitable. (Kumar, undated).

Handling of viscera, paunch and intestines

Viscera can be recovered as edible products (e.g. heart, liver). They can also be separated for inediblerendering 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 ofgross solids, which are subsequently removed.

3: Dry dumping. The paunch contents are dumped for subsequent rendering or for disposal as solid wastewithout needless water flushing.

4: Whole paunch handling. The entire paunch may be removed, intact, for rendering or for disposal assolid waste.

Intestines may be rendered directly, or hashed and washed prior to rendering. For the processing ofintestines de-sliming prior to thorough washing is necessary.

Categories of slaughter-plants

Plants for red meat slaughtering may be categorized on the basis of the final products. A plant thatprocesses meat into products such as canned, smoked and cured meats is significantly different from aplant with facilities for slaughtering without further processing.

Slaughterhouses and packinghouses (slaughtering and meat processing) may each be divided into twocategories 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 mainproducts 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 thefollowing operations take place: rendering, paunch and viscera handling, blood processing, and hide andhair processing.

Packinghouses

- Low-processing packinghouse:

A plant that both slaughters and processes fresh meat into cured, smoked, canned and other meatproducts. 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 hasfacilities for tanning operations.

There are also plants that do not slaughter themselves but restrict their activities to the processing ofmeat (meatpacking). These plants have a waste production comparable to that of a simpleslaughterhouse.

2.1.2. Quantities of by-products

The products resulting from slaughtering of cattle are carcasses and by-products. The quantity of animalby-products often exceeds 50% of the LWK. The weight of the carcass, expressed as a LWK-percentageis 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 dressingpercentages for cattle in France. As shown in these tables, a wide variation in dressing percentagesexists, mainly related to factors like breed, age and feeding. In many developing countries low dressingpercentages (i.e. less then 50%) are common as animals receive less feed and/or feed that is of lowerquality than the feed offered in developed countries and because the animals are slaughtered at a higherage than is done in developed countries.

Carcasses still contain quantities of fat and bones (see table 2), most of which will be removed if thecarcasses are processed further. This further processing leads to increased amounts of by-products.

U.S. cattle grades Dressing percentagesRange Average

Prime 62-67 64Choice 59-65 62Good 58-62 60Standard 55-60 57Commercial 54-62 57Utility 49-57 53Cutter 45-54 49Canner 40-48 45

Young bulls Steers Cull cowsF* LI* CH* CH* LI* F*

Carcass (% LWK) 55.6 65.0 61.3 57.0 59.6 50.1Carcass:Bone (%): 16.6 13.0 14.3 16.5 16.1 17.8Musle (%): 68.1 74.7 70.0 65.0 66.1 62.9Fatty tissue (%): 15.3 12.3 15.7 18.5 17.8 19.3*: Breeds: F: Dutch/Holstein Friesian LI: Limousin CH: Charolais

Kumar (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, condemnedcarcass, 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 productcategories. It shows in principle that by-products may be used in full (which would result in low wasteproduction).

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 materialfor processing.

- there must be a facility for storage of the perishable product before it is processed and for storage of themanufactured 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.

Cattle PigsDenmark England U.S. Denmark Sweden U.S.* U.S.*

Carcass and edible products 62-64 75-80Carcass, meat and bone 69 56 56Retail cuts (bone in) 42Retail cuts (boneless) 41Organs 4 7 4 2.4Red offal 6Bone 8Edible fats 3-4 10 11 3 16 16White offal 10Blood 3-4 3 4 3 4 3Inedible raw material 8-10 17 6 8 15Hide and/or hair 7 8 6 1Hide (cured weight) 6Waste 20 14 6 12 4Paunch and manure 8Shrinkage 2-10*: different sources

2.2. Poultry slaughtering process

2.2.1. Description2.2.2. Quantities of by-products

2.2.1. Description

Receiving areas

The inlet to the plant is normally designed in such a way that fluctuations in bird deliveries can be dealtwith adequately. This is necessary since the processing capacity has a fixed maximum. At regularintervals birds are unloaded onto the holding areas and attached by their feet to a conveyor belt,transported to the slaughter area.

Slaughtering and packing

The birds are suspended from the conveyor after which the following actions take place:

- Stunning;

- Killing and bleeding by cutting the jugular veins;

- Collection of blood. The conveyor travels through a blood collection tunnel at a preselected travellingspeed;

- 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 rubberfingers. Removed feathers drop in underlying troughs;

- Washing. The defeathered carcasses receive a spray wash prior to evisceration;

- Opening of the carcass by cutting manually;

- Inspection of the viscera;

- Evisceration, removal of head, feet and viscera;

- Sorting of the viscera to recover heart, liver and gizzard;

- Final washing to remove blood and to loosen tissues;

- Chilling of the carcasses in a waterbath;

- Draining;

- Grading, weighing and packing; and

- Chilling and freezing.

2.2.2. Quantities of by-products

Table 4 gives dressing percentages for poultry in the U.S.

U.S. grades Dressing percentagesAverage

Chicken, broilers 70Chicken, capon 68Turkey, broiler 77Duck, Peking 58Pheasant 78

The various components of the raw offal can be summarized as follows (El Boushy and van der Poel,1994):

- total offal (heads, feet, intestine): 15.8%- blood: 3.5%- feathers: 6.0%- moisture: 9.0%Total: 34.3%.

2.3. Emissions

2.3.1. Solid waste2.3.2. Wastewater2.3.3. Air pollution

2.3.1. Solid waste

Table 5 shows the estimated solid waste of slaughterhouses and the meat processing industry in TheNetherlands (RIVM, 1994). All the solid waste mentioned in Table 5 has a potential use as fertilizer(manure) or animal feed (fat).

Slaughter process:manure 5.5 kg/ton carcass weightfat (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 productpaunch manure 100 kg/ton product

It would appear that rumen contents and the manure of the stockyards has not been included in the valueof manure.

2.3.2. Wastewater

2.3.2.1. Wastewater by red meat slaughtering2.3.2.2. Wastewater by poultry slaughtering

Kumar (undated) remarks that effluents of slaughterhouses constitute one of the most serious causes ofenvironmental 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 estimatedby the RIVM (1994), while in Table 7 international but older values of wastewater characteristics of thevarious types of red meat slaughterhouses (see chapter 2.1.1) are presented.

Pigs CattleBOD 2.4 4.4 kg/ton carcass weightNkj 0.6 1.1 kg/ton carcass weight

Slaughterhouses (1) Slaughterhouse (2)Simple complex

Typical Range Range RangeBOD 5 1.5 - 14 1.5 - 40 5.5 - 19COD 10 2 - 40 2.7 - 25Nkj-N 0.68 0.23 - 1.4 0.2 - 1.4 0.1 - 2.1SS 5.6 0.6 - 12.9 0.6 - 13 2.8 - 21P 0.05 0.014 - 0.09 0.014 - 0.086 0.05 - 1.2

Packinghouse (1) Packinghouses (2)low-processing high-processing

Typical Range Range RangeBOD 11 5.4 - 18.8 2.3 - 18 6.2 - 31COD 22 7 - 60 4.1 - 32 11.2 - 56NKj-N 0.84 0.13 - 2.1 0.04 - 1.3 0.7 - 2.7SS 9.6 2.8 - 20.5 1.5 - 17 1.7 - 23P 0.33 0.05 - 1.2 0.05 - 1.2 0.2 - 0.6

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 inPoland with Dutch data (Table 8).

Consumption in m3/ton “throughput”: Poland Netherlands(4 plants) (11 plants)

Slaughter 11.6 1.78Cutting and deboning 3.44 1.41Processing 7.45Various 3.77

Effluent:COD (mg/l) 648 700 (n=3)COD (kg/ton “throughput”); recalculated 17 2.2

Clearly the Polish industry uses much more water for its processes than the Dutch industry. Thedifference is enormous, especially as far as slaughtering is concerned (6 times as much). The chemicaloxygen demand per m3 of wastewater after pre-treatment is approximately the same as in theNetherlands. The total waste production in slaughterprocess in Poland is much higher (over 7 times) thanin the Netherlands.

Comparison of the Polish COD-production figures (Table 8) to the figures of Table 6, shows that thePolish 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 shareof 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 thanthe values given in Table 8.

2.3.2.1. Wastewater by red meat slaughtering

Major 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. (Domesticwastewater has a BOD of 300 mg/l). In the killing, bleeding and skinning phases, blood is producedwhich, when completely sewered, leads to a total waste load of 10 kg BOD per ton of LWK. A waste loadof 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 contributeto the total waste load if not properly handled. Dumping (sewering) of the entire paunch content gives aBOD 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 cleaningagents. The waste will reach the sewer by means of water overflowing from water troughs, by rain andsnowwater and pen washdown water. The sewered raw waste, assuming that solid contaminants havebeen 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 excludedbecause these are considered as meat (by-products)):

- Blood and tissue produced during hide removal fall on the floor. External contamination of the hide withdirt and manure is a secondary source of pollutants. The waste load is also increased as a result ofcleaning-up operations in this area.

- Wastewater is produced from intentional overflow from scalding tanks that contain blood, dirt, manureand hair (0.15 kg BOD per ton of LWK). The fluming of the mechanically removed hair also results inwastewater containing residual hair, blood and dirt after recovery of the bulk of the hair (0.4 kg BOD perton of LWK). Recovered hog hair may be be dumped as solid waste, washed and baled for marketing (0.7kg 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 tothe raw waste load;

- 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 totalof 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 cleaning activities;

- The curing of solutions containing sugar and salt. Pickling can cause a high chloride waste, only 25% ofthe 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 pollutedtank 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 waterprevention).

kg BOD/ton LWK Remarks1 stockyards and pens 0.25 solid contaminants are removed2 blood 10 all blood sewered3 cleanup hide removal 3 depends on cleanup practices4 scalding, dehairing 0.15 overflow scalding tank

0.4 flume water0.7 washing of recovered hair

5 paunch 2.5 in case of total dumping sewer1.5 - 2 in case of wet dumping

0.2 in case of dry dumping0.6 - 1.0 in case of whole paunch handling

6 intestine handling 0.67 rendering 28 general cleanup 3* depends strongly on cleanup practicesPotential emission: 24.9 - 25.8

9 meat packing 6 kg BOD/ton product!!*: authors’ estimate (not mentioned by Barnes).

2.3.2.2. Wastewater by poultry slaughtering

Table 10 shows characteristic values of waste flows of a poultry slaughterhouse.

Major contribution to the total waste load

Evisceration: For medium-to-high capacity poultry plants, it has been estimated that offal flume-waterfrom continuous flowaway fluming contributes a raw waste load of approximately one-third of the totalplant load (presented in Table 10). Values of 1.7 - 13.2 kg BOD per ton of LWK with a common averageof 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 thecontribution of blood to the total waste load applies to poultry plants. Chicken blood contributes 4.5 kgBOD per ton of LWK if completely sewered.

Minor contributions to the total waste load

Receiving areas: Waste load values of the receiving area vary widely since they are derived from thequantity of dirt, manure and feather deposits which vary with the length of holding time.

(1) (2)Poultry slaughterhouses Poultry slaughterhouses

Chicken Turkey Range TypicalRange Range

BOD 3.3 - 25 1 - 9 5 - 30 6.8COD 5.9 - 45 1.8 - 16 1 - 30 15NKj-N 0.15 - 12.2 0.4 - 1.9SS 0.1 - 22 0.6 - 10.9 3 - 25 3.5P 0.054 - 2.5 0.034 - 0.2Values 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 birdare 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)

- Defeathering; The underlying troughs are flumed to collect the feathers.

- General plant clean-up; up to 50% of the BOD can come from cleaning operations.

Solid waste:

- Feathers recovered from the flume water of the collecting troughs;- Head, feet and viscera.


Slaughtering is an activity that requires great amounts of hot water and steam for sterilisation andcleaning 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 strippingof 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 tothe 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 137kWh/ton of carcass and about 28.7 m3 gas/ton of carcass (RIVM, 1994). The degree of air pollutioncaused by the generation of energy depends on the type of process for which the energy is needed. Theprocesses of “dehairing”, “water heating” or “production of electricity” each lead to different levels ofemission.

Based on estimates of the RIVM (1994), emissions of CO2, CO and NOx resulting from the burning of gasfor heating and steam production are for the dutch situation as indicated in table Table 11.

Process: Air emission:Heating by burning gas: CO: 0.02 kg/ton carcass weight

CO2: 28 kg/ton carcass weightNOx: 0.01 kg/ton carcass weight

Dehairing pigs: (using gas) CO: 0.06 kg/ton carcass weightCO2: 6.5 kg/ton carcass weightNOx: 0.015 kg/ton carcass weight

Table 12 shows the energy use of Polish large scale slaughterhouses and comparable figures for thedutch 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 lowerthan that of industrial scale plants, probably because of a lower level of process-automation. The amountof energy needed for non-industrial cutting and deboning is considerably lower than that required in largescale plants, but the energy needed for non-industrial processing is more than twice as high, probably amatter of economies of scale (Heinen, 1994).

Gas (m3) Steam (GJ) Electricity (kWh)Polish Dutch Polish Dutch Polish Dutch

Slaugther (per ton carcass) 1.52 10.02 4.83 227 50Cut and debone (per ton carcass) 2.28 1.10 55.6 12Processing (per ton product) 15.0 4.61 187 200Rendering (per ton input) 21.1 3.7 338 117Other (per ton overall) 2.1 1.57 39 11

2.4. Prevention of waste production

Practices as discussed in this section are generally called ‘housekeeping practices’. The quality of overallcleaning-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 Table8).

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 amountof wastewater (and thus the waste load), compared with direct heating from 1.3 to 0.3 kg BOD per ton ofLWK.

- 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 LWK

2. wet dumping (washing out and screening the wet slurry on gross solids); estimated waste load of 1.5 -2 kg BOD per ton of LWK

3. dry dumping (dumping for subsequent rendering or disposal as solid waste without needless waterflushing): 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 aremarketable as pet food);

b: washing and bleaching lead to an estimated waste load of 1 kg BOD per ton of LWK (paunches aremarketable as tripe).

- Dry animal pen clean-up reduces the amount of wastewater. If the pens are covered, no rain orsnowwater 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 fordirect marketing, or hydrolysed by pressure cooking for marketing as a feed supplement.

- Heads and lungs should be rendered;

- 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 surgicalsutures.

- 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 toCO2 production.

Poultry:

- Flow-away systems have resulted in quick and efficient processing in modern plants. However, the costsof flowaway systems and of wastewater treatment may be such that the development and use ofautomated dry viscera handling methods are encouraged.

- Stunning before killing reduces the overall loss of blood. Without prior stunning, blood will be splashedover a wide area and may also contaminate feathers.

- Dry cleaning before washing the receiving area;

- Use of chiller overflow water as make up water in scalding tanks;

- Recovered feathers may be disposed of as solid waste or pressure cooked to hydrolyse the otherwiselow nutritional value protein, keratin.

- Use of screened water from defeathering operations in feather flumes;

- 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 that minimizewater use;

- Potential re-use of screened chiller water overflown elsewhere in the plant.

RIVM (1994) reported also some possibilities for waste prevention: Table 13.

Process Waste-preventionSlaughterprocess:Air: - mainly energy savingWater: - 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, fat).Meatpacking:Air: - mainly energy savingWater: - 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 (fat).Intestine handling:Air: - energy-savingWater: - application of dry rendering

- keep paunch manure separated as much as possibleSolid Waste: - increases when waste water prevention increases (manure, fat).

Utility-processes*:Air: - improve efficiency chilling-machines and chilling practices (keep doors close, repair leakages)Water: - use as less (warm) water as possible during cleaning-up

*: e.g. waste water purification, chilling, cleaning-up

One of the conclusions of an investigation of waste prevention in ten slaughterhouses in the Netherlandsis 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 havereceived little attention compared to the attention for the efficiency of the slaughter process.

3. TANNERIES

3.1. Description of the tanning-process3.2. Emissions3.3. Prevention of waste production

3.1. Description of the tanning-process

Figure 3 presents a flow diagram of a the tanning-process. Hides are a by-product of slaughter activitiesand can be processed into a wide range of end products. For each end product, the tanning process isdifferent and the kind and amount of waste produced may vary enormously.

The chemicals traditionally used for tanning have been derived from plants, whereas the most commonprocess nowadays is a combination of chrome salts (chrome tanning) and readily usable vegetableextracts (vegetable tanning) (Buljan 1994). While chrome tanned shoe leather is the most widelyproduced leather, this kind of leather will receive most attention in the following.

In most cases raw hides produced at slaughterhouses are preserved by pickling and drying for transportto tanneries and further treatment. In the very few cases that hides are instantly tanned there is no needfor preservation. During the tanning process at least ±300 kg chemicals (lime, salt etc.) is added per tonof hides.

Pretanning (Beamhouse operations)

Soaking:

The preserved raw hides regain their normal water contents. Dirt, manure, blood, preservatives(sodiumchloride, bactericides) etc. are removed.

Fleshing and trimming:

Extraneous tissue is removed. Unhairing is done by chemical dissolution of the hair and epidermis with analkaline medium of sulphide and lime. When after skinning at the slaughterhouse, the hide appears tocontain excessive meat, fleshing usually precedes unhairing and liming.

Bating:

The unhaired, fleshed and alkaline hides are neutralised (deliming) with acid ammonium salts and treatedwith enzymes, similar to those found in the digestive system, to remove hair remnants and to degradeproteins. During this process hair roots and pigments are removed. The hides become somewhat softerby this enzyme treatment.

Pickling:

Pickling increases the acidity of the hide to a pH of 3, enabling chromium tannins to enter the hide. Saltsare added to prevent the hide from swelling. For preservation purposes, 0.03 - 2 weight percent offungicides and bactericides are applied.

Tanning

There are two possible processes:

1: Chrome tanning:After pickling, when the pH is low, chromium salts (Cr3+) are added. To fixate the chromium, the pH isslowly increased through addition of a base. The process of chromium tanning is based on the cross-linkage of chromium ions with free carboxyl groups in the collagen. It makes the hide resistant to bacteriaand high temperature. The chromium-tanned hide contains about 2-3 dry weight percent of Cr3+. Wetblue,i.e. the raw hide after the chrome-tanning process, has about 40 percent of dry matter.

2: Vegetable tanning:

Vegetable tanning is usually accomplished in a series of vats (first the rocker-section vats in which theliquor is agitated and second the lay-away vats without agitation) with increasing concentrations oftanning liquor. Vegetable tannins are polyphenolic compounds of two types: hydrolysable tannins (i.e.chestnut and myrobalan) which are derivatives of pyrogallols and condensed tannins (i.e. hemlock andwattle) which are derivatives from catechol. Vegetable tanning probably results from hydrogen bonding ofthe tanning phenolic groups to the peptide bonds of the protein chains. In some cases as much as 50%by weight of tannin is incorporated into the hide (Ockermann and Hansen, 1988).

Finishing

Wetblue:

Chromium tanned hides are often retanned - during which process the desirable properties of more thanone tanning agent are combined - and treated with dye and fat to obtain the proper filling, smoothnessand colour. Before actual drying is allowed to take place, the surplus water is removed to make the hidessuitable for splitting and shaving. Splitting and shaving is done to obtain the desired thickness of the hide.The most common way of drying is vacuum drying. Cooling water used in this process is usuallycirculated and is not contaminated.

Crust:

The crust that results after retanning and drying, is subjected to a number of finishing operations. Thepurpose of these operations is to make the hide softer and to mask small mistakes. The hide is treatedwith an organic solvent or water based dye and varnish. The finished end product has between 66 and 85weight percent of dry matter.

A more detailed description of the tanning process is found in the publication “Animal by-productprocessing” by Ockerman and Hansen, 1988.

3.2. Emissions


The discharge of solid waste and wastewater containing chromium is the main environmental problem.Chromium is a highly toxic compound and the dumping of chromium containing material is in mostcountries restricted to a few special dumping grounds. Reduction of chromium discharge is thereforeessential. Emissions into the air are primarily related to energy use, but also the use of organic solventsand dyes causes emissions into the air.

3.2.1. Solid waste

The production of fresh hides has been estimated at about 8-9 million tonnes per year (FAO, 1990a).During the processing of these hides a total of 1.4 million tonnes of solid waste is produced (El Boushyand Van der Poel, 1994). This means that in all likelihood ca 16% of the processed hides is leather waste.Buljan (1994) puts the figures for trimmings and splittings (i.e. leather waste) at a total of 225 kg/ton hide(i.e. ca 23%). This is almost the same amount of waste produced as meat from fleshing activities (7 -23%). For every ton of raw hide processed, the amounts of solid waste and by-products may be producedas given in Table 14 (Buljan, 1994). These figures show that the solid waste produced per ton of raw hideis about 450-600 kg. About half of this contains 3% chrome on a dry matter basis.

Pretanning Tanning FinishingTrimmings 120* 110 32Fleshings 70-230Wet blue split 115Buffing dust 2Total 190-350 225 34GRAND TOTAL Approx. 450-600*: hides not trimmed in the abattoir itself

Buljan (1994) states:

“Collection and safe disposal of solid waste, especially chrome containing solid waste and sludge isnormally monitored by environmental authorities and associated with costs. Conversion of solid waste intoby-products not only reduce pollution load, it can also be commercially beneficial. This represents greatpotential for producing increased returns to tannery processing through deriving value from wastes. In anyevent, reduction of waste is essential in order to meet demands for reduced pollution load from tanneries.”

3.2.2. Wastewater

As for the production of wastewater, over 80 per cent of the organic pollution load in BOD termsemanates from the beamhouse (pretanning); much of this comes from degraded hide/skin and hairmatter. The beamhouse is also the source of all non-limed and limed solid waste such as fleshing,trimming and waste split. As already mentioned, during the tanning process at least ca 300 kg ofchemicals (lime, salt etc.) are added per ton of hides. Excess of non-used salts will appear in thewastewater. Because of the changing pH, these compounds can precipitate and contribute to the amountof solid waste or suspended solids (Department of the Environment, 1978).

Every tanning process step, with exception of the crust finishing operations, produces wastewater. Anaverage of 35 m3 is produced per ton of raw hide. This wastewater contains:

- salts (Cl), fat, protein, preservatives (soaking);

- lime and ammonium salts, ammonia, protein (hair), and sulphides (fleshing, trimming, bating);

- chromium(salts) and polyphenolic compounds (tanning); and

- dye and solvent chemicals (wet-finishing).

Solid waste produced consists of fleshings containing lime, chromium containing ‘wet-blue’ shavings andof trimmings (leather).

Water will not only have a diluting effect, it also increases the number of kg of BOD per ton of hides.Rajamani (1987) gives a BOD range of 1000 - 3000 mg/l depending upon the volume of water used andon other impurities. TNO gives BOD and COD values both for precipitated and mixed wastewater. BOD-and COD-values for precipitated wastewater show a reduction of BOD and COD of ca 50% (Pelckmans,undated). This implies that it is worth precipitating dissolved organic compounds and treating this as solidwaste. It is known that treatment of solid waste can in general be undertaken without too many efforts andthat the costs and energy required are lower than those for the treatment of wastewater.

Tanneries that perform the complete tanning procedure, produce mixed wastewater. The composition ofthis wastewater is not solely the result of separate waste streams that merge together. The different pH’sand the different compounds influence each others’ solubility. In composite wastewater, compoundsprecipitate while they stay dissolved in the wastewater from the separate processes (Pelckmans,undated). Most reports give reliable values for composite wastewater. Some reports only give data for theseparate wastewater streams. These values should be used with great care and should not be merelyadded in order to arrive at a compound value.

In Table 15 high and low values for BOD, COD, SS and Cr3+ are given. This variation might be caused bya high amount (45 m3 per ton of hide) or low amount (25 m3per ton of hide) of water used during thetanning process. Mulder and Buijssen (1994) give values of 50 m3 per ton of hide for traditionalmanufacturing processes of Wet-blue and 20 m3 per ton of hide when water saving actions are applied.

(1) (2) (3)BOD 110 40-100 80COD 265 120-280SS 216 70-200Cr 8.8 5

Values are estimated from data from:

(1): Rajamani (1987); values from Kanpur, Pakistan.(2): Clonfero (1990); refering to a UNIDO-study (1975).(3): Taiganides (1987); an average and quit general value.

In Table 16, RIVM (1992) presents the quantity and composition of wastewater for every step of thetanning process in a Dutch situation. Per ton of hide a total of 35 m3wastewater is produced. The Dutchfigures of the COD produced during the pretanning process are higher than the figures mentioned inTable 15. RIVM noted that measured chromium-concentrations were 3-7 times higher than the estimatedfigures. Moreover, in the Netherlands about 50% of the hides processed in tanneries have already beenpretanned or tanned.

Process step Amount of water pH COD NKj Cr(m3/ton) - kg COD/m3 kg N/m3 kg Cr/m3

Pretanning:Soaking 4-6 6-9 30-40 1-1.5 -Unhairing, liming 5-9 12-13 40-60 3-5 -Fleshing 1-3 - - - -Deliming, bating 5-7 8.5-9 5-8 3.5-4 -

Tanning:Chrome tanning 0.5-1 3.8-4 2-3 0.3-0.6 0.5-5Pressing 0.4-0.6 3.6-4.5 1.2-1.8 0.11-0.22 0.5-5Neutralisation 1-1.5 4.5-4.7 2.5-3 0.5-0.8 0-1.0

Painting, fatting 3-4.5 3.8-4.5 5-6 0.2-0.3 0-5.0Finishing:Drying 3-6Finishing 1-2Cleaning 5

Clonfero (1990) gives in annex 1 the characteristics of the wastewater of each step of the tanning processfor an Italian tannery. This tannery had produced a huge amount of water (about 310 m3 wastewater perton of raw hides), and high amounts of SS and a COD of 2500 kg per ton of raw hides. No explanation isgiven for the differences between the figures of UNIDO (table 15) and the figures of the Italian tannery(annex 1).


Table 17 gives the emissions into the air during the tanning process. Few figures are available about theamount of air pollution.

An important part of the air pollution by leather tanneries is caused by the need for energy. RIVM (1992)estimated the need for the Dutch tanneries at: 439 kWh (electricity) per ton of raw hides and 108 m3 ofgas per ton of raw hides. Gas is used for heating. Table 17 gives the emissions into the air as a result ofgas-combustion. No figures are available about the emissions into the air as resulting from the use ofelectricity.

Process-step Air pollutants kg/ton raw hideUnhairing/liming H2SDeliming/Bating NH3

Finishing solvents, formaldehyde 25*heating with gas CO 0.033*

CO2 190*NO2 0.17*

*: Netherlands situation, based on figures of RIVM (1992)

H2S may be emitted into the air when the pH of the processwater is less then 7. During the finishing-process volatile organic compounds are used.


Considerations for the reduction of the amount of polluting value of the produced wastewater are:

- a reduction of the total water use by re-use of produced wastewater and by the development oftechnologies that minimize the quantity of water needed during the tanning process; and

- a reduction of the used chemicals such as lime, salt, sulphide etc and a reduction of chromium.

The following gives a more detailed discussion (from Higham, 1991).

Water conservation

A reduction of water use can lead to a reduction of the total waste load. Re-use of wastewater with aminimal harmful or even a moderately beneficial effect on earlier processes may be considered as anoption.

Curing hides and skins

A reduction of the use of salt for preservation can be considered as an option. Fifteen percent of salt onweight basis may preserve the hides for even 6 weeks, and 5 per cent of salt plus biocide lead to apreservation for two months. Chilling without salt can preserve hides for a few days. Another alternativepreservation method is radiation by electron beam or gamma rays. Where possible, biodegradablepreservatives (insecticides etc.) should be used instead of derivatives of chlorinated aromatichydrocarbons. The latter persist in the waste and are highly toxic to the environment.

Beamhouse processes

Hair saving methods are recommended to prevent degraded keratin from entering the waste streams.Unhairing/liming fluids can be recycled after recharging. It is also recommended that the unhairing andliming stages should be seperated. Both liquids can be recharged and hair can be screened out. Theintermediate wash can be re-used as a soak liquid.

Tanning

Low chrome systems, possibly requiring an aluminium salt for pretannage will produce a wet-whiteleather. Splitting and shaving wastes will contain less chromium. Alternative mineral salts such asaluminium, zirconium, titanium and iron are might be used as substitutes for chromium salts. However,under certain conditions aluminium is known to be more poisonous to aquatic life than trivalent and evenhexavelant chromium. Re-use of chromium is a more realistic alternative (see par. 5.2.2). The unusedtanning fluids which contain chromium can be collected separately. From these fluids and from the solidsthat contain chromium, chromium can be recovered. The remainder may be used as source material forglue and animal feedstuff. In countries where discharge of chromium is strictly prohibited, great efforts aremade to recover and re-use chrome.

Alternative vegetable tanning methods can replace chrome tanning to a high degree. An example is the‘Liritan’ process, developed in South Africa. A high chemical uptake, low pollution load, uniformpenetration of the tan and a shortened process time with consequent financial efficiency are claimed to bethe main advantages of this process (Higham, 1991), but little is known on the practical implications.

Finishing

A reduction of volatile organic compounds (VOC) can be accomplished by using aqueous finishes forbase and middle finishing coatings.

4.1. Description of milk processing4.2. Emissions4.3. Prevention of waste production

4.1. Description of milk processing

Dairy plants are found all over the world, but because their sizes and the types of manufactured productsvary tremendously, it is hard to give general characteristics. The dairy industry can be divided into severalproduction sectors. Each division produces wastewater of a characteristic composition, depending on thekind of product that is produced (milk, cheese, butter, milkpowder, condensate). Figure 4 presents aschematic flow sheet of the main dairy products.

Milk receiving

Irrespective of the product, every factory has a section where milk is delivered and stored.

Liquid milk products

In developed countries (parts of Europe, North-America, Australia etc.), raw milk is decreamed andpasteurised or sterilised. After these steps, several products are made: consumer milk, chocolate milk,custard etc.

In developing countries/regions (Southern and Eastern Africa, the Middle East - Syria and India etc.)boiling but also fermenting may be used as a means to preserve milk in the absence of refrigerationfacilities. Usually, as a sanitizing method, the vessels for the storage of milk are smoked. Fermented milkmay be used in fermented form but often it is churned so as to produce butter and buttermilk.

Cheese/Whey/Curd

There are about 500 varieties of cheese produced throughout the world. These are classified in ninemajor cheese families. These varieties come about as a result of different types of production processes.The composition of the wastewater of each specific production process varies from variety to variety. Forthe purpose of discussing the environmental impact, the production of cheese will be related to theproduction of whey. For hard cheeses (Cheddar cheese, Dutch cheese, etc.), the quantity of wheyproduced is high and equals more or less the amount of milk used. During the production of other types ofcheeses, such as soft types, the whey production is much lower or there is no production of whey at all.

Butter/Ghee

In developed countries, butter is made from cream that has been churned (separation of sweet butter andsweet buttermilk). In developing regions the technology in use for the making of butter and ghee is closely

related to the technology to make fermented milk. Traditional butter is made from fully soured whole milkthat is churned.

Milk powder

Milkpowder is made from raw milk, skimmilk or sweet buttermilk. After pasteurization, decreaming etc. thewater from the milk is removed through evaporation.

Condensate/Cream/Khoa

For condensed milk and cream, a portion of the water is removed by evaporation. Khoa is a producttypically found in India and neighbouring countries. It is produced by thermal evaporation of milk to 65-70% solid state and serves as base material for a variety of Indian sweets.

4.2. Emissions


4.2.1. Solid waste

Hardly any solid waste is produced by the dairy industry. The main solid waste produced by the dairyindustry is the sludge resulting from wastewater purification. There are figures available about the amountof sludge production: in aerobic systems the sludge production is about 0.5 kg per kg of removed CODand in anaerobic systems about 0.1 kg per kg of removed COD.

4.2.2. Wastewater

Wastewater from dairy industry may originate from the following sources:

Milk receiving

Wastewater results from tank, truck and storage tank washing, pipe line washing and sanitizing. Itcontains milk solids, detergents, sanitizers and milk wastes.

Whole milk products

Wastewater is mainly produced during cleaning operations. Especially when different types of product areproduced in a specific production unit, clean-up operations between product changes are necessary. Indeveloping countries, the main problem is pollution through spoilage of milk.

Cheese/Whey/Curd

Waste results mainly from the production of whey, wash water, curd particles etc. Cottage cheese curd forexample is more fragile than rennet curd which is used for other types of cheese. Thus the whey andwash water from cottage cheese may contain appreciably more fine curd particles than that from othercheeses. The amount of fine particles in the wash water increases if mechanical washing processes areused.

Butter/Ghee

Butter washing steps produce wash water containing buttermilk.

Skim milk and buttermilk can be used to produce skimmilk powder in the factory itself or itself or thesematerials may be shipped to another dairy food plant by tank truck.

The continuous butter production process materially reduces the potential waste load by eliminating thebuttermilk production and the washing steps (Harper et. al., 1971).

Milk powder

Environmental problems are caused by high energy consumption (= emission of CO2, CO etc.), bycleaning and by emission of fine dust during the drying process.

Condensed milk/Cream/Khoa

Environmental problems related to the production of condensate and khoa are mainly caused by the highenergy consumption during the evaporation process.

The main suspended solids mentioned in the literature are coagulated milk and fine particles of cheesecurd.

Table 18 gives an overview of the waste production data for the dairy industry.

Reference (1) (2)Average Range Average Range

Waste water prod. 2400 100 - 12400 2400 100 - 7100BOD 6 0.2 - 71.2 5.5 0.2 - 7.1SS (2.0) (0.06 - 10.8)Nitrogen (0.15) (0.002 - 0.43)Phosphorus (0.012) (0.007 - 0.16)(1): Taiganides (1987), refering to EPA (1971).

(2): Barnes et al (1984), refering to EPA (1971) and Kearney (1973). Values between brackets arerecalculated, assuming 2400 kg waste water/ton milk processed, thereby overestimating the range tosome extent.

Table 18 confirms that it is hard to give general characteristics of dairy plants. This is, as mentionedbefore, caused by the variation in the sizes of the plants and variation in types of product manufactured.The effect of the type of product produced is illustrated in Table 19.

Type of product Wastewater volume BODAverage Range Average Range

(1)Milk 3250 100 - 5400 4.2 0.20 - 7.8Condensed milk 2100 1000 - 3000 7.6 0.20 - 13.3Butter 800 0.85Milkpowder 3700 1500 - 5900 2.2 0.02 - 4.6Cottage cheese 6000 800 - 12400 34.0 1.30 - 71.2

(2)Milk (canned) 320 - 1870 0.02 - 1.13Condensed milk 800 - 7290 0.17 - 1.48Butter 800 - 6550 0.19 - 1.91Natural cheese 200 - 5850 0.30 - 4.04Cottage cheese 830 - 12540 1.30 - 42

(3)Milk 0.2 - 4.0Cheese 0.9Butter/milkpowder 0.3

Total 4000(1): Taiganides (1987), refering to EPA (1971).(2): Middlebrooks (1979), refering to EPA (1974).(3): RIVM (1993): Dutch situation in 1990.

The ranges in Table 19 also indicate that the production of wastewater is highly influenced bymanagement practices (see next paragraph). It is not possible to identify particular waste producingpractices. The way in which the water consuming and operation processes are carried out is indicative ofthe management quality. The major contribution to he waste load comes from cleaning operations, whichtake place throughout the production process. Only in the production process of (hard) cheese, is wheysewering one of the main contributors to the waste load.

Waste generating processes of major significance include:

- Washing, cleaning and sanitizing of pipelines (metals), pumps, processing equipment, tanks, tank,trucks and filling machines (high N load);

- Start-up, product change over and shut down of HTST and UHT pasteurizers;

- Breaking down of equipment and breaking of packages resulting in spilling during filling operations;

- Lubrication of casers, stackers and conveyors


In dairy plants air pollution is mainly caused because of the need for energy. In the process gasses maybe discharged such as CO2, CO, NOx and SO2.

Table 20 gives the emissions into the air as a result of gas- and oil-combustion. No figures are availableabout the emissions into the air resulting from the use of electricity.

Emissions of CFC’s and NH3 into the air may come about as a result of leakage and stripping of chillingmachines when out of use.

Process: Air emission (kg/ton processed milk)Heating by burning gas or oil CO: 0.03

CO2: 92Nox: 0.1SO2: 0.05

Producing milkpowder Fine dust: 0.39Cleaning VOC: 0.05


The waste load, expressed as BOD depends to a large degree on the style of management. Table 21gives an example of the relationship between management practices and waste production in terms ofBOD and the amount of wastewater produced. The table shows that a large quantity of processed milkdoes not necessarily lead to higher waste loads or to higher levels of wastewater production.

Management practices cover a wide range of water consumption and process operation activities. Wellcontrolled processes reflect good management qualifications, while bad practices are a reflection of poormanagement. Table 21 shows the relationships. The qualification “fair” signifies that good as well as badpractises occur. With good management practices, values of BOD 1 kg/ton and produced wastewaterbelow 1 kg/kg may be reached. Poor management will result in values greater than 3 kg/ton resp. 3 kg/kg.

For the evaluation of management practices, the following indicators are useful:

1. Housekeeping practices;

2. Water control practices; frequency with which hoses and other sources of water are left running whennot in actual use;

3. Degree of supervision of operations contributing to either the volume of wastewater or to BODcoefficients;

4. Extent of spillage, pipe-line leaks, valve leaks and pump seals;

5. Extent of carton breakage and product damage in casing, stacking and cooler operations;

6. Practices followed during the handling of whey;

7. Practices followed in handling spilled curd particles during cottage cheese transfer and/or fillingoperations

8. The following of practices that reduce the amount of wash water from cottage cheese or butteroperations;

9. Extent to which the plant uses procedures to segregate and recover milk solids in the form of rinsesand/or products from pasteurization start-up and product change-over;

10. The procedures used to handle returned products;

11. Management attitude towards waste control.

Product Milk processed BOD Wastewater Management level(kg/day) (kg/ton) (kg/kg)

Milk 181,600 0.3 0.4 excellent: 19, 25, 26227,000 0.2 0.1 excellent: 19, 21, 26, 27113,500 0.7 1.0 good: 8, 10, 18, 2068,100 7.8 5.2 poor: 1

Cottage cheese 272,400 2.0 0.8 good: 8, 15, 16135,200 1.3 4.7 good: 8, 17295100 71 12.4 poor: 2

Milk, cottage cheese 454,000 4.1 1.2 good: 2, 19211,110 1.8 1.1 good: 21, 22408,600 3.3 1.1 fair: 8, 9454,000 8.6 2.0 poor: 8, 3, 4

Milk, butter 135,200 0.9 0.8 good: 23, 24, 28Whey powder 227,000 0.2 5.9 good-fair: 11, 12, 13Milk powder, butter 90,800 3.0 2.5 fair: 14, 7, 3Description of management levelPoor = 1. no steps taken to reduce waste, 2. whey included, 3. many drips, leaks, 4. returns included, 5.sloppy operations, 6. spillage leaks, 7. hoses running,

Fair = 8. whey excluded, 9. good water volume control, 10. wash water excluded, 11. no entertainmentlosses, 12. all powder handled as solid waste, 13. no leaks/drips, 14. continuous churn,

Good = 15. fines screened out, 16. wash water to drain, 17. spilled curd handled as solid waste, 18.rinses segregated, 19. rinses saved, 20. returns to feed use, 21. returns excluded, 22. good water control,23. buttermilk excluded, 24. few leaks,

Excellent = 25. hoses off, 26. filler drip pans, 27. cooling tower, 28. dry floor conditions

Source: EPA, 1971

In the following a summary is given of suggestions for the prevention of dairy waste. At the same timethey are indicative of what is to be understood when speaking about good management of waste control(EPA, 1971):

1. Instruction of plant personnel concerning the proper operation and handling of dairy processingequipment. Major losses are due to poorly maintained equipment and to negligence by inadequatelytrained and insufficiently supervised personnel.

2. The carrying out of a study of the plant and the development of a material balance to determine wherelosses occur. Modification and replacement of ill-functioning equipment. Where improper maintenance isthe cause of losses, a specific maintenance programme should be set up.

3. The use of adequate equipment for receiving, cooling, storing and processing of milk, so as to takecare of the maximum volume of flush production and of special products. All piping, around storage tanksand other areas, should be checked on mis-assembly and damage that may lead to leakage.

4. Accurate temperature control on plate, tubular and surface coolers to prevent freeze-on, which mayresult in loss of products.

5. Elimination of valves on the outlet sides of internal tubular or plate heaters and coolers andmaintenance of plates and gaskets in good repair so as to eliminate waste due to blown or brokengaskets

6. Installation of suitable liquid level controls with automatic pump stops, alarms, and other devices at allpoints where overflows could occur (storage tanks, processing tanks, filler bowls etc).

7. Keeping in good order of vats, tanks and pipelines so as to eliminate and reduce to a minimum thenumber of leaky joints, gaskets, packing glands and rotary seals.

8. Proper design and installation of vats and tanks at a level high enough above the floor for easydrainage and rinsing if hand cleaned. Tanks should be pitched to insure draining.

9. Correct connections on plate type heat exchangers so as to avoid milk being pumped into the waterside of the exchanger or water being pumped into the milk side.

10. Provision and use of proper drip shields on surface coolers and fillers so as to avoid that productsreach the floor. Avoidance of cheese vats, vat processors or cooling tanks being overfilled so that nospillage occurs during product agitation. The liquid level in cheese vats should be at least three inchesbelow the top-edge of the vat.

11. Avoidance of foaming of fluid dairy products, since foam readily runs over processing vats and othersupply bowls and contains large amounts of solids and BOD. The use of air tight separators, proper sealson pumps and proper line connections to prevent inflow of air when lines are under partial vacuum, willavoid foam production.

12. Turning off of water hoses when not in use. Use should be made of hoses equipped with automaticshut-off valves so as to avoid excessive water usage.

5. HANDLING OF BY-PRODUCTS AND TREATMENT OF WASTE

5.1. Introduction5.2. By-products and solid waste5.3. Treatment of wastewater5.4. Treatment of polluted air

5.1. Introduction

As mentioned before in par. 1.2, generally three different types of waste are distinguished:

(1): solid waste, which may cause problems with respect to dumping grounds;(2): wastewater, which may decrease the quality of surface waters; and(3): volatile compounds, which cause air pollution.

Several ways may be followed to reduce the occurrence of waste:

(1): waste prevention;(2): development of clean processing methods; and(3): end of pipe treatment.

The most important one: the prevention of waste production, has been discussed in the previous chaptersof this study. Through a careful examination of the production processes, one may identify the source(s)of pollution. The development of new and clean processing methods is the next step. In the present reportthis approach will not receive attention, because of the specific technical and economic know-howinvolved.

The third step is the treatment of the produced waste before it will be discharged into the environment.This is generally referred to as ‘end-of-pipe’ treatment which will be discussed below. Because thistreatment is usually very expensive, the amount of waste to be treated “at the end-of-pipe” should be assmall as possible.

Practically all by-products may be used in one way or another. The amounts of solid waste that need tobe dumped can be kept small. With the exception of cooling water which in most cases is not polluted,wastewater can usually not be re-used. There are several methods of treating wastewater that can beapplied before it is discharged into the sewer system or surface water. Polluted air can be filtered beforedischarge.

The KTPCP-project (Kasur Tannery Pollution Control Project) may serve as an example of why it is worthpaying attention to environmental problems, which in this case had been caused mainly by the 160tanneries of Kasur, Pakistan (Wegelin et al, 1993). Owing to insufficient attention to waste disposal fromthese tanneries, artificial and stagnant lakes had received environmental pollutants. This in turn led tomajor health problems, decreased crop yields (up to 50%) and to contaminated groundwater and fish.

5.2. By-products and solid waste

5.2.1. Slaughterhouses5.2.2. Tanneries5.2.3. Dairy Industry

5.2.1. Slaughterhouses

At slaughterhouses usually, everything produced by or from the animal, except dressed meat, isconsidered as by-product. These by-products are either ‘edible’ or ‘inedible’. The variety of by-products isenormous, as can be seen in the diagram in figure 5 which shows a few of the by-products of the meatindustry. Ockerman and Hansen (1988) offer an extensive introduction to the use of by-products. There isa large number of publications on the use of animal by-products (National Renderers Association, 1990;Scaria, 1988; Kreis, 1978; Davis, 1985; Skrede, 1979; Mann, 1982; Pearson and Dutson, 1988; Pearsonand Dutson, 1992).

In many countries, all the waste that is unsuitable for human consumption is processed by renderingcompanies as animal feed, glue etc. In large slaughterhouses, screening devices through which wastewater has to flow prior to being treated, remove large solids such as hair, paunch manure, pieces ofviscera and meat, dirt, and other materials. Some of these solids have an economic value and arerendered so as to produce a salable product. Materials of little economic value may be dumped at alandfill, spread out on the land or treated together with the solids from biological treatment processes. It isclaimed by Ockerman and Hansen (1988) that in the animal processing industry about 1% of protein islost to the sewer and that it is of economic importance to recover as much of this protein as possible. Ifhalf of the protein were recovered this would be worth about $400 million (1987 dollars).

In developing countries, some or all of these products are dumped as solid waste without any furtherprocessing or composting, or they are washed away. This causes pollution in the form of bad smell andpotential water pollution, leading to health hazards. If solid waste is dumped, the possibility of using thiswaste is lost. Solid waste can also be handled by using the waste as fertilizer after composting. Duringthe process of composting considerable quantities of nitrogen are lost in the form of ammonia. Accordingto Kumar (undated), slaughterhouse wastes are ideally suited for fermentation. An important advantage ofhandling animal waste by fermentation is the low loss of nitrogen if the liquid is handled properly (seeTable 22). Kumar (undated) investigated a number of other important avenues (Kumar, undated). Of theproduced sludge, the dark solid portion which settles at the bottom (about 10%), was found to be rich inprotein, fat fibre and also vitamin B12. It was free from parasites and probably free of salmonella as well.Such part of the slurry can be utilized as feed material or manure.

The remaining part of the sludge, the liquid component, can be used as irrigation water, or for fish andalgae cultures. If not used in time a major part of the nitrogen from the liquid will be lost as a result ofvolatilization.

Destination solid waste Utilization of nitrogena: Dumped 100% lost of nitrogen

b: Composting -> fertilizer Large quantity of nitrogen lostc: Anaerobic treatment:1: solid part -> animal feed Small nitrogen losses2: liquid part: Small nitrogen losses possible if diluted quickly with watera: irrigation waterb: fish culturec: algae culture

Sludge:

In western countries the larger part of solid waste out of the slaughterhouses consists of sludge from thewastewater treatment plants. In the Netherlands sludge, including the sludge of the slaughterhouses andmeat processing industries, may probable no longer be used as fertilizer in the future because of Dutchenvironmental rules, which however are still heavily debated. One argument is that this kind of sludge isbeing discriminated as a fertilizer only because in the Netherlands a surplus of organic fertilizers exists.

The environmental rules may lead to (financial) problems because the sludge has to be considered aswaste to be disposed of which has the consequence that after obligatory dewatering, it must be brought toa dumping-ground.

In principle there are no objections against using the sludge from slaughterhouses as fertilizer, provided itdoes not contain toxic compounds.

5.2.2. Tanneries

Waste, produced as meat from fleshing activities (7 - 23%), can be used as animal feed if fleshing willhave been done before liming. Fleshings that contain lime components are only suitable for glueproduction. A bigger environmental problem is caused by wet-blue shavings and trimmings that contain3% chromium on a dry matter basis. This material is not allowed to be used at rendering plants. A smallamount is used for artificial leather but most of it is dumped at special dumping grounds. The waste inthese dumping grounds must be isolated to prevent toxic compounds leaving the dump e.g. bypercolation water.

An alternative for dumping might be the new process of extracting chrome from wet-blue waste (Koeneand Dieleman, 1987). The recovered chromium is recycled in the tanning process and the dechromedprotein material can be used as a source material for glue or as an animal feedstuff (El Boushy et al.,1991). Sludge from wastewater treatment plants of tanneries is too toxic to be usable, owing to toxiccompounds like chromium. This kind of sludge has to be dumped at special dumping grounds.

5.2.3. Dairy Industry

Except for packing material etc. and sludge (in case of wastewater purification), dairies do not producesolid waste. The potential use as fertilizer of stabilized sludge from wastewater treatment plants of dairieshas no environmental limitations, provided the sludge contains no toxic compounds.

5.3. Treatment of wastewater

Main wastewater problems

The problems of the wastewater from the slaughterhouses, tanneries and dairies result from thedischarge of:

a: large amounts of BOD (slaughterhouses, tanneries and dairies).BOD-problems can be handled, as already mentioned, by biological wastewater treatment.

b: high values of NKj (slaughterhouses).

NKj can be lowered by oxidation of organic compounds (proteins) followed by nitrification: conversion ofammonium (NH4

+) into nitrate (NO3-). To reduce the eutrophication potential of the wastewater, nitrate

must be removed. This can be achieved by denitrification: conversion of nitrate (NO3-) into nitrogen (N2).

c: chromium (tanneries).

Chromium can be handled by precipitation reactions, these are simple processes.

There are basically two types of biological wastewater treatment systems: aerobic and anaerobicsystems. In Tables 21 and 22 the characteristics and the (dis)advantages of these systems arementioned.

Aerobic AnaerobicApplicability low strength: low, medium and high strength:(BOD, mg/l) (100 - 2000 mg/l) (250 - > 100.000 mg/l)BOD-removal: 93-99% 90%NH3-conversion: 95% lowNO3-removal: 90%* high*: depends on BOD-load.

In view of the high BOD-load in the wastewater of tanneries, dairies and slaughterhouses, anaerobicsystems seem to be appropriate wastewater purification systems. Simple anaerobic systems may achieve50% of BOD-purification (table 21), while high-rate anaerobic systems may result in 90% of BOD-purification (table 22). Anaerobic systems do not remove such nutrients as ammonium-nitrogen. If liquidand slurry are used as fertilizer this does not need to pose specific problems. Nutrient removal systemsshould be applied only if water authorities set limits for the discharge of nutrients. As in most countriesthis is not the case, there are no reasons for industry to make high investment costs for tertiary treatment.

Advantage DisadvantageAnaerobic * possible production of energy

* low need for land* power failure or shutdown will not affect thesystem* no energy consumption* low production of excess sludge

* optimal process temperature is about 30°C* post-treatment for BOD-removal is often required

Aerobic * low process temperature* end treatment of waste-water

* energy need for aeration* high need for land* power failure or shutdown will affect the entire system* post-treatment for further nutrient removal is oftenrequired* high production of excess sludge

Source: Hulshoff Pol, 1993.

General:

The process that may be used for the treatment of wastewater produced by the industries mentioned inthis report do not differ very much from each other. In general, these systems are applied to a large extentin developed countries. In developing countries adoption rates are much lower. Especially for these lattercountries, treatment methodologies and technologies should be cheap, efficient and easy to operate.Important differences of wastewater treatment in the different industries will be mentioned.

For large dairies in many developing countries, treatment of wastewater is not even considered as anoption. Because in developing countries the amount of milk processed industrially is minor, wastewaterproblems will mainly occur at the plant site and the surrounding surface waters. This implies that dairywastewater problems in these countries are very local in contrast to those in developed countries. Thedairy wastewater problem is larger in developed countries because all milk is processed industrially. Fordairies in these countries it is very important that proper wastewater treatment system are installed.

As mentioned before, the primary action to reduce pollution by wastewater discharge, is efficient watermanagement. According to EPA (1974) this can reduce the load of wastewater ca 5 fold. After a thoroughsearch for ways to reduce water use and wastewater production, the inevitable produced wastewater canbe treated in different ways as discussed below.

Usually wastewater produced during the day has a variable composition. For the optimal performance ofmost treatment system it is necessary that the load is rather constant and that the plant is fed with arather constant wastewater flow. Wastewater is therefore collected in equalization or balance tanks.

Most treatment plants follow the following steps.

Preliminary treatment. This type of treatment includes screening, skimming and settling which can lead tothe recovery of by-products, grease and fat and removal of coarse solids. For an optimal performanceand to avoid overload of the screening devices, it is important that large amounts of produced solids suchas (hog)hair, feathers etc. are collected during the processing itself as discussed in part 2. For developingcountries, the salt laden tannery effluent from the soaking process can be collected in solar evaporationspans, possibly pretreated with coagulant, after which salt can be recovered. In case of chrome tanningeffluents, the wastewater that contains chromium should not be allowed to become mixed with other typesof wastewater: it must be collected separately. Depending on the quality of the composite effluents,neutralising chemicals like lime alum, ferric chloride etc. should be added for an effective precipitation ofchromium and removal of suspended solids in the sedimentation process. From this material chrome canbe recovered, or dumped separately.

Primary treatment. This involves separation of solids in a settling tank (primary clarifier), or by flotation.The settleable solids and up to 60% of the suspended solids corresponding to approximately 35% of theBOD, can be eliminated during the primary treatment. Subsequently the solids may be treated byanaerobic sludge digestion. This produces biogas and solids that are suitable for soil conditioning andfertilization. Primary treatment is a essential activity that needs to be undertaken for a proper applicationof various secondary treatment systems. In case of aerobic secondary treatment, a further function of thisstep is the reduction of electric energy required for aeration.

Secondary treatment. This usually consists of biological treatments by means of high rate anaerobictreatment systems, anaerobic (lagoons) suitable for high organic loads, or aerobic (lagoons) suitable forlow organic loads, activated sludge, oxidation ditch or a combination. Present research is mainly focusedon low energy demand and low volume treatment systems and optimum process control. Usually, acombination of high rate anaerobic treatment and aerobic activated sludge is required to meet effluentquality demands. Removal efficiencies reached with these kinds of combination are up to 98-99%.Depending on the operational conditions, removal efficiencies for slaughterhouses range from 70 to morethan 99% for BOD and grease and from 80 to more than 97% for Suspended Solids (SS). The processperformance depends strongly on the amounts of SS that can be removed in the primary treatmentphase.

Tertiary treatment. This includes chemical-physical methods such as adsorption, stripping, coagulation,sedimentation, chlorination as well as biological methods like slow sand filtration and maturation ponds.This post-treatment serve to remove nutrients such as phosphorus, sulphide, suspended solids,remaining BOD as well as pathogens.

Another method of wastewater treatment is that of irrigation on land. Before wastewater is applied onland, toxic compounds such as chromium, salt sulphide, etc. have to be removed. Small amounts ofnitrate and phosphate however may serve as fertilizers. The BOD5 value is usually not allowed to behigher than 300 mg/l.

At present, this kind of wastewater treatment is carried out mainly in developing countries. The method ischeap, rather easy to perform, does not require highly sophisticated techniques and can be aplliedbecause of the usually low pollutional strength of the produced wastewater.

Economic considerations

The costs of wastewater treatment are a factor of major importance for the selection the appropriatetreatment system. Estimates should be made of the investment costs and the expected annual costs. Theinvestment costs are largely determined by construction costs, the costs of land and the required degreeof removal of pollutants. The annual costs will depend on the price of the energy and chemicals requiredfor the operation of the plant, the discharge fees and the capital costs on investment. A problem for theestimation of the costs of treatment plants is that prices are rapidly changing. Cost estimates shouldtherefore be referenced to an index.

From a comparison of the costs of 6 treatment systems (stabilisation ponds; aerated ponds; high rateanaerobic treatment + ponds; high rate anaerobic treatment + trickling filters; activated sludge process;and oxidation ditch; DHV, 1993) it can be concluded that high rate anaerobic treatment + post treatmentof the effluent offers a very economic and effective solution.

The relatively high initial costs are compensated for by the low costs of energy and maintenance, whichresults in low running costs and a limited need for land. Costs of a stabilisation pond, high-rate anaerobictreatment plant + post-treatment in a pond and an activated sludge process for the sewage treatmentplant for a town of 50,000 inhabitants (producing ca 550 ton BOD and ca 135 ton N) given as a reference,are: resp. around 3,5.106, 2.106 and 2.106 USD for investment costs and running cost resp. around400,000, 300,000 and 430,000 USD on an annual basis. In this calculation it is assumed that electricitycosts are 0.10 USD per kWh, sludge disposal costs 10 USD per 1000 kg and that the price of land is 25USD per m2. Lagoons will become more economical if land costs are below 10 to 20 USD/m2. Wastewaterfrom slaughterhouses, tanneries, and the dairy industry are more heavily loaded with pollutants thansewage. This will have the effect that anaerobic processes are more competitive than aerobic processesowing to the much lower energy costs of anaerobic treatment.

Taiganides (1987) gives an overview of relative cost indices and ranking for various treatment systems.According to him, the selection of the treatment system has to be undertaken on the basis of economiccosts, environmental considerations, and the technical complexity of the system. Both the initialinvestment and the operating costs of the system must be taken into consideration. However,environmental and technical aspects cannot be quantified. Therefore subjective rankings must be used.Table 24 indicates that aerobic ponds is the least desirable method of concentrated wastewater treatmentin places were productive land is to be used for construction of the ponds. Anaerobic lagoons are theleast expensive and are used more often than any other treatment in the management of wastewater fromfeedlots. However, they are not recommended as a permanent solution.

Treatment Initial Operating Land Energy Ecology IndexType cost indexb cost indexb area indexb rankingc rankingc rankd

1: Anaerobic lagoonsa 1 1 20 1 6 12: Aerobic ponds 6 4 300 2 5 203: Aerated lagoonsa 6 13 3 4 4 24: Oxidation ditches 8 16 9 3 35: Physical/biological 25 40 10 5 2 66: Physical/biological/chemical 50 70 2 6 1 10a Exclusive of land acquisition costs. It is assumed that land used in the construction of the treatment plantis owned by the feedlot.

b Index is the ratio of the treatment cost to that of the least cost treatment. Thus, the least cost treatmentwould have an index of 1. An index of 6 means 6 times more expensive than the least cost treatment inthat category.

c Ranking is a judgement ranking of the six potential systems ranked in order of preference from 1 to 6.The ranking is not on the basis of cost, nor does a ranking of 6 means it is 6 times less diserable than thatranked 1 in the same category.

d Index/rank is a combination of cost rations and judgement rankings reflecting the author’s preferencebased on technical, economic, and ecological feasibility of the system.

5.4. Treatment of polluted air

Prevention of waste production, as a method mentioned for solid waste and wastewater, is an even moreimportant method for polluted air. Compared to solid waste and wastewater, awareness of air pollutionhas only recently developed. As a result data of produced polluted air are hardly available and methodsfor prevention or treatment have as yet not been developed on a wide scale. Research of methods fortreatment of polluted air is in progress.

Available reports state that air pollution from red meat processing operations is minor, and that mostproblems usually involve odours from improper waste treatment. These had better be controlled bycorrection of deficiencies in the troublesome process than by attempts to treat the odorous air. Also forpoultry plants is true that a good design and good operating practices may help prevent odours.

In the dairy industry much energy is required for all kinds of activities and in particular for cooling andheating (pasteurizing, sterilizing, vaporisation). Energy production may lead to excessive discharge ofCO2, NOx and CO. Reduction of energy consumption leads to an decrease of the discharge of thesegases.

Air pollution from tanneries and slaughterhouses may also be caused by such components as NH3, SO2,Volatile Organic Compounds (VOC), etc. These can in principle be removed by means of adsorption,absorption, chemical reactions, microbial conversion. These processes often require highly sophisticatedtechnics and entail high costs.

Adsorption is a process in which gasses are adsorbed to solid material such as carbon. In the case ofabsorption a liquid is used. Usually these physical processes are combined with a chemical conversionprocess to fixate the polluting compound. Other chemical reactions involve oxidation at high or lowtemperatures, reduction with hydrogen or methane. Biodegradable compounds can be converted bymicro-organisms, suspended in water or fixated on solid material such as compost.

6. CONCLUSIONS AND RECOMMENDATIONS

6.1. Waste production and its consequences6.2. Data availability and reliability6.3. 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 producewastewater, frequently in large quantities. This wastewater is polluted with biodegradable organiccompounds, suspended solids, nutrients and toxic compounds (particularly chromium and tannins fromtanneries). Via the reduction of dissolved oxygen this pollution directly or indirectly leads to a decreasingsuitability 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 occurowing to differences of scale and in house-keeping and management practices of factories or plants. Thequantity of water used for the various processes is a major determining factor, high levels of waterusebeing related to high emission values.

expressed per: BOD (kg) SS (kg) NKj-N (kg) P (kg)Red meat slaughterhouses ton LWK 5 5.6 0.68 0.05Red meat packinghouses ton LWK 11 9.6 0.84 0.33Poultry slaughterhouses ton LWK 6.8 3.5 n.a. n.a.Tanneries ton raw hide 100 200 n.a. n.a.

Dairies (consumption milk) ton milk 4.2 0.5 <0.1 0.02

If the density of animal product processing is so low that the concentration of pollutants in the receivingwater bodies remains low, the production of wastewater does not necessarily lead to environmentalproblems. However, when from the comparison of the values of Table 26 with the European target valuesfor urban wastewater discharge (e.g. 25 mg BOD, 10-15 mg N and 1-2 mg P per litre), it becomes clearthat, from a wastewater production point of view, that there is a trend towards increasing densities ofproduct 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 likelihoodcontinue to cause, serious environmental problems. It is common practice that most of the chromium isreleased in wastewater. There are no indications of other heavy metals in the waste of the animalprocessing industry causing environmental problems.

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

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

For a proper discussion of the environmental impact of slaughtering, tanning, and dairy industry, theeffects 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 concerningthe advantages and disadvantages of the various production processes and the scale at whichprocessing is undertaken.

6.2. Data availability and reliability

In Table 26 typical values of wastewater production for several processes are given. They are given formost common parameters to characterize wastewater production. The data originate mainly, though notexclusively, from OECD-countries. Data from developing countries on waste production and itsenvironmental impact are difficult to find. Those data that have been reported canoften not be interpreted adequately owing to major shortcomings in the description of the relevantprocesses or the data collection methods. In some cases waste parameters have been recorded withoutindications 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 ofthe manure, probably the scrapings, but with no reference to other solid waste production (e.g. rumencontent).

Most of the reported values originate from EPA-studies published in the period 1970-1975. Even studiespublished at the end of the eighties refer mainly to these studies. Moreover, huge variations in wasteproduction per unit of product processed have been found. This variation can be partly explained bylooking at the types of products made or processes used, but some variation remains unexplained. Buteven worse, also in OECD-countries exceptions have been recorded which exceed emission values bymanifold, 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 morereliable environmental impact assessment of animal product processing than is presently the case. Thesemonitoring programmes should result in emission factors per unit of product processed. Because of thediversity in processes and waste production, proper data collection on waste processing will be anexpensive and time consuming undertaking.

The obtained reference values on waste production will always need to be translated to locally relevantprocessing methods and production situations. Thus, monitoring programs must be arranged so as tomake 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 andtype of product processed;

In addition steps must be made that measurements are taken prior to wastewater treatment and beforethe water is diluted with other (waste-)water. If a wastewater treatment plant is available, the reactorperformance should be determined for the evaluation of the effectiveness of the water treatment. In suchcases 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 attentionhas been given to the development of clean processing methods as these entail specific fundamentaltechnical and economical knowledge.

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

Furthermore, environmental problems may also be reduced by converting as much waste as possible intoa solid product instead of washing the waste away into the wastewater. In general solid waste is fairlyeasy 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 ofchromium is an easy process. Solid waste containing chromium should be dumped in special dumpinggrounds where facilities should be available to minimize the amount of percolation water. Precipitationalso results in large reductions of SS and BOD emissions.

In slaughterhouses, blood and paunch contribute enormously to the wastewater load. These and othersolid by-products should be prevented being washed away. By-products can be used for severalpurposes and unusable solid waste can be easily handled properly, e.g. via composting. This process andmore 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 systemswould seem to be the most suitable wastewater purification systems. Simple anaerobic systems reach50% 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 qualitystandards for discharged water. To meet these standards, a combination of anaerobic and aerobic isrequired, often coupled to nutrient removal systems.

As most of the air pollution is related to fossil energy consumption, prevention as a method to reduceenvironmental 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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Annex 1: Effluents of an Italian tannery

(Source: Clonfero, 1990; values refer to 800 kg raw hides).

Pressing cycle Waterm3

Water(% total)

CODmg/l

CODkg

COD %on total

BOD 5mg/l

SSmg/l

SS Kg SS. %on total

Chromemg/l

S inmg/l

pH

Salt Washing 10.00 7.51 8,800 167.2 6.220 4.200 3.340 63.46 4.88 6.9First Washing 5.00 1.97 2,000 10.0 0.370 730 3.65 0.28 7.2Sec. Washing 5.00 1.97 1,850 9.2 0.340 970 4.85 0.37 7.1Soaking 19.00 7.51 17,240 327.5 12.200 7.500 5.420 102.98 7.93 138 12.6Liming 19.00 7.51 60,400 1147.6 42.750 24.500 42.900 815.10 62.70 3.200 12.6Washing 32.00 12.66 8,200 262.4 9.770 3.580 114.56 8.80 420 11.9Fleshing 2.00 0.97 2,000 4.0 0.140 8.4Tot. beamh. 101.00 39.92 19,089 1928.0 71.820 10.936 1104.60 85.00 761(av)First Washing 12.00 4.74 7,000 34.0 3.120 1.920 23.040 1.80 300 11.5Sec. Washing 50.00 19.78 1,250 62.5 2.320 770 38.500 2.96 8 10.5Deliming &Bating

10.00 3.95 19,700 197.0 7.330 14,300 3.790 37.900 2.90 7.0

Washing 34.40 13.61 6,900 237.3 8.840 1.070 36.800 2.83 7.2Pickling &Pretanning

10.00 3.95 5,350 53.5 1.990 1,450 1.590 15.900 1.22 1.380 2.6

Tanning 10.00 3.95 4,550 45.5 1.690 740 1.240 12.400 0.95 3.120 3.8Pressing 1.00 0.39 5,500 5.5 0.200 1.200 1.200 0.09 1.850 3.9Total tanning 127.40 50.37 5,379 685.3 25.830 1.300 165.740 12.90 367 (av) 31 (av)

(av) (av) Total: 46.85 kg 4 kgRetanning(chrome)

4.15 1.64 4,700 19.5 0.720 870 3.610 480 4.0

Neutralization 4.02 1.59 2,520 10.1 0.370 1.500 6.030 6.0Fatliquoring &Dyeing

5.75 2.27 6,220 35.8 1.330 2.700 15.520 3.4

Total grain sideprocess

13.92 5.50 4,697 65.4 2.430 1.800 25.160 1.90 143 (av)

(av) Total: 1.99 kg 1.99 kgRetanning (Cr) 1.37 0.54 1,200 1.6 0.061 540 0.740 250 3.5Washing 0.95 0.37 1,000 1.0 0.035 270 0.256 55 4.6Neutralization 2.06 0.84 560 1.1 0.042 420 0.865 6.6Washing 3.44 1.36 150 0.5 0.020 170 0.584 6.1Retanning 0.68 0.27 230 0.2 0.005 50 0.034 5.9Fatliquoring 0.68 0.27 170 0.1 0.004 240 0.163 4.2Dyeing 1.20 0.47 950 1.1 0.042 120 0.144 3.4Total crustprocess

10.38 4.09 544 5.7 0.210 280 2.786 0.20 37 (av)

(av) average Total: 0.39 kgGeneral 252.70 100.00 10,600 2684.4 100.000 5,160 5,100 1298.3 100.00 195 (av) 319

(av)Total (av) average 49.23 kg 80.85

kg

FAO Report on Vegetarianism

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