Adapted from the article by the author that appeared in the 3rd edition of this Encyclopaedia. Acknowledgements to Gary Meisel and to Tom Cunningham of the United Food and Commercial Workers Union for reviewing and adapting this article

Rudimentary means of preserving furs have been used since very early times and are still practised in many parts of the world. Typically, after the pelt is scraped and cleaned by washing, the skin is impregnated with animal oil, which serves to preserve it and make it more pliable. The pelt may be beaten or chewed after the oil treatment in order to effect better impregnation by the oil.

In the modern fur industry, pelts are obtained from fur farmers, trappers or hunters. At this stage they have been stripped from the carcass, flesh and fatty deposits have been removed by scraping and the pelts have been stretched and air dried. The fur industry grades the pelts according to factors such as the general condition of the pelt, fur length, curl and patterning. The pelts go through a series of treatment steps, called fur dressing, to preserve them (see figure 1). The furs may also be dyed. Fur dressing and dyeing are done in batches, with the pelts usually being transferred from one step to another using hand carts.

Figure 1. Flow chart of fur dressing

Fur Dressing

First, the pelts are sorted, stamped with an identifying mark, and cut open using knives and snippers. They are then soaked in salt water in tubs or barrels for several hours to re-soften them (see figure 2). Rotating paddles are often used to help this soaking. Sometimes formic acid, lactic acid or sulphuric acid is used in the soaking step. The excess water is then removed in revolving drums.

Figure 2. Soaking department in a fur-processing works

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Next, the underside of the pelt is drawn across razor-sharp round-knife fleshing machines by workers known as fleshers (figure 3). Hand turning (turning the pelt inside out) and trimming with knives is also done. This operation removes the loose connective tissue from the underside of the skin. The object is to remove, as far as possible, any tissue which is not involved in the attachment of the fur, thus producing the maximum degree of lightness and flexibility of the pelt.

Figure 3. Machine fleshing of lamb skins

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The pelts are now ready for tanning and are soaked in alum solution in pits or tubs. As with soaking, paddles are used. The alum solution is usually acidified somewhat with hydrochloric or sulphuric acid. The alum treatment may be carried out in either an aqueous or an oil solution. Excess liquid is extracted and the pelts are dried in special drying rooms to set the skin collagen.

The tanned pelts are then treated with an oil solution in a kicking machine or similar type of machine to force the oil into the skin. They are then cleaned in rotating drums containing sawdust, which absorbs moisture and excess oil.

Pelts contain guard hairs as well as the softer fur fibres. The guard hairs are stiffer and longer than the fur fibres and, depending on the type of fur and the final product desired, these hairs may be either partially or totally removed by machine or by hand plucking. Some pelts also require shearing or trimming with knives (see figure 4).

Figure 4. Shearing operation on Canadian beaver pelts

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Other steps can include shaving or “paring out” with round-knife fleshers, buffing with buffing machines, drying and finishing. The latter can include degreasing, stretching, cleaning, buffing, brushing and lusterizing with lacquers and resins.

Dyeing

Although dyeing of furs was at one time not looked upon favourably, it is now an accepted part of fur preparation and is practised extensively. This can be done at the same time as tanning or in a subsequent step. The usual procedure involves treatment of the pelts with a weak alkaline solution (e.g., sodium carbonate) to remove dirt and oil residues. The pelts are then soaked in a mordant solution (e.g., ferric sulphate), after which they are steeped in dye solution until the desired colour is obtained. They are then repeatedly rinsed and drum-dried with the aid of sawdust.

Many other chemicals may be used in dyeing, including ammonia, ammonium chloride, formaldehyde, hydrogen peroxide, lead acetate or nitrate, oxalic acid, sodium perborate,
p-phenylenediamine dyes, benzidine dyes and so forth.

Fur Garment Manufacture

Before being made into garments, pelts may be cut and “let out”. This involves making a series of closely spaced diagonal or V-shaped slits in the skin, after which the pelt is pulled in order either to lengthen or to broaden it as needed. The pelt is then re-sewn (see figure 5). This type of operation requires great skill and experience. The pelts are next thoroughly moistened and then laid out and tacked on a board according to a chalked-on pattern, left to dry and sewn together. Finally, lining and other finishing steps complete the garment.

Figure 5. Operators engaged in the machine sewing of skins

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Hazards and Their Prevention

Accidents

Some of the machines used in fur processing present serious hazards unless sufficient guarding is maintained: in particular, all drums should be protected with an interlocking gate and the centrifuges used for extraction of moisture should be fitted with interlocking lids; fur clipping and fur cutting machines should be totally enclosed except for the feed and discharge openings.

Vats should be covered or effectively railed to prevent accidental immersion. Falls on wet and slippery floors can be largely prevented by maintenance of sound, impervious surfaces, well-drained and frequently cleaned. Dyeing vats should be surrounded by drainage channels. Accidents caused by hand tools can be reduced if the handles are well designed and the tools well maintained. In the fur manufacturing sector, sewing machines require similar protection to those used in the garment trade (e.g., guarding of driving mechanisms and of needles).

Health Hazards

The use by the fur industry of such a large proportion of pelts from animals bred in captivity has considerably reduced the likelihood of transmission of animal diseases to fur workers. Nevertheless, anthrax may occur in workers handling carcasses, skins, hides or hairs from infected animals; a vaccine may be administered to all likely to have contact. All concerned should be aware of the risk and trained to report any suspicious symptoms immediately.

Various chemicals used in the fur industry are potential skin irritants. These include alkalis, acids, alum, chromates, bleaching agents, oils, salt and the compounds involved in the dyeing process, which comprise various types of dyes as well as mordants.

Unpacking of bales which have been treated with dusting powder in their countries of origin, drumming, plucking, unhairing and shearing can all produce irritant dust. In dye houses and dye kitchens, where salts of lead, copper and chromium (and possibly carcinogenic dyes) are weighed and cooked, there is also a risk of ingestion of toxic dusts. Injurious vapours may arise from degreasing solvents and fumigating chemicals. There is also the possibility of development of contact sensitization (allergy) to some of these chemicals or to the dust from one or more of the types of fur being handled.

The main protection against the hazards of dust and vapours is the provision of local exhaust ventilation; good general ventilation is also necessary throughout the process. Good housekeeping is important to remove dust. Personal respiratory protective equipment may be necessary for short-term jobs or in addition to local exhaust at particularly dusty operations. Particular attention should be paid to potential confined space hazards in pits and vats used for soaking/washing, tanning and dyeing.

Protective clothing appropriate to the process is necessary at most stages of fur processing. Rubber hand protection, foot and leg protection and aprons are required for wet processes (e.g., at the dye and mordant vats) and as a protection against acids, alkalis and corrosive chemicals. Good sanitary and washing facilities, including showers, should be provided. Bleaches and strong alkali soaps should not be used for hand cleansing.

Ergonomic problems can result from manual lifting and moving of materials, especially pushing hand carts, and manual loading and unloading of pelts (particularly when wet). Automation of these processes can help solve these problems. Repetitive motions in fur garment manufacture are also a source of ergonomic problems.

Heat stress diseases can occur while working in the drying room. Preventive measures include adequate exhaust of hot air and supply of cool air, limiting exposure time, readily accessible drinking water and training in the recognition of heat stress symptoms and in first aid measures.

Noise can be a problem with many of the machines used, especially in drums and combing, shearing and lusterizing machines.

Pre-placement medical examination can assist in the prevention of dermatitis by proper placement of employees with a history of sensitivity. Medical supervision is desirable; well maintained first-aid provisions in the charge of trained personnel are essential. Strict attention to hygiene, ventilation and temperature are necessary in the many small workrooms in which much of the making of fur garments is done.

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Adapted by P. Portich from the article in the 3rd edition of this Encyclopaedia by F.L. Conradi.

The term footwear covers a vast range of products made from many different materials. Boots, shoes, sandals, slippers, clogs and so forth are made wholly or partly of leather, rubber, synthetic and plastics materials, canvas, rope and wood. This article deals with the footwear industry as generally understood (i.e., based on traditional manufacturing methods). The manufacture of rubber boots (or their synthetic equivalents) is essentially a section of the rubber industry, which is covered in the chapter Rubber industry.

Shoes, boots and sandals made from leather, felts and other materials have been made by hand over the centuries. Fine shoes are still made wholly or partly by hand, but in all the industrialized countries there are now large mass-production plants. Even so, some work may still be given out to be done as home work. Child labour continues as one of the more serious problems in the footwear industry, although several countries have taken action against child labour with the help of various international programmes in this area.

Boot and shoe plants usually locate close to leather-producing areas (i.e., near cattle-raising country); some slipper and light-shoe making developed where there was a plentiful supply of felts from the textile trade, and in most countries the industry tends to be localized in its original centres. Leathers of different type and quality, and some reptile skins, formed the original materials, with a tougher quality skin for the soles. In recent years leather has been increasingly displaced by other materials, in particular rubber and plastics. Linings may be made of wool or polyamide (nylon) fabric or sheepskin; laces are made of horsehair or synthetic fibres; paper, cardboard and thermoplastics are used for stiffening. Natural and coloured wax, aniline dyes and colouring agents are used in finishing.

Economic and other factors have transformed the footwear industry in recent years. Tennis shoe manufacturing is one of the major growth sectors of the industry and has moved from production in predominantly one country to worldwide production, especially in developing countries in Asia and South America, in order to increase production and reduce costs. This migration of production to developing countries has also occurred in other sectors of the footwear industry.

Processes

There may be over a hundred operations in the making of a shoe, and only a brief summary is possible here. Mechanization has been applied at all stages, but the pattern of the hand process has been closely followed. Introduction of new materials has modified the process without changing its broad outline.

In the making of the uppers (tops of shoes), the leather or other material is sorted and prepared, and the uppers are then cut out on stitching (or dinting) presses by shaped, loose-knife tools. The parts, including the linings, are then “closed” (i.e., sewn or stuck together). Perforating, eyeletting and button-holing may also be carried out.

For making the bottom stock, soles, insoles, heels and welts, pieces are cut out in revolving presses using loose-knife cutters, or in sole-moulding presses; heels are made by compression of leather or wood strips. The stock is trimmed, shaped, scoured and stamped.

The uppers and bottom stock are assembled and then stitched, glued, nailed or screwed together. These operations are followed by shaping and levelling between rollers. The final finishing of the shoe includes waxing, colouring, spraying, polishing and packaging.

Among the raw materials used in the manufacturing process, the most important from the point of view of occupational hazards are the adhesives. These include natural solid and liquid adhesives and adhesive solutions based on organic solvents.

Hazards and Their Prevention

The intensive use of flammable liquids constitutes a considerable fire hazard, and the widespread use of presses and assembling machines has introduced an increased risk of mechanical accidents into this industry. The main health hazards are toxic solvents, high atmospheric dust concentrations, ergonomic risks and noise from the machines.

Fire

The solvents and sprays used in adhesives and finishing materials may be highly flammable. Precautions include:

• using the lowest flash point solvents possible

• using good general ventilation and local exhaust ventilation in spray booths and drying racks to reduce the concentration of flammable vapours

• removing combustible residues from cabinets and workbenches and provide closed containers for solvent-containing and oily wastes

• maintaining unobstructed exits and gangways

• minimizing the amount of stored flammable liquids; keep them in approved containers, cabinets and storage rooms

• ensuring that all electrical equipment and wiring near flammable solvents meets appropriate electrical codes

• grounding adequately polishing machines and other sources of static electricity.

Accidents

Many of the operating parts of the machines present serious hazards, in particular presses, stampers, rollers and knives. The loose-knife cutters at stitching and revolving presses can cause serious injury. The appropriate precautions minimally include two-hand controls (a photo-electric cell device for automatically cutting power may be preferable), the reduction of stroke rate to a safe level in relation to the size of the cutter, and the use of well-designed, stable cutters of adequate height, with flanges fitted perhaps with handles. Sole-moulding and heel presses should be guarded to prevent hand access. Stamping machines can cause burns as well as crushing injuries unless hand access is prevented by guarding. Nips of rollers and knives of milling and shaping machines should be fitted with suitable machinery guarding. The shading and polishing wheels of finishing machines and the spindles on which they are mounted should also be guarded. There should be an effective lockout/tagout programme for repair and maintenance work.

Health hazards

Organic solvents can cause acute and chronic effects on the central nervous system. Benzene, which was formerly used in adhesives and solvents, has been replaced by toluene, xylene, hexane, methyl ethyl ketone (MEK) and methyl butyl ketone (MBK). Both n-hexane and MBK can cause peripheral neuropathy and should be replaced by heptane or other solvents.

Outbreaks of a disease known popularly as “shoemakers’ paralysis” have appeared in a number of factories, presenting a clinical picture of a more or less severe form of paralysis. This paralysis is of the flaccid type, it is localized in the limbs (pelvic or thoracic) and gives rise to osteo-tendinous atrophy with areflexia and no alteration in superficial or deep sensitivity. Clinically, it is a syndrome resulting from functional inhibition or injury of the lower motor neurons of the voluntary motor system (pyramidal tract). The common outcome is neurological regression with extensive proximo-distal functional recuperation.

Good general ventilation and exhaust ventilation at the point of origin of the vapours should be provided to maintain concentrations well below maximum permissible levels. If these levels are observed, the fire risk will also be diminished. Minimizing the amount of solvent used, enclosure of solvent-using equipment and closing solvent containers are also important precautions.

Finishing machines produce dust, which should be removed from the atmosphere by exhaust ventilation. Some of the polishes, stains, colours and polychloroprene glues may carry a dermatitis risk. Good washing and sanitary facilities should be maintained and personal hygiene encouraged.

The increased intensive use of machines and equipment creates a significant noise hazard, necessitating source control of the noise or other preventive measures to prevent hearing loss. There should also be a hearing conservation programme.

Prolonged work on nailing machines which produce high levels of vibration may produce “dead hand” (Raynaud’s phenomenon). It is advisable to restrict the time spent at these machines.

Low-back pain and repetitive strain injuries are two musculoskeletal diseases that are major problems in the footwear industry. Ergonomic solutions are essential for prevention of these problems. Pre-placement and periodic medical examinations linked to workplace hazards are an effective factor for protection of employees’ health.

Environmental and Public Health Hazards

Earth Summit 1992, held in Rio de Janeiro, dealt with environmental concerns, and its proposals for future action, known as Agenda 21, could transform the footwear industry with its emphasis on recycling. In general, however, most waste materials are disposed of in landfills. Without proper precautions, this can result in contamination of the ground and groundwater.

Although home work has social advantages in decreasing unemployment and in the formation of cooperatives, the problems of ensuring proper precautions and working conditions in the home are enormous. In addition, other family members can be at risk if they are not already involved in the work. As discussed previously, child labour remains a serious problem.

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Leather Tanning

The major International Standard Industrial Classification (ISIC) group for the leather and fur processing is 323. In the United States, the Standard Industrial Classification (SIC) group for leather and leather manufacturing products industry is SIC 311 (OMB 1987). This group includes establishments engaged in tanning, currying and finishing hides and skins, as well as establishments manufacturing finished leather and artificial leather products and some similar products made of other materials. Leather converter, belting and chamois leather are also included in SIC 311. In addition, parts of SIC 23 (i.e., SIC 2371 and 2386) include establishments involved in the manufacturing of coats, garments, accessories and trimmings made of fur and establishments involved in sheep-lined clothing.

There are many varieties of leather with different characteristics depending upon the animal species and the specific part of the body of the animal from which the hide is obtained. Hides are made from cattle or horse skins; fancy leather from the skin of the calf, pig, goat, sheep and so on; and reptile leather from crocodile, lizard, chameleon and so on.

Employment in the leather and leather manufacturing products industry has been associated with various diseases caused by biological, toxicological and carcinogenic agents. The specific disease associated with exposure in the leather industry depends upon the extent to which the worker is exposed to the agent(s), which is dependent upon the occupation and work area within the industry.

For the tanning process, the epidermis of the hide is first removed and only the dermis transformed into leather. During this process, infection is a constant hazard, since the hide serves as a medium for numerous micro-organisms. Colonies of fungi may develop, specifically Aspergillus niger and Penicillus glaucum (Martignone 1964). To avoid the development of fungi, chlorinated phenols, specifically pentachlorophenol, have been widely used; unfortunately, such chemicals have been found to be toxic to the worker. Yeasts of three genera (Rhodotorula, Cladosporium and Torulopsis) have also been found (Kallenberger 1978). Tetanus, anthrax, leptospirosis, epizootic aphtha, Q fever and brucellosis are examples of diseases that workers could contract during the tanning process due to infected hides (Valsecchi and Fiorio 1978).

Skin disorders such as eczema and contact (allergic) dermatitis have also been diagnosed among leather tanners exposed to preservatives applied to the hides (Abrams and Warr 1951). The leather tanning and finishing process has been shown to have the highest incidence of dermatoses of any working group in the United States (Stevens 1979). Irritations of the mucous membranes of the throat and nose and perforations of the nasal septum may also occur after inhaling chromic acid fumes liberated during the chrome-tanning process.

Tannery workers have the potential for exposure to numerous known or suspected occupational carcinogens, including hexavalent chromium salts, benzidine-based azo dyes, organic solvents (e.g., benzene and formaldehyde), pentachlorophenol, N-nitroso compounds, arsenic, dimethylformamide and airborne leather dusts. These exposures may result in the development of various site-specific cancers. An excess of lung cancer has been observed in studies carried out in Italy (Seniori, Merler and Saracci 1990; Bonassi et al. 1990) and in a case-control study carried out in the United States (Garabrant and Wegman 1984), but this result is not always supported by other studies (Mikoczy, Schutz and Hagmar 1994; Stern et al. 1987; Pippard and Acheson 1985). Chromium and arsenicals were mentioned as possible contributors to the lung cancer excess. A significantly increased risk of soft tissue sarcoma has been observed in at least two separate tannery studies, one in Italy and one in the United Kingdom; the investigators of both studies suggest that the chlorophenols used at the tanneries may have produced these malignancies (Seniori et al. 1989; Mikoczy, Schutz and Hagmar 1994).

A threefold statistically significant excess in pancreatic cancer mortality was noted in a Swedish case control study (Erdling et al. 1986); a 50% increase in pancreatic cancer was also noted in another study examining three Swedish tanneries (Mikoczy, Schutz and Hagmar 1994) and in a study of an Italian tannery (Seniori et al. 1989). Despite the excess risk of pancreatic cancer, no specific environmental agent was identified, and dietary factors were considered a possibility. An excess risk of testicular cancer was observed among leather tanners from the finishing department of one tannery; all three workers with testicular cancer had worked during the same time period and were exposed to dimethylformamide (Levin et al. 1987; Calvert et al. 1990). An excess risk of sinonasal cancer among leather tannery workers was observed in a case-control study in Italy; chromium, leather dust and tannins were indicated as possible aetiological agents (Comba et al. 1992; Battista et al. 1995). However, IARC research in the early 1980s found no evidence of an association between leather tanning and nasal cancer (IARC 1981). The results of a study of the Chinese leather tanning industry showed a statistically significant excess morbidity from bladder cancer among those tanners ever exposed to benzidine-based dyes, which increased with duration of exposure (Chen 1990).

Accidents are also a leading cause of disability in leather tannery workers. Slips and falls on wet and greasy floors are common, as are knife cuts from the trimming of hides. In addition, the machines used to process the hides are capable of crushing and inflicting bruises, abrasions and amputations. For example, United States Bureau of Labor Statistics (BLS) data for 1994 have shown an incidence rate in SIC 311 for injuries and illnesses combined of 19.1 per 100 full-time workers and an incidence rate for injuries alone of 16.4. These results are over 50% higher than the all-manufacturing incidence for illnesses and injuries combined, 12.2 per 100 full-time workers, and the incidence of 10.4 for injuries alone (BLS 1995).

Footwear

The handling and processing of leather in the manufacturing of shoes and boots may entail exposures to some of the same chemicals used in the tanning and finishing processes as cited above, giving rise to similar diseases. Furthermore, different chemicals used may also produce other diseases. Exposures to the toxic solvents used in adhesives and cleaners and to airborne leather dusts are of particular concern. One solvent of specific concern is benzene, which can produce thrombocytopenia; depression of the red blood cell, platelet and white cell counts; and pancytopenia. Benzene has largely been eliminated from the footwear industry. Peripheral neuropathy has also been found among workers in shoemaking factories due to n-hexane in the adhesives. This, too, has largely been substituted for by less toxic solvents. Electroencephalographic changes, liver damage and behavioural alterations have also been reported in connection with exposure to solvents in shoeworkers.

Benzene has been judged to be a human carcinogen (IARC 1982), and various investigators have observed excess leukaemias among workers exposed to benzene in the shoe industry. One study included the largest shoe manufacturing facility in Florence, Italy, consisting of over 2,000 employees. The study results revealed a fourfold excess risk of leukaemia, and benzene was cited as the most likely exposure (Paci et al. 1989). A follow-up to this study showed an over fivefold risk for those shoe workers employed in jobs where benzene exposure was substantial (Fu et al. 1996). A study in the United Kingdom examining mortality among males employed in shoe manufacturing found an elevated risk for leukaemia among workers handling glues and solvents which contained benzene (Pippard and Acheson 1985). Various studies of shoe industry workers in Istanbul, Turkey, have reported an excess risk of leukaemia from exposure to benzene. When benzene was later replaced by petrol, the absolute number of cases and risk of leukaemia dropped considerably (Aksoy, Erdem and DinCol 1974; 1976; Aksoy and Erdem 1978).

Various types of nasal cancer (adenocarcinoma, squamous-cell carcinoma and transitional-cell carcinoma) have been associated with employment in shoe manufacture and repair. Relative risks in excess of tenfold have been reported from studies in Italy and the United Kingdom (Fu et al. 1996; Comba et al. 1992; Merler et al. 1986; Pippard and Acheson 1985; Acheson 1972, 1976; Cecchi et al. 1980) but not in the United States (DeCoufle and Walrath 1987; Walker et al. 1993). The elevated nasal cancer risks were almost entirely accounted for by employees “heavily” exposed to leather dust in the preparation and finishing rooms. The mechanism by which exposure to leather dust may increase the risk of nasal cancer is not known.

Excesses of digestive and urinary tract cancers, such as bladder (Malker et al. 1984; Morrison et al. 1985), kidney (Walker et al. 1993; Malker et al. 1984), stomach (Walrath, DeCoufle and Thomas 1987) and rectal (DeCoufle and Walrath 1983; Walrath, DeCoufle and Thomas 1987) cancers, have been found in other studies of shoe workers but have not been consistently reported and have not been linked with particular exposures in the industry.

Ergonomic hazards causing work-related musculoskeletal disorders (WRMDs) are major problems in the shoe manufacturing industry. These hazards are due to the specialized equipment used and hands-on work requiring repetitive movements, forceful exertions and awkward body postures. BLS data show men’s footwear to be one of the “industries with the highest rates of nonfatal illness disorders associated with repeated trauma” (BLS 1995). The incidence rate for the total footwear industry for illnesses and injuries combined was found to be 11.9 per 100 workers, with 8.6 being the incidence rate for injuries alone. These rates are slightly less than the incidence rates for all manufacturing. WRMDs in the shoe manufacturing industry include conditions such as tendinitis, synovitis, tenosynovitis, bursitis, ganglionic cysts, strains, carpal tunnel syndrome, low-back pain and cervical spine injuries.

Fur Workers

Fur processing involves the activities of three categories of workers. Fur dressers flesh and tan skins; fur dyers then colour or tint the skins with natural or synthetic dyes; and finally fur service workers grade, match and bale dressed furs. Dressers and dyers are exposed to potential carcinogens including tannins, oxidative dyes, chromium and formaldehyde, whereas fur service workers are potentially exposed to residual tanning materials while handling previous dressed furs. Very few epidemiological studies have been conducted on fur workers. The only comprehensive study among these workers revealed statistically elevated risks of colo-rectal and liver cancer among the dyers, lung cancer among the dressers and cardiovascular diseases among the service workers as compared to overall rates in the United States (Sweeney, Walrath and Waxweiler 1985).

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The treatment and processing of animal skins and hides can be a source of considerable environmental impact. Discharged wastewater contains pollutants from the hides, products from their decomposition and chemicals and various spent solutions used for hide preparation and during the tanning process. Solid wastes and some atmospheric emissions also may arise.

The major public concern over tanneries has traditionally been about odours and water pollution from untreated discharges. Other issues have arisen more recently from the increasing use of synthetic chemicals such as pesticides, solvents, dyes, finishing agents and new processing chemicals which introduce problems of toxicity and persistence.

Simple measures intended to control pollution can themselves create secondary cross-media environmental impacts such as groundwater pollution, soil contamination, sludge dumping and chemical poisoning.

Tanning technology that is now available, based on a lower chemical and water consumption, has less impact on the environment than traditional processes. However, many obstacles remain to its widespread application.

Figure 1 presents the different wastes and environmental impacts associated with the various processes used in the tanning industry.

Figure 1. Environmental impacts & tannery operations

Pollution Control

Water pollution control

Untreated tannery wastes in surface waters can bring about a rapid deterioration of their physical, chemical and biological properties. Simple end-of-pipe effluent treatment processes can remove over 50% of suspended solids and biochemical oxygen demand (BOD) of effluent. More sophisticated measures are capable of higher levels of treatment.

As tannery effluents contain several chemical constituents that need to be treated, a sequence of treatment processes in turn must be used. Flow segregation is useful to allow separate treatment of concentrated waste streams.

Table 1 summarizes technological choices available for treatment of tannery effluents.

Table 1. Technological choices for treatment of tannery effluents

Air pollution control

Air emissions fall into three broad groups: odours, solvent vapours from finishing operations and gas emissions from the incineration of wastes.

Biological decomposition of organic matter as well as sulphide and ammonia emissions from wastewaters are responsible for the characteristic objectionable odours arising from tanneries. The siting of installations has been an issue because of the odours that have historically been associated with tanneries. Reduction of these odours is more a question of operational maintenance than of technology.

Solvent and other vapours from the finishing operations vary with the type of chemicals used and the technical methods employed to reduce their generation and release. Up to 30% of the solvent used may be wasted through emissions, while modern processes are available to reduce this to around 3% in many cases.

The practice by many tanneries of incinerating solid wastes and offcuts raises the importance of adopting good incinerator design and following careful operating practices.

Waste management

Treatment of sludge constitutes the largest disposal problem, apart from effluent. Sludges of organic composition, if free from chrome or sulphides, have value as a soil conditioner as well as a small fertilizer effect from nitrogenous compounds contained therein. These benefits are best realized by ploughing immediately after application. Agricultural use of chrome-containing soils has been a matter of controversy in various jurisdictions, where guidelines have determined acceptable applications.

Various markets exist for the conversion of trimmings and fleshings into by-products used for a variety of purposes, including the production of gelatin, glue, leatherboard, tallow grease and proteins for animal feed. Process effluents, subject to suitable treatment and quality control, are sometimes used for irrigation where water is in short supply and/or effluent disposal is severely restricted.

To avoid problems of leachate generation and odour, only solids and dewatered sludges should be disposed of at landfill sites. Care must be taken to ensure that tannery wastes do not react with other industrial residues, such as acidic wastes, which can react to create toxic hydrogen sulphide gas. Incineration under uncontrolled conditions may lead to unacceptable emissions and is not recommended.

Pollution Prevention

Improving production technologies to increase environmental performance can achieve a number of objectives, such as:

• increasing the efficiency of chemical utilization

• reducing water or energy consumption

• recovering or recycling rejected materials.

Water consumption can vary considerably, ranging from less than 25 l/kg of raw hide to greater than 80 l/kg. Water use efficiency can be improved through the application of techniques such as increased volume control of processing waters, “batch” versus “running water” washes, low float modification of existing equipment; low float techniques using updated equipment, re-use of wastewater in less critical processes and recycling of individual process liquors.

Traditional soaking and unhairing account for over 50% of the BOD and chemical oxygen demand (COD) loads in typical tanning effluents. Various methods can be employed to substitute for sulphide, to recycle lime/sulphide liquors and to incorporate hair-saving techniques.

Reduction in chromium pollution can be achieved through measures to increase the levels of chrome that are fixed in the tanning bath and reduce the amounts that are “bled out” in subsequent processes. Other methods to reduce release of chromium are through direct recycling of used chrome liquors (which also reduces salinity of waste effluent) and the treatment of collected chrome-bearing liquors with alkali to precipitate the chromium as hydroxide, which can then be recycled. An illustration of a communal chrome recovery operation is shown in figure 2.

Figure 2. Flow chart for a communal plant for chrome recovery

Where vegetable tanning is employed, preconditioning of hides can enhance the penetration and fixation of hides and contribute to decreased tannin concentrations in effluents. Other tanning agents such as titanium have been used as substitutes for chromium to produce salts of generally lower toxicity and to generate sludges that are inert and safer to handle.

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