media effects [5]. The quantity of chemicals utilized varies considerably depending
on the quality description of the final product, the pelts treated and the procedures
employed in processing. Consumption of chemicals can therefore only be given
within a broad range. In addition, lack of standards in terms of quality of chemicals
supplied to tanneries by different manufacturers in developing countries poses safety
challenge and difficulty in finding the environmental impact of the used chemicals.
Lack of material safety data sheets on most chemicals of which some are toxic to
humans and environment has been a major challenge for tanneries [5].
Water used must also be taken into account when comparing consumption and
emission figures. An average of 30–35 m
3 of wastewater is generated per ton of raw
hide processed [6]. About 20–50% of the pelt weight is added as inorganic standard
chemicals and about 3–40% as organic chemicals [5]. The inability by tanneries to
treat waste and uncontrolled discharge or disposal of untreated wastes is the major
course of environmental degradation facing tanneries across the globe. Huge quantities of claimable by-products are generated in the leather industry but cannot be
recycled due to cross contamination with toxic chemicals. For example, when
1,000 kg raw hide is processed using traditional leather processing method, 30 m
3
of water are required and yields 150 kg hair-free leather, 30 m
3 wastewater and
700 kg solid trash [7]. In another study undertaken by Black et al. [5], processing
1,000 kg of salted raw hide using conventional leather-manufacturing method
requires 22 m
3 water, 425 kg of process chemicals and 9.2 GJ of energy. The yields
consist of 145 kg leather, 22 m
3 wastewater, 391 kg by-product, 906 kg solid waste,
277 kg of sludge from wastewater and 1.5 kg air emission. Disposal of toxic solid
waste and huge quantities of highly polluted wastewaters is a dilemma for tanneries.
Figure 1 gives an input/output overview from an advanced tannery producing
upholstery leather [5].
Pre-tanning and tanning processes contribute 80–90% of the total pollution load
in tanneries [8]. The waste generated by depilation/dehairing process accounts for
60% of the suspended solid, 68% of salt, 83% of BOD, 73% of COD and 76% of
toxic chemicals [9]. The probable escape to the atmosphere is emissions from wet
processing, finishing and effluent treatment. They include dust particles, sulphur
dioxide, aerosols, hydrogen sulphide, ammonia, fume of formic acid, water vapour,
carbon dioxide, chlorine, solvent vapours, volatile organic compounds (VOCs), etc.
Air emissions have a negative environmental effect since some of the gases initiate
photochemical reactions, increase greenhouse gases, destroy ozone layer, reduce
visibility in the urban area and form acid rain or fog [10]. Traditionally, tanneries
have been condemned for the discharge of noxious niff rather than any other air
emissions, although the emissions of organic solvents have been a major problem.
Air emissions do not only have negative health effects on tannery workforce but
affect people several kilometres beyond the tannery site. Tannery ventilation requirement for health and safety of employees may limit the degree of air pollution in the
buildings but not the environment outside the building [5].
The main liquid and solid outputs from leather-making process arise from
decaying flesh, suspended and dissolved solids, fats, dyestuffs, organic matters,
colouring pigments, dissolved lime, splitting, soluble proteins, shaving, toxic
Alkaliphilic Enzymes and Their Application in Novel Leather Processing. . .
199
on the quality description of the final product, the pelts treated and the procedures
employed in processing. Consumption of chemicals can therefore only be given
within a broad range. In addition, lack of standards in terms of quality of chemicals
supplied to tanneries by different manufacturers in developing countries poses safety
challenge and difficulty in finding the environmental impact of the used chemicals.
Lack of material safety data sheets on most chemicals of which some are toxic to
humans and environment has been a major challenge for tanneries [5].
Water used must also be taken into account when comparing consumption and
emission figures. An average of 30–35 m
3 of wastewater is generated per ton of raw
hide processed [6]. About 20–50% of the pelt weight is added as inorganic standard
chemicals and about 3–40% as organic chemicals [5]. The inability by tanneries to
treat waste and uncontrolled discharge or disposal of untreated wastes is the major
course of environmental degradation facing tanneries across the globe. Huge quantities of claimable by-products are generated in the leather industry but cannot be
recycled due to cross contamination with toxic chemicals. For example, when
1,000 kg raw hide is processed using traditional leather processing method, 30 m
3
of water are required and yields 150 kg hair-free leather, 30 m
3 wastewater and
700 kg solid trash [7]. In another study undertaken by Black et al. [5], processing
1,000 kg of salted raw hide using conventional leather-manufacturing method
requires 22 m
3 water, 425 kg of process chemicals and 9.2 GJ of energy. The yields
consist of 145 kg leather, 22 m
3 wastewater, 391 kg by-product, 906 kg solid waste,
277 kg of sludge from wastewater and 1.5 kg air emission. Disposal of toxic solid
waste and huge quantities of highly polluted wastewaters is a dilemma for tanneries.
Figure 1 gives an input/output overview from an advanced tannery producing
upholstery leather [5].
Pre-tanning and tanning processes contribute 80–90% of the total pollution load
in tanneries [8]. The waste generated by depilation/dehairing process accounts for
60% of the suspended solid, 68% of salt, 83% of BOD, 73% of COD and 76% of
toxic chemicals [9]. The probable escape to the atmosphere is emissions from wet
processing, finishing and effluent treatment. They include dust particles, sulphur
dioxide, aerosols, hydrogen sulphide, ammonia, fume of formic acid, water vapour,
carbon dioxide, chlorine, solvent vapours, volatile organic compounds (VOCs), etc.
Air emissions have a negative environmental effect since some of the gases initiate
photochemical reactions, increase greenhouse gases, destroy ozone layer, reduce
visibility in the urban area and form acid rain or fog [10]. Traditionally, tanneries
have been condemned for the discharge of noxious niff rather than any other air
emissions, although the emissions of organic solvents have been a major problem.
Air emissions do not only have negative health effects on tannery workforce but
affect people several kilometres beyond the tannery site. Tannery ventilation requirement for health and safety of employees may limit the degree of air pollution in the
buildings but not the environment outside the building [5].
The main liquid and solid outputs from leather-making process arise from
decaying flesh, suspended and dissolved solids, fats, dyestuffs, organic matters,
colouring pigments, dissolved lime, splitting, soluble proteins, shaving, toxic
Alkaliphilic Enzymes and Their Application in Novel Leather Processing. . .
199