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Environmental Concerns in Leather Manufacture
Raw leather requires extensive washing to remove dirt, salt and
organic matter. Lime and sulfides are used to dehair the skin. As
a result, large amounts of toxic waste and chemicals are released
into the water system causing environmental pollution.The skin is
then de-limed and softened by enzymatic action. Again, on washing,
ammonium sulfate, enzymes and some protein is released into the
water.
The solution used for tanning the hide contains chromium sulfate
salt and free acid. About 75 per cent of the chromium present combines
with the hide. This chromium tanning process, though a major cause
of environmental pollution, is popular because it enhances the physical
and chemical properties of finished leather.
Environmental and health concerns have resulted in a number of initiatives
to reduce the presence of chromium in the waste stream, improve
fixation on the leather, recycle chromium from effluents, and use
aluminium and titanium as alternatives. The step is the colouring
and oiling of the leather to make it as soft or as firm as desired.
Once again, many chemicals are used and about 90 percent of it is
fixed to the leather. The spent solutions are mildly acidic, with
a pH between 4 and 6.
The Indian government has numerous laws in place that effect the
leather industry. Although compliance is low, State Pollution Control
Boards have in the last few years ordered closures of, and imposed
fines on hundreds of tanneries for pollution infractions. Common
effluent plants have been set up by both Central and State governments
in all areas of where large numbers of tanneries are located. Establishing
and enforcing proper waste treatment is an essential proactive step
for the export sector.
The typical waste streams for leather production are outlined in
Table 3 which documents the results of a pilot project on cleaner
production in a developing country's tannery. The costs of remedying
the pollution problems and the payback period are quantified.
Summary of Recommended Pollution Prevention
Opportunities
| Unit operation |
Pollution prevention action
and environmental/product auality benefit |
Cost |
Payback period |
| Chromium Tanning |
Recycle chrome tanning - decreases
Chromium to less than 3 mg/l |
$20,000 (saves $60,000 per year) |
4 months |
| Solvent Discharge |
Change to water-based lacquer finish
decreases VOC usage by 60-90 per cent |
None |
To be determined |
| Water use |
Change to batch wastes - decreases
water usage by 20-40 per cent |
None |
To be determined |
| Solid waste |
Save leather trimmings for reconstituted
leather - decrease leather waste by 60-80 percent |
$10,000 |
To be determined |
| Sulfide waste |
Destroy sulfides by air oxidation
- decreases sulfide waste by 95-98 percent |
$30,000 |
To be determined |
| Suspended solids |
Primary treatment - dresses suspended
solids by 70-85 percent |
$100,000 |
To be determined |
| Sludge from Effluent |
Dry sludge for land application
- allows disposal of sludge as fertilizer |
$20,000 |
To be determined |
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