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 involves 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 per cent 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 have 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 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 quality
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 per cent |
$10,000 |
To be
determined |
| Sulfide
waste |
Destroy
sulfides by air oxidation - decreases sulfide waste by
95-98 per cent |
$30,000 |
To be
determined |
| Suspended
solids |
Primary
treatment - dresses suspended solids by 70-85 per cent |
$100,000 |
To be
determined |
| Sludge from
Effluent |
Dry
sludge for land application - allows disposal of sludge
as fertilizer |
$20,000 |
To be
determined |
|
