Environmental Concerns in Leather Manufacture

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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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