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Minimizing Waste and Water Waste: Reusing Materials Leads to Economic and Environmental Benefits

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Thai Tannery Recycles Chromium Liquor

In brief

A widely used tanning agent, trivalent chromium, provides desirable qualities of softness, feel, and texture to leather. The level of chromium tanning agent normally used for high quality leather is 7-8% by weight of semi-processed hide (pelt). To achieve high quality leather through conventional chrome tanning processes, some 30-40% of the chrome (one of the tannery’s most expensive auxiliaries) offered to the hide is left behind in the tanning liquor and discharged into waste water—contributing to a high level of dissolved and suspended toxic metal salts.

The challenge

Aware of the potentially serious health effects, legislators in Thailand (as in nearly every country) implemented stringent limits for chromium discharge—to levels as low as 2 mg/litre in combined and treated waste water. This was a major challenge for most operations. Recycling chromium liquor was one method that offered hope in this regard. The Production Manager in this medium-sized tannery (which employed 230 people and processed 1’000 hides or 20 tons per day) was primarily concerned that the end quality of the leather would be negatively affected by recycling the chromium liquor.

Actions taken within the enterprise (after application of the PREMA GHK guide)

A test run was carried out with one batch to assess the possibilities for recycling chromium liquor.

Seeing that the quality of the end product was not affected, the tannery invested in the needed tanks, pump, pipes, and screens to facilitate routine chromium recycling.

“Shorter floats” are now being used; this reduces fresh water use by 40% and consequently the amount of waste water that requires treatment.

Environmental benefits

By recycling chromium liquor, this tannery reduced its input of chrome tanning agents by 89%. As the process became more fine-tuned, it was expected that 95-98% of waste chromium could be recycled, thereby significantly reducing the generation of hazardous waste and the costs for safe disposal of the treated sludge.

By replacing its chrome tanning agent with one that (despite its higher cost) allows a higher exhaustion and increasing basicity, this company further reduced its overall chemical consumption by 2%. Such an action gives the company additional cost savings and reduces its environmental impact.

Furthermore, the company’s reduction in fresh water use through the use of shorter floats and eventual elimination of excess washing between steps was important in conserving fresh water.

Economic benefits

Investment cost

₱ 30,000
for a tannery with a
daily processing capacity
of 1,000 hides

For the purchase and installation of:

pump, pipes, and screens (2 – 5 mm in diameter)

reaction and storage tanks, valves

Savings

₱ 40,000
(daily savings of ₱ 160)

Due to reduced use of chromium tanning agents
(₱ 8-10 per 10 tons of raw hides)

Payback period

Less than 1 year

 

Organizational improvements

Similar to many Thai tanneries, this operation has been a family-run business for two generations. Changing processes—especially the idea of making any changes to the tanning process, which is considered to be as much of an art as a science involving chemicals—is very difficult for companies to consider. Despite her initial scepticism about whether chromium recycling would actually work, the Production Manager in this tannery was open to trying a new approach. This willingness to experiment carried over into other areas—with the result that despite the tannery’s modest size, it was one of the most productive operations in the area in terms of hides processed per employee each day.

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