Reducing the environmental and economic impact of the unhairing-liming process in the leather tanning industry.

Abstract

The environmental impact of the tanning industry is generally significant with outputs of wastes, i.e. high concentrations of organics, salts and heavy metals (chromium compounds), both in solid and liquid form, as a result. In order to bring the tanning industry more in line with present environmental thinking, various methods have been devised to reduce impacts. The underlying study proposes a modification of the method for unhairing–liming of hides where the unhairing–liming liquids are reused several times after being recharged by reduced quantities of chemicals. The study, therefore, aims at reducing both the economic and environmental costs of the unhairing–liming process. Experiments were carried out at lab scale with a simulation apparatus designed for the purpose. Life cycle assessment was used to evaluate the net environmental benefits of the modified method. The present value approach was used to evaluate the economic feasibility of the modified method. The quality of the produced leather was assessed by experts from the tanning sector (tanners). On the environmental level, the modified method reduced the environmental impact of the process by 24%, COD was reduced by 50% as well as sulfide which was reduced by 73% when the process water was recycled four times. The modified method requires some investment in new equipment and is a little more labor intensive as compared with the conventional method but does permit for savings in water up to 58% and chemicals up to 28% as well as wastewater treatment cost which was reduced by 58%. The modified method allowed for four times reuse of the unhairing–liming liquor without visibly affecting the quality of the final product of leather. It was concluded that both the economic and the environmental costs of the unhairing–liming process were reduced relative to the same of the conventional method.