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Leather processing

In an age of plastics, metals and synthetics, leather has kept its place as a product of superior quality. As a result, tanning remains an essential economic activity. Leather processing can be done at the small-scale or large-scale level, all to varying degrees of sophistication.

The tanning industry has been subject to important challenges and changes. Foremost has been the introduction of processing technologies with less impact on the environment. As the production of finished leather is concentrated in developing countries, UNIDO, together with other partners, have provided support to enhance tanning industry practices in developing countries.

Cleaner leather production technologies remain UNIDO’s main focus in the field of leather processing. Cleaner production applications include green hide and skin processing (supply of raw material from slaughterhouses without preservation, e.g. salting), water management (use minimum volume of process water), recycling (e.g. in liming) and chromium recovery (after tanning), hair saving (to reduce dissolved solids in effluent) and application of environmentally friendly chemicals (e.g. enzymes). Special attention is also given to occupational health and safety (OHS) in tanneries.

What is future of the chrome tanning? What will be used as a tanning agent in horizont of 50 years? In this paper prepared in 1999 Mr. Frendrup analyzed possible trends and scenarios of leather manufacture. Many issues and predictions are still relevant, especially those concerning the recent EU regulations. For additional information see also IULTCS papers concerning chrome tanning http://www.iultcs.org/pdf/IUR-1_Chromiumandleatherresearch_Abalancedview...

 


 

Chrome tanning is the most common type of tanning in the world. Chrome tanned leathers are characterised by top handling quality, high hydro-thermal stability, user-specific properties and versatile applicability. Waste chrome from leather manufacturing, however, poses a significant disposal problem. Throughout the world, chrome discharge from tanneries is subject to strict regulations. That notwithstanding, chrome is a component that has to be strictly monitored. The environmental impact of chrome discharged from tanneries has been a subject of extensive scientific and technical dispute. Although the legislative limits on the disposal of solid chrome-containing waste have been relaxed in some countries, liquid emissions remain strictly regulated throughout the world. Given the close link between chrome tanning and the environmental impact of leather manufacturing, chrome management is of primary importance in tanning operations. This paper provides information on chrome management and those techniques most frequently used to reduce the amount of chrome in tannery wastewater. By providing information and citing practical experience, the paper aims at contributing to sustainable development of leather manufacture without avoidable harm to environment.

UNIDO through its Regional Programme for Pollution Control in the Tanning Industry in South-East Asia has been actively looking for solutions to tackle saline tannery effluent. The following technologies have been tested at pilot scale demonstration units (PDUs):

  • Mechanical / manual removal of excess salt from wet salted hides and skins
  • Reverse osmosis (RO) of treated tannery effluent
  • Improved (accelerated) solar evaporation
  • Recycling of floats in the beamhouse
  • Use of ultrafiltration in tannery effluent.

This report provides preliminary estimates of costs of setting up a multistage evaporation system for recovery of salt from the concentrate (reject) resulting from the Reverse Osmosis (RO) of treated effluents..

This survey prepared and presented during the 17th UNIDO Leather Panel is a follow-up to Worldwide Study of the Leather and Leather Products Industry, which was the outcome of an exhaustive survey carried out by UNIDO in the 1970s. It is intended to assist the Organization in the formulation of future assistance programmes and in detecting areas where further study of various kinds may be useful. This report assesses the worldwide prospects of the leather and leather products industry in the coming decade. It examines the major underlying trends of recent years and how they are expected to evolve in the short to medium term. In its attempt to provide a thorough picture of the leather sector, the report covers its various aspects: the availability of raw material, the tanning industry, and the manufacture of footwear and other leather products. The basic intention is to help discern prevailing trends in global trade and to support efforts to design an effective role for organizations in the industrial development arena. The findings and forecasts published here are meant to be indicative rather than definitive and to form a basis for further surveys and studies. The need to compile this report arose out of the 16th session of the UNIDO Leather and Leather Products Industry Panel held in Brazil in May 2007. The panel recommended that UNIDO undertake a comprehensive study on the future development of the world leather and leather products industry, a study that would cover demand, technology, production, and trade. Consequently, the UNIDO study provides an analysis of the contemporary demand for leather products (footwear, leather goods, gloves, leather garments, sports goods, upholstery, etc.) vis-à-vis the availability of resources (raw hides and skins, manufacturing capacities, skilled labour, knowledge, support industries, and services). It also contains information on other important aspects of the leather industry: trade statistics, the geographic distribution of production, technology developments, physical infrastructure, environmental conditions, and social aspects involved in the production of leather.

Total dissolved solids (TDS), specifically chlorides, in effluent are a major concern for its discharge into surface waters and its use for irrigation. Conventional treatment systems do not help reduce TDS in the industrial effluent. Taking advantage of the sunshine available for most part of the year, tanneries in Tamil Nadu, India, were required by the regulatory authority to segregate highly saline effluent (soak and pickle streams)  and evaporate it in solar pans. Due to very dissapointing results of evaporation in solar pans attempts have been made to accelerate the evaporation by simple means like combination of improved warming of the effluent and use of sprinklers. This paper reports on results of these pilot scale tests carried out under UNIDO Regional Programme in India during late 90's.

This short paper presented during the 14th UNIDO Leather Panel in Zlin/Czech Republic reports on the general situation, issues and methodology adopted as well as practical experience in implementation of occupational safety and health standards (OSH)  at work in tanneries under UNIDO’s Regional Programme for Pollution Control in the Tanning Industry in South East Asia in late 90-ies involving .international and local experts. For a practical OSH manual see the document Occupational Safety and Health Aspects of Leather Manufacture.

This manual has been primarily prepared for use by tanners and tannery supervisors. It has been designed to provide guidance and ideas on how to improve the occupational safety and health standards at work in tanneries and effluent treatment plants by presenting the sources of hazards in a tannery and pointing out simple measures, in a practical and easily understandable manner, for ready implementation on-site. A special attention is given to risks associated with hydrogen sulphide gas, H2S. The manual was prepared under UNIDO Regional Programme for tannery pollution control in South-East Asia.

Presented publications documents UNIDO's involvement in promoting Eco-Labelling in the leather industry. Life-cycle assessments or the evaluation of the potential environmental impact of a product system from cradle to grave are fundamental features of some ecolabelling schemes and environmental management systems. Nowadays rhe environmental auditing protocol and reporting mechanism developed and maintained by the Leather Working Group aims to tackle important topical issues, and reflect improvements or changes of technology within the sector.

The essential part of any tannery waste audit is assessing the efficiency of existing operations carried out during the leather manufacturing process. Typically, tannery staff have a good idea of, and comparatively accurate figures on the waste resulting from specific operations such as fleshing, splitting, trimming or chrome tanning. Only rarely, however, they have a proper overview of the entire range of waste generated. Thus, when considering various cleaner technologies or waste treatment systems, having access to a complete computation of the overall mass balance certainly makes it easier for a tanner facing arduous choices. Dialogue with environmental authorities is also simpler if such figures are readily available. This paper attempts to provide a comprehensive computation of a mass balance and the efficiency of the leather manufacturing process for a tannery, seen as a closed entity. The calculations are deliberately based on operations in a hypothetical tannery processing bovine hides and producing upper leather for shoes. With minor exceptions (batch washing instead of continuous rinsing, splitting in lime, roller coating), it follows the conventional process.

Utilization and/or safe disposal of sludges generated in the course of effluent treatment still represents a great challenge; worldwide many methods have been explored and proposed. This report describes the attempt made under UNIDO Regional Programme in South-East Asia to test another path. The idea was to convert the hazardous tannery sludge  into an inert, physically stable mass, with very low leachability and sufficient strength to allow making building materials like nonfired bricks for fencing or for landfilling or land reclamation. Solidification  (cementation) was achieved by mixing the sludge with various materials to form a solid product hoping that immobilisation/chemical stabilisation) will also be achieved.

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