You are here

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.

The paper presents the results of the implementation of solar collectors in three Bangladeshi tanneries as well as of energy audit in four Bangladeshi tanneries to evaluate and improve their electrical performance.

It is well known that tanneries use high amounts of hot water and electricity, and today energy costs are raising very fast all over the world, with energy costs increasing their share in the costs of leather production. Other problem especially in developing countries are frequent power cuts and problems with energy supply. Tannery relocation planned in Bangladesh from Hazaribagh to new Tannery Estate Dhaka is an opportunity to implement measures to reduce energy consumption which should lead to reduced costs for production but also reduced GHG production. Therefore, within the Re-Tie-Bangladesh project (Reduction of Environmental Threats and Increase of Exportability of Bangladeshi Leather Products1) UNIDO has implemented two actions to reduce energy costs in Bangladeshi tanneries: use of solar energy - solar water heating and electrical performance improvement.

The Global Leather Coordinating Committee (GLCC) in 2013 sought to identify real and perceived strengths, weaknesses, opportunities and threats of importance to the leather industry. This paper sets down a mosaic of major issues stemming from these considerations.This paper was published in the World Leather (February/March 2014).

Th report provides an overview of publications, standards and references for the calculation of the Product Carbon Footprint (PCF) of the product Finished Leather together with recommendations for harmonization and the main elements needed to define system boundaries. The inherent complexity and inadequate exactness of carbon footprint analyses contrasts with the need to communicate the results in a simple, clear and unambiguous way. The report was prepared for and presented by Mr. F. Brugnoli  in the 18th  UNIDO Leather Panel in Shanghai/China September/2012

International concern has increased over the years on Climate Change. The ten hottest years on record have all occurred since 1998. Out of the last 21 years 18 are among the 20 warmest years since 1880. Data and findings add weight to the common conclusion that the clear long-term trend is one of global warming. Most of the observed increase in global average temperature since the mid - 20th century is very likely due to the observed rise in anthropogenic greenhouse gas concentrations. Among these, particular attention is paid on CO2 (carbon dioxide). Latest estimates show that global CO2 emissions increased to 30,600 million tonnes in 2010. Industry and manufacturing contribute for 19% of all Greenhouse Gas Emissions. Interest has been developed in estimating the total amount of GHG produced during the various stages in the life cycle of products. The outcome of these calculations, are referred to as Product Carbon Footprints (PCFs). Currently, there is no single methodology and no agreement has been reached internationally on Leather PCF calculation methods.

Dissolving the hair substance in the course of liming and unhairing entails a high load of organic pollution in wastewater; as the environmental demands have grown acute, it has become necessary to further reduce wastewater pollution load as much as possible. Hair-save technology, using only chemicals traditionally applied in liming, is among simple and good options towards achieving that aim. Hair-save unhairing is far from being a general practice as yet, but in future the increase of environmental costs and external pressures might make it more attractive. In addition to process description, equipment requirements, the scope for utilization of hairs obtained as well as cost considerations are also provided.

For an easy reference older papers are also available.

In view of ever increasing legal and social pressures, no tanner can afford to be unfamiliar with the main issues and principles of environmental protection pertaining to tannery operations. Among these, preventing pollution and promoting cleaner leather processing, which ultimately leads to lower treatment costs, clearly remain a priority. Through the application of industrially proven low-waste advanced methods - such as using salt-free preserved raw hides and skins, hair-save liming, low-ammonia or ammonia-free deliming and bating, advanced chrome management system, etcetera - it is possible to decrease the pollution load expressed as COD and BOD5 by more than 30%, sulphides by about 60 to 70 %, ammonia nitrogen by 80%, total (Kjeldahl) nitrogen by 50%, chlorides by 70%, sulphates by 65 % and chromium by 90%. Yet, despite all preventive measures, there is still a considerable amount of pollution load to be dealt with by the end-of-pipe methods. The purpose of this booklet is to help a tanner or a tannery manager (possibly a well-trained leather technologist) to get familiarized with basic principles and methods of treatment of tannery effluents. This knowledge should make him better equipped for communications with the factory’s environmental unit, environmental authorities and NGOs. To keep the manual short and concise, there are many simplifications and omissions of details; for in-depth understanding of the complexities of treatment of effluents and solid wastes (sludge) we recommend you to consult extensive literature on this subject. Finally, and contrary to the widespread misperception that vegetable tanning is environmentally harmless (in reality its effluents have very high, difficult-to-treat COD), the manual basically refers to the combined chrome tanning (i.e. chrome tanning supplemented by vegetable and synthetic tanning agents) because it is by far the most prevailing leather tanning method.

This paper attempts to discuss the main, predominantly technical, issues with regard to benchmarking; it is intended to assist those who are willing to admit to the fact that despite all explanations and definitions available, they are not quite sure what it is all about and whether and how it could be applied in the tanning industry. The paper outlines "cock-pit" check lists for ten areas - components: 1. Tannery location, infrastructure 2. Production parameters 3. Cleaner technologies 4. Energy management and consumption 5. Quality assurance, reprocessing, delivery time, failures 6. Product development, strategies 7. Occupational safety and health at work, maintenance 8. Effluent treatment, solid waste, air emissions 9. Financial indicators 10. Human resources and staff welfare, CSR. Some typical production parameters are also provided.

The Tannery of the Future Foundation developed self-assesment tool for tanneries

 

Towards the end of the 20th century the tanning industry has made a considerable progress in controlling the environmental pollution caused by its activities, yet the situation varies from country to country and even from region to region within some large countries. Some tanners in industrialized countries hold the view that lax environmental regulations and poor enforcement account for lower production costs, higher competitiveness and hence further expansion of the tanning industry in developing countries.

This study compares the costs of treatment of tannery effluents, including indicative investments costs in selected industrialized and developing countries. While the figures concerning the investment and operational costs by now are quite obsolete and technologies change, the comparisons of the cost structures are still quite elightening.

Typically only a small part of fleshings is used for manufacture of glue and animal protein while the major part is dumped as waste at landfill or disposed of along with other solid wastes. The unutilised fleshings, containing high concentration of lime and sulfide, putrefy and produce obnoxious odour. They also cause groundwater pollution, attract flies, rodents and stray dogs and thus represent a public nuisance. Due to high moisture content handling and transportation of fleshings is quite difficult. On the other hand, one tonne of wet fleshing with 85% moisture is estimated to generate 20-30 m3 of biogas. To solve the disposal problem of fleshings, one of the options considered and tested during UNIDO Regional Programme in South-East Asia was biomethanation. The results of testing at the pilot plant, the first of its kind in the region, are given in this report.

With increasing pressure from the pollution control authorities, tanners in many countries of South East Asia region are faced with the urgent task of utilization or safe disposal of solid wastes from tanneries, particularly fleshings. Likewise, sludge generated by tannery effluent treatment plants has to be either put to use or safely disposed. These two issues were highlighted by the industry and government representatives of countries participating in the Regional programme for South-East Asia.

The report contains details of the large scale pilot project implemented under Programme, characteristics of fleshings and sludge charged to the digestors, volume of gas generated vis-à-vis projection, coping with the hydrogen sulphide gas (H2S) and the many valuable lessons learnt. Details of the problems encountered – both process-related and mechanical – have been narrated. At the time of the report preparation (2002) it was the only operational plant of its kind in the world

Conventional technologies for treatment of tannery effluent are generally energy & chemical intensive and continuous process monitoring and control are required to achieve optimum results. In search for alternatives, robust, easy to operate and low maintenance technologies, constructed wetland system, also known as root zone treatment system, using reeds for treatment of effluent, has been considered a possible option. This system is widely used in Europe and elsewhere to treat municipal sewerage. However, there was no practical experience, at least at semi-industrial scale, about its applicability in purification of tannery effluents. Accordingly, in cooperation with willing tanneries and management of common effluent treatment plants (CETP)  in Tamilnadu, India, UNIDO, under its Regional Programme, established four pilot and demonstration reed beds, each with different features, to deal with effluent of different characteristics. Practical experience and results are reported in this paper.

Pages