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Tannery Effluent Treatment

Despite all preventive measures, a sizeable portion of pollutants can only be removed by the end-of-pipe methods, i.e. treating effluents discharged in the course of leather processing. One of the most successful areas of interventions implemented or facilitated by UNIDO was designing and managing the construction of cost effective [Common] Effluent Treatment Plants ([C]ETP). More than 250 such plants have been designed, established or upgraded through various technical assistance projects. Achievements and experiences were documented in technical papers, reports and manuals which are available in this section. A special Animated Visual Training Tool was also developed by UNIDO and is available in the section “e-Learning".

The precarious situation with water and soil pollution in the area of tannery clusters along the Palar River prompted the state environmental authorities to press for adherence to TDS discharge limits as well as to impose an approach not practiced in the tanning industry: a Zero Liquid Discharge (ZLD) concept.

Essentially, the ZLD systems concentrate dissolved solids by Reverse Osmosis (RO) and some kind of Multi Effect Evaporation (MEE) until only damp solid waste remains. Solid waste is disposed and nearly all water is reclaimed and reused. Accordingly, some of the existing Common Effluent Treatment Plants (CETPs) have been supplemented by RO and MEE, together with auxiliary steps (tertiary treatment, water softening etc.).

The analysis investigates and relates raw and equalized effluent inflows, RO feed, permeate and reject, evaporator feed and condensate and the yield of recovered, reusable water. Since the energy costs are critical for the viability of the entire concept, data about energy consumption (thermal, electrical main and Diesel) at key stages (RO, multistage evaporation) are consolidated, analysed and correlated. Additional energy needs and costs are compared with those for conventional (CETP) treatment and estimates made of the carbon footprint increase caused by the ZLD operations.


Hydrogen supplied gas present in tanneries and effluent treatment plants (ETPs) has proven fatal to workers exposed to it many times.

It is therefore necessary that the owners and managers of tanneries and effluent treatment plants are fully aware of the dangers posed by this poisonous gas and take all preventive and precautionary measures to protect the workforce from exposure to this gas. In the event of accidental exposure of a worker, they should know how to deal with the situation.

UNIDO’s activities in the leather processing has as one of its important objectives, improvement of occupational safety and health practices in tanneries and effluent treatment plants. Under this objective, the project has been seeking to demonstrate in selected tanneries improvement practices for better occupational health and safety of the workers.

It is hoped that the industry representatives and other concerned with the occupational health and safety of workers in tanneries and effluent treatment plants will find this publication useful.

UNIDO on-line learning How to deal with hydrogen sulphide gas

Confronted with increasing legal and social pressures, no tanner can afford the luxury of not being familiar with the main issues and principles of occupational, safety and health protection pertaining to tannery operations.

Hydrogen sulphide gas present in tanneries and effluent treatment plants has proven fatal to workers exposed to it many times.

It is therefore necessary that the owners and managers of tanneries and effluent treatment plants are fully aware of the dangers posed by this poisonous gas and take all preventive and precautionary measures to protect the workforce from exposure to this gas. In the event of accidental exposure of a worker, they should know how to deal with the situation.

The lessons that follow are to help tanners, tannery managers and operators to acquaint themselves with the basic principles How to deal with hydrogen sulphide gas.

The on-line course developed by UNIDO including test provides an opportunity for the proper training within tanneries related to danger associated with hydrogen sulphide gas. After finishing the test with minimum score 80%, participants will receive the certificate and will be able to download it.

How to enrol into the UNIDO on-line course “ How to deal with hydrogen sulphide gas”?

Follow a link:

Enrolment key: H2Safety


It is hoped that the certificate will be accepted also by Occupational Safety and Health Authorities as a proof that staff was properly trained.

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.

In Chennai and Tamil Nadu/India, which was the basis for demonstration of UNIDO regional projects, circumstances at the time of project (mid 90's) commencement were such that the tanning Industry was under considerable pressure vis-à-vis effluent treatment. As a result several tanneries or clusters had already undertaken investments in primary or secondary effluent treatment. Rather than create a possible redundant model plant, the project strategy was oriented towards demonstration of four full scale model effluent treatment plants representing different aspects of tannery effluent treatment plant in terms of influent, treatment process and size. Thus, the Ranitec CETP with treatment capacity of 4,000 m3/d receiving effluent from 76 tanneries processing from raw to finished and using amongst others an anaerobic treatment system (lagoon) was upgraded to serve as a model for similar treatment plants in the region. The Vishtec CETP with a capacity of 3,400 m3/d of effluent using two stage aerobic treatment system was upgraded (mainly process control) to be a second model site. The President Kid Leather Company ETP, 120 m3/d receiving effluent from semi-finished to finished tanning processes from an isolated was upgraded as a model site (automatic dosing, laboratory). The MHT Company ETP, capacity 100 m3/d, receiving effluent from a traditional isolated vegetable tannery, a low cost anaerobic treatment system, was upgraded and serves as a model for similar units.

Detailed reports describing assisted tannery effluent treatment plants:

i) Common Effluent Treatment Plant, Amburtec, Ambur, India

ii) Common Effluent Treatment Plant, Kolkota, Leather Complex Kolkota, India

iii) Effluent Treatment Plant,  Meera Hussain Tannery, Melvsiharam, India

iv) Common Effluent Treatment Plant, Pallavaram, Chennai, India

v) Common Effluent Treatment Plant, Ranitec, Ranipet, India

vi) Common Effluent Treatment Plant, SIDCO, Ranipet, India

vii) Common Effluent Treatment Plant, VISHTEC, Melvisharam, India

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.

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


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.

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.

Under the Regional Programme for pollution control in the tanning industry in South-East Asia UNIDO has been actively looking for methods to improve conventional treatment processes which simultaneously reduce the nitrogen content and give the possibility of dealing with TDS/chlorides present in the effluent. The following technologies relating to the issues mentioned were implemented in pilot demonstration units:

  •  Mechanical/manual removal of excess salt from wet salted hides and skins
  • Reverse osmosis (RO) of treated tannery effluent
  • Improved solar evaporation
  • Carbon dioxide (CO2) deliming in a small scale tannery to reduce ammonical nitrogen
  • Constructed wet land treatment system (reed beds) possibly resulting in nitrification/denitrification
  • Ultrafiltration

A study with preliminary estimates of costs of multistage evaporation system to recover salt from reject generated by RO has also been prepared.

In another study, the scope of replacement of secondary clarifier in the biological treatment stage by ultrafiltration has been assessed. (Mladen Bosnic, December, 1997).

This report deals specifically with ultrafiltration.