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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".

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..

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.

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.

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.

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.

Based on new data and requests from interested users, the revised second edition of the paper Pollutants in tannery effluents was prepared drawing on technical inputs by J. Buljan, I. Král, M. Bosnić, R. Daniels. This training material is primarily intended to meet the needs of tanners and people of different profiles associated with environmental protection in the leather industry in developing countries.

The environment is under increasing pressures from solid and liquid wastes as by-products from leather manufacture and tannery effluent create significant pollution unless there has been a form of treatment before discharge.  The industry has gained a negative image in the society with respect to its pollution potential and therefore the leather processing activity is facing a serious challenge.

The paper presents the main sources of pollution and typical pollution loads generated by tanning processes adopted by the tanneries in developing countries, volume(s) of wastewater discharged, the corresponding concentrations of main pollutants as well as the the table of widely prevailing discharge standards.

In this edition the main pollutants' parameters are elaborated in great detail, together with descriptions of their negative environmental impact. Air pollution and toxicity aspects are expanded and a concise chapter on Substances of Very High Concern, SVHC ( carcinogenic, mutagenic, bioaccumulative, persistent etc.) introduced. One can also find photos of equipment used for laboratory analysis.

For the country-wise overview of discharge standards (admittedly somewhat obsolete) please refer to Part II of the first edition.

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.

The Regulation of the European Union (EU) on Registration, Evaluation, Authorisation and Restriction of Chemicals, REACH entered into force on 1st June 2007. Its proclaimed aims were to ensure a higher level of protection of human health and the environment as well as free movement of substances, on their own, in preparations and in articles, while enhancing competitiveness and innovation.

This Regulation should also promote the development of alternative methods for the assessment of hazards of substances. REACH was also expected to streamline and improve the former legislative framework on chemicals in order to improve the protection of human health and the environment from the risks that can be posed by chemicals, especially by those listed as Substances of Very High Concern (SVHC) The purpose of this desk study was to give some background information and practical advice to the leather industry so as to maintain or establish business in the EU market.

 

Conventional treatment of tannery effluents does not affect the TDS content (colloquially: salinity); they remain unsuitable for lifestock watering or irrigation which, especially in arid areas, represents a great loss of natural resource. This paper reports on successful irrigation trials with treated effluent from a CETP servicing a cluster of tanneries processing wet blue and crust leather into finished leather and with TDS not exceeding 5000 mg/l and chlorides not exceeding 900 mg/l. Eventually a plot of barren land was converted into a pleasant park-like area.This paper, based on the project implemented by a women-only team, provides information on saline resistant plants and assess their growth properties; and the impact that the continuous application of treated effluent had on the soil and ground water.

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