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Sustainability

  • UNIDO Solar Water Heating - Ayuub Brothers, Hazaribagh, Dhaka, Bangladesh
  • UNIDO Solar Water Heating
  • UNIDO leather Screen - Hair saving liming technology

Sustainable and cleaner production technolgies is an efficient method of preventing or minimizing pollution caused by industrial activities. UNIDO continues to place an emphasis on the introduction of cleaner leather processing technology in developing countries. The primary task of all cleaner technologies is to reduce the amount pollution emissions; and where possible change the nature of pollution emissions to reduce the pressure and costs of end-of-pipe treatment. The expected results primarily include:

  • Lower water consumption – better preservation of rapidly diminishing water resources.
  • Lower total dissolved solids (TDS) content (including salinity) – lower risk of affecting the usability of the receiving water bodies for irrigation and livestock watering.
  • Avoidance of use in processing and/or presence in leather of substances from the Restricted Substances Lists (RSL) promulgated by national or regional legislation, leading (multinational) brands and/or ecolabel due to their proven negative impact on human health and eco-systems.               
  • Proportionally higher volume of solid wastes suitable for processing into saleable by-products.
  • Lower levels of BOD, COD and Nitrogen; their respective contents in conformity with local and widely prevailing legislative norms.
  • Low level of chromium in (C)ETP sludge – the scope for land application and/or composting.
  • Lower hazardous and/or unpleasant air emissions.
  • Appropriate occupational health and safety (OSH) standards – better work conditions, fewer accidents.

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.

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.

Processing of one tonne of raw hides results in approximately 100 kg of wetblue shavings, the utilization and/or safe disposal of which is globally a serious challenge. Currently a part of the chrome shavings is used in the manufacture of leather board by combining with shavings of vegetable tanned leather. There have been also other methods tested and used to convert shavings into sellable product, e.g. application in paper, wood and other industries.

The method described in this report is enzymatic digestion.

Conversion of chrome shavings into usable products employing the technique of enzymatic digestion as developed in the United States of America and already implemented in a 3 tonnes/day commercial plant in the Czech Republic. Three products, namely, gelatable protein, protein hydrolyzate and filter cake are obtained from enzymatic digestion of chrome shavings. While the products obtained find use in construction and plywood industry and also as nitrogenous fertilizer, the chrome-containing filter cake can be used as a reducing agent in the preparation of basic chromium sulphate.

The method was successfully demonstrated at pilot scale in India using wooden tanning drums.

Generally 35-60% of the total solids in tannery sludge is organic matter. A number of solutions for utilization and/or safe disposal of tannery sludge have been proposed, practiced, tested and applied at pilot and industrial scale. Composting is one of these options and this report describes results of tests and application of sludge composting on low, non-mechanized scale together with its utilization as soil conditioner for nonedible plants.

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

Due to climatic conditions the scope for green processing is limited in many countries, sodium chloride is widely used to preserve raw hides and skins. It contributes to a high volume of total dissolved solids (TDS) in the soak waste liquor. No commercially viable technology for treating effluent has been developed to date. A large amount of the salt sticking to the hide and skin surface can be removed by shaking the hides mechanically or manually.
Within the framework of the UNIDO regional programme for pollution control in the tanning industry in South-East Asia, a pilot demonstration unit was set up to demonstrate different options for

(a) desalting hides and skins prior to soaking and

(b) reusing dusted salt in the pickling operation after purifying the salt recovered.

This report covers the demonstrations carried out during the period January 1997 to February 2001 of desalting of salted raw stock and use of the recovered salt in pickling.

The Technology package "A System for Recovery and Reuse of Chromium From Spent Tanning Liquor Using Magnesium Oxide and Sulphuric Acid" provides practical overview of the chrome recovery process including equipment specification.

This study is primarily focused on the pollution load discharged in effluents and the scope for decreasing that load. In addition to knowing how to produce and sell high quality leather, tanners must also be familiar with techniques for decreasing the pollution load discharged in effluents from individual processing operations. The study aims at heightening tanners’ awareness of those techniques. It calculates the decreases possible in a well-managed tannery processing bovine hides into chrome tanned leathers and describes how pollution load can be reduced by introducing advanced technologies based on low-waste processing methods that have been proven on an industrial scale will be taken into account. The study does not consider industrially unproven and purely experimental methods.

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.

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