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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".

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

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