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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".

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.

Utilization or safe disposal of sludge generated by tannery effluent treatment plants poses a challenge worldwide; landfill disposal should be considered only in case when no other viable option is possible.  Unfortunately, in some areas and/or developing countries properly designed and constructed landfills are not available either.
With the technical assistance of UNIDO, CETP-Ranitec in Ranipet, Tamil Nadu, India, established a low cost pilot scale demonstration landfill in October 1997, the first of its kind in the region. The report describes requirements for a safe landfill disposal and practical recommendations for replication.

Reliable on- and/or off-line monitoring is essential for ensuring good performance of any effluent treatment plant; specific analysis are conducted either within the existing tannery process and quality control laboratory or (in the case of larger plants and certainly Common Efflent Treatment Plants, CETPs) in speicialized laboratories.

This manual (originally prepared in French and tranlated into English, Chinese and Spanish) provides a rather detailed overview of analysis, methods and equipment needed to conduct the main (C)ETP peformance tests. Suggestions about the type and frequencies of analysis are also given. Given the fact that the manual was prepared in 1994 it is highly recommendable to get acquainted with changes in procedures and equipment that took place since then.

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