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Systematic analysis of material fluxes at tanneries

Abstract:

The process of transforming animal skin to leather is characterised by a large consumption of fresh water and the generation of a high quantity of solid waste. As a consequence of the high water consumption tanneries are responsible for a huge quantity of waste water containing chromium, suphide and/or organic matter. In developing countries where treatment of solid waste and waste water treatment is not state of the art, tanneries cause a serious negative environment impact. Systemising the material fluxes at a tannery in order to provide rules of thumb for estimating their impact and developing pollution prevention opportunities is difficult. Nonetheless such an attempt is made in this paper. The data deriving from input/output-analyses which were carried out at 5 different tanneries (3 Chilean, 1 Spanish and 1 Ecuadorian) were concentrated to generalised material streams of two idealised tanning processes. Scenario 1 is a conventional chromium-tanning process with the splitting stage in the beamhouse and paddle technology in the beamhouse. To transform 1 ton of wet salted hides (all data in this paper are based on 1 ttwsII) into 500kg product (grain- and split-leather and wet-blue) 63m3 of fresh water and 442 kg of chemicals are required. 58 m3 of effluent and 696 kg of solid waste are generated. Scenario 2 describes a chromium-tanning process with splitting in the tanyard (wet-blue stage) and drum technology applied in the beamhouse. By these two changes the water consumption and solid waste generation could be reduced significantly. Per ton wet salted hides, 55 m3 fresh water and 442 kg chemicals are consumed. 50 m3 of waste water and 477 kg solid waste are generated. At each tannery a high potential for reducing water consumption and solid waste generation was detected. However, the figures presented in this paper describe the prevailing situation at most tanneries; Implementation of the pollution prevention and recycling measures suggested by the INCO-DC "EILT" working groups will still take time and will depend on the impact of legal restrictions and an active interest in reducing environmental impact.