Jutta Knoedler uses years of experience as a renowned consultant to explain how far the leather industry has come in terms of water reduction in recent years.
“The tanning industry is one of the main industries with a high water consumption” – this century-old statement can be read in nearly every thesis about water usage in tanneries. But does this indicate the industry has done nothing over the past few decades to reduce the amount of water it uses? Globally, the annual amount of water used across all types of use is 3,893,000 million m3 per year; 70% is used in agriculture, 20% in industry and 10% in domestic use (UN/FAQ/Aquastat). The largest industry use of water is for cooling in thermal power generation. According to 1986 data, tanneries used 0.02% of the total and 0.11% of the industrial consumption (see Panel 1).
Signs of hope
The huge global water use figure does not mean that the world is running out of water; but, critically, the water it is not always available when and where it is needed. Therefore, different areas have different regulations. A high proportion of leather production is now located in developing or low and middle income areas such as China, India and Latin America. It is assumed that the water consumption here is higher than in developed areas.There are various reasons that tanners might want to reduce water consumption: as part of their own quest for sustainable production, due to legal directives, cleaner production demands, customer requirements or to reduce costs. It is possible that tanneries might contribute to water stress by excessively using surface or underground water, applying inefficient techniques or systems or by polluting freshwater sources. It is essential to know the current level of specific water use (2011-2013) and what the tanning industry can do to alleviate water stress. The required, recommended or measured water consumption in tanneries in some of the most important areas of the tannery is summarised in Panel 2. Measurements are mostly from medium and large tanneries. We can see that in the main tanning areas, China and Pakistan allow or recommend 50 m3/t, while most other areas have limitations of between 15 and 29 per tonne of raw hides for the production of finished leather (bovine).
The weighted average of the water amount with specific consumption data for bovine tanneries (raw hide to finished leather) can be calculated to: worldwide average: appr. 250 l/m2 finished leather or appr. 38 m3/ton raw hides (2011-2013) (Panel 3).
The data can be used for the complete tanning process. If a tannery is only part-processing, the benchmark data from the water amount in the three main production steps are given in the BAT-Notes (2013) from the EU and confirmed by measurements in tanneries (Panel 4).
Water management systems
The tanning industry has a complex structure in terms of materials, processes and manufacturing practices. Therefore, every tannery must develop a management system adapted to its specific needs in terms of production and location. However, some general solutions can be reviewed by every tannery and recommendations should be applied in sequence: reduce, reuse, recycle.
• Measure and monitor water use in inflow, effluent, different production areas and equipment.• Understand, calculate and benchmark the water footprint of the tannery.• Use water-efficient production processes such as low float length (for example use 83% instead of 100%), fewer washing processes (check it by conductivity); and use modern drums instead of paddles and pits.• Install water-efficient machines and technology (good drums and machines for splitting, samming).• Use high-pressure cleaners and cleaning machines for floors, drums, equipment. • Reuse and recycle water, for instance washing water, cooling water, split-flow water.- Optimise chemical consumption (no overdosing), use biodegradable chemicals- Reuse water and chemicals (eg sulphides and lime in liming splits)- Split-flow water reuse, instead of recycling final treated mixed water- Have a material-overlapping view for innovative and sustainable treatment technologies for water reuse and recycling. Use methods with low energy consumption, low chemical use, less sludge and lower air emissions. Not all water recycling methods are sustainable.
The most recent data available (2007-2013) shows improvements have taken place in many parts of the industry. The water needed to produce leather from bovine hides has fallen around 37% over the past 25 years from around 60 m3/t to around 38 m3/t. When we include sheep skin, the share of the tanning industry in global water use has fallen from 0.02% to 0.015% and from 0.11% to 0.075% of industrial water consumption.
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