In previous articles, we’ve talked about the way that water management in modern tanneries aligns the UN’s Sustainable Development Goal on water. Most European tanneries had already various working methods in place that helped them reduce their water consumption. But on the whole, we can’t do without water so it’s all about how it is sourced, treated and returned.

Blue, green or gray water?

Water is sourced from various origins, and industrial applications very rarely use any of our drinking water. There are three types of water that can be sourced for the leather making process:

  • Blue water – clean water drawn from service providers, rivers, lakes and groundwater
  • Green water – rainwater or water collected through evaporation (not part of surface or groundwater)
  •  Gray water – water recovered from domestic use, containing mild pollutants (excluding sewage)

Mapping the sourcing of water is important to get an idea of the water impact of production. For example, a kilogram of beef uses 15 thousand liters of water to produce. Of this, on average, 93% is green, 4% blue and 3% grey (Mekonnen & Hoekstra, 2010). Sourcing varies wildly depending on which part of the world you are in and what the locally available resources are, and that says a lot about the sustainability of practices and their overall impact on the environment and human welfare.

Currently, there are at least 17 nations facing extreme water stress (Hofste et al, 2019) and the UN recognizes the urgency of efforts towards the water quality SDG. Yet, the SDGs form a network and efforts often have a knock-on effect. A good example are SDGs related to food production (SDG goal 2: Zero Hunger). Food production relies on agriculture and industrial processes, that need copious amounts of water. Efforts on one goal can negatively affect the other, which forms a significant challenge.

The water footprint of leather

Since leather is a by-product of the meat industry, the water footprint is relevant. Product category rules have determined that animal rearing and agriculture water-use should not be allocated to leather completely (here follow the leather PEFCR (Product Environmental Footprint Category Rules), which state a 3,5% allocation). Regardless, in the public eye, the water footprint of meat will be connected leather as well. But how much does the water footprint actually tell us about the sustainability of leather production?

There’s a correlation between a tannery water footprint, carbon footprint and energy footprint though there are many influencing factors such as on-site recycling, renewables, and so on. Two tanneries could have the same water and energy consumption, but have completely different carbon footprints. Comparative research found that tanners with a high-water footprint often have a low energy footprint and vice versa (Laurenti et al, 2016). There are tanneries who manage to lower both, but it serves to indicate the complexity of environmental stewardship. Really assessing the sustainability of leather based on water usage alone is therefore risky.

Water is sourced from various origins, and industrial applications very rarely use any of our drinking water.

Reduce, reuse and recycle

No drop of water is wasted in European tanneries and nothing re-enters surface water bodies without extensive purification. Most tanneries go a lot further though and water leaves their processes even cleaner than it came in or is used in circular processes. EU-wide, extensive systems monitor and reduce water consumption and continuous improvement helps reduce consumption. In Italy and other parts of the world, tanneries are clustered together and directly connected to treatment plants to complete the process of returning clean and healthy water: a textbook example of industry collaboration driven by a shared commitment to environmental sustainability.

Below are many of the best practice adopted by modern tanneries to minimize their water footprint and protect their local water resource:

  1. They reduce water consumption with smarter processes, economic water use and integrated processes (combined process steps), with more efficient chemical use. UNIDO (2011) reports much water can be wasted, and reducing water waste also involves reducing the amount of solid waste in the water itself with filtration and waste processing solutions.
  2. They reuse water in second or even third batches to optimally use the active agents in the water. Sustainable chemical solutions can play a major part in realizing this with biodegradable and fossil/petroleum-free base materials. The more effectively chemicals bind and degrade, the easier it is to reuse or discharge wastewater.
  3. They recycle water sources by working towards closed loop systems with integrated on site filtration and effective waste disposal and processing. Reclaiming chemicals fits the same mold which many tanneries already do.

Innovations in tanning technologies (chemical and mechanic) and water management play a major role in increasing the water footprint. The challenge is developing a tailored management system that fits a tanners’ unique mix of materials, processes and practices. Monitoring and measuring water inflow and effluent helps get a better grip on water usage. In this way, tanneries can help contribute to cleaner surface waters. Excellent purification facilities and performance make a world of difference. A few examples of innovative methods for water purification include:

Primary treatment (effluent wastewater)

  • Gravitational settling allows heavy solids to fall out of the solution and settle at the bottom of the water as sludge, which is easily removed.
  • Skimming is the physical act of removing fats on the surface of the water, preventing them from remaining part of the effluent.
  • Secondary treatment (partly-cleaned wastewater)
  • Anaerobic digestors break down the organic content in the waste water in an absence of oxygen.
  • Chemical flocculation helps produce a sludge and make chemicals reusable without the use of biological sources.
  • Filtration is done by using a membrane and machines to remove pollutants. This is a physical means of treatment.
  • Tertiary treatment (clean water)
  • Trickle beds let the water flow over rocks covered with microbes that scrub out the pollutants.
  • Reed beds have plant roots into the wastewater stream, which are able to absorb pollutants and clean the water.

Each tannery (or effluent treatment plant) will have a range of these technologies as well as others, selected to produce the best results for their particular requirements. The result for European Tanneries is water discharged that meets the EU Industrial Emissions Directive (often exceeding it, a source of pride for tanners). So what is next?

The next frontier: a better water footprint

The water footprint is currently calculated using ISO 14046. This standard only covers direct water use, where indirect water use (virtual water, that is used in indirect processes like the cattle rearing) could tell us much about the full impact of a process. Part of it is in the allocation in the PEFCR, which is a step forward for transparency. Secondly, the water footprint is directly connected to the ecological, energy and carbon footprint. An integrated, holistic approach is necessary to fully comprehend the impact of tanners, so we get the full picture and not isolated effects. That way, we can truly reduce the environmental footprint. .

Selected source material:

  • Buljan, J., Král, I. (2019) The framework for sustainable leather manufacture (second edition). UNIDO. Retrieved from: Leather Panel. [Accessed on 30 July 2020]
  • Water Footprint Network. What is a water footprint? Retrieved from: Water Footprint. [Accessed on 8 July 2020]
  • Mekonnen, M.M., Hoekstra, A.Y. (2010) The green, blue and grey water footprint of farm animals and animal products, Value of Water Research Report Series No. 48, UNESCO-IHE, Delft, the Netherlands. Retrieved from: Water Footprint. [Accessed on 8 July 2020]
  • Mekonnen, M.M., Hoekstra, A.Y. (2012) A Global Assessment of the Water Footprint of Farm Animal Products. Retrieved from: Water Footprint. [Accessed on 8 July 2020]
  • Laurenti, R., Redwood, M., Puig, R., Frostell, B. (2016) Measuring the environmental footprint of Leather Processing Techniques. Journal of Industrial Ecology. Retrieved from: Research Gate. [Accessed on 8 July 2020]
  • Hofste, R.W., Reig, P., Schiefer, L. (2019) 17 Countries, Home to One-Quarter of the World’s Population, Face Extremely High Water Stress. World Resources Institute. Retrieved from: World Resources Institute. [Accessed on 13 July 2020]
  • UN (2020) Press Release: United Nations Launches framework to speed up progress on water and sanitation goal. Retrieved from: UN Sustainable Development. [Accessed on 13 July 2020]
  • UNIDO (2011) Introduction to the treatment of tannery effluents. Retrieved from: UNIDO. [Accessed on 13 July 2020]
  • White, C., McNeillis, P., Mathews, R., Chapagain, A., (2014) Energising the drops: Towards a holistic approach to carbon & water footprint assessment. Retrieved from: Water Footprint. [Accessed on 13 July 2020]

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