Background Context: Tanneries are infamous for being the leading cause of environmental pollution within the leather industry. Tanning 1 kg of leather uses up to 2.5 kg of chemical substances, 250 liters of water and generates 6.1 kg of solid waste. This, however, was not always the case. The earliest form of tanning used for preserving animal hides was vegetable tanning. Even the word tanning comes from the substance used originally for the process, namely tannin, a natural substance found in tree bark, leaves, and fruits. While vegetable tanning produces leather of high quality, the activity is time-consuming, taking months for the process to be completed. Due to this disadvantage, mass production of leather implies chromium tanning has become the most popular tanning process for most large manufacturers.
Flaws in Chromium Tanning Stars: Chromium tanning can be completed within 24 hours and has several other merits over vegetable tanning on the final leather product's properties, like water resistance. However, there has been evidence of its severe effects on the environment and on the people working in tanneries. Chrome (III) salts like chromium sulfate are used in the tanning baths in which the animal hide/skin is submerged to get the tanned leather. However, during the tanning process, the Chromium (III) gets converted into Chromium (VI), a known carcinogenic and allergen. This leads to the importance of safety precautions and wastewater treatment plants.
Innovation Spotlight: Environmental regulations are becoming more stringent and there is a continuous spotlight on the polluting nature of tanneries, most leather manufacturing companies are investing in research developing innovative tanning methods that would give the same efficiencies as the chrome tanning process without its cons. This has resulted in over 2000 patented inventions in the last decade related to tanning methods and their process improvement.
Upcoming solution from early-stage companies’ & universities: #TanneriesInnovation
Vegetable/Zeolite Tanning: There has been an increased focus on bringing vegetable tanning back to the forefront of mass leather production. One of the start-ups doing this is Deepmellow Leather, which has developed a product named rhubarb leather. The German start-up uses the rhubarb plant for extracting a unique tannin extract which is used in vegetable tanning. The rhubarb plant has a high regrowth rate, reducing the possible environmental consequences in comparison to the impact of mining chromium from the earth. The company is also a member of IVN (International Association of Natural Textiles), a group that has one of the strictest guidelines for leather production.
For chrome-free high-performance leather production, the China Leather & Footwear Research Institute has researched the use of biomass-based polymeric dyes in dyeing biomass-derived aldehyde-tanned leather which is biodegradable.
Zeolites have also started gaining traction as tanning agents. Nera Tanning uses a zeolite-based tanning agent under the brand name Zeology. This patented technology is a modified form of zeolite that has properties like water absorption without swelling of the material. The leather shavings from this process have good biodegradability.
University of Craiova, Romania, has researched using Oxidized Alginate as a biodegradable tanning agent, which is a metal, aldehyde, and phenol-free process. The tanned leather using Oxidized Alginate is biodegradable and has properties like commercial leather.
Metal-free Tanning: German start-up that has developed a unique tanning solution is Schill+Seilacher. They have developed a metal-free tanning process using Triose sugar from vegetable oil waste streams to create pre-tannage and tannage that is biodegradable and renewable.
Waterless Tanning: The primary reason why Chromium tanning is harmful to the environment is due to the low uptake of 60-70%, and the remaining 30-40% Chromium is washed along with the water and released as effluent. This has led to the development of waterless methods of chromium tanning to preclude wastewater completely. Ecco Leather developed a hybrid tanning method for their in-house tannery by consuming 50% less chrome. The company boasts of a unique waterless organic tanning method called Dritan, a method that produces no solid waste or wastewater. Dritan tanning process emits 34% less emission in comparison to traditional chrome tanning.
CSIR, an Indian research institute, has also developed a waterless chrome tanning process, eliminating the need for pickling and basification steps. There is no impact on quality compared to conventionally processed chrome-tanned leather and since there is no discharge of wastewater, the technology can bring about cost savings.
However, even if through waterless tanning an uptake of 100% is achieved, there is still the risk of chromium being released into the environment when the leather is disposed of. There is also the non-biodegradability of chrome-tanned leather to be considered. Therefore, there is a need for chrome-free tanning processes to be developed that produce biodegradable leather.
What's Next: Companies are striving to become more environmentally conscious, but face challenges, especially in top leather-producing countries like Brazil, China, and India, where weak regulations, cost constraints, and lack of industrial sophistication hinder progress. Despite these challenges, growing awareness of the harmful effects of chemical effluents is driving tanneries to urgently adopt sustainable practices, necessitating a deep understanding of tanning research and the swift implementation of innovative solutions.