RELIEF: Reducing Environmental impact of the Leather-tanning Industry with Electron beam Facilities

Leather production is a vital contributor to the economy in many Official Development Assistance (ODA) recipient countries, such as Mexico. The Guanajuato region in central Mexico is home to approximately 350 tanneries, which have caused a substantial impact to the local environment, resulting in widespread pollution of water supplies and poisoning of the ecosystem. While regulations have been implemented to attempt to limit pollution produced by the tanning industry, these are rarely enforced and do little to improve the local environment.

The leather production process consists of many different stages, starting with the curing stage to preserve the animal skins while they are transported between the slaughterhouse and the tannery. The hides then undergo several steps, collectively known as the beamhouse operations, to prepare the hides for the tanning stage. Tanning is a process whereby chemicals are used to create crosslinking between protein chains in the processed hide (collagen). This crosslinking is caused by the tanning agent, such as Chromium(III) Sulphate, which chemically bonds to the protein chains. These crosslinks make the leather more durable and less prone to damage from mould and bacteria than the original hide. The tanning process is very similar to the process used to industrially manufacture plastic, where an electron beam is used to create crosslinking between long-chain hydrocarbons to make the material more durable.

The tanning stage is considered to be the most significant cause of pollution with the largest impact on the local environment. The unused Chromium(III) is often disposed of as wastewater, which then gets into the local ecosystem. We propose to replace the conventional tanning stage with an electron beam facility to create crosslinking in the leather with an electron beam, in the same way as electron beams are used to create crosslinking in plastics. An additional organic chemical, such as an aldehyde or acrylate, will be used to create the "bridges" between protein chains.

In this project, we will study the effect of an electron beam on a biological sample to estimate the maximum irradiation dose before the damage to the protein chains outweighs the strengthening of the leather from crosslinking. We will investigate potential reagents for the bridging between protein chains, focussing on reagents with minimal environmental impact. A study of the requirements of an electron beam facility from the perspective of the tanneries will be undertaken in Mexico and this study will also look to identify other industries that would benefit from such as device. The outcome of this study will be used to undertake an initial design study of the electron accelerating structure and the beam transport line. This will investigate options such as whether to use a stationary, wide beam or a small beam that scans across the leather.

This project is an initial study to demonstrate the feasibility of an electron beam leather tanning process and to identify the most likely design options for a final product. This will include an initial study of the impact of an electron beam on biological material, a basic study of the likely chemical process required for electron beam tanning, and the initial design study of a final product.

The leather production industry is a global market worth an estimated £80 billion. Many of the largest leather producing countries are on the DAC list of ODA recipient countries, such as Mexico, Brazil, China, Argentina, India and Pakistan. In many of these countries, environmental protection and industrial emissions laws are either non-existent or rarely enforced; resulting in a detrimental impact on the local environment due to the high toxicity of wastewater produced by many of the stages in the leather production process. For this proposal, we currently focus on the region near Leon, Mexico, but the research will have potential benefit all leather producing countries. The biggest benefit will be for countries where leather production causes a severe impact on the local environment and particularly for the larger leather producing countries. For other leather producing countries, where harmful waste products are disposed of responsibly or reused, the research undertaken in this project may also be of benefit by providing a cleaner method of leather tanning; however the commercial viability for such countries will be studied during the proposed work.

During the proposed work, we will aim to determine other industries that may benefit from the technology, particularly where an electron beam can be used to replace a process to reduce the impact to the environment, such as treatment of wastewater and flue gases.