The manufacture of high quality leather goods results in an almost equal weight of solid tannery waste. The U.S. leather industry generates more than 50,000 metric tons of shavings and trimmings each year; the world-wide total is about ten times as much. This solid tannery waste consists largely of collagen crosslinked with chromium. Although some shavings are used in the manufacture of leather-board, most at present still go into land disposal. Reduced industrial demand and escalating landfill costs prompted us to look for alternative uses for this waste material. Several years ago, we demonstrated the feasibility of using enzymes as part of a process to detan this chromium-protein complex and isolate inorganic chromium salts and partially hydrolyzed collagen. In this process, the collagen was digested to small peptides useful as constituents of fertilizer or animal feed. A more recently developed two-step process treats the chrome shavings first under mild alkaline conditions to produce a high molecular weight gelable protein fraction for value-added production of gels, adhesives and films. The remaining sludge is then treated with an enzyme as a step in a process to recover the chromium and smaller peptides. A sample of potential uses for the isolated products is included.
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