Progress in sustainable technologies of leather wastes valorization as solutions for the circular economy

The tanning industry generates a large amount of waste, which should be managed following the principles of the circular economy . It is estimated that leather processing produces 200 times more waste than total product output. This paper presents a review of the methods that offer recycling of materials or energy from tannery waste , including chemical, thermal and biological techniques. These processes can recover a number of secondary feedstocks such as chromium, nutrients, collagen hydrolysate , fat, biogas , and anaerobic digestate , which can be used in other industrial processes. The review also covers the current legislative status of waste and its impact on the environment. Smart and sustainable valorization technologies enable a high degree of recycling with no burden on the environment.