Sustainable management of waste - reduction of the chromium content of tannery solid waste as a step in the cleaner production of gelatin

Treatment of chrome shavings, a solid waste from the leather industry, by reducing its chromium content was investigated to determine whether it could be used in the production of high value-added products like gelatin. An oxidative dechroming process was used to remove the chromium from the shavings achieving a dechroming ratio of 96%. Thermal behaviour of chrome shavings with different chromium content was studied using DSC analysis, revealing that chromium is responsible for imparting stability to the collagen fibres. Gelatin, with different chemical and mechanical properties, was obtained by thermal and chemical hydrolysis of the collagen fibres using different alkaline hydrolytic agents, such as sodium hydroxide (NaOH) and ammonia (NH3). The denaturation temperature (TD) of the gelatins was found to be 30 ºC and 62 ºC for NaOH and NH3-derived gelatins, respectively. The effect of the chromium content on the physical and thermal properties of gelatin was also investigated, confirming the stabilising role of chromium in the fibres. Gelatin can be used in applications such as encapsulation, binding, adhesive production, film forming or finishing agent in the paper, wood, ink, textile and leather industries. Therefore, this treatment can add value by using a cleaner production pathway to a valuable product extracted from what was previously hazardous waste