Leather Industry, Degreasing

In the degreasing step, fats and grease are removed from the interfibrillary spaces with the use of lipases, detergents, or solvents in order to allow the penetration of various tanning materials and dyes. This operation is necessary especially for sheepskins where the percentage of fat substances on raw weight is of about 30-40 %. Enzymatic degreasing is a better way of carrying out degreasing than the use of solvents and detergents. Lipases are much safer and less toxic to workers and the environment. Ultrafiltration (UF) can be used to treat the exhausted bath from the degreasing operation in order to recover surfactants in the permeate stream which can be recycled to the degreasing step leading to a reduction in raw material costs. Fat substances removed from the skins can be concentrated in the retentate stream and reused, after physical and chemical treatments, in the fat liquoring step with significant reduction of the wastewater treatment costs (Koltuniewicz 2010). In another approach the UF process can be combined to an enzymatic degreasing step (Fig. 1) with a continuous recycling of the permeate stream in the drum (Cassano et al. 1998). The proposed methodology permits to obtain a high removal efficiency of fatty substances from the degreasing bath and a reduction of washing cycles normally mployed to remove the lipidic substances from skins and, consequently, of water consumption. Polysulfone membranes with molecular weight cutoff of 20 kDa, in spiral-wound configuration, exhibited rejections toward chemical oxygen demand (COD) and fat substances higher than 97 %.