Leather Industry, Deliming-Bating

The deliming step is carried out to reduce the excess of liming agents used in the previous unhairing operation by using acids and/or acidic salts. Since the pH must be slowly lowered, ammonium salts are commonly used for this purpose. In the bating operation, skins are treated with proteolytic enzymes in order to open the fibrous structure of skins, increasing their softness. Generally, deliming and bating operations are performed in the same drum. Wastewaters from these operations are characterized by high nitrogen content, coming from both the hide structure and from the ammonium sulfate used as chemical auxiliary. In order to reduce the nitrogen concentration in the deliming/bating exhausted bath, the replacement of ammonium salts by carbon dioxide (CO2) and the reuse of wastewater and chemicals after membrane filtration (MF or UF) of the exhausted liquor has been proposed (Gallego-Molina et al. 2013). MF or UF membranes lead to a remarkable reduction of COD and fat substances of the exhausted liquor (Cassano et al. 2001). The permeate solution can be reused for the preparation of new bating baths or as washing water (Fig. 1), providing environmental and economic benefits due to the water consumption reduction and the reduction in nitrogen and salt discharge.