Leather Industry

In the leather industry, the animal rawhide is converted into finished leather, a durable and flexible material, through a series of chemical and mechanical treatments. The steps in the production of leather between curing (a salt treatment to prevent putrefaction of the collagen) and tanning (a treatment of leather stabilization with vegetable or mineral substances) are collectively referred to as beamhouse operations. They include, in order, soaking, unhairing/liming, deliming/bating, and pickling. All these processes are realized in chemical reactors (tumblers) in which the skins react with different chemicals (acids, alkalis, chromium salts, tannins, solvents, sulfides, dyes, auxiliaries, etc.) in aqueous solutions (Fig. 1). Wastewaters coming from different tanning operations contain high concentrations of organic and inorganic substances causing significant pollution phenomena. Organic pollutants come from the skins (it is calculated that the raw skin has 30 % loss of organic material during the working cycle), or they are introduced during the working cycle (e.g., tanning). Inorganic pollutants are a residual of the used chemicals (i.e., chromium salts) that are not completely fixed by the skins owing to the low efficiency of the operations (Cassano et al. 2001).