Leather Industry, Soaking

In this operation, raw skins are exposed to water and chemicals (small quantities of imbibing substances) in order to hydrate proteins and fibers, to solubilize the denatured proteins, and to eliminate salt compounds with dirt (blood, excrement, earth) which are attached to the skins. The soaking-exhausted effluent-containing excrements, salts, and chemical additives are normally discharged into a water-treatment plant (Sharphouse 1983). UF membranes can be used to concentrate organic components in the feed tank of the UF plant. A clear permeate, enriched in salt compounds, could be reused in the pickling step after adjustment of the salt concentration with NaCl (Fig. 1). Preliminary treatments are necessary in order to remove the suspended materials; a sedimentation step allows to reduce the suspended solids of 90 %; then steel spring filters (200-300 mm net size) could be employed to remove large particles avoiding clogging phenomena of UF membranes (Cassano et al. 2001).