Leather/Skin/Hide Processing Industry - Environmental Clearance

Leather / Skin / Hide Processing Industry (Tannery)for commercial use. Discharge of solvents is unavoidable with solvent degreasing, butalternative technologies can be applied for the high quality skin production.On wool-on lambskins, it is a common practice to undertake a dry solvent extractionwhen crusted.The use of non-solvent methods implies the use of higher amounts of surfactants.Ethoxylated fatty alcohols should be recommended instead of the more widely usedethoxylated alkylphenols, because they are more easily degraded and the use of the laterare to be restricted in the EU. The COD from aqueous treatment may amount as much as200,000 milligrams per litre (mg/l), due to the content of natural grease and surfactants (1grams per litre (g/l) of natural grease is about 2,900 mg/l COD, and 1 g/l ethoxylatedalkylphenol is about 2,300 mg/l COD).To ensure complete mobilization, aqueous degreasing would, ideally, be carried out at atemperature above the melting point of the grease. However, the melting point of thegrease is normally very close to the shrinkage temperature of the skin. For example, themelting point of sheepskin grease is approximately 42°C, whereas the shrinkagetemperature of sheepskin pickled pelt is approximately 50°C. Therefore, the risk of heatdamage to the pelt precludes the use of temperatures above the melting point of thegrease. The grease may also be contained within lipocytes, further limiting its dispersal.The aqueous degreasing of pigskins may be assisted by the use of proteolytic enzymes todegrade the lipocyte and, thus, mobilize the grease. However, this may not be possible forsheepskins where the fibre structure is more susceptible to the proteolytic activity of theenzyme.p) Wet-white pre-tanningThe rationale behind this notion is to pre-tan or pre-treat the hide, in order to be able tosplit and shave prior to chrome tanning, so that less tanned waste is created. The rationaleis to confer resistance to the frictional heating of the pelt surface during shaving. Ideally,the pre-treatment should be reversible, so that chrome tanning is conducted on unchangedpelt.This process, can be considered as a cleaner technology if the chemicals used are neithertoxic nor cause adverse environmental impact. Aluminum (III), titanium (IV) andzirconium (IV) have been suggested for this role. They are not listed as hazardous,although restricted in several countries, but their degree of reversibility depends on howthey have been applied. Aldehydic tanning agents can be considered as leading to acleaner process, according to local regulations, but their reactions are completelyirreversible, so contribute to a different character in the leather. Syntans are an option,because their action is more reversible.The alternative approach is to change the properties of the pelt, to make it less prone todistort when the surface is struck by the shaving blade. This can be achieved by reducingthe ability of the fibre structure to slip over itself: this is best achieved with hydratedsilica, used in the fabric industry for the same purpose. Silica interacts weakly withcollagen, in a non-tanning manner, and the effect can be reversed: any discharged silicahas negligible environmental impact.TGM for Tanneries August 20103-18