Abstract
The tanning of hides is a traditional and important sector of Italian industry. Recovery operations of raw materials and energy in this sector range from operations which have been tested through years of industrial practice to experimental initiatives with promising prospects. One of the most interesting forms is the recovery of chrome from exhausted tanning baths: this process allows cost saving of up to 50% and is about to be applied in a large centralized plant at S. Croce Valdarno in Tuscany. Another operation is the recovery of sodium sulphide from the lime pit bath, carried out by means of ultrafiltration, Energy can be recovered with the anaerobic digestion of chrome-free tanning sludges (mixed with pulverized shreds): the yield in biogas can be comparable with that obtained with domestic sludges. The composting technique can be applied to digested tanning sludge and shreds, in some cases mixed with pre-sorted domestic waste.
All the processes described have the important effect of reducing the pollution load connected with liquid and solid wastes from the tanning industry, as well as the recovery of economical resources.
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