Abstract

The research was aimed at the decrease of sewage salinity. The aim was to be achieved by means of recirculation, i.e., technological reuse of chromium-free pickling/tanning baths (supernatant). Supernatant was used in pickling/tanning process of hides. Before the subsequent use chlorides were supplemented. In the paper the number of technological cycles that can be carried out without any damage to the quality of hides has been determined. The results have been compared with results achieved in traditional technology, without the use of recirculation.

After subsequent recirculation cycles, the supernatant was assessed by the following factors: chlorides, sulphates, general chromium, Kiejdahl general nitrogen, organic nitrogen, chemical oxygen demand (COD), 5- day biological oxygen demand (BOD5). The quality of hides was assessed in wet blue and crust semi-finished products.

It has been found that supernatant recirculation in chromium pickling/tanning of hides is fully possible and it does not lower the quality of hides. After eight recirculations the general consumption of sodium chloride decreased by about 45% compared with the amount used in traditional hide pickling process.