PILOT-PLANT STUDIES ON TANNERY WASTE-WATER TREATMENT WITH THE OBJECTIVE TO REDUCE SLUDGE PRODUCTION

The objective of the work was to verify the possibility to reduce the quantity of the sludge produced during the treatment of chrome tannery waste waters. The modified Ludzack-Ettinger process for high nitrogen content waste waters was tested without a chemical-physical pretreatment, normally adopted to eliminate from the tannery waste waters the compounds potentially inhibitory for biological processes. The results obtained in a pilot plant during 4 runs differing in waste waters flow and strength and in MLSS recycling ratio demonstrate the lack of inhibition of denitrification and nitrification by a high content of sulphides and chromium. In the comparison with traditional treatment of tannery waste waters the 60% reduction of the sludge to be wasted and the improvement of a final effluent quality were achieved. The mean overall rate of COD and N removal was 0.38 mgCOD/mgMLVSSxday and 0.125 mgN/mgMLVSSxday, respectively.