Combined oxidative and biological treatment for separated streams of tannery wastewater

The biological treatment of the tannery wastewater substreams beamhouse (BH, pre-tanning steps) and tan-yard wastewater (TY, tanning, & wet-finishing process steps) and the application of an oxidative treatment by ozone, followed by a second aerobic treatment are investigated. Due to the extremely changing quality of the raw wastewater, esp. TY the biological pre-treatment could not be stabilized all the time and nitrification was sometimes inhibited. Oxidative treatment distinctly improved the aerobic biodegradability of refractory organic compounds and it was found to be optimal in the range of a specific ozone consumption of about 2 g O-3/g DOC0 for both batch experiments and continuous operating conditions. Moreover, full nitrification could be established during the subsequent aerobic degradation and the remaining ammonia was completely removed. Summing up, it can be stated that the combined oxidative and biological treatment of BH and TY was effective and ensures the meeting of given COD and ammonia-limits for the direct discharge of this special industrial wastewater into rivers. (C) 1997 IAWQ. Published by Elsevier Science, Ltd.