Influence of ozonation process on characteristics of pre-alkalized tannery effluents

The effect of ozonation process on characteristics of chromium tanning stage wastewater after pre-alkalization was investigated in terms of the effluent COD and color removals in a bench-scale set-up using a full factorial experimental design. In the pre-alkalization process, about 99%, 60% and 62% removals for chromium, COD and color, respectively, was observed using sodium hydroxide at the optimum pH of 9. Then, ozonation of the pre-alkalized wastewater showed a COD removal from 30% to 70% after 120 min when ozone flow rate increased from 1 to 8 g/h. A proposed model obtained from the statistical analysis for the COD removal predicted the ozone dose of more than 15 g/h is required to the complete COD removal after 120 min at different pH values of the wastewater. Color removals also increased from 40% to 64% at the ozone flow rate of 1 g/h with reducing the initial pH values from 9 to 3. An enhancement to about 85% was then observed in the color removals with increasing the ozone flow rate to 8 g/h regardless of the initial pH values of the wastewater. In the present study, using the zonation of the pre-alkalized tannery wastewater, the COD and color of the effluent reduced about 88% and 93%, respectively. It is concluded that the zonation after pre-alkalization process may be considered as an alternative to the biological system for the tannery wastewater treatment, although further experiments and feasibility analysis are necessary to the potential application of ozonation. (C) 2012 Elsevier B.V. All rights reserved.