Chemical oxidation combined with biological oxidation in removal of biorefractory compounds

The paper presents the first results of experimental work carried out to investigate the possibility of increasing COD removal efficiency in tannery effluents combining biological and chemical oxidation with ozone. Tannery wastewater has been chosen as a good example of industrial wastewater characterized by a significant content of organic compounds (200-400 mg/L as COD) particularly resistant to biological oxidation. In this study has been utilized the biological stage effluent of a plant treating the wastewater of a large tanning district in Central Italy. An accurate kinetic study of the ozonization reaction has been performed to define the best operating conditions in terms of process efficiency and cost reduction. As regards the biological stage, even if the short period of experimental activity in the biological plants is not sufficient to draw definite conclusions, the first results show that the efficiency obtained treating the ozonated effluent is higher than that obtained with the non ozonated effluent.