Continuous ozonation of biologically pretreated molasses fermentation effluents

Abstract

In this work, continuous chemical oxidation processes (single ozonation and ozone combined with hydrogen peroxide) of biologically pretreated wastewaters from a beet molasses fermentation factory have been studied. Oxidation processes were carried out in a stirred tank reactor at the natural pH of the wastewater and 25°C, analyzing the effect of the hydraulic residence time and applied ozone mass flow on color and organic matter removals. Ozone consumption was also measured in each experiment. The results show that continuous ozonation was effective for decolorization of molasses wastewater. Operating with a hydraulic residence time of 45 minutes and an applied ozone mass flow of 1.7 g/h, color and chemical oxygen demand (COD) reductions were about 80% and 14%, respectively. Increasing the hydraulic residence time or ozone mass flow led to a considerably increase in the ozone consumption, with similar color and organic matter reduction percentages. Slightly higher removal percentages were obtained combining ozone with hydrogen peroxide, attaining 83% color reduction and 20% COD removal. As consequence of the oxidation processes, biodegradability of the decolorized effluent increased about 40–50% and the ratio BOD₅/COD was twofold higher.

Keywords:

• Molasses effluents
• Melanoidins
• Continuous ozonation
• Decolorization
• Gel permeation chromatography.

Acknowledgments

The authors acknowledge the financial support of this research to the Ministry of Education of Spain (Research Project AMB99-0940) for its contribution to the development of the project. Mónica Coca also thanks the Ministry of Education for providing her PhD grant.