Color removal of melanoidin-rich industrial effluent by natural manganese oxides

• Effective removal of color and COD by natural manganese oxides.
• More removal of color than that of DOC.
• The kinetics of color removal showed a strong pH dependence.
• Removal mechanisms may include chemical transformation, precipitation, and adsorption.

Melanoidin-rich industrial effluents, e.g. from coffee extraction plants and molasses distilleries, can cause potential environmental problems due to the high content of remnant dissolved organic carbon and dark color. It mainly consists of melanoidins and other organic colorants, which are recalcitrant to biological treatment. The current study was aimed to develop a polishing step after anaerobic digestion for the colorant elimination from melanoidin-rich wastewater (molasses distillery wastewater, MDW) using natural manganese oxides. Anaerobically digested MDW was used to test the removal of organic contents and color at different pH values. It was observed that the kinetics of colorant elimination was best described by the second order equation, with a significant dependence on pH. Furthermore, the liquid chromatography with organic carbon detection was applied to analyze the changes in molecular composition during the reaction. There was a preferential removal of low weight melanoidin molecules over higher weight molecules.

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