Chemical Studies on the Ozonation of Synthetic Glucose-Glycine Melanoidin as Model Color Pollutant


Ma. Desiree A Belina, Donna May I De Roxas, Mary Grace E Guardian, Ernesto J del Rosario
Vol 9 No 1 (2006), pp. 44-59

 

Abstract:

 

Synthetic melanoidin (a model color pollutant) was prepared by heating a aqueous solution of 1.0 M glucose, 1.0 M glycine and 0.5 M sodium carbonate at 121°C for 3 hours. It was dialyzed against distilled water, eluted through a Sephadex G-75 column and then freeze-dried. The kinetics of ozonation of the prepared melanoidin was studied in unbuffered and buffered solutions (pH 3.5, 5.0, 6.5, 7.0, 8.5 and 10). The reaction was found to obey first-order and half-order kinetics based on absorbance data at 475 nm and 280 nm, respectively. After two hours of ozonation, melanoidin decolorization was in the range 64-94%; decolorization was greater at lower pH values. Decolorization of the unbuffered melanoidin solution was 97.2%. Reduction in absorbance at 280 nm generally increased from 31% to 51% as the pH was changed from 10 to 3.5; the value for unbuffered solution was 74.9%. Reduction of MW was 78% and indicated melanoidin depolymerization. The UV-visible spectra of synthetic melanoidin after ozonation showed a decrease in absorbance at 230-280 nm, a shift towards shorter wavelengths of the absorption peak at 300-400 nm and a decrease in absorbance in the visible region. The IR spectra showed the presence of -OH, C=C and C-O groups in both unozonated and ozonated melanoidins. An increase in peak intensity corresponding to the C-O stretch was observed for the ozonated sample. The results showed that ozonation is effective in decolorizing melanoidin.

 

Keywords: decolorization, melanoidin, ozonation, color pollutant


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