Fractionation and characterization of brown colored components in heat treatment liquor of waste sludge

To characterize the colored components in the heat treatment liquor of waste sludge, three distinct liquor samples were fractionated into four fractions (I–IV) by HCl-precipitation and with XAD-7 resin. In all the samples tested fractions III, which were acid-soluble and eluted from the resin with methanol, contained 55–77% of the total color. In one sample fraction I, which was acid-insoluble, also had relatively high color content (22% of the total). Therefore, we defined fractions III and I as main color fractions of the heat treatment liquor. The color of fraction I decreased, but that of fraction III did not decrease during incubation of the liquor with activated sludge. Furthermore, the color of fraction I decreased as that of fraction III increased during the incubation. It was suggested that the colored components in fraction I are converted into the colored components fractionated into fraction III through the biological treatment. Molecular shape of the colored components in fractions I and III were affected by ionic strength: their molecular weight fell in higher ionic strength solvent. The two colored components were degraded with alkaline hydrogen peroxide. Identification of their degradation products revealed that both of them had partially the same chemical structures as the melanoidin pigment synthesized from glucose and glycine, and they had considerable common structures regardless of their presence in different fractions I and III.