COMPARATIVE CHEMICAL AND SPECTROSCOPIC CHARACTERIZATION OF HUMIC ACIDS FROM SEWAGE SLUDGES AND SLUDGE-AMENDED SOILS

Abstract

The main objectives of the present work were to evaluate the compositional and functional differences between a sewage sludge humic acid (HA) and nonamended soil HA and to determine the effects of various sewage sludge amendments on the composition, structure, and chemical properties of HAs from uncultivated and cultivated soils. For this purpose, the HA fraction was isolated by conventional methods from a sewage sludge used as soil amendment, the nonamended soil, and soils amended with two rates of dewatered and liquid sludges, either in the presence or absence of barley. The HAs isolated were characterized comparatively for their compositional, structural, and chemical properties by use of elemental analysis and by Fourier Transform infrared (FT IR), fluorescence, and electron spin resonance spectroscopies. The sludge HA was predominantly aliphatic and, therefore, markedly different from the nonamended soil HA and was characterized by a low oxygenated functional group content, high contents of S- and N-containing groups and polysaccharide components, very low free radical concentration, high molecular heterogeneity, low ring polycondensation and polymerization, and low humification degree. The application of the dewatered sludge induced only limited modifications in the structural and chemical properties of HAs from amended soils, which were only partially affected by the amendment rate used. However, marked modifications of HAs did occur in soils amended with liquid sludge, especially at high rates. The absence or presence of barley cultivation did not show any measurable effect on the composition and properties of sludge-amended soil HAs.