Fractionation and characterization of dissolved organic matter derived from sewage sludge and composted sludge

Dissolved organic matter(DOM) is an important component affecting the avail ability of heavy metals in sludge-amended soils. In this study, DOM derived from anaerobically digested dewatered sludge and sludge compost were fract ionated by a macroreticular exchange resin and characterized by Fourier Tra nsform-Infrared spectroscopy (FT-IR) technique to evaluate their potential effects on soil metal mobility. The acid fractions of DOM sludge and sludge compost respectively were 78% and 73%, which included hydrophilic (HiA) an d hydrophobic (HoA) adds. The hydrophobic fraction of DOM increased during composting, with the hydrophobic neutral (HoN) and HoA increasing from <1 t o 22% and from 38 to 52%. respectively. The relative amount of each compone nt in the hydrophilic fraction of DOM was as follows: hydrophilic add (HiA) >> hydrophilic base (Hig) > hydrophilic neutral (HiN). The HiA, HiB, and H iN fraction of the sludge DOM was 1.9, 6.7, and 2.2 times higher than the r espective fractions of the sludge compost DOM. The FT-IR spectrum shows tha t the hydrophobic fraction had considerably higher aromatic acids or aromat ic phenols, while the hydrophilic fraction was richer in carboxyl and polyh ydroxyl groups. Sludge DOM appeared to have more C-N and C-O ligand charact er, possibly from organic acid, amino add, and amines than compost DOM, esp ecially for the HiA, HiB, and HoA fractions. Since the hydrophilic fraction of sewage sludge was higher than that of sludge compost, the addition of s avage sludge would likely have a higher ability in reducing the trace metal adsorption capacity of soils as compared to that of sludge compost.