INFRARED SPECTROSCOPIC CHARACTERIZATION OF SEWAGE-SLUDGE HUMIC ACIDS - EVIDENCE OF SLUDGE ORGANIC MATTER-METAL INTERACTIONS

Infrared studies were conducted to characterize qualitatively aerobic and anaerobic sewage sludge humic acids (HA). These HA, formed during a short period of transformation by a technological process, were compared with a humic acid (from leonardite) formed by a natural process. Infrared spectra of HA precipitated at Ph of 2 revealed that compared to leonardite sludge HA had a higher content of N-compounds and polysaccharide-like materials as well as higher aliphatic chain content and a lower proportion of carboxyl groups. The shifts observed in the spectra after addition of Na+, Ca2+, Mn2+ and Zn2+ to the HA solutions indicated the formation of carboxylate groups with some covalent character.