Organic radicals and paramagnetic metal complexes in municipal solid wastecomposts. An EPR and chemical study

The physicochemical properties of composted municipal solid wastes (MSW) we re investigated by chemical and spectroscopic methods (EPR, NMR, IR, UV-Vis , ICP). Transformations of the composted organic matter during 150 days wer e observed. The water content was controlled in the composts; in some cases the composted MSW were nitrogen enriched by urea addition. The maturation of the composts was observed using standard methods. Quantitative EPR measurements were made on isolated humic and fulvic acids; the concentration of semiquinone free radicals and g parameters were deter mined. The maximum radical concentration (1.2 . 10(17) spins/gram) in isola ted humic acids was observed in about the 6th week of the composting proces s in good quality composts. Moreover, distinct linear changes in g paramete rs of isolated humic acids (HA) from 2.0031 to 2.0037 were observed during the composting process. These changes were correlated to increasing E-4/E-6 ratio characterizing the intensity of the oxidation processes and formatio n of oxygen-rich functional groups. The heavy metal (Cu, Fe, Mn, Pb) concentrations were examined in the compos ts and humic (HA) and fulvic acid (FA) fractions. The increase of copper bi nding by HA extracted from composts enriched in nitrogen was observed; the coordination sites of the ligand were characterized on the basis of EPR spe ctra. The various Fe(III) and Mn(II) complexes in the HA and FA fractions d etected by EPR were used as additional indicators of oxidation-reduction pr ocesses in the composts. (C) 1999 Elsevier Science Ltd. All rights reserved .