Molecular alterations of organic fractions from urban waste in the course of composting and their further transformation in amended soil

The evolution of various analytical characteristics including the concentrations of water-soluble fractions, free and esterified lipids, and humic-like substances. of solid urban waste in the course of a 7-week composting process have been monitored in two independent piles composted during different seasons SpringrAutumn.. Whereas the concentration of water-soluble and mineral fractions tended to increase during composting, the opposite was observed for total organic matter and free lipid. Unmatured compost showed comparatively high amounts of esterified lipid. The absence of monotonic trends shown by this fraction, and by total humic-like substances indicate two successive stages of compost microbial reworking. Gas chromatography-mass spectrometry GC-MS. analysis of the lipid fractions progressively removed by step-wise chemolysis allows the appraisal of different lipid species, which differ in their resistance to biodegradation. Extended composting does not contribute to the accumulation of progressively aromatised humic-type materials similar to those present in soil. Both pyrolysis Py.-GC-MS and spectroscopic techniques Fourier transform infrared spectroscopy, FT-IR, and 13C nuclear magnetic resonance spectroscopy, NMR. confirm that compost-derived humic acid-like substances are not structurally comparable to soil humic acids. Finally, the fate of the compost organic fractions has been investigated in two soils amended with different doses of the final compost. In general, the most conspicuous compost-induced effects were reflected by the differences in the qualitative and quantitative composition of the soil lipid. The results indicate that compost application cannot be considered to contribute to the mid-term accumulation of stable forms of organic matter in soil.