The application to soil of composts generated by biological recycling of organic wastes is a traditional practice required for the sustainable management of productive systems. Nevertheless, only a limited number of composts produced by current technologies offers the maturity degree suitable for improvement of agricultural soils. Among the well specified standards for compost quality, those related to organic matter stability assume a particularly important role. A proper piling and composting time of the wastes can be sufficient to ensure biological stability. However for good management of the composting process it is essential to dispose of criteria to assess the evolution with time of chemical parameters in order to set the optimum composting time from an economical viewpoint. Although simple biological tests have been used to define compost maturity, they do not yield relevant information as regards economy in a process in which mechanical rotation and temperature control during the whole composting time are of capital importance in rentabilizing an industrial production system. Therefore new criteria based exclusively in simple and reproducible analytical techniques are required. In this work we have recorded the chemical changes of different organic fractions isolated from urban refuse wastes at discrete intervals in the course of the composting process. We have examined the water soluble fraction, the lipid fraction and the humic acid-like fraction by spectroscopic (DC-NMR and FT-IR) and chromatographic techniques (GC/MS and Py-GC/MS). Sampling have been performed at different seasons for two years. From a structural viewpoint, some significant chemical changes were detected in the composition of lipid fractions, but the most striking observation was the detection by Py-GC/MS of increasing degree of aromatization in the humic acid-like fraction isolated from compost samples collected at the advanced transformation stages.

Peer reviewed