A CHEMICAL-STRUCTURAL STUDY OF ORGANIC WASTES AND THEIR HUMIC ACIDS DURING COMPOSTING BY MEANS OF PYROLYSIS-GAS CHROMATOGRAPHY

Changes in the chemical-structural composition of urban wastes (sewage sludge and city refuse) and their humic acids during composting were studied by pyrolysis-gas chromatography. A low degree of humification was observed in both the wastes and the humic acids extracted from them as determined by the high furfural content of the former and high acetic acid content of the latter and by low benzene content for both. For this reason, the indices of humification (calculated by the ratio of specific pyrolytic fragments) applicable to soils are of no use for composts of organic wastes. Nevertheless, the ratio benzene/toluene can be considered as a good index of condensation or depolymerization, depending on the starting material of the compost. No increase in benzene was observed with composting unlike with phenol, which indicates that the lignin was not degraded with this process. Among the aromatic fragments considered, whether from the mixtures or their humic acids and regardless of the composting process, the most abundant was toluene and the least abundant were phenols and cresols. With composting further changes were noted in the structure of the solid city refuse compared with the sewage sludge, probably due to the heterogeneous nature of city refuse. Py-GC studies showed that initially both the organic wastes possessed very different structures, but during composting, they evolved to more similar structures, as indicated by the indices of similarity.