Compost maturity assessment using calorimetry, spectroscopy and chemical analysis

This work is aimed at characterizing compost maturity and, organic matter t ransformation during this process, by the use of nondestructive spectroscop ic and thermal techniques, together with some chemical analysis. Composting was conducted in a laboratory over a period of one year using the organic fraction of domestic wastes, fresh farmyard manure, spent coffee and sawdus t as the raw materials. Samples were retired after different periods of com posting and were analyzed by differential scanning calorimetry (DSC) and fo urier transform infrared (FTIR) spectroscopy as well as by routine chemical parameters including temperature, pH, C/N, ash content and humic-like subs tances content. Results Showed that in case of domestic wastes, spent coffe e and farmyard manure, the C/N ratios, ash and humic acid content showed a typical high rate of change during the first 197 days of composting and ten ded to stabilize thereafter, probably as a result of the maturity of the pr oduced composts. In contrast, sawdust underwent only a very limited transfo rmation even after one year of composting. Thermoanalytical and spectroscop ic data confirms these finding and gives useful and complementary informati on with respect to the structure, the heterogeneity and the relative stabil ity of the compost products. In particular, as the decomposition proceeded, there was an increase in aromatic to aliphatic structure ratio and a decre ase in the importance of peptide structures of composts. Besides, both the spectroscopic and the thermal behavior of compost samples, retired beyond 1 97 days of composting, tended to be regular, less dependent on the raw mate rial and close to that characterizing mature composts, with the exception o f sawdust samples. We concluded that the spectroscopic and thermal techniqu es used are complementary to one another and to chemical tests and could be a powerful and fast approach for the study of compost maturity.