Characterization of natural organic matter (NOM) derived from sewage sludge compost. Part 2: multivariate techniques in the study of compost maturation

This study presents the results of chemometric data analysis which describes the maturation of sewage sludge compost. The compost was characterized at different stages of maturation by various chemical and spectroscopic parameters including carbon and nitrogen content, humic substances content, UV–Vis and 13C NMR. The data set of compost characteristics was analyzed using multivariate methods: cluster analysis (CA) and principal component analysis (PCA). The results enabled the determination of three groups of compost samples at different stages of maturation that correspond to three stages of composting: (i) domination of rapid decomposition of non-humic, easily biodegradable organic matter, (ii) domination of organic matter humification and formation of polycondensed, humic-like substances (the next 2 weeks), (iii) stabilization of transformed organic material and weak microbial activity. The multivariate techniques also enabled the identification of main parameters that change during different stages of composting the most.