Biotransformation of organic matter during composting of solid wastes from traditional tanneries by thermochemolysis coupled with gas chromatography and mass spectrometry

In the present paper, Thermochemolysis (or Thermally Assisted Hydrolysis/Methylation) is used as a way of following the biotransformation of organic matter during composting of solid wastes from traditional tanneries. The qualitative analysis of the pyrograms allowed us to discriminate between four main families of compounds: aromatic compounds, lipids, polysaccharides and nitrogen-containing substances. The quantitative data revealed some variations in the chemical composition of the macromolecular content.Lipids are the most transformed fraction during the composting process. Animal and plant fatty acids showed a sensible decrease. Fungal fatty acids mainly increased during the thermophilic phase whereas bacterial fatty acids increased when the growth of fungi is repressed. During composting of solid wastes from traditional tanneries an adapted microbial community has been developed. Various lignin-derived units during composting showed a strong increase in p-hydroxyphenyl type-compounds in comparison with the other aromatic structures due to high decomposition of grass cuttings. Tannin derived compounds also increased throughout the composting. Lignin and condensed tannins polymers are partially degraded and stabilized by covalent linkage to more complex organic molecules such as humic substances.Nitrogen containing compounds increased during composting as a consequence of the high rate of degradation of the other fractions and/or their combination with polyphenolic structure leading to the formation of humic substances. In our study a correlation was found between NTK and nitrogen containing substances.