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Title

Changes in lignin pyrolytic assemblages and the assessment of maturity in composted lignocellulosic materials

AuthorsHernández, Zulimar ; González-Vila, Francisco Javier ; Almendros Martín, Gonzalo
Issue Date2004
AbstractThere is a practical interest in establishing conspicuous compost maturity indices valid for lignocellulosic materials irrespectively to their origin (e.g. in the present study consisting of manures, straw, forest and crop residues). This suggests the need of analytical methodologies not only responsive to the concentration of the major constituents (humic acid-type, carbohydrate, lignin, protein and lipid) but mainly on the molecular composition resulting from the microbial transformations. In fact, the sole concentration of humic acid-type substances is seldom correlated with the maturity of composted waste materials. In this work, a series of potential indices of maturity or humification in composts from lignocellulosic materials was studied by analytical pyrolysis. For this purpose it has been taken advantage, as conventional reference, of the changes in organic matter stoichiometry reflected by the classical Van-Krevelen diagram (H/C vs. O/C atomic ratios), which indicate the condensation of the aromatic backbone and the changes on the OH-containing moieties. The results suggested that mainly the atomic C/H ratio could be used as an independent descriptor of compost quality, in particular in composts derived from lignocellulosic biomass. Lower maturity should be ascribed to comparatively aliphatic composts from manures or grape seed, their high amounts of triglycerides or grass waxes being reflected in the Van Krevelen diagram, and in the concomitantly low yield or aromatic pyrolytic fragments. The classification of the descriptors by using multidimensional scaling (Pearson correlation index as similarity distance) could be used to find out pyrolytic descriptors behaving as maturity indices. Composts with lignins in the early stages of transformation probably include a major humic-like lignoprotein fraction of relatively low condensation indicated by: i) the yields of protein-derived N-compounds correlated with ii) the lignin fragments with alkyl side-chain substitutions and iii) the high methoxyl content, which in lignins is known to be also associated to low levels of intramolecular cross-linking. Progressive maturity ¿correlations with the C/H ratio¿ is associated to increased yields of unsubstituted aromatic guaiacyl or p-hydroxyphenyl fragments, which agrees with the classical hypothesis on the progressive transformation of lignins into condensed polyphenolic macromolecules in the course of natural diagenetic processes.
URIhttp://hdl.handle.net/10261/82669
Appears in Collections:(MNCN) Comunicaciones congresos
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