Assessment of Compost-Derived Humic Acids Structure from Ligno-Cellulose Waste by TMAH-Thermochemolysis

• Published in: Waste and biomass valorization Vol. 10; no. 9; pp. 2661 - 2672
• Main Authors: El Ouaqoudi, Fatima Zahra, Meddich, Abdelilah, Lemée, Laurent, Amblès, André, Hafidi, Mohamed
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.09.2019; Springer Nature B.V; Springer
• Subjects: Abundance; Agricultural wastes; Aldehydes; Aromatic compounds; Biodegradation; Biotransformation; Cellulose; Chemical composition; Composting; Composts; Decomposition; Derivatives; Engineering; Environment; Environmental Engineering/Biotechnology; Environmental Sciences; Ferulic acid; Genetic transformation; Grasses; Humic acids; Humification; Indoles; Industrial Pollution Prevention; Lignin; Lignocellulose; Macromolecules; Metabolism; Microorganisms; Nitrogen; Organic chemistry; Original Paper; Phenolic compounds; Phenols; Polysaccharides; Protein turnover; Renewable and Green Energy; Saccharides; Substrates; Waste Management/Waste Technology; Thermochemolysis-TMAH; Lignin; Composting; Decomposition; Ligno-cellulose waste; Derived humic acids
• ISSN: 1877-2641; 1877-265X
• DOI: 10.1007/s12649-018-0268-z

In this study, we used the TMAH-thermochemolysis to characterize more precisely the chemical structure of the humic acids (HAs) extracted from two composts a basically lignocellulosic substrate and to follow up their biotransformation during the composting process. The analysis of the pyrograms obtained for both composts [date palm waste alone (DPW) and date palm waste-couch grass clippings mixture (DPCG)] allowed to distinguish a dominance of aromatic compounds from lignin and from nonspecific origin (92.7 and 85.5% respectively for DPW and DPCG mixture). A few nitrogen-derived and polysaccharides compounds was recorded in our HAs. For both composts, the lignin structures were represented by guaiacyl (G) and syringyl (S) units. The lack of lignin derived from p-coumaric structures could be ascribed to their degradation by influence of the extraction. This support can be confirmed by the absence in our samples of compounds with the C3 alkyl side-chain of ferulic acid. The high level of lignin-derived compounds explains the slow biodegradation and humification observed especially during DPW composting. The lignocellulose nature of date palm substrate limits the microbial proliferation responsible of the degradation and transformation of OM which is partially ameliorated by couch grass addition. This is in correlation with temperature evolution observed for DPW compost. Some variations in the chemical composition of the macromolecular content were recorded for both composting. An increase of the abundance of the nitrogen products from 6.4 and 11.6% to 8.2 and 13.8% respectively for DPW and DPCG mixture was observed. This increase can attributed to the decomposition of certain protein structures and microbial metabolism with a possible incorporation into the new formed HAs. The strong increase of methylpyrrole (isomer 8) and the strong decrease of 1H-indole for DPCG mixture indicate that the degradation phenomena were more extensive for this mixture than for DPW compost. The decrease of the total abundance of aromatic compounds of non specific origin for DPW compost against an increase for DPCG mixture indicate that humification process was more advanced in this latter leading to the incorporation of some structures into the new formed HAs. The decrease of phenol (14) toward the end DPW composting suggests its degradation and transformation into others variety of phenolic derivatives, whereas its increase for DPCG mixture can be related to its incorporation during humic structure formation. This can confirm that the speed of degradation and humification is more important for DPCG mixture than DPW compost. Also a significant decrease of guaiacyl derivatives was observed for DPCG mixture. The results of the calcul of S/G ratios were not in agreement with the literature. The support of the preferential degradation of S or G moieties is not valid here. The decomposition of the lignin structures is connected to the accessibility of the biomass microbial to the S or G lignin. The slight increase by the same value of the acid/aldehyde ratio for both composts indicates a low and equal degree of oxidization of the lignin.