Organic Matter Fractions Involved in Degradation and Humification Processes

The changes in the different organic matter (OM) fractions of lignocellulosic wastes during composting were studied and related to OM humification parameters and compost maturation degree. For this purpose, four mixtures of lignocellulosic materials (lemon tree prunings, cotton waste, brewery waste, olive husk, olive leaves and the solid fraction of olive mill wastewater) were composted in a static pile system with forced ventilation. The evolution of the parameters humic acid to NaOH-extractable organic carbon proportion or PAH (HAC/EXC x 100), humic to fulvic acid ratio (HAC/FAC), cation exchange capacity to total organic carbon ratio (CEC/TOC), and water-soluble organic carbon to organic nitrogen ratio (HOC/Organic-N), clearly reflected the increase in the degree of humification and stability of the OM during the composting process in all four mixtures. The concentration of water-soluble carbohydrates was significantly correlated with PAH, HAC/FAC and the HOC/Organic-N ratio in only two mixtures along the composting processes. In general, there were statistically significant correlations between the polyphenol concentration in different fractions (water soluble, NaOH extractable, and fulvic and humic acids) and the humification parameters and maturity indices, especially with PAH, HAC/FAC and HOC/Organic-N, which shows the participation of these compounds in the synthesis of humic substances. On the other hand, the lignocellulosic compounds, lignin, cellulose and hemicellulose, seem to play an important role in the increase of cationic exchange sites in the OM, as can be seen from their correlation with CEC/TOC ratio.