Molecular behaviour of humic acid-like substances during co-composting of olive mill waste and the organic part of municipal solid waste

Humic acids extracted at different stages of co-composting, of olive mill waste with municipal solid waste, were analysed spectroscopically. The findings highlight the contrasting variations in the proportions of C-aromatic and C-carbonyl (C-13-NMR) as the H/C atomic ratio changes. The decrease in the infrared FT-IR absorption bands of aliphatic bonds -CH-, -CH2-, carboxylic acids, esters, amides C=O, the C-O- bonds of polysaccharides and alcohols with respect to ether bonds C-O-C, was linearly correlated with the H/C ratio. Moreover, the gradual reduction of UV-Visible ratios E212/E280 and E465/E665 and the increase in the C-HA/C-FA ratio with increasing humic acid aromaticity, is representative of a remarkable aspect of the restructuring brought, as discussed with respect to the mechanisms of polymerization and rearrangement of humic acid structures found to occur during composting. (C) 2012 Elsevier Ltd. All rights reserved.