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 (13C-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 CO, 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 CHA/CFA 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.

► Humic acid-like during co-composting of olive mill waste and the organic part of municipal solid. ► Spectroscopic analysis of humic acid-like. ► The mechanisms of molecular rearrangement and transformation, in relation with the stability and the maturity of the composts.