Characterisation of humic acids extracts at the time composting of olive oil mill wastes on gel sephadex

Molecular weight of humic acids extracted at different stages of composted olive mill wastes was estimated by gel chromatographic analysis by sephadex G25, G75 and G100. The obtained fractions were characterized by UV-visible spectroscopy, FTIR and E-4/E-6 ratio. Humic acids of composted olive mill wastes were similar to soil humic acids. During composting, fractions with low molecular weight decreased. However, the intensity of excluded fractions on G25, G75 and G100 increased. This could indicated that there was a polymerization of units with low molecular weight to fractions with high molecular weight. FTIR spectroscopy and E-4/E-6 ratio analyses confirmed these results and have shown that with increasing time of composting, aromaticity degree and polycondensation increased and aliphatic structures decreased.