Structural changes of humic acids during olive mill pomace composting

The aim of this work was to characterize the humic acids during composting using both chemical and spectroscopic analytical methods. Humic acids (HA) were extracted from olive mill pomace (OMP) after 5, 10, 21, 32, 48, 60, 84 , 95, 109 and 153 days of composting and their elemental composition, funct ional groups, molecular weight, C-13 CP-MAS NMR and FTIR spectra were deter mined. Elemental composition of HA showed a decrease of carbon content from 56.8% to 47.1% and an increase of oxygen content from 32.7% to 43.3%. A sl ight increase of carboxylic groups was observed with no variation of phenol ic groups. The molecular weight of HA determined by gel chromatography show ed that after 95 days of composting the molecular weight of about 40% of th e polymers was greater than 10(2) KDalton. The C-13 CPMAS NMR and FTIR spec tra of HA showed compositional and structural changes indicating a slight i ncrease of polysaccharides and aromatic groups and a decrease of long aliph atic chains during the composting.