EPR and DRIFT spectroscopic characterization of humic fractions during composting of sawdust and paper mill sludge.

The spectroscopic characteristics (DRIFT, UV-visible and EPR) of humic fractions were studied during composting of sawdust and paper mill sludge. Infrared spectroscopy reveals a compost rich in hydroxyl and alkyl groups and carboxylates and carbohydrates. The alkyl fraction is abundant in the humic acids and humin. The decreasing of the E4/E6 ratio during composting indicates an enhancement of the organic chains number, with conjugated double bonds. This decreasing would correspond to a reduction of the lignin content and/or formation of porphyrins. The EPR shows that humin presents the highest concentration of free radical and the lowest intensities of the Fe3+