Olive mill wastewater was treated by an aerobic bio-process at different values of pH (with or without addition of lime), for 45 days on a laboratory scale, to evaluate the reduction of the organic load. The lipid content showed an appreciable change in relation to the applied treatment both for total lipids and for the different fractions (neutral lipids, monoglycerides and phospholipids). C-13 NMR spectroscopy was performed on initial and final samples both raw and after lipid extraction. The main spectral differences were observed in the C-alkyl region (0-50 ppm), in the C O-alkyl/N-alkyl region (50-110 ppm), and in the C-carboxylic (160-200 ppm) region, providing information on the alterations occurring in the different biochemical entities composing this complex biomatrix (e.g. lipids, and carbohydrates) according to the treatment. (C) 2007 Elsevier B.V. All rights reserved.