BACKGROUND: The effects of chemical and thermochemical pretreatments on the composition and anaerobic biodegradability of sunflower oil cake were studied to compare these pretreatments and to assess their effectiveness. Four reagents (lime, sodium hydroxide, sulphuric acid, and sodium bicarbonate) at concentrations of 25% (w/w) of dry weight of substrate and 20 g L1 substrate concentration were used for the chemical pretreatment for 4 h. The same conditions were used for thermochemical pretreatment with heating at 75 degrees C. After the pretreatments, the solid and liquid fractions were separated and subjected to biochemical methane potential tests. RESULTS: The methane yields of the solid fraction obtained with lime, sodium hydroxide, sulphuric acid and bicarbonate were 130 +/- 9, 54 +/- 4, 61 +/- 6 and 88 +/- 7 mL CH4 g-1CODadded, respectively, and after thermochemical pretreatment were 26 +/- 2, 84 +/- 7, 74 +/- 7, and 77 +/- 6 mL CH4 g-1CODadded, respectively. The methane yields for liquids were 152 +/- 13, 2 +/- 0, 0 +/- 0, 249 +/- 19 mL CH4 g-1CODadded, for the chemical pre-treatment, respectively, and after the thermochemical pretreatment were 273 +/- 13, 58 +/- 5, 0 +/- 0 and 145 +/- 12 mL CH4 g-1CODadded, respectively. CONCLUSION: Only the solid fraction obtained after the chemical pretreatment with lime gave a methane yield higher (130 mL CH4 g-1CODadded) than the obtained for the untreated solid material (114 mL CH4 g-1CODadd). No thermochemical pretreatment enhanced the methane yield of the solid or liquid fractions of the untreated material. (c) 2012 Society of Chemical Industry