BACKGROUNDGrapes are one of the largest crops produced worldwide and are used mainly to produce wine, which generates a large volume of waste. Certain designations of origin, such as the Montilla-Moriles PDO of Cordoba (Spain) produce liqueur wines at low yield. The possibility of generating by-products from the waste during the winemaking process might provide an additional economic input. RESULTSAnaerobic digestion of grape marc waste derived from the Pedro Ximenez variety (ecological crop) was evaluated under mesophilic conditions at laboratory scale. The loads added to the reactors varied from 0.50 to 1.25gVS (volatile solids)L-1, with an average methane production coefficient of 25231mL(STP) CH(4)g(-1)VS(added) (STP: 0 degrees C, 1atm). The highest methane rate production was found to be 47.97 +/- 4.29 mL(STP) CH(4)L(-1)h for 1.25gVSL(-1) of grape marc waste. The volatile fatty acids concentration increased, and the pH and alkalinity slightly decreased over the experimental time. Moreover, the digestate contained lower metal concentration in comparison with waste derived from nonecological crops. CONCLUSIONAnaerobic digestion of Pedro Ximenez grape marc waste is feasible and might be implemented for waste management, thus reducing the large volume of waste generated. (c) 2018 Society of Chemical Industry