Delignified wheat straw was fermented by a mixed bacterial anaerobic culture obtained from a UASB reactor to produce organic acids (OAs). Kissiris was used as immobilization carrier in a 2-compartment 82 L bioreactor filled with 17 L of fermentation broth for the first 7 fermentation batches and up to 40 L for the subsequent batches. The amount of straw used was 30 g/L and the temperature was set at 37 degrees C for all experiments. The total OAs reached concentrations up to 17.53 g/L and the produced ethanol ranged from 0.3 to 1 mL/L. The main OAs produced was acetic acid (6-8 g/L) and butyric acid (3-8 g/L). The OAs were recovered from the fermentation broth by a downstream process using 1-butanol, which was the solvent with the best recovery yields and also served as the esterification alcohol. The enzymatic esterification of OAs resulted to 90% yield. (C) 2017 Elsevier Ltd. All rights reserved.