Within the carboxylate platform, carboxylic acids are seen as important building-blocks for the chemical industry, but their recovery is challenging. Membrane based reactive extraction (MBRE) was evaluated for the recovery of these acids from a fermentor in which a mixed culture is converting biorefinery wastewater to carboxylates. Both off-line and in-line experiments were performed. The off-line experiments were promising and extraction efficiencies of 15 (acetic acid) to almost 100% (caproic acid) were reached. The in-line experiments confirmed the selective and near complete extraction of carboxylates with longer chain length. However the overall extraction rates were lower than in off-line tests and the total carboxylate production rate was also decreasing. This was probably caused by limited but repeating contact between organic phase and fermentation broth via the membrane interface.