This work reports of the use of a bench scale chemostat (CSTR) in continuous mode and of a pilot scale membrane bioreactor (MBR) in fed-batch mode to intensively produce acetic and butyric acids using Cl. butyricum grown on synthetic media. These studies were then used to perform a cost estimation study of the MBR system to assess the potential economic impact of this proposed methodology. The MBR system was found highly productive reaching 37.88 g L-1 h-1 of acetic and 14.44 g L-1 h-1 of volumetric cell productivity, favoring acetic acid production to butyric at a ratio 3:1. The cost of preparation and production of carboxylic acids using this system was found as 0.0062 £PS/kg respectively and an up to 99% carbon recovery.