Recycling the stillage condensates to dilute worts in the fermentation stage would be an effective way to decrease wastewater production and ground water consumption. However, condensates contain fermentation inhibiting solutes, such as volatile acids, alcohols and aromatic compounds that should be removed. Reverse osmosis was investigated as a clean process for such a purpose. Pilot scale experiments were carried out with industrial condensates and using Hydranautics ESPA2 membrane. The influence of transmembrane pressure (TMP), volume reduction factor (VRF) and pH on permeate flow rate and rejection rates of inhibitory compounds were investigated. The optimal operating conditions were TMP=10 bar to get the maximal admissible permeate flow, a low VRF to produce the less concentrated permeate and a pH ? 6 to obtain the highest rejection rates of the acids. Results were confirmed by trials at pre-industrial scale in a distillery. However, the permeate produced at pH 6 proved to be less fermentable than the permeate produced at natural pH because of an increase in the osmotic pressure. Natural pH permeate displayed a fermentation activity almost equivalent to tap water chosen as the blank. The remaining inhibitory acids did not seem to significantly hinder yeast growth nor yeast physiology.
©2011 Walter de Gruyter GmbH & Co. KG, Berlin/Boston
