Usefulness of reverse osmosis in the treatment of condensates arising from the concentration of distillery vinasses

This work forms part of a global study on the recycling into alcoholic fermentation of condensates arising from the concentration of vinasses. Its purpose is to demonstrate the usefulness of reverse osmosis (RO) in the treatment and exploitation of these condensates, i.e., elimination of the anti-fermentation molecules they contain (formic, acetic, propionic, butyric, valeric, hexanoic acids, 2,3-butanediol, furfural and phenyl-2-ethyl-alcohol) so that they could be recycled. The experimental system used was a DSS Labstack M20-0.72 filtration system with flat, Filmtec FT30 Sea Water (SW) membranes from Dow. As the inhibitory compounds include organic acids, the effect of pH was studied: trials at pH 3.0, 5.2, 7.5 and 10 were performed at 40 bar and 25–30°C, and monitored by chemical analysis and inhibition tests. Rejection coefficients were found to be higher than 85% for all compounds at pH >5. RO permeates arising from the treatment of condensates with a pH 7.5 and 10 proved not inhibitory. Because of a strong rise between 6 and 12 during the titration, working at pH higher than 6 needs a fine tuning of pH value or the use of membranes resisting high pH values. At pH 6, however, 10% inhibition is still present; in order to eliminate all traces of inhibition, it would then be necessary to envisage double RO or coupling with another process.