Efficient conversion of wine lees into medium-chain carboxylic acids by mixed culture using an in-line extraction system

This study evaluates a process to generate medium-chain carboxylic acids (MCCA) from wasted wine lees. The effect of pH, feeding mode, organic loading rate, and the in-line extraction of the acids on the MCCA production rate was evaluated. Both the electron donor (ethanol) and acceptor (acetate) were generated in situ from the waste. First, the reactor was operated as a sequencing batch reactor (SBR), and pH 5.5 and 5.2 were evaluated. The caproate productivity was ten times higher at pH 5.5 than at 5.2. An in-line extraction system was next implemented, and the operation as SBR and the continuous mode was studied. The continuous mode allowed an increase of the residual ethanol; however, the feeding with concentrated wine lees caused an acetate overaccumulation. Caprylate was produced and extracted over caproate (caprylate/caproate ratio of 1.2) by avoiding the bioreactor overload and keeping a low ethanol broth concentration. In conclusion, the maximal MCCA production rate (143.4 +/- 14.8 mmol C/L-d) was obtained when the organic loading rate was gradually increased in the continuous operation; under such conditions, Eubacterium pyruvativorans predominated. The in-line extraction system allowed the production and recovery of MCCA.