Evaluation of sediments of the waste from beer fermentation broth for bioethanol production

As our previous studies showed, the waste from beer fermentation broth (WBFB) is a potential resource for bio-ethanol production. The original WBFB was superior to the supernatant in this regard. The current study investigates the potential of the WBFB sediment alone for bio-ethanol production after it has been diluted with distilled water or a chemically-defined medium. The effect of stock time on WBFB sediments for ethanol production was also studied. The fermentations were carried out using 50 ml vials placed in a bioreactor in static conditions. There was relatively little increase in ethanol production with fermentation time (up to 2 h) and stock time (up to 7 days) using 20% (v/v) sediment in distilled water which did not contain any nutrients or enzymes. A 2.09% increase in ethanol production was recorded after 2 h fermentation with 20% (v/v) WBFB sediments (1 day old) in a chemically-defined medium. The increase was 3.25% for WBFB sediments with a stock time of three days in a chemically-defined medium. The results also showed some residual activity of starch hydrolyzing enzymes in the sediments, especially at 60 °C. The overall results of this study revealed that the sediments alone were capable of bio-ethanol production even though they were five-fold diluted with distilled water or the chemically-defined medium.