Enhanced Bioethanol Fermentation by Sonication Using Three Yeasts Species and Kariba Weed (Salvinia molesta) as Biomass Collected from Lake Victoria, Uganda

Kariba weed (Salvinia molesta) was used as biomass feedstock for ethanol production by separate hydrolysis and fermentation (SHF). Monosaccharides from Kariba weed hydrolysate were produced using thermal acid hydrolysis, sonication, and enzymatic saccharification. The optimal conditions for thermal acid hydrolysis of 12% (w/v) Kariba weed slurry were evaluated as 200 mM HNO3 at 121 degrees C for 60 min yielding 10.2 g/L monosaccharides. Sonication for 45 min before enzymatic saccharification yielded more monosaccharides to 18.7 g/L. Enzymatic saccharification with 16 U/mL Cellic CTec2 produced 35.4 g/L monosaccharides. Fermentation was performed using Saccharomyces cerevisiae, Kluyveromyces marxianus, or Pichia stipitis with sonicated Kariba weed hydrolysate. The control fermentations were carried out using Kariba weed hydrolysate without sonication. The improvement of ethanol production from sonicated Kariba weed hydrolysate using P. stipitis produced 15.9 g/L ethanol with ethanol yield coefficient Y-EtOH = 0.45, K. marxianus produced 14.7 g/L ethanol with Y-EtOH = 0.41. S. cerevisiae produced the lowest yield of 13.2 g/L ethanol with Y-EtOH = 0.37 as it utilized only glucose not xylose. Sonication of Kariba weed was essential in the ethanol production to enhance the productivity of monosaccharides. P. stipitis was determined as the best yeast species using hydrolysates with the mixture of glucose and xylose to produce ethanol.