Gracilaria verrucosa, red seaweed, is a promising biomass for bioethanol production due to its high carbohydrate content. The optimal hyper thermal (HT) acid hydrolysis conditions are 12% (w/v) G. verrucosa with 0.2 M HSO at 130 °C for 15 min, with a severity factor of 1.66. This HT acid hydrolysis produces 50.7 g/L monosaccharides. The maximum monosaccharide concentration of 58.0 g/L was achieved with 96.6% of the theoretical monosaccharide production from 120 g dry weight/L G. verrucosa slurry after HT acid hydrolysis and enzymatic saccharification. Fermentation was carried out by removing an inhibitory compound and via yeast adaptation to galactose. Both Pichia stipitis and Kluyveromyces marxianus adapted to galactose were excellent producers, with the ethanol yield (Y) of 0.50 and 29.0 g/L ethanol production. However, the bioethanol productivity with Pichia stipitis adapted to galactose is higher than that with Kluyveromyces marxianus adapted to galactose, being 0.81 and 0.35 g/L/h, respectively. The results from this study can be applied to industrial scale bioethanol production from seaweed.
Bioethanol was produced using polysaccharide from soybean residue as biomass by separate hydrolysis and fermentation (SHF). This study focused on pretreatment, enzyme saccharification, and fermentation. Pretreatment to obtain monosaccharide was carried out with 20% (w/v) soybean residue slurry and 270 mmol/L HSO at 121 °C for 60 min. More monosaccharide was obtained from enzymatic hydrolysis with a 16 U/mL mixture of commercial enzymes C-Tec 2 and Viscozyme L at 45 °C for 48 h. Ethanol fermentation with 20% (w/v) soybean residue hydrolysate was performed using wild-type and Saccharomyces cerevisiae KCCM 1129 adapted to high concentrations of galactose, using a flask and 5-L fermenter. When the wild type of S. cerevisiae was used, an ethanol production of 20.8 g/L with an ethanol yield of 0.31 g/g consumed glucose was obtained. Ethanol productions of 33.9 and 31.6 g/L with ethanol yield of 0.49 g/g consumed glucose and 0.47 g/g consumed glucose were obtained in a flask and a 5-L fermenter, respectively, using S. cerevisiae adapted to a high concentration of galactose. Therefore, adapted S. cerevisiae to galactose could enhance the overall ethanol fermentation yields compared to the wild-type one.
This study employed a statistical method to obtain optimal hyper thermal acid hydrolysis conditions using Gelidium amansii (red seaweed) as a source of biomass. The optimal hyper thermal acid hydrolysis using G. amansii as biomass was determined as 12% (w/v) slurry content, 358.3 mM HSO, and temperature of 142.6 °C for 11 min. After hyper thermal acid hydrolysis, enzymatic saccharification was carried out. The total monosaccharide concentration was 45.1 g/L, 72.2% of the theoretical value of the total fermentable monosaccharides of 62.4 g/L based on 120 g dry weight/L in the G. amansii slurry. To increase ethanol production, 3.8 g/L 5-hydroxymethylfurfural (HMF) in the hydrolysate was removed by treatment with 3.5% (w/v) activated carbon for 2 min and fermented with Pichia stipitis adapted to high galactose concentrations via separate hydrolysis and fermentation. With complete HMF removal and the use of P. stipitis adapted to high galactose concentrations, 22 g/L ethanol was produced (yield 0.50). Fermentation with total HMF removal and yeast adapted to high galactose concentrations increased the fermentation performance and decreased the fermentation time from 96 to 36 h compared to traditional fermentation.
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