Biofuel productions from soybean residue and seaweed via separate hydrolysis and fermentation (SHF) process

Abstract

Bioenergy can be produced via fermentation from any biomaterial containing sufficient polysaccharide or equivalent materials that can be degraded into monosaccharides, such as starch or cellulose. Traditionally, bioenergy has been produced from first-generation biomass, such as starch or sugars using sugarcane, wheat, and corn. However, first-generation biomass can also be used as a human food or animal feed, which has caused moral problems and concerns regarding increasing prices. Bioenergy has also been produced from second-generation biomass such as lignocellulosic biomass and agricultural waste products as second-generation biomass, such as the stalks of corn and wheat, straw, grass and wood chips. However, feedstock has low yields and high costs with efficient hydrolysis processes using current technologies. Therefore, the soybean residue and seaweed were used as a new biomass in this study for bioenergy production. The polysaccharide from the soybean residue was used for bioethanol production via the separate hydrolysis and fermentation (SHF). The study focused on the pretreatment, enzymatic saccharification and fermentation. The pretreatment to obtain monosaccharide was carried out with 20% (w/v) soybean residue slurry and 270 mM H2SO4 at 121℃ for 60 min. More monosaccharide was obtained from enzymatic hydrolysis with 16 Units/mL mixture of commercial enzymes CTec 2 and Viscozyme L at 45℃ for 48 h. Ethanol fermentation with 20% (w/v) soybean residue hydrolysate was performed using wild-type and adapted Saccharomyces cerevisiae KCTC 1126 to high concentrations of galactose using a flask and 5 L fermenter. When wild-type of S. cerevisiae was used, the ethanol production of 20.77 g/L with ethanol yield of 0.31 was obtained. The ethanol production of 33.89 g/L and 31.64 g/L with ethanol yield of 0.49 and 0.47 were produced using adapted S. cerevisiae to the high concentration of galactose in a flask and 5 L fermenter, respectively. As a results, S. cerevisiae adapted to galactose increased the ethanol yield comparing to wild-type of S. cerevisiae. Bioethanol was produced using the separate hydrolysis and fermentation (SHF) process with macroalgae polysaccharide from the seaweed, Gelidium amansii as a biomass. The study focused on the thermal acid hydrolysis pretreatment, enzymatic saccharification, detoxification and fermentation of red macroalgae, G. amansii. The thermal acid hydrolysis was carried out with H2SO4, slurry content (8~16%) and treatment time (15~75 min). As results, 12% (w/v) seaweed slurry, 182 mM H2SO4 at 121℃ for 45 min were selected as optimal conditions for thermal acid hydrolysis obtaining 6.8g/L glucose and 26.1g/L galactose. A monosaccharide (mainly glucose) was obtained from enzymatic hydrolysis of thermal acid hydrolysate, with 16 Units/mL commercial enzyme (Celluclast 1.5 L) at 45℃ for 36 h. Detoxification were carried out with adsorption method using activated carbon, overliming method using Ca(OH)2, and ion-exchange method using polyethyleneimine. Among those detoxification methods, activated carbon showed the best result for removal of hydroxymethylfurfural. Ethanol fermentation with 12% (w/v) seaweed hydrolysate was performed using wild-type Saccharomyces cerevisiae and adapted S. cerevisiae to galactose. Acetone, butanol and ethanol (ABE) were produced following the separate hydrolysis and fermentation (SHF) method using polysaccharides from the green macroalgae Enteromorpha intestinalis as biomass. We focused on the optimization of enzymatic saccharification as pretreatments for the fermentation of E. intestinalis. Pretreatment was carried out with 10% (w/v) seaweed slurry and 270 mM H2SO4 at 121°C for 60 min. Monosaccharides (mainly glucose) were obtained from enzymatic hydrolysis with a 16 Units/mL mixture of Celluclast 1.5 L and Viscozyme L at 45°C for 36 h. ABE fermentation with 10% (w/v) E. intestinalis hydrolysate was performed using the anaerobic bacteria Clostridium acetobutylicum with either uncontrolled pH, pH controlled at 6.0, or pH controlled initially at 6.0 and then 4.5 after 4 days, which produced ABE contents of 5.6 g/L with an ABE yield (YABE) of 0.24 g/g, 4.8 g/L with an YABE of 0.2 g/g, and 8.5 g/L with an YABE of 0.36 g/g, respectively. As a results, The maximum ethanol concentration was 33.89 g/L, with YEtOH of 0.49 and obtained using SHF with S. cerevisiae adapted to the high concentration of galactose when soybean residue was used as a biomass.The activated carbon can be suitable for detoxification of G. amansii hydrolysate using for ethanol fermentation which showed the highest efficiency reducing HMF by 89.5% and ethanol concentration of 20.28 g/L with YEtOH of 0.47 were obtained. ABE fermentation from E. intestinalis was carried out with pH controlled at 6.0 and then at 4.5 on day 4, which produced an ABE content of 8.5 g/L with a YABE 0.36 g/g.