Ethanol Production from Seaweed, Enteromorpha intestinalis, by Separate Hydrolysis and Fermentation (SHF) and Simultaneous Saccharification and Fermentation (SSF) with Saccharomyces cerevisiae

Abstract

Ethanol productions were performed by separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) processes using seaweed, Enteromorpha intestinalis (sea lettuce). Pretreatment conditions were optimized by the performing thermal acid hydrolysis and enzymatic hydrolysis for the increase of ethanol yield. The pretreatment by thermal acid hydrolysis was carried out with different sulfuric acid concentrations in the range of 25 mM to 75 mM H 2 SO 4 , pretreatment time from 30 to 90 minutes and solid contents of seaweed powder in the range of 101 6% (w/v). Optimal pretreatment conditions were determined as 75 mM H 2 SO 4 and 13% (w/v) slurry at 121 o C for 60 min. For the further saccharification, enzymatic hydrolysis was performed by the addition of commercial enzymes, Celluclast 1.5 L and Viscozyme L, after the neutralization. A maximum reducing sugar concentration of 40.4 g/L was obtained with 73% of theoretical yield from total carbohydrate. The ethanol concentration of 8.6 g/L of SHF process and 7.6 g/L of SSF process were obtained by the yeast, Saccharomyces cerevisiae KCTC 1126, with the inoculation cell density of 0.2 g dcw/L.

Bioethanol from macroalgae: Prospects and challenges

“…75 mM H 2 SO 4 [120]. Sequential acid hydrolysis was carried out to concentrate the sugar: hydrolysate of first cycle was utilized as hydrolyzing liquid for the 2nd cycle and up to 5th cycle [117] and generated 72 g/L of reducing sugar at the end of 5th cycle during 0.9 N H 2 SO 4 hydrolysis from the seaweed granules.…”

“…Higher ethanol yield of 1.63 g and 25.8% efficiency was recorded for EITY combination, whereas ULCY produced lower ethanol yield of 0.37 g achieving 12.1% efficiency. Co-fermentation of E.intestinalis hydrolysate yielded 0.8 g with 21.7% efficiency, whereas U.lactuca yielded 0.63 g/g achieving 20.4% efficiency [120]. Pretreated E.intestinalis to 75 mM H 2 SO 4 and subjected to SHF and obtained ethanol of 8.6 g/L (0.86 g) achieving 30.5% efficiency at 48 h. At the end of fermentation 10 g/L of reducing sugar remained unutilized indicating presence of non-fermentable sugar not consumed by the yeast S.cerevisiae.…”

“…SHF and SSF of Enteromorpha intestinalis or Ulva (Enteromorpha) intestinalis produced 8.6 g/L and 7.6 g/L with 30.5% and 29.6% fermentation efficiency respectively. Conversion of ethanol to acetic acid by yeast and suboptimal temperature of 30 � C than the optimum temperature of 55 � C for enzyme activity was attributed to the lower ethanol yield in SSF [120].…”

“…Higher temperature shortens the exponential phase of the yeast cell [121] affecting the ethanol production. However, this has been overcome through thermotolerant yeast strains or cell immobilization technique which allows higher processing temperatures [120][121][122][123]. Thermotolerant yeast species such as Candida tropicalis and Kluyveromyces marxianus (38-45 � C) are mainly utilized to produce bioethanol from lignocellulosic biomass [123,124].…”

Seaweeds: a sustainable fuel source

“…contains xylose and glucose (Isa et al, 2009). The SSF and SEHF of Ulva intestinalis (as Enteromorpha intestinalis) using S. cerevisiae KCTC1126 produced 8.6 g/L (30.5% of theoretical yield) and 7.6 g/L ethanol (26.9% of theoretical yield) concentration, respectively (Cho et al, 2013a). hydrolysate, ∼10 g/L ethanol concentration was produced, translating to 90% fermentation efficiency of glucose (Isa et al, 2009), while only 5% of ethanol concentration was obtained from the fermentation of Cladophora spp.…”