Ecofriendly Approach for Bioethanol Production …
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Ultrasonic assisted extraction (UAE) was an effective biomass pre-treatment for
carbohydrates extraction, as compared with conventional solvent extraction (CSE)
and fluidized bed extraction (FBE) methods (Zhao et al. 2013).The glucose extraction by UAE showed an increment of almost fourfold (36.94 g/100 g of DCW
biomass), as compared with CSE and FBE methods. In addition, (Hwang et al.
2016) also found that the yeast promoted fermentative bioethanol production can
be further enhanced by joint sonication, heat and enzyme (SHE) on biomass pretreatments, which led to complete destruction of biomass cell walls. Initially, filamentous microalgae were partially disrupted by sonication, whereas complete cells
wall (filamentous and cyclotella) destruction was achieved by thermal heating and
enzymes.
5.2 Chemical Pre-treatment
The chemicals hydrolysis method appeared to be a rapid and cheaper method than
enzymatic hydrolysis. Usually, acids or alkalis are used for microalgae biomass
saccharification, with acids is more commonly employed. Acid hydrolysis is capable
to break the intra- and inter-molecular hydrogen bonds across the glycosidic link
and thus, further enhance the breakdown of carbohydrates (Simas-Rodrigues et al.
2015). Among the available acids, sulfuric acid (H2SO 4 ) is the most attractive
choice for biomass saccharification process. This is due to the advantage of released
anions (SO 4
2− ) as nutrient source for yeast fermentation process (Miranda et al.
2012). The optimization parameters of chemical pre-treatment includes: (i) time; (ii)
temperature; and (iii) acid or alkaline concentration.
By referring to the acid hydrolysis performed by Miranda et al. (2012), it was
found that the optimum operating conditions for Scenedesmus obliquus biomass
could be achieved by using 2 N of H 2 SO 4 , at temperature of 120 °C for 30 min. The
sugar yield attained was 95.6%, indicating that low cost and low energy chemical pretreatment method could be employed to release the sugar from microalgae biomass
efficiently.
Besides, alkaline-peroxide also demonstrated a significantly impact on sugars
extraction (maximum 87%) from microalgae biomass cultivated in domestic and pig
manure wastewaters. This is due to the enhancement of oxidation of sugars to form
organic acids during fermentation process (Martin et al. 2016).
5.3 Enzymatic Pre-treatment
Enzymatic pre-treatment degrades the cellulose for the subsequent hydrolysis
process. As compared with the previous discussed pre-treatment (physical and chemical) methods, enzymatic pre-treatment appeared to be advantages as this method
consume less energy, mild conditions and will not incurred corrosion issue to the
311
Ultrasonic assisted extraction (UAE) was an effective biomass pre-treatment for
carbohydrates extraction, as compared with conventional solvent extraction (CSE)
and fluidized bed extraction (FBE) methods (Zhao et al. 2013).The glucose extraction by UAE showed an increment of almost fourfold (36.94 g/100 g of DCW
biomass), as compared with CSE and FBE methods. In addition, (Hwang et al.
2016) also found that the yeast promoted fermentative bioethanol production can
be further enhanced by joint sonication, heat and enzyme (SHE) on biomass pretreatments, which led to complete destruction of biomass cell walls. Initially, filamentous microalgae were partially disrupted by sonication, whereas complete cells
wall (filamentous and cyclotella) destruction was achieved by thermal heating and
enzymes.
5.2 Chemical Pre-treatment
The chemicals hydrolysis method appeared to be a rapid and cheaper method than
enzymatic hydrolysis. Usually, acids or alkalis are used for microalgae biomass
saccharification, with acids is more commonly employed. Acid hydrolysis is capable
to break the intra- and inter-molecular hydrogen bonds across the glycosidic link
and thus, further enhance the breakdown of carbohydrates (Simas-Rodrigues et al.
2015). Among the available acids, sulfuric acid (H2SO 4 ) is the most attractive
choice for biomass saccharification process. This is due to the advantage of released
anions (SO 4
2− ) as nutrient source for yeast fermentation process (Miranda et al.
2012). The optimization parameters of chemical pre-treatment includes: (i) time; (ii)
temperature; and (iii) acid or alkaline concentration.
By referring to the acid hydrolysis performed by Miranda et al. (2012), it was
found that the optimum operating conditions for Scenedesmus obliquus biomass
could be achieved by using 2 N of H 2 SO 4 , at temperature of 120 °C for 30 min. The
sugar yield attained was 95.6%, indicating that low cost and low energy chemical pretreatment method could be employed to release the sugar from microalgae biomass
efficiently.
Besides, alkaline-peroxide also demonstrated a significantly impact on sugars
extraction (maximum 87%) from microalgae biomass cultivated in domestic and pig
manure wastewaters. This is due to the enhancement of oxidation of sugars to form
organic acids during fermentation process (Martin et al. 2016).
5.3 Enzymatic Pre-treatment
Enzymatic pre-treatment degrades the cellulose for the subsequent hydrolysis
process. As compared with the previous discussed pre-treatment (physical and chemical) methods, enzymatic pre-treatment appeared to be advantages as this method
consume less energy, mild conditions and will not incurred corrosion issue to the