Ethanol production from brown seaweed using non-conventional yeasts

Abstract

Abstract:The use of macroalgae (seaweed) as a potential source of biofuels has attracted considerable worldwide interest. Since brown algae, especially the giant kelp, grow very rapidly and contain considerable amounts of polysaccharides, coupled with low lignin content, they represent attractive candidates for bioconversion to ethanol through yeast fermentation processes. In the current study, powdered dried seaweeds (Ascophylum nodosum and Laminaria digitata) were pre-treated with dilute sulphuric acid and hydrolysed with commercially available enzymes to liberate fermentable sugars. Higher sugar concentrations were obtained from L. digitata compared with A. nodosum with glucose and rhamnose being the predominant sugars, respectively, liberated from these seaweeds. Fermentation of the resultant seaweed sugars was performed using two non-conventional yeast strains: Scheffersomyces (Pichia) stipitis and Kluyveromyces marxianus based on their abilities to utilise a wide range of sugars. Although the yields of ethanol were quite low (at around 6 g/L), macroalgal ethanol production was slightly higher using K. marxianus compared with S. stipitis. The results obtained demonstrate the feasibility of obtaining ethanol from brown algae using relatively straightforward bioprocess technology, together with non-conventional yeasts. Conversion efficiency of these non-conventional yeasts could be maximised by operating the fermentation process based on the physiological requirements of the yeasts.

Isolation of Different Clostridium Isolates for Acetone-Butanol-Ethanol (ABE) Production from Sargassum sp.

“…On the other hand, Solarin et al [23] found that the carbohydrates content in Sargassum hystrix was (58.72%). Obata et al [24] studied other examples of the brown macroalgae (Ascophylum nodosum and Laminaria digitate), they found that carbohydrates content was (57.84 and 64.47%) respectively which supported our results that the brown macroalgae have high carbohydrates content. Also, Jang et al [25] reported another study on Laminaria japonica which considered an example of brown algae, he found that the carbohydrates content (54.5%).…”

Experimental processing of seaweeds for biofuels

“…Nowadays, hydrothermal treatment with diluted acids at concentrations between 0.2% and 2.5% (w/w) or alkali at temperatures ranging between 130 and 210°C is the most widely used pretreatment method (Jiang et al, ; Lee et al, ). Jiang et al () paid particular attention to the fact that in some studies treatment with dilute acid (<5%) was considered as “pretreatment,” whereas in others it was called “acid hydrolysis.” Acid or alkali hydrolysis is generally followed by enzymatic treatments (please see Table ; e.g., Borines et al, ; Jiang et al, ; Khan & Hussain, ; Korzen et al, ; Obata et al, ). The first method has many advantages such as simplicity, speed, and relatively low costs.…”

“…Jiang et al (2016) paid particular attention to the fact that in some studies treatment with dilute acid (<5%) was considered as "pretreatment," whereas in others it was called "acid hydrolysis." Acid or alkali hydrolysis is generally followed by enzymatic treatments (please see Table 2; e.g., Borines et al, 2013;Jiang et al, 2016;Khan & Hussain, 2015;Korzen et al, 2015;Obata et al, 2016). The first method has many advantages such as simplicity, speed, and relatively low costs.…”

“…Fermentation of the sugars in seaweed hydrolysate is performed mainly by Saccharomyces cerevisiae, which is the most exploited yeast species for industrial ethanol production (Enquist-Newman et al, 2014;Horn et al, 2000;Obata et al, 2016) and bacterium Zymomonas mobilis (Horn et al, 2000). Saccharomyces cerevisiae cannot ferment a wide range of sugars, including pentose sugars (e.g., xylose), which is why scientists are also looking for new, pentose-fermenting yeast strains, such as Pichia (Scheffersomyces) stipites and Kluyveromyces marxianus, a thermotolerant yeast (Obata et al, 2016). The same problem is with polysaccharides from brown and red seaweeds.…”

“…• Fermentation to bioethanol can be performed for wet algal biomass (Milledge et al, 2014) • Significant sugar content (Kostas et al, 2016;Philippsen et al, 2014) • Successful lab-scale conversion to ethanol (Philippsen et al, 2014) • Only few macroalgal species contain lignin, most of them contain no lignin at all, which makes macroalgal biomass on average a relatively easy material to digest by microbes in bioethanol production (Kostas et al, 2016;Obata et al, 2016;Suutari et al, 2015;Yanagisawa et al, 2013), delignification is not required in contrast to lignocellulosic biomass (Yanagisawa et al, 2013) • The pretreatment temperature, as well as the enzyme saccharification conditions are relatively milder for seaweeds compared to that of terrestrial biomass (Borines et al, 2013) • For the fermentation process, microorganisms can be metabolically modified (higher capability of utilizing the sugars released from polysaccharides) in order to reach higher yield (Horn et al, 2000;Jiang et al, 2016) • Organic residue from the hydrolysis of seaweeds can be fermented to methane (Horn et al, 2000) • Significant fluctuations in the content of fermentable carbohydrates-seasonal changes (Philippsen et al, 2014) • Microorganisms able to utilize different carbohydrates are required, specific to the given sugar in order to convert it into ethanol (Horn et al, 2000;Kostas et al, 2016;Obata et al, 2016) • Existing ethanologenic microbes cannot convert alginate (polysaccharide in brown seaweeds) to ethanol-necessity to use of metabolically engineered bacteria (Takeda et al, 2011) • High content of metals/minerals in macroalgae released to the fermentation liquid during pretreatment and saccharification can inhibit the microbial fermentation (Khambhaty et al, 2013;Milledge et al, 2014;van Hal et al, 2014) • Hydrolysates derived from acid hydrolysis of seaweeds can contain yeast-inhibitory compounds (a range of phenolic compounds, organic acids and furan compounds) which are formed in the acid pretreatment of lignocellulosic biomass at high temperatures (negative impact on ethanol production during fermentation) (Kostas et al, 2016) • The large content of chloride-containing salts in seaweeds can corrode common alloys such as stainles...…”