Bioethanol (a renewable resource), blended with gasoline, is used as liquid transportation fuel worldwide and produced from either starch or lignocellulose. Local production and use of bioethanol supports local economies, decreases country's carbon footprint and promotes self-sufficiency. The latter is especially important for bio-resource-rich landlocked countries like Nepal that are seeking alternative transportation fuels and technologies to produce them. In that regard, in the present study, we have used two highly efficient ethanol producing yeast strains, viz., Saccharomyces cerevisiae (CDBT2) and Wickerhamomyces anomalous (CDBT7), in an electrochemical cell to enhance ethanol production. Ethanol production by CDBT2 (anodic chamber) and CDBT7 (cathodic chamber) control cultures, using 5% glucose as substrate, were 12.6 ± 0.42 and 10.1 ± 0.17 mg•mL −1 respectively. These cultures in the electrochemical cell, when externally supplied with 4V, the ethanol production was enhanced by 19.8 ± 0.50% and 23.7 ± 0.51%, respectively, as compared to the control cultures. On the other hand, co-culturing of those two yeast strains in both electrode compartments resulted only 3.96 ± 0.83% enhancement in ethanol production. Immobilization of CDBT7 in the graphite cathode resulted in lower enhancement of ethanol production (5.30 ± 0.82%), less than free cell culture of CDBT7. CDBT2 and CDBT7 when cultured in platinum nano particle coated platinum anode and neutral red-coated graphite cathode, respectively, ethanol production was substantially enhanced (52.8 ± 0.44%). The above experiments when repeated using lignocellulosic biomass hydrolysate (reducing sugar content was 3.3%) as substrate, resulted in even better enhancement in ethanol production (61.5 ± 0.12%) as compared to glucose. The results concluded that CDBT2 and CDBT7 yeast strains produced ethanol efficiently from both glucose and lignocellulosic biomass Joshi et al. Enhancement of Ethanol Production in Electrochemical Cell hydrolysate. Ethanol production was enhanced in the presence of low levels of externally applied voltage. Ethanol production was further enhanced with the better electron transport provision i.e., when neutral red was deposited on cathode and fine platinum nanoparticles were coated on the platinum anode.
In view of crude oil prices, and its environmental issues, utilization of sustainable renewable alternative energies such as biofuels is rapidly progressing in many countries. The increasing global energy demand and depleting fossils fuels sources has led to search alternative clean and renewable fuels. One of the best alternatives to the gasoline is lignocellulosic bioethanol. Recent researches on lignocellulosic bioethanol focuses on advancement of pretreatment techniques for improved sugar yields and decreased inhibitors production. Pretreatment technique with no or less use of chemicals and cost effectiveness is the main purpose of most of the researches. Biological pretreatment techniques produce less fermentation inhibitors than chemical pretreatments. In order to cope with fermentation inhibitors different strategies can be adopted during pretreatment processes. In the course of time, advancements in production process over separate hydrolysis and fermentation have been introduced. Simultaneous saccharification and co/fermentation; and consolidated bioprocessing for bioethanol production are gaining popularity among researchers. Int. J. Appl. Sci. Biotechnol. Vol 10(1): 1-11.
Production of lignocellulosic ethanol using microbial consortium can be an economical strategy. Consortium of ligninolytic and cellulolytic microbe(s) that can depolymerize lignin and hydrolyze cellulose along with fermenting yeast (CDBT-2) can replace the separate techniques used for biomass pretreatment and hydrolysis prior to fermentation. So, the aim of this study was to screen fungi capable of producing laccase (lignin depolymerizing enzyme) and cellulase (converts cellulose to fermentable sugars), and use the strains along with Saccharomyces cerevisiae (CDBT-2) to develop an integrated method of simultaneous pretreatment saccharification and electro-fermentation of Saccharum spontaneum powder to produce ethanol. 18-s rRNA sequencing and BLAST analysis of screened isolates confirmed, cellulolytic isolate (F1) resembled as Aspergillus niger and, ligninocellulolytic isolate (F2) resembled to Ganoderma sessile. These fungi were used along with CDBT2 for ethanol production. Different consortiums sets of these isolates were tested for fermentation efficiency. All the analysis were done using crude untreated as well as hot water pretreated S. spontaneum powder to compare the ethanol production efficiency. In controlled environment of 28oC, shaking at 80 rpm and 5.0 pH, culture with consortium of G. sessile and CDBT2 produced higher ethanol with yield 57 mg/g biomass powder followed by consortium of G. sessile, A. niger and CDBT2 with yield of 44±0.18 mg/g biomass. Monoculture of G. sessile produced higher amount of phenol ie 292.48±17.74 µg/mL. Similarly, G. sessile, A. niger and CDBT2 consortium produced higher furfural of 58.48±3.86 µg/mL. However, the amount of phenol and furfural generated were very low in both cases. The ethanol yield was higher in crude biomass compared to hot water pretreated S. spontaneum powder. In addition, electro-fermentation of crude S. spontaneum enhanced ethanol production by 12% with G. sessile and CDBT2 consortium while 18% with the set of G. sessile, A. niger and CDBT2 consortium. This monophasic method of integrated pretreatment saccharification and electro-fermentation can be an alternative approach for lignocellulosic bioethanol production as it does not require separate pretreatment and fermentation approach. Keywords: Bioethanol, Saccharum spontaneum, microbial consortium, simultaneous saccharification and fermentation, and electro-fermentation Figure 1
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