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Advanced Process Options for Bioethanol Production
Published in Charles E. Wyman, Handbook on Bioethanol, 2018
Significant developments have been made in the individual areas of xylose- and cellulose-to-ethanol conversion. Jeffries [6] and McMillan [7] present reviews of the current technology for xylose fermentation. High-yield yeast strains of Candida shehatae and Pichia stipitis have helped to achieve product levels greater than 0.45 g ethanol/g xylose (about 88% of theoretical yield) [8,9]. The volumetric productivities, however, remain low (below 0.5 g/L/h), even in continuous culture experiments [6,7]. Genetic engineering has been attempted on bacteria and yeast to improve xylose conversion; only the bacterial recombinant strains of Escherichia coli [10-12] and Klebsiella oxytoca have successfully enhanced yields and productivity. Recent developments with Zymomonas mobilis indicate a significant potential of its use in the ethanol process [13]. In the area of cellulose conversion, SSF has shown considerable promise by alleviating glucose inhibition of cellulase activity [4]. However, differences in the optimal conditions of the cellulase system for hydrolysis and of the yeast for sugar fermentation require that a compromise set of cultivation conditions be selected for efficient conversion.
Development of Biorefinery Systems: From Biofuel Upgrading to Multiproduct Portfolios
Published in Carlos Ariel Cardona Alzate, Jonathan Moncada Botero, Valentina Aristizábal-Marulanda, Biorefineries, 2018
Carlos Ariel Cardona Alzate, Jonathan Moncada Botero, Valentina Aristizábal-Marulanda
Palm is one of the most important oleo-chemical feedstocks in Indonesia, Malaysia, and Colombia. Currently, palm is used for biodiesel production, and glycerol is the main by-product obtained from this process. Additionally, the processing of palm for oil extraction leads to the formation of several residues such as empty fruit bunches (EFB). In this sense, the configuration of this biorefinery comprises four main processes: (i) biodiesel production, (ii) glycerol purification, (iii) ethanol production, and (iv) PHB production corresponding to Scenario 3. Scenario 4 considers the production of biodiesel, fuel ethanol, and PHB with mass integration of materials and recovery of waste streams [11]. Figure 7.6 indicates the generalized diagram of oil palm biorefinery. The biodiesel production can be described by three main sequential stages: esterification reaction, trans-esterification reaction, and distillation or vacuum flash. Raw glycerol, coming from the biodiesel process, can be used as a carbon source to produce PHB. The glycerol is purified by removing and neutralizing the remaining methanol and the catalyst for obtaining a glycerol stream at high purity. The glycerol obtained in this process is used as a substrate for the PHB production by fermentation using C. necator (R. eutropha) as a microorganism [8]. Another product of this biorefinery is lignocellulosic ethanol, which uses EFB as a feedstock. When this type of raw material is used, the process to produce fuel ethanol can be described in six stages: dilute-acid hydrolysis, detoxification, enzymatic hydrolysis, fermentation, distillation, and dehydration [11], [12]. The fermentation step is carried out using Zymomonas mobilis as the fermenting microorganism [13].
Modeling of bioethanol production through glucose fermentation using Saccharomyces cerevisiae immobilized on sodium alginate beads
Published in Cogent Engineering, 2022
Astrilia Damayanti, Zuhriyan Ash Shiddieqy Bahlawan, Andri Cahyo Kumoro
The continuous development of industrialization and transportation activities around the world has led to an incredible annual increase in fossil energy consumption by 2% to 3% per year, which triggers rapid fossil fuel resources depletion (Azhar & Abdulla, 2018). To respond to this continuous decline of fossil fuel reserves, alternatives of energy sources have to be renewable, sustainable, environmentally benign, affordable, safe, and convenient (Bušić et al., 2018; Hossain et al., 2017). As the most popular alternative to gasoline, ethanol has gained remarkable attention from researchers, which lead to the rapid development of microbial ethanol production (Rastogi & Shrivastava, 2017). Various microorganisms, such as Saccharomyces cerevisiae (Azhar et al., 2017), Saccharomyces pastorianus (Harcum & Caldwell, 2020), Saccharomyces bayanus (Gil & Maupoey, 2018), Kluyveromyces marxianus (Murari et al., 2019), Clostridium sp. and Zymomonas mobilis (Beltran et al., 2020) have been proven to be the appropriate candidates to produce ethanol in commercial-scale. Naturally, both S. cerevisiae as the mesophilic and K. marxianus as the thermotolerant yeasts are acidophilic microorganisms. Therefore, they can grow well if the conditions are under an acidic environment with a pH range of 4.0 to 6.0, high and low temperatures, the presence of oxygen, and the type of yeast strain (Tkavc et al., 2018).
Bioconversion and bioethanol production from agro-residues through fermentation process using mangrove-associated actinobacterium Streptomyces olivaceus (MSU3)
Published in Biofuels, 2019
Sanjivkumar Muthusamy, Silambarasan Tamil Selvan, Palavesam Arunachalam, Immanuel Grasian
Huang et al. reported the (150 IU/g) xylanolytic hydrolysis of bamboo residue yielded the maximum degree of saccharification (83.15%) and ethanol production (12.50 g/L) at pH 6, temperature 40°C and 72 h of incubation [52]. Adiguzel and Tuncer studied hydrolysis of wheat straw pretreated with 1% NaOH, which exhibited the maximum degree of saccharification (43.29%) at pH 8, temperature 40°C and 12 h of incubation time [53]. In the present study, among the tested temperatures, the saccharification and bioethanol production were recorded respectively as 29.50% and 1.33 g/L at 20°C, and increased further to 37.50% and 1.67 g/L at 30°C. Beyond 30°C, production gradually decreased (from 34.00 to 17.91% and from 1.49 to 0.78 g/L at 40 to 70°C, respectively). Similarly, Magdy et al. pointed out that a temperature range of 25–30°C was commonly found to be optimal for S. cerevisiae for the production of bioethanol through a fermentation process [54]. In an another report, Saritha et al. documented the highest saccharification yield (97.8%) from accelerase-pretreated paddy straw using Streptomyces griseorubens at pH 6, temperature 30°C, inoculum size of 1.5% and 48 h of incubation time [38]. In this investigation, the effect of nutritional sources on bioethanol production indicated that among the tested carbon sources, dextrose-substituted medium displayed the maximum saccharification (43.0%) and bioethanol production (2.35 g/L), whereas fructose-substituted medium displayed the minimum bioethanol production (0.88 g/L) and lactose-substituted medium displayed the minimum saccharification (20.13%). Similarly, among the tested nitrogen sources, urea-substituted medium showed maximum (52.5%) saccharification and production of bioethanol (2.55g/L), followed by tryptone (42.0% and 2.33 g/L), peptone (39.0% and 2.27 g/L) and yeast extract (35.0% and 2.19 g/L) etc., but the beef extract-substituted medium resulted in the least production (1.25 g/L) of bioethanol, and ammonium sulphate-substituted medium resulted in the minimum saccharification (24.50%). Davis et al. observed a maximum ethanol production of 28.0% by Zymomonas mobilis ZM4 using hydrolysate of wheat silage supplemented with 5.0 g/L yeast extract, 40 g/L glucose and 2.6 g/L xylose through solid state fermentation [55]. In terms of the effect of inoculum size on bioethanol production and saccharification, the present study showed that at the lowest inoculum size (0.5%), the bioethanol production and saccharification were recorded as 0.79 g/L and 19.87% respectively; however, when the size of inoculum was increased, the bioethanol production and saccharification also increased and attain their maximum (47.23% and 1.88 g/L) at 2.5% inoculum size. Further increase in inoculum size resulted in a decrease in both saccharification and ethanol production. In accordance with these results, Patel et al. reported that the use of pretreated wheat and rice straw on bioethanol production by S. cereviseae (NCIM 3095) yielded 2.5 g/L of ethanol at 3% inoculum size [56].