Effect of High Solids Loading on Bacterial Contamination in Lignocellulosic Ethanol Production

Ishola, Mofoluwake M.; Babapour, Ayda Barid; Gavitar, Maryam Nadalipour; Brandberg, Tomas; Taherzadeh, Mohammad J.

doi:10.15376/biores.8.3.4429-4439

Cited by 9 publications

(6 citation statements)

References 19 publications

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“…Several attempts have been made to study and control bacterial contamination in lignocellulosic ethanol production including: (1) adding NaCl and ethanol to wood hydrolysate (Albers et al 2011 ), (2) high solid loading in simultaneous saccharification and fermentation (SSF) (Ishola et al 2013 ), (3) usage of an antibiotic like gentamicin and biomass autoclaving (Serate et al 2015 ), and (4) usage of bacteriophages (Worley-Morse et al 2015 ). These strategies encounter challenges including: (1) additional cost and need for extensive fine tuning and testing of concentrations of NaCl and ethanol (Albers et al 2011 ), (2) loss of cell viability due to mechanical stress caused by solid particles in high cell loading (Ishola et al 2013 ), (3) cost and environmental challenges posed by gentamicin, energy expenditure and formation of inhibitors due to autoclaving (Serate et al 2015 ), and (4) rise of bacteriophage-insensitive mutants and possibilities of gene transfer from bacteriophages to yeast (Worley-Morse et al 2015 ). One of the potentially scalable and economically feasible solutions to control bacterial contamination is to run the lignocellulosic fermentation at low pH, around pH 4 where the growth and viability of bacteria are drastically reduced (Kádár et al 2007 ).…”

Section: Introductionmentioning

confidence: 99%

Adaptation to low pH and lignocellulosic inhibitors resulting in ethanolic fermentation and growth of Saccharomyces cerevisiae

et al. 2016

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Lignocellulosic bioethanol from renewable feedstocks using Saccharomyces cerevisiae is a promising alternative to fossil fuels owing to environmental challenges. S. cerevisiae is frequently challenged by bacterial contamination and a combination of lignocellulosic inhibitors formed during the pre-treatment, in terms of growth, ethanol yield and productivity. We investigated the phenotypic robustness of a brewing yeast strain TMB3500 and its ability to adapt to low pH thereby preventing bacterial contamination along with lignocellulosic inhibitors by short-term adaptation and adaptive lab evolution (ALE). The short-term adaptation strategy was used to investigate the inherent ability of strain TMB3500 to activate a robust phenotype involving pre-culturing yeast cells in defined medium with lignocellulosic inhibitors at pH 5.0 until late exponential phase prior to inoculating them in defined media with the same inhibitor cocktail at pH 3.7. Adapted cells were able to grow aerobically, ferment anaerobically (glucose exhaustion by 19 ± 5 h to yield 0.45 ± 0.01 g ethanol g glucose−1) and portray significant detoxification of inhibitors at pH 3.7, when compared to non-adapted cells. ALE was performed to investigate whether a stable strain could be developed to grow and ferment at low pH with lignocellulosic inhibitors in a continuous suspension culture. Though a robust population was obtained after 3600 h with an ability to grow and ferment at pH 3.7 with inhibitors, inhibitor robustness was not stable as indicated by the characterisation of the evolved culture possibly due to phenotypic plasticity. With further research, this short-term adaptation and low pH strategy could be successfully applied in lignocellulosic ethanol plants to prevent bacterial contamination.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-016-0234-8) contains supplementary material, which is available to authorized users.

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Section: Introductionmentioning

confidence: 99%

Adaptation to low pH and lignocellulosic inhibitors resulting in ethanolic fermentation and growth of Saccharomyces cerevisiae

et al. 2016

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“…Ethanol production from lignocellulosic materials, such as woody biomass, forest, and agricultural residues, has the potential of reducing society’s dependence on fossil fuels [ 1 , 2 , 3 ]. Lignocellulosic materials consist of three main structural components: cellulose, hemicellulose, and lignin [ 4 , 5 , 6 ].…”

Section: Introductionmentioning

confidence: 99%

Co-Utilization of Glucose and Xylose for Enhanced Lignocellulosic Ethanol Production with Reverse Membrane Bioreactors

2015

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Integrated permeate channel (IPC) flat sheet membranes were examined for use as a reverse membrane bioreactor (rMBR) for lignocellulosic ethanol production. The fermenting organism, Saccharomyces cerevisiae (T0936), a genetically-modified strain with the ability to ferment xylose, was used inside the rMBR. The rMBR was evaluated for simultaneous glucose and xylose utilization as well as in situ detoxification of furfural and hydroxylmethyl furfural (HMF). The synthetic medium was investigated, after which the pretreated wheat straw was used as a xylose-rich lignocellulosic substrate. The IPC membrane panels were successfully used as the rMBR during the batch fermentations, which lasted for up to eight days without fouling. With the rMBR, complete glucose and xylose utilization, resulting in 86% of the theoretical ethanol yield, was observed with the synthetic medium. Its application with the pretreated wheat straw resulted in complete glucose consumption and 87% xylose utilization; a final ethanol concentration of 30.3 g/L was obtained, which corresponds to 83% of the theoretical yield. Moreover, complete in situ detoxification of furfural and HMF was obtained within 36 h and 60 h, respectively, with the rMBR. The use of the rMBR is a promising technology for large-scale lignocellulosic ethanol production, since it facilitates the co-utilization of glucose and xylose; moreover, the technology would also allow the reuse of the yeast for several batches.

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“…The SSF of the substrate obtained by integrating the ensiled corncob and diluted molasses without the addition of enzymes, supplements, or yeast strains was referred to as simultaneous saccharification and fermentation with native microorganisms (SSFNM). A conventional SSF is operated at 30 -40 °C with an initial pH of 4.8 -5.5 [4,24], whereas the growth of beneficial microorganisms, such as yeast, is optimal at 24 -34 °C with a pH of 3.5 -4.8 [25]. Therefore, the SSFNM was then studied at low temperatures of 25 -35 °C to retain nutrients for supporting microbial growth and at acidic pH levels of 4.5 -5.5 to activate the functions of beneficial microorganisms for saccharification and ethanol fermentation for 84 h. SSFNM variables were investigated in the desire to produce satisfactory ethanol.…”

Section: Introductionmentioning

confidence: 99%

Integration of Ensiled Corncob to Diluted Molasses as Carbon and Microbial Sources for Ethanol Production

Chongkhong

2023

Trends Sci

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To improve ethanol production, carbon and microbial sources were derived from corncob and molasses. Before investigating simultaneous saccharification and fermentation (SSF), the boiled corncob was vacuum-ensiled and the molasses was diluted. The optimal ensiling time of 4 days increased not only the amount of fermentable sugar but also the population of beneficial microorganisms. The proper dilution of molasses at a ratio of 1:3 molasses to boiled water reduced both the contamination problem and the inhibition of ethanol fermentation. The combination of the ensiled corncob and the diluted molasses could provide a substrate that is suitable for SSF without the addition of enzymes, supplements, or yeast strains. The substrate contained the optimal concentration of initial sugar (174.631 ± 0.975 g/L) and viable microorganisms (1.9×106 ± 0.1×106 CFU/mL of total bacteria and 1.0x105 ± 0.1×105CFU/mL of yeast) that could continue to hydrolyze and ferment carbohydrates in the substrate for the SSF. Using a ratio of 1:3 of ensiled corncob to diluted molasses, a pH of 4.5, and a temperature of 27 °C for 72 h, the SSF produced the highest concentration of ethanol at 93.345 ± 0.062 g/L. This work provides a cost-effective process that requires no enzyme or yeast, is simply technology, and is friendly to the environment, while the remaining solid fraction can be utilized as a suitable feedstock for biogas production. HIGHLIGHTS Vacuum-ensiling increased hydrolytic microbe activity, improving biomass hydrolysis Vacuum-ensiling increased not only sugar content but also microbe population Molasses dilution reduced contamination problem and ethanol fermentation inhibition Ensiled corncob mixed with diluted molasses was a suitable substrate for SSF SSF was completed efficiently without the addition of enzymes or yeasts GRAPHICAL ABSTRACT

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Effect of High Solids Loading on Bacterial Contamination in Lignocellulosic Ethanol Production

Cited by 9 publications

References 19 publications

Adaptation to low pH and lignocellulosic inhibitors resulting in ethanolic fermentation and growth of Saccharomyces cerevisiae

Adaptation to low pH and lignocellulosic inhibitors resulting in ethanolic fermentation and growth of Saccharomyces cerevisiae

Co-Utilization of Glucose and Xylose for Enhanced Lignocellulosic Ethanol Production with Reverse Membrane Bioreactors

Integration of Ensiled Corncob to Diluted Molasses as Carbon and Microbial Sources for Ethanol Production

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