Cellulosic Bioethanol from Industrial Eucalyptus globulus Bark Residues Using Kraft Pulping as a Pretreatment

The pulp and paper industry faces an emerging challenge for valorising wastes and side-streams generated according to the biorefinery concept. Eucalyptus globulus bark, an abundant industrial residue in the Portuguese pulp and paper sector, has a high potential to be converted into biobased products instead of being burned. This work aimed to evaluate the ethanol production from E. globulus bark previously submitted to kraft pulping through separate hydrolysis and fermentation (SHF) configuration. Fed-batch enzymatic hydrolysis provided a concentrated hydrolysate with 161.6 g·L−1 of cellulosic sugars. S. cerevisiae and Ethanol Red® strains demonstrated a very good fermentation performance, despite a negligible xylose consumption. S. passalidarum, a yeast known for its capability to consume pentoses, was studied in a simultaneous co-culture with Ethanol Red®. However, bioethanol production was not improved. The best fermentation performance was achieved by Ethanol Red®, which provided a maximum ethanol concentration near 50 g·L−1 and fermentation efficiency of 80%. Concluding, kraft pulp from E. globulus bark showed a high potential to be converted into cellulosic bioethanol, being susceptible to implementing an integrated biorefinery on the pulp and paper industrial plants.

New Insights for the Future Design of Composites Composed of Hydrochar and Zeolite for Developing Advanced Biofuels from Cranberry Pomace

This study provides fundamental insight and offers a promising catalytic hydrothermal method to harness cranberry pomace as a potential bioenergy and/or hydrochar source. The physical and chemical properties of Canadian cranberry pomace, supplied by Fruit d’Or Inc., were examined and the optimum operational conditions, in terms of biocrude yield, were obtained by the I-optimal matrix of Design Expert 11. Afterward, cranberry pomace hydrochar (CPH) and zeolite were separately introduced to the hydrothermal liquefaction (HTL) process to investigate the benefits and disadvantages associated with their catalytic activity. CPH was found to be a better host than zeolite to accommodate cellulosic sugars and showed great catalytic performance in producing hydrocarbons. However, high amounts of corrosive amino and aliphatic acids hinder the practical application of CPH as a catalyst. Alternatively, zeolite, as a commercial high surface area catalyst, had a higher activity for deoxygenation of compounds containing carbonyl, carboxyl, and hydroxyl groups than CPH and resulted in higher selectivity of phenols. Due to the low hydrothermal structural stability, coke formation, and narrow pore size distribution, further activations and modifications are needed to improve the catalytic behavior of zeolite. Our results suggest that a composite composed of CPH and zeolite can resolve the abovementioned limitations and help with the development and commercialization of advanced biofuels from cranberry pomace.

Guanidine Riboswitch-Regulated Efflux Transporters Protect Bacteria against Ionic Liquid Toxicity

ABSTRACT Plant cell walls contain a renewable, nearly limitless supply of sugar that could be used to support microbial production of commodity chemicals and biofuels. Imidazolium ionic liquid (IIL) solvents are among the best reagents for gaining access to the sugars in this otherwise recalcitrant biomass. However, the sugars from IIL-treated biomass are inevitably contaminated with residual IILs that inhibit growth in bacteria and yeast, blocking biochemical production by these organisms. IIL toxicity is, therefore, a critical roadblock in many industrial biosynthetic pathways. Although several IIL-tolerant (IILT) bacterial and yeast isolates have been identified in nature, few genetic mechanisms have been identified. In this study, we identified two IILT Bacillus isolates as well as a spontaneous IILT Escherichia coli lab strain that are tolerant to high levels of two widely used IILs. We demonstrate that all three IILT strains contain one or more pumps of the small multidrug resistance (SMR) family, and two of these strains contain mutations that affect an adjacent regulatory guanidine riboswitch. Furthermore, we show that the regulation of E. coli sugE by the guanidine II riboswitch can be exploited to promote IIL tolerance by the simple addition of guanidine to the medium. Our results demonstrate the critical role that transporter genes play in IIL tolerance in their native bacterial hosts. The study presented here is another step in engineering IIL tolerance into industrial strains toward overcoming this key gap in biofuels and industrial biochemical production processes. IMPORTANCE This study identifies bacteria that are tolerant to ionic liquid solvents used in the production of biofuels and industrial biochemicals. For industrial microbiology, it is essential to find less-harmful reagents and microbes that are resistant to their cytotoxic effects. We identified a family of small multidrug resistance efflux transporters, which are responsible for the tolerance of these strains. We also found that this resistance can be caused by mutations in the sequences of guanidine-specific riboswitches that regulate these efflux pumps. Extending this knowledge, we demonstrated that guanidine itself can promote ionic liquid tolerance. Our findings will inform genetic engineering strategies that improve conversion of cellulosic sugars into biofuels and biochemicals in processes where low concentrations of ionic liquids surpass bacterial tolerance.

Residual biomass from food processing industry in Cameroon as feedstock for second-generation biofuels

The yields in bioconversion of residues produced in the Cameroon food industry to liquid and gaseous biofuels were evaluated and the potential of these residues as feedstock for renewable energy production in Cameroon were assessed. Residues generated after processing avocado, cocoa, and peanut crops were converted at laboratory-scale to second-generation gaseous biofuels (biogas) and liquid biofuels (ethanol). Mechanical (milling), thermal-chemical (steam-NaOH), and microwave pretreatments were applied before hydrolysis of biomass using cellulolytic enzymes. Cellulosic sugars production potential was also assessed. The energy conversion rate was higher when anaerobic digestion technology was applied to convert the tested biomass to methane. The total Cameroon potential under anaerobic digestion technology is over 330,000 m3, which represents 28% from oil consumption or 5.39% from electricity consumption when lignocellulosic ethanol technology was applied. The national potential was assessed up to 200,000 kg, representing 17% from oil consumption in transport or 3.19% from electricity consumption. Overall, the share of energy potential of the tested residual biomass is important when compared to fossil fuel consumption in Cameroon and represents an important potential feedstock for electricity production.