María García-Torreiro

Alkali treatment of fungal pretreated wheat straw for bioethanol production

Abstract Bioconversion of lignocellulosic materials into ethanol requires an intermediate pretreatment step for conditioning biomass. Sugar yields from wheat straw were previously improved by the addition of a mild alkali pretreatment step before bioconversion by the white-rot fungus Irpex lacteus. In this work, an alternative alkaline treatment, which significantly reduces water consumption, was implemented and optimized. Sugar recovery increased 117% with respect to the previously developed alkaline wash process at optimal process conditions (30°C, 30 minutes and 35.7% (w/w) of NaOH). In order to further reduce operational costs, a system for alkali recycling was implemented. This resulted in the treatment of 150% more wheat straw using the same amount of NaOH. Finally, enzymatic hydrolysis was optimized and resulted in a reduction of enzyme dose of 33%.

Production and Emerging Applications of Bioactive Oligosaccharides from Biomass Hemicelluloses by Hydrothermal Processing

Hemicelluloses are the second most abundant heterogeneous polysaccharides in nature. Among the several treatments that can be used for the solubilization of hemicelluloses to produce oligosaccharides from lignocellulosic biomass, the autohydrolysis reaction is the most widely used. Under suitable conditions, autohydrolysis enables high ligosaccharides yields, however this reaction is not selective and undesired compounds are also present in the reaction media. Because of this, the autohydrolysis media has to be subjected to further processing to improve the purity of oligosaccharide hydrolysate. The chemical and structural characterization of the solubilized products from hemicelluloses is an important aspect as it allows to know the application for which they are more suitable. Oligosaccharides from hemicelluloses can find applications in several fields such as biomedical, food, and biomaterials.

Application of flow cytometry for monitoring the production of poly(3‐hydroxybutyrate) by Halomonas boliviensis

In this study, a flow cytometry (FC) protocol was implemented to measure poly(3‐hydroxybutyrate) (PHB) content in a halophilic bacterium, to have a faster and easier control of the process. The halophilic bacterium Halomonas boliviensis was stained with BODIPY 493/503 and analyzed using FC. Bacterial polymer accumulation induced by two different nutrient limitations during the operation of a 2 L bioreactor was studied using traditional gas chromatography (GC) analysis and FC. The application of this rapid and straightforward method is useful to obtain complex and precise information about PHB accumulation that could be used for the monitoring, control and optimization of the production of PHB. A clear correlation between the PHB concentration determined by GC and the fluorescence signal obtained from stained bacteria by using FC was observed. Additionally, the heterogeneity of bacterial population as a function of PHB content was measured.

Application of Fungal Pretreatment in the Production of Ethanol From Crop Residues

Abstract The fungal pretreatment of lignocellulosic biomass for the production of ethanol is a low-cost, safe, and environmentally friendly process that can be used as an alternative to the more energy-demanding physicochemical pretreatments. It is based on the special features of white-rot fungi (WRF), which have the ability to degrade lignin by using extracellular ligninolytic enzymes. Fungal pretreatment has the advantage of selectively removing lignin and increase the digestibility of cellulose and hemicellulose at mild operational conditions, without producing inhibitors. Fungal pretreatment has been applied to different crop residues for producing ethanol, demonstrating that it is capable of handling feedstocks of variable origin. However, the integration of the fungal pretreatment in a biorefinery needs to be adapted to the special characteristics of WRF, to take full advantage of its great potential and to overcome the inherent drawbacks

Lessons learned from the treatment of organosolv pulp with ligninolytic enzymes and chemical delignification agents

Although organosolv pretreatment allows extensive delignification of beech wood, the residual lignin present in the pulp may hinder the subsequent hydrolysis of the cellulose into fermentable sugars. With the purpose of increasing sugar production from cellulose hydrolysis, enzymatic and chemical oxidation stages were applied to the pulp previously to a stage of enzymatic hydrolysis with cellulases. Neither lignin content was reduced, nor sugar yield was improved after the versatile peroxidase treatment. On the other hand, laccase oxidation caused an increase in total lignin and kappa number and did not influence digestibility. Similarly, the chemical oxidation with H2O2 had also a negligible impact on the sugar yield. Only a significant removal of the lignin content in fibers was attained after ethanol wash, also confirmed by FT-IR analysis, which allowed increasing cellulose digestibility by 8.4%, and reducing the phenol content of the hydrolysate by 45.5%. Although the improvement of cellulose digestibility was lower than expected, this work provides valuable lessons for practical use on the opportunities of organosolv pulp.