Electrochemical quantification of d-glucose during the production of bioethanol from thermo-mechanically pre-treated wheat straw.

Mechanical pre-treatment (disc refining) of wheat straw, at both atmospheric and elevated pressure, is shown to be an efficient process to access fermentable monosaccharides, with the potential to integrate within the infrastructure of existing first-generation bioethanol plants. The mild, enzymatic degradation of this sustainable lignocellulosic biomass affords ca. 0.10-0.13 g/g (dry weight) of d-glucose quantifiable voltammetrically in real time, over a two hundred-fold range in experimental laboratory scales (25 mL to 5.0 L), with pressure disc refining of the wheat straw enabling almost twice the amount of d-glucose to be generated during the hydrolysis stage than experiments using atmospheric refining (0.06-0.09 g/g dry weight). Fermentation of the resulting hydrolysate affords 0.08-0.10 g/g (dry weight) of ethanol over similar scales, with ethanol productivity at ca. 37 mg/(L h). These results demonstrate that minimal cellulose decomposition occurs during pressure refining of wheat straw, in contrast to hemicellulose, and suggest that the development of green, mechanochemical processes for the scalable and cost-effective manufacture of second-generation bioethanol requires improved cellulose decomposition.

Pressurised disc refining of wheat straw as a pre-treatment approach for agricultural residues: A preliminary assessment of energy consumption and fibre composition.

This preliminary study assesses a potential pre-treatment approach for agricultural residues, in order to improve enzyme access and cellulose digestibility that increased with increasing refining pressure. Wheat straw, an important European agri-residue, was chopped then refined at pilot-scale under different pressures (4-10 bar) and two refiner plate configurations. The most energy efficient runs used 0.94-0.96 kWh electricity; 8.9-11.0 MJ heat per kg dry matter fibre. A scaling factor specific to the machinery used in the trial suggested that wheat straw could be refined using approximately 160 kWh electricity and 980-1900 MJ heat per tonne DM yield at commercial-scale. Hemicellulose content in wheat straw at 31.8% decreased to the lowest level of 14.6% after refining at 10 bar. Pressurised disc refining did not appear to produce significant quantities of acetic acid, a key fermentation inhibitor, that could limit microbial fermentation.

Comparative study of lignins isolated by alkali and ultrasound-assisted alkali extractions from wheat straw.

Treatment of the dewaxed wheat straw with 0.5 M KOH at 35 degrees C for 2.5 h without ultrasonic irradiation and with ultrasound assistance for 5, 10, 15, 20, 25, 30, and 35 min resulted in a dissolution of 43.9%, 43.9%, 43.9%, 44.4%, 44.4%, 45.6%, 46.8%, and 49.1% of the original lignin, respectively. Much better results were achieved under the ultrasonic irradiation time for 35 min where nearly 50% of the original lignin was solubilized at 35 degrees C for 2.5 h. The purity of the lignin preparations isolated by alkali with ultrasound assistance was higher than that of the lignin fraction obtained by alkali without ultrasonic irradiation, and their purity increased with an increment of irradiation time between 5 and 35 min, in which the content of associated polysaccharides in the former lignin preparations (0.87-1.06%) was lower than that of the latter lignin fraction (1.16%). In addition, the lignins isolated by alkali with ultrasonic irradiation time between 5 and 30 min showed a slightly higher molecular weight and thermal stability than the lignin obtained by alkali without ultrasound assistance. No substantial differences in the main structure features between the lignin preparations isolated by alkali and ultrasound-assisted alkali extractions were found.