Arturo Sanchez

The economic feasibility of lignocellulosic ethanol production depends on obtaining high yields and productivity. This condition requires extensive research to identify strategies that maximize yield and productivity in lignocellulosic ethanol production. Self-cycling fermentation (SCF) has been shown to increase ethanol productivity. To validate whether the SCF system could enhance productivity during ethanol fermentation, we simulated the process using experimental results obtained from six cycles in a stirred bioreactor and compared the outcomes with separate hydrolysis and fermentation (SHF) and simultaneous saccharification-fermentation (SSF) for ethanol production from wheat straw using Kluyveromyces marxianus SLP1. The volumetric ethanol productivity (Q_p) was 1.11 g/Lh, 1.13 g/Lh, and 0.42 g/Lh for SCF, SHF, and SSF, respectively. The system with the highest global productivity (Q_g) was SCF with 0.65 g/Lh. Moreover, the estimated annual ethanol productivity for SCF (P_SCF) improved by 21.7% compared with SHF and by 3.1-fold improvement over SSF. This result confirms that SCF can be an effective strategy for increasing productivity during lignocellulosic ethanol production. However, the SCF system is limited by the physiological states of the yeasts. Graphical Abstract

The high cost of commercial enzymes for depolymerizing fermentable carbohydrates of lignocellulosic biomass represents one of the main drawbacks to its use as a renewable feedstock to produce bioenergy and bioproducts. This work employs the dilution-to-stimulation method to produce simplified microbiotas with a high capacity for cellulose degradation. These microbiotas were obtained from four lignocellulosic composts cultivated under aerobic and anaerobic conditions during ten transfers using carboxymethylcellulose (CMC) as carbon source. After the eighth transfer, the depolymerization percentage of CMC reached the same values (70 ± 3%) for all microbiotas and respiration conditions. The microbial structure of all enriched microbiotas was simplified, mostly to Lactobacillus and Clostridium in anaerobic conditions while the more diverse aerobic enriched microbiotas were composed mainly of Rhizobium, Enterobacter, Alcaligenes, and Enterococcus. After the enrichment process, the two enriched microbiotas were grown on four biologically-pretreated xylan-free lignocellulosic biomasses achieving a maximum cellulose degradation rate of 0.063 g/L-h, and 0.061 g/L-h, respectively. These cellulose-degrading microbiotas are a promising alternative to high-cost enzymes for their capacity to obtain fermentable sugars from different lignocellulosic biomasses that could be used in synergy with selected fermenting bacteria to obtain a desired fermentation product.

Con la finalidad de promover la diversificación de la caña de azúcar en la producción de biocombustibles y bio-productos este trabajo estudia el desempeño económico del diseño de una biorrefinería que coproduce azúcar, melaza y alcohol. Los gases de fermentación se consideran también como coproducto. También se capturan los gases de combustión de caldera con la finalidad de reducir las emisiones de gases de efecto invernadero. Dicha biorrefinería, se identifica como “biorrefinería negativa en carbono” (BNC). El análisis de rentabilidad se formula como un problema de optimización multiobjetivo en el que se maximiza la eficiencia de uso de azúcares totales recuperables (EATR) y ganancia neta (NP) en función de la coproducción de bioetanol, azúcar, melaza, aceite fusel y dióxido de carbono. Las variables de decisión en el problema de optimización multiobjetivo son definidas como fracciones de flujo másico, que modifican la producción de un producto u otro para maximizar los funcionales arriba definidos. El desempeño económico de BNC se compara con el diseño de una biorrefinería multi-producto que usa la caña de azúcar como materia prima sin la revalorización del dióxido de carbono (BB). Los resultados muestran a BB con el mejor desempeño en la producción de azúcar y BNC para la producción de bioetanol. A pesar de que BNC y BB tienen su origen en la reconversión de ingenios azucareros con el objetivo de producir biocombustibles convencionales y avanzados, BNC considera al dióxido de carbono como un producto y no una emisión a la atmósfera mejorando la rentabilidad del proceso. Por ello, BNC es una alternativa de producción de biocombustibles para el sector transporte que puede contribuir a combatir el cambio climático.

Hydrothermal pretreatment (HP) is an eco-friendly process for deconstructing lignocellulosic biomass (LCB) that plays a key role in ensuring the profitability of producing biofuels or bioproducts in a biorefinery. At the laboratory scale, HP is usually carried out under non-isothermal regimes with poor temperature control. In contrast, HP is usually carried out under isothermal conditions at the commercial scale. Consequently, significant discrepancies in the values of polysaccharide releases are found in the literature. Therefore, laboratory-scale HP data are not trustworthy if scale-up or retrofitting of HP at larger scales is required. This contribution presents the results of laboratory-scale batch HP for wheat straw in terms of xylan and glucan release that were obtained with rigorous temperature control under isothermal conditions during the reaction stage. The heating and cooling stages were carried out with fast rates (43 and −40 °C/min, respectively), minimizing non-isothermal reaction periods. Therefore, the polysaccharide release results can be associated exclusively with the isothermic reaction stage and can be considered as a reliable source of information for HP at commercial scales. The highest amount of xylan release was 4.8 g/L or 43% obtained at 180 °C and 20 min, while the glucan release exhibited a maximum of 1.2 g/L or 5.5%. at 160 °C/180 °C and 30 min.