BioEnergy Research最新文献

The role of buffer in modulating the enzymatic hydrolysis environment of lignocellulose is crucial. However, studies on the impact of buffer on high-solid enzymatic hydrolysis remain limited. This study discovered that utilizing deionized water as a reaction medium, rather than the conventional buffer, did not influence the enzymatic hydrolysis of steam-exploded corn stover when the solid loading ranged between 15 and 25%. At 15% solid loading, the glucan conversion in the group treated with buffer was recorded at 89.8%, with a corresponding glucose concentration of 51.1 g/L. In contrast, the group without buffer exhibited a conversion of 88.9% and a glucose concentration of 50.5 g/L. The increase of acid groups in lignin was attributed to the formation of phenolic hydroxyls during steam explosion, which provided the substrate with the necessary conditions for buffering effects. Sequentially, during the high-solid enzymatic hydrolysis process, the substrate’s increased pore volume and specific surface area could potentially offset the buffering capacity, which led to the buffering effect becoming ineffective. Leveraging the self-buffering effect of the substrate, a fed-batch strategy was developed. This strategy replaced the water supplementation with buffers, augmenting the solid loading from 20 to 33% across six distinct feeding sessions over a span of 72 h. This not only reduced costs but also laid the foundation for the industrial viability of lignocellulosic high-concentration sugar production, thereby advancing the biofuels and bioproducts sector. These findings provide valuable insights for the exploration of solid reaction processes.

Lignocellulosic biomass is of significant industrial and scientific interest. Residues derived from different activities (agro-industrial work, food consumption, wood use, urban solid waste, etc.) and their subsequent use are key to extending circularity models to the different technological sectors that are beginning to implement circular economy cycles. Biorefineries are integrated platforms that value waste conversion into various value-added products. The generation of bioproducts derived from lignocellulosic waste (green fuels, green chemicals, and biomaterials) has promoted a shift from a fossil fuel–based economy to a more sustainable one. In addition, integrating biorefineries into the circular economy framework promotes a comprehensive approach to resource management, waste reduction, and sustainable development, which contributes to the overall resilience and efficiency of societal systems. There has been increased focus on the application of “canonical microorganisms” for residual biomass conversion, such as fungi, bacteria, and yeast. However, there is a plethora of other potential microorganisms that can be candidates for new biotechnological applications. This review aims to describe the valorization of different sources of lignocellulosic biomass in the global context, with a focus on Brazilian practice, and to emphasize how the use of microbial diversity is critical to enhancing current technologies, such as advanced liquid fuels. Finally, there is a discussion of the potential of anaerobic fungi, archaea, protists, and oomycetes as microbial product conversion technologies.

Three delignification treatments of corncob residues (CCR), including NaOH, formic acid, and sulfite treatments, were compared at the respective optimized condition and in light of chemical compositions, sugar recovery, and ethanol production. NaOH and sulfite treatment can remove lignin in the CCR efficiently. Though NaOH treatment showed a superior ability of delignification, its solid cellulose recovery is lower than that of sulfite treatment. The sulfite treatment has the highest selectivity between delignification and cellulose conservation. The formic acid-treated CCR still had high lignin contents because formic acid also accelerated the solvation of cellulose. In fed-batch simultaneous saccharification and fermentation (SSF) with 25% substrate loading, the highest 77.1 ± 2.33 g/L ethanol was from NaOH-treated CCR, corresponding to a CCR-to-ethanol yield of 0.208 ± 0.0021 g/g. However, the sulfite pretreated CCR also produced 68.2 ± 2.22 g/L ethanol, with a higher CCR-to-ethanol yield of 0.219 ± 0.0012 g/g. The high substrate dosage is beneficial to ethanol concentration but not beneficial to CCR-to-ethanol yield. The optimal substrate dosage required for ethanol production depends on the targeted aim (ethanol concentration or CCR-to-ethanol yield).

The characteristics of biochar vary widely depending on the type of biomass and thermochemical conversion method. In this study, four types of biomass (kenaf, rice husk, corncob, and wood chips) were subjected to hydrothermal carbonization and torrefaction at 220 °C, 260 °C, and 300 °C for 30 min. The acquired biochars showed significant differences in the type of reaction and biomass. At each temperature, the decomposition of volatiles was more severe in hydrochar (HC) than in torrefied char (TC). The mass yields of HC were 44.30–61.63 wt.% (220 °C), 20.89–37.04 wt.% (260 °C), and 12.59–29.19 wt.% (300 °C), whereas the mass yields of TC were 94.73–97.69 wt.% (220 °C), 87.19–95.04 wt.% (260 °C), and 68.22–80.78 wt.% (300 °C). The elemental and thermal characteristics of TC changed gradually as the reaction temperature increased, and the characteristics of HC were enhanced rapidly. Wood chip biochar that was reacted at 300 °C showed the highest heating values of 28.77 MJ/kg (HC) and 21.09 MJ/kg (TC). The results of chemical analyses showed that hydrothermal carbonization strongly affected the cleavage of inter- and intra-molecular carbon bonds in cellulose and hemicellulose. In contrast, torrefaction removed the thermally fragile moisture and hemicellulose content from biomass.

Graphical Abstract

Reed sawdust is a kind of paper mill waste with high cellulose and hemicellulose content. To promote the rational use of resources, it is essential to make full use of waste resources and transform them into new values. In this work, reed sawdust was pretreated with liquid hot water (LHW) at 170 °C for 30 min. A total of 39.00 g/L glucose was obtained after enzymatic saccharification of cellulose at 50 °C, 20 FPU/g-_{reed sawdust} cellulase, 25% (w/v) reed sawdust, in 5 replenishments. When the fermentation was performed 96 h, the medium contained xylo-oligosaccharides (XOS) 11.74 g/L and biomass 15.21 g/L, in which lipid was 4.14 g/L. After spray drying, feed additives containing 29.17% XOS and 10.29% docosahexaenoic acid (DHA) can be prepared. In particular, the hemicellulose and cellulose in reed sawdust are creatively used at the same time without separation, which greatly reduces the cost of purification in traditional processes and provides a new way for the high-value transformation of sawdust resources.

The surge in global biofuel demand is propelled by intensifying concerns over climate change and effective waste management. Government mandates on biofuel blending further boost this trend, underlining the significance of selecting renewable feedstocks, such as bioethanol and biodiesel, for biofuel production. The importance of selecting an efficient biomass pretreatment method cannot be overstated, given its status as the most energy-intensive and chemical-reliant step in the biofuel production chain. Thus, pretreatment becomes a crucial determinant in the feasibility and economic viability of biofuel technologies. Amid a wide array of pretreatment strategies, identifying a method that is both effective and sustainable is crucial for advancing biofuel commercialization. This review aims to rigorously evaluate both traditional and novel pretreatment techniques and their environmental footprints, leveraging life cycle assessment (LCA) studies from existing literature. By examining the sustainability of various pretreatment methods, this paper provides a holistic and clear view, serving as an essential resource for policymakers and industry stakeholders. It outlines the challenges faced in each phase of an LCA and proposes viable solutions. Additionally, the review furnishes valuable insights, recommendations, and directions for future research in achieving sustainable biofuel production.

This study investigated self-heating and off-gassing of Scots pine (Pinus sylvestris) wood pellets made from sawdust generated from separated mature and juvenile wood. The pellets were produced at an industrial scale and stored in large piles of about 7.2 tonnes. The production process involved drying the sawdust using three different methods and to varying moisture contents. The results indicated significant influences of both raw material type (F ₍₆₎ = 61.97, p < 0.05) and drying method (F ₍₂₎ = 65.38, p < 0.05) on the self-heating of the pellets. The results from the multiple regression analysis further showed that both the raw material type and pellet moisture content significantly influenced the temperature increase, with strong correlations observed for pellets produced using low-temperature drying (F _{(3, 14)} = 83.52, multiple R² = 0.95, p < 0.05), and medium temperature drying (F _{(3, 13)} = 62.05, multiple R² = 0.93, p < 0.05). The pellets produced from fresh mature wood sawdust were found to be more prone to self-heating and off-gassing while steam drying the sawdust at high temperature and pressure led to a significant reduction in heat and gas generation across all materials. The heightened self-heating and off-gassing in mature wood pellet can be attributed to a higher proportion of sapwood in the raw material. The probable explanations to the observed differences are in line with biological mechanisms for self-heating and off-gassing, as well as the chemical oxidation of fatty and resin acids.

To enhance cellulose hydrolysis under high solid loadings, increasing the mixing intensity is often necessary, but this can lead to heightened product inhibition. In this work, the effect of mixing on high-solid cellulose hydrolysis was investigated. Through response surface optimization experiments, the optimal mixing intensities for 15%, 25%, and 35% (w/v) cellulose hydrolysis were obtained under different levels of product inhibition. A combined mixing optimization strategy was developed for different solid concentrations, aiming to enhance both the glucose yield and the conversion rate of microcrystalline cellulose and corn cobs. After optimization, the hydrolysis of microcrystalline cellulose resulted in glucose concentrations of 85 g/L, 130 g/L, and 167 g/L, corresponding to maximal conversion enhancements of 23%, 13%, and 8.6%, respectively. Similarly, the hydrolysis of corn cobs achieved glucose concentrations of 81 g/L, 124.6 g/L, and 140 g/L, with maximal conversion improvements of 4%, 5%, and 13%. These results indicate that the optimized strategy can effectively improve the conversion rate of high-solid enzymatic hydrolysis of cellulose.

There are no reports of production and characterization of polysaccharides in the genera Chlorella and Spirulina cultivated in seawater (SW) and brackish groundwater (BGW). Furthermore, there are few studies on the cultivation of these microalgae in seawater for this purpose. Therefore, the aim of the study was to evaluate the production and composition of polysaccharides in Spirulina sp. LEB 18 and Chlorella fusca LEB 111 grown in seawater and brackish groundwater, with and without nutrient supplementation. In this study, 100% SW and 100% BGW were used as nutrient sources and supplemented with different concentrations of nitrogen, phosphorus, iron, and EDTA sources that make up the Zarrouk/BG-11 culture media. Cultivating Chlorella fusca LEB 111 in SW, without the addition of nutrients, resulted in an approximately 23% increase in starch production (g/g). The cultivation of Spirulina sp. LEB 18 in SW and BGW, without the addition of nutrients, showed an increase in glycogen concentrations (50.5 and 40.75 g/100 g_biomass, respectively) and highest levels of exopolysaccharides (0.34 and 0.50 g/100 g_biomass, respectively) compared to the control. Moreover, exopolysaccharides compositional analysis has shown an increase in glucose content with salinity, and a decrease in xylose and glucuronic acid. This cultivation strategy demonstrates the viability of utilizing SW and BGW as alternatives to freshwater culture medium for microalgae that have high nutritional requirements, with the potential to produce exopolysaccharides.

Graphical Abstract

Poplar (Populus species and their hybrids) plantations can produce large amounts of biomass on agricultural land during the first rotation. However, there is limited knowledge regarding plantation re-establishment through re-sprouting (second rotation) after harvest, stand management options for such plantations, and biomass production during rotation length up to 20 years. In this study, we analysed biomass production responses to thinning treatments in an 18-year-old second rotation poplar plantation in Southern Sweden. The first rotation plantation was established with clone OP42 (Populus maximowiczii A. Henry × P. trichocarpa Torr. and Gray). The thinning experiment was conducted seven years after the first rotation harvest, comprising four treatments: unthinned – 6000 stems ha⁻¹, light thinning – 3000 stems ha⁻¹, medium thinning – 1100 stems ha⁻¹, and heavy thinning – 550 stems ha⁻¹. Eleven years after thinning, standing volume/biomass reached 484 m³ ha⁻¹ (162 Mg DM ha⁻¹) in the unthinned and medium thinning plots, 443 m³ ha⁻¹ (148 Mg DM ha⁻¹) in lightly and 338 m³ ha⁻¹ (113 Mg DM ha⁻¹) in heavily thinned plots. The mean annual increment was not different among the unthinned, light, and medium thinnings, 26 m³ ha⁻¹ yr⁻¹ (9 Mg DM ha⁻¹ yr⁻¹). The total production, including living, dead and removed trees, was highest following the medium thinning, 695 m³ ha⁻¹ (233 Mg DM ha⁻¹). Gradual self-thinning in the unthinned and lightly thinned plots was increased by a drought period. Overall, this study suggests that the second rotation of poplar plantations has high biomass production and provides an alternative to planting after harvest.