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This paper critically reviews and discusses the utilization of ultrasound as an eco-friendly approach for enhancing biomass valorization efficiency. In contrast to other methods, this process requires no additional chemicals, no post-treatment (such as wastewater treatment), and helps achieve industrial electrification goals. Ultrasound irradiation has been employed as a powerful tool in biomass pretreatment and biorefining, as well as a green extraction method for recovering bioactive molecules. By partially degrading lignin structures, ultrasound irradiation significantly improves the biological conversion of waste materials and lignocellulose, facilitating the exposure of valuable macromolecules, i.e., cellulose and hemicelluloses. This research begins with an introduction to sonication technology, and subsequently presents comprehensive discussions focusing on the application of ultrasound in the pretreatment of sludge and lignocellulosic materials for anaerobic digestion. Furthermore, various facets of ultrasound usage in bioethanol production, including substrate pretreatment, enzymatic and acid hydrolyzes, and fermentation techniques, are also examined. Additionally, the benefits of employing ultrasound technology to recover high-value, heat-sensitive bioactive compounds at temperatures below their degrading points, thereby preserving their functionality, are explored. Looking ahead, this review explores current trends in ultrasound technology adoption and its potential for scaling up and commercialization, introducing pathways for a more sustainable and efficient approach for biomass valorization.

A two-stage pretreatment toward lignocellulosic biomass fractionation was devised. The process consisted of dilute acid hydrolysis using oxalic acid, followed by oxalic acid–assisted ethanol organosolv pretreatment. A biomass mixture consisting of four regional lignocellulosic materials, namely, brewer’s spent grain, tomato waste biomass, cucumber waste biomass, and spent coffee grounds, was used. In the first stage, the optimum mixture composition was determined using a full factorial design coupled with a simplex-centroid design. The interactive effects of the solid-to-liquid ratio, holding time, acid type, and concentration were also considered. In the attempt to lower solid yields and increase hemicellulose dissolution, elevated levels of furfural (15.73 g/L) and 5-hydroxymethylfurfural (8.56 g/L) were formed, due to increased pretreatment severity (180 min, 135C, 83.15 mg oxalic acid/g biomass, and 100 g biomass/L). The solid yield achieved was 50.53%. In the second stage, the effect of ethanol-to-water solvent ratio, holding time, and temperature were investigated using a central composite experimental design. Solid yields ranged between 72.57 and 85.20% (w/w), mainly due to lignin removal. Pretreatment with 75% (v/v) ethanol at 120 min and 190 °C resulted in the highest lignin recovery (44.69%). Post-experimental verification runs were performed to evaluate the validity of the response surface models with a maximum error of 15.17%. Characterization by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and heteronuclear single quantum coherence spectroscopy (HSQC) were conducted to assess biomass fraction integrity and structural changes during pretreatment.

Preheating with hot air at 85 – 125 °C was evaluated for its effectiveness in removing terpenes and terpenoids in softwood sawdust, thereby enhancing fungal preprocessing and subsequent saccharification of softwood-based mushroom substrates. Sawdust from pine (Pinus sylvestris L.) and spruce (Picea abies (L.) H. Karst.) was preheated prior to shiitake (Lentinula edodes (Berk.) Pegler) cultivation. Preheating removed up to 96 % of terpenes in pine- based substrates and up to 50 % in spruce-based substrates. Additionally, preheating decreased total terpenoids content in spruce by up to 78 %. For the pine-based substrate, the mild heating generally led to faster colonisation and improved mushroom yield, with the fastest mycelia colonisation and highest yield observed for 105 °C treatment. This temperature was associated with the lowest content of total terpenes and absence of major monoterpenes. The content of terpenes and terpenoids continued to decrease during cultivation, alongside fungal degradation of lignocellulose. As a result of more extensive lignin degradation, the enzymatic digestibility of cellulose was higher for spruce-based spent mushroom substrate than for pine-based one (up to 89 % vs. 49 % conversion). Enzymatic digestibility showed a negative correlation with the α-pinene content, and a positive correlation with increasing preheating temperatures.

This work corresponds to the optimization of the operating variables of the enzymatic hydrolysis of corn starch to obtain glucose syrups using the genetic algorithm of Matlab (2020a). For this reason, the hydrolytic process is mathematically modeled by response surface methodology. Pareto chart indicated that saccharification variables exert the highest influence on starch conversion. This mathematical model is beneficial for a better understanding and operational control of hydrolysis at the industrial level. The optimization problem solution shows that a maximum dextrose equivalent of 98.13% can be reached if the hydrolysis is performed under optimal operating conditions, which were also confirmed experimentally. The results show that to achieve the highest yield, liquefaction should be carried out at a temperature of 92oC, pH of 6.3, α-amylase dose of 1.5 mg enzyme/g starch and hydrolysis time of 1 hour; while saccharification should be conducted at a temperature of 57oC, pH of 4.9, glucoamylase dose of 1.15 mg enzyme/g starch and hydrolysis time of 34 hours. The reversion phenomenon is detected when the hydrolysis time exceeds 35 hours, with a negative incidence on the dextrose equivalent.

Este trabajo corresponde a la optimización de las variables de operación de la hidrólisis enzimática de almidón de maíz para la obtención de jarabes de glucosa utilizando el algoritmo genético de Matlab (2020a). Para ello, el proceso de hidrólisis se modeló matemáticamente mediante la metodología de superficie de respuesta. El diagrama de Pareto indicó que las variables de sacarificación ejercen la mayor influencia en la conversión del almidón. Este modelo matemático es de gran utilidad para una mejor comprensión y control operacional de la hidrólisis a nivel industrial. La solución del problema de optimización muestra que puede alcanzarse un equivalente máximo de dextrosa del 98,13% si la hidrólisis se realiza en las condiciones operacionales óptimas, las cuales se comprobaron experimentalmente. Los resultados muestran que, para alcanzar el mayor rendimiento, la licuefacción debe llevarse a cabo a una temperatura de 92oC, pH de 6,3, dosis de α-amilasa de 1,5 mg de enzima/g de almidón y tiempo de hidrólisis de 1 hora; mientras que la sacarificación debe realizarse a una temperatura de 57oC, pH de 4,9, dosis de glucoamilasa de 1,15 mg de enzima/g de almidón y tiempo de hidrólisis de 34 horas. El fenómeno de reversión se detectó cuando el tiempo de hidrólisis superó las 35 horas, con una incidencia negativa sobre el equivalente en dextrosa.

This article aims to offer a detailed review of bacterial nanocellulose (BNC), addressing its growing global relevance and exploring sustainable approaches through the use of agro-industrial residues as viable cultivation alternatives. BNC is a biopolymer produced by different microorganisms, with Komagateibacter xylinum being the most commonly used in this process. Its distinction in relation to vegetable cellulose lies mainly in its nanometric properties, such as water retention capacity, large surface area and structural resistance. The search for alternative sources has been explored for the large-scale production of biopolymers such as polyhydroxybutyrate (PHB) and exopolysaccharides (EPS) from lignocellulosic biomass. The application of different residues from agroindustry, food and forestry as a source of carbon and nutrients in the biosynthesis of BNC has proven to be a promising strategy to make the production process economically viable. A significant advantage of the BNC biosynthesis process is the virtually natural purity of the cellulose produced, eliminating the need for expensive purification steps. There has been a significant increase in the number of patents related to the use of lignocellulosic biomass, filed by academic institutions and private companies in the last five years. In this context, this study condenses the fundamental principles of BNC, offers a trend analysis through bibliometric review and investigates the current panorama in BNC production, as well as its diverse applications in a wide range of sectors, such as medicine (medical devices, tissue engineering), packaging (biodegradable films, coatings), textiles (smart materials, functional fabrics), construction (sustainable materials), electronics (flexible electronic components) and other innovative areas that benefit from the unique properties of bacterial nanocellulose.

Bioethanol is the most commonly used biofuel. It is an alternative to replace fossil fuels in renewable energy; it can be produced from lignocellulosic feedstock using a biotechnological process. Their participation of microorganisms is crucial in the bioconversion process of fermentation for ethanol production and can involve bacteria, fungi, and yeasts. However, when working within bioethanol processes from lignocellulose feedstock, microorganisms face some challenges, such as high temperature, high solids content, and the ability to ferment sugars for high ethanol concentration. Such challenges will depend on operative strategies, such as simultaneous saccharification and fermentation, separate hydrolysis and fermentation, semi-simultaneous saccharification and fermentation, and consolidated bioprocessing; these are the most common configurations. This review presents different trends of the microbial role, biochemical application, and fermentation operative strategies for bioethanol production of the second generation.

Sugarcane bagasse was pretreated with dilute phosphoric acid or sulfuric acid to facilitate cellulose hydrolysis and lignin extraction. With phosphoric acid, only 8 % of the initial cellulose was lost after delignification, whereas pretreatment with sulfuric acid resulted in the solubilization of 38 % of the initial cellulose. After enzymatic hydrolysis, the process using phosphoric acid produced approximately 35 % more glucose than that using sulfuric acid. In general, the lignins showed 95–97 % purity (total lignin, w/w), an average molar mass of 9500–10,200 g mol⁻¹, a glass transition temperature of 140–160 °C, and a calorific value of 25 MJ kg⁻¹. Phosphoric acid lignin (PAL) was slightly more polar than sulfuric acid lignin (SAL). PAL had 13 % more oxidized units and 20 % more OH groups than SAL. Regardless of the acid used, the lignins shared similar properties, but differed slightly in the characteristics of their functional groups and chemical bonds. These findings show that pretreatment catalyzed with either of the two acids resulted in lignin with sufficiently good characteristics for use in industrial processes.

Bioconversion in biorefineries is a way to valorize residues from agriculture and food processing. Pretreatment is an important step in the bioconversion of lignocellulosic materials, including crop residues. This Special Issue includes nine articles on several pretreatment and bioconversion approaches applied to different agricultural residues and food-processing by-products. The materials addressed in this collection cover straw from wheat, rye, and miscanthus, olive tree pruning residue, almond shells and husks, avocado waste, sweet sorghum bagasse, soybean meal, and residues of non-edible oilseeds.

Spent mushroom substrate (SMS) is the residual biomass generated after harvesting the fruitbodies of edible and medicinal fungi. Disposal of SMS often leads to serious environmental problems and is financially demanding. Efficient recycling and valorization of SMS are crucial for the sustainable development of the mushroom industry in the frame of the circular economy principles. Several valorization alternatives, such as biofertilizer, soil amendment, wastewater bioremediation agent, ingredient of animal feed formulations, or substrate for new mushroom cultivation cycles, have been proposed for SMS. In this work, we propose a possible valorization option for SMS as raw material for biorefineries. This valorization possibility is supported by the high content of hydrolysable cellulose in SMS and the presence of bioactive compounds, such as polyphenols, polysaccharides, proteins, and sterols. Following a biorefinery concept, we have developed a stepwise processing approach for valorizing. The process includes recovery of bioactive compounds from SMS, enzymatic saccharification of the polysaccharides, bioconversion of obtained sugars into valuable products, and upgrading lignin from the saccharification residue. Our preliminary trials, performed mainly with SMS from Lentinula edodes and Pleurotus spp. (oyster mushrooms) reveal that the proposed approach is a suitable alternative for upgrading the residual substrate from mushroom cultivation.

Utilization of biomass and reuse of industrial by-products and their sustainable and resource-efficient development into products that are inherently non-toxic is important to reduce the use of hazardous substances in the design, manufacture and application of biomaterials. The hypothesis in this study is that spent mushroom substrate (SMS), a by-product from mushroom production, has already undergone a biological pretreatment and thus, can be used directly as a starting material for fibrillation into value-added and functional biomaterial, without the use of toxic substances. The study show that SMS can be effectively fibrillated at a very high concentration of 6.5 wt % into fibrils using an energy demand of only 1.7 kWh kg−1, compared to commercial and chemically pretreated wood pulp at 8 kWh kg−1, under same processing conditions. SMS is a promising resource for fibrillation with natural antioxidant activity and network formation ability, which are of interest to explore further in applications such as packaging. The study shows that biological pretreatment can offer lower environmental impact related to toxic substances emitted to the environment and thus contribute to reduced impacts on categories such as water organisms, human health, terrestrial organisms, and terrestrial plants compared to chemical pretreatments.