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Biogas production via anaerobic digestion (AD) is a long-standing renewable technology and a continuously growing bioprocess worldwide. Lignocellulosic materials (LMs) present several features that make them especially attractive among the organic substrates commonly employed in anaerobic bioreactors. In particular, LMs under the form of agricultural residues have been acknowledged as the most suitable feedstock for biomethane production due to their high availability, low cost, sustainability and no direct competition with food and feed production. However, their recalcitrance to biological conversion hinders their application for full-scale production of biogas and requires a pretreatment step to improve the LM microbial degradability. In addition to the challenges posed by the lignocellulosic structure, the supply of trace elements (TEs) has often been found insufficient within biogas digesters. The microbial growth depends on the availability and optimal amount of several specific TEs, which are essential constituents of cofactors in enzyme systems involved in the biochemistry of methane formation. Different chemical pretreatments, namely the solvent N-methylmorpholine-N-oxide (NMMO), the organosolv process, and an alkaline pretreatment using NaOH, were investigated during several batch experiments to enhance the biogas production yields from different LMs (i.e. rice straw, hazelnut skin, cocoa bean shell and wheat straw). Changes in the cellulose crystallinity, water retention value and chemical composition were assessed to better evaluate the effect of the different pretreatments studied on the lignocellulosic structure. Furthermore, the addition of different doses of Fe, Co, Ni and Se on the AD of rice straw was studied, evaluating the influence of the inoculum origin, as well as the performance and synergistic effect of combining an alkaline pretreatment with the addition of trace elements prior to the AD of rice straw. The bioavailability of TEs during batch biomethane potential tests was also evaluated applying a sequential extraction technique. The three pretreatments investigated were effective methods for enhancing the biomethane production from the employed LMs. The biomethane yield from the AD of rice straw increased by 82 and 41% after the NMMO and organosolv pretreatment, respectively. When compared within the same experiment, the NMMO, organosolv and NaOH pretreatment were able to improve the AD of wheat straw, differently affecting the chemical composition of the raw LM. The cumulative biomethane production yield of 274 mL CH4/g VS obtained with the untreated wheat straw was enhanced by 11% by the NMMO pretreatment and by 15% by both the organosolv and alkaline pretreatment. Hazelnut skin and cocoa bean shell, which were never investigated before as AD substrates, showed a good potential for biogas production, with cumulative biomethane yields of 223-261 and 199-231 mL CH4/g VS, respectively, for the untreated feedstocks. However, both NMMO and organosolv pretreatments did not lead to a significant enhancement of the biomethane production yields from these two LMs. The TE supplementation had only a minor effect compared to the pretreatment methods. The addition of Fe, Co, Ni and Se did not result in a significant improvement of the AD of rice straw, whereas the use of the NaOH pretreatment, during the same batch experiment, caused a considerable enhancement of the AD, increasing the biogas production yield by 21%. The negligible effect observed after TE supplementation on the AD of rice straw could be linked to its complex lignocellulosic structure, which requires an enhancement of the hydrolysis, which, rather than the methanogenesis, is the rate-limiting step; La production de biogaz par digestion anaérobie (DA) est une technologie renouvelable de longue date et un bioprocessus en croissance continue. Les matériaux lignocellulosiques (ML) présentent plusieurs caractéristiques qui les rendent particulièrement attrayants parmi les substrats couramment employés dans les bioréacteurs anaérobies. En particulier, les ML sous la forme de résidus agricoles ont été reconnus comme la matière première la plus appropriée pour la production de biométhane en raison de leur haute disponibilité, de leur faible coût, de leur durabilité et de leur absence de concurrence directe avec la production alimentaire. Cependant, leur récurrence à la conversion biologique entrave leur application pour la production à grande échelle de biogaz et nécessite une étape de prétraitement pour améliorer la dégradabilité microbienne. En plus des défis posés par la structure lignocellulosique, la fourniture de oligo-éléments (OE) a souvent été jugée insuffisante dans les digesteurs de biogaz. La croissance microbienne dépend de la disponibilité et de la quantité optimale de plusieurs OE spécifiques, constituants essentiels des cofacteurs dans les systèmes enzymatiques impliqués dans la biochimie de la formation de méthane. Différents prétraitements chimiques, à savoir le N-méthylmorpholine-N-oxyde (NMMO), le procédé organosolv et un prétraitement alcalin à l'aide de NaOH ont été étudiés pendant plusieurs expériences en lots pour améliorer les rendements de production de biogaz différents peau, coquille de fève de cacao et paille de blé). Les changements dans la cristallinité de la cellulose, la valeur de rétention d'eau et la composition chimique ont été évalués pour mieux évaluer l'effet des différents prétraitements étudiés sur la structure lignocellulosique. En outre, l'addition de différentes doses de Fe, Co, Ni et Se sur la DA de paille de riz a été étudiée, évaluant l'influence de l'origine de l'inoculum, ainsi que la performance et l'effet synergique de la combinaison d'un prétraitement alcalin avec addition de trace éléments avant la DA de paille de riz. La biodisponibilité des OE lors des tests de potentiel de biométhane par lots a également été évaluée en appliquant une technique d'extraction séquentielle. Les trois prétraitements étudiés étaient des méthodes efficaces pour améliorer la production de biométhane à partir des LM utilisées. Le rendement en biométhane de la DA de paille de riz a augmenté de 82 et 41% respectivement après le NMMO et le prétraitement organosolv. Comparé à la même expérience, le prétraitement NMMO, organosolv et NaOH a permis d'améliorer la DA de la paille de blé, ce qui affecte différemment la composition chimique de la LM brute. Le rendement cumulatif de production de biométhane de 274 mL de CH4/g VS obtenu avec la paille de blé non traitée a été augmenté de 11% par le prétraitement du NMMO et de 15% par le prétraitement organosolv et alcalin. Les coquilles de noisettes et de fèves de cacao, qui n'avaient jamais été étudiées auparavant comme substrats AD, présentaient un bon potentiel de production de biogaz, avec des rendements cumulatifs de biométhane respectivement de 223-261 et 199-231 mL CH4/g VS pour les charges non traitées. Cependant, les prétraitements à la fois de NMMO et d'organosolv n'ont pas conduit à une amélioration significative des rendements de production de biométhane de ces deux LM. La supplémentation des OE n'a eu qu'un effet mineur par rapport aux méthodes de prétraitement. L'ajout de Fe, Co, Ni et Se n'a pas entraîné d'amélioration significative de la DA de paille de riz, alors que l'utilisation du prétraitement de NaOH au cours de la même expérimentation a provoqué une augmentation considérable de la DA, augmentant la production de biogaz de 21%. L'effet négligeable observé après la supplémentation des OE sur la paille de riz pourrait être lié à sa structure lignocellulosique complexe qui nécessite une amélioration de l'hydrolyse qui est l'étape limitante

Biogas production via anaerobic digestion (AD) is a long-standing renewable technology and a continuously growing bioprocess worldwide. Lignocellulosic materials (LMs) present several features that make them especially attractive among the organic substrates commonly employed in anaerobic bioreactors. In particular, LMs under the form of agricultural residues have been acknowledged as the most suitable feedstock for biomethane production due to their high availability, low cost, sustainability and no direct competition with food and feed production. However, their recalcitrance to biological conversion hinders their application for full-scale production of biogas and requires a pretreatment step to improve the LM microbial degradability. In addition to the challenges posed by the lignocellulosic structure, the supply of trace elements (TEs) has often been found insufficient within biogas digesters. The microbial growth depends on the availability and optimal amount of several specific TEs, which are essential constituents of cofactors in enzyme systems involved in the biochemistry of methane formation. Different chemical pretreatments, namely the solvent N-methylmorpholine-N-oxide (NMMO), the organosolv process, and an alkaline pretreatment using NaOH, were investigated during several batch experiments to enhance the biogas production yields from different LMs (i.e. rice straw, hazelnut skin, cocoa bean shell and wheat straw). Changes in the cellulose crystallinity, water retention value and chemical composition were assessed to better evaluate the effect of the different pretreatments studied on the lignocellulosic structure. Furthermore, the addition of different doses of Fe, Co, Ni and Se on the AD of rice straw was studied, evaluating the influence of the inoculum origin, as well as the performance and synergistic effect of combining an alkaline pretreatment with the addition of trace elements prior to the AD of rice straw. The bioavailability of TEs during batch biomethane potential tests was also evaluated applying a sequential extraction technique. The three pretreatments investigated were effective methods for enhancing the biomethane production from the employed LMs. The biomethane yield from the AD of rice straw increased by 82 and 41% after the NMMO and organosolv pretreatment, respectively. When compared within the same experiment, the NMMO, organosolv and NaOH pretreatment were able to improve the AD of wheat straw, differently affecting the chemical composition of the raw LM. The cumulative biomethane production yield of 274 mL CH4/g VS obtained with the untreated wheat straw was enhanced by 11% by the NMMO pretreatment and by 15% by both the organosolv and alkaline pretreatment. Hazelnut skin and cocoa bean shell, which were never investigated before as AD substrates, showed a good potential for biogas production, with cumulative biomethane yields of 223-261 and 199-231 mL CH4/g VS, respectively, for the untreated feedstocks. However, both NMMO and organosolv pretreatments did not lead to a significant enhancement of the biomethane production yields from these two LMs. The TE supplementation had only a minor effect compared to the pretreatment methods. The addition of Fe, Co, Ni and Se did not result in a significant improvement of the AD of rice straw, whereas the use of the NaOH pretreatment, during the same batch experiment, caused a considerable enhancement of the AD, increasing the biogas production yield by 21%. The negligible effect observed after TE supplementation on the AD of rice straw could be linked to its complex lignocellulosic structure, which requires an enhancement of the hydrolysis, which, rather than the methanogenesis, is the rate-limiting step; La production de biogaz par digestion anaérobie (DA) est une technologie renouvelable de longue date et un bioprocessus en croissance continue. Les matériaux lignocellulosiques (ML) présentent plusieurs caractéristiques qui les rendent particulièrement attrayants parmi les substrats couramment employés dans les bioréacteurs anaérobies. En particulier, les ML sous la forme de résidus agricoles ont été reconnus comme la matière première la plus appropriée pour la production de biométhane en raison de leur haute disponibilité, de leur faible coût, de leur durabilité et de leur absence de concurrence directe avec la production alimentaire. Cependant, leur récurrence à la conversion biologique entrave leur application pour la production à grande échelle de biogaz et nécessite une étape de prétraitement pour améliorer la dégradabilité microbienne. En plus des défis posés par la structure lignocellulosique, la fourniture de oligo-éléments (OE) a souvent été jugée insuffisante dans les digesteurs de biogaz. La croissance microbienne dépend de la disponibilité et de la quantité optimale de plusieurs OE spécifiques, constituants essentiels des cofacteurs dans les systèmes enzymatiques impliqués dans la biochimie de la formation de méthane. Différents prétraitements chimiques, à savoir le N-méthylmorpholine-N-oxyde (NMMO), le procédé organosolv et un prétraitement alcalin à l'aide de NaOH ont été étudiés pendant plusieurs expériences en lots pour améliorer les rendements de production de biogaz différents peau, coquille de fève de cacao et paille de blé). Les changements dans la cristallinité de la cellulose, la valeur de rétention d'eau et la composition chimique ont été évalués pour mieux évaluer l'effet des différents prétraitements étudiés sur la structure lignocellulosique. En outre, l'addition de différentes doses de Fe, Co, Ni et Se sur la DA de paille de riz a été étudiée, évaluant l'influence de l'origine de l'inoculum, ainsi que la performance et l'effet synergique de la combinaison d'un prétraitement alcalin avec addition de trace éléments avant la DA de paille de riz. La biodisponibilité des OE lors des tests de potentiel de biométhane par lots a également été évaluée en appliquant une technique d'extraction séquentielle. Les trois prétraitements étudiés étaient des méthodes efficaces pour améliorer la production de biométhane à partir des LM utilisées. Le rendement en biométhane de la DA de paille de riz a augmenté de 82 et 41% respectivement après le NMMO et le prétraitement organosolv. Comparé à la même expérience, le prétraitement NMMO, organosolv et NaOH a permis d'améliorer la DA de la paille de blé, ce qui affecte différemment la composition chimique de la LM brute. Le rendement cumulatif de production de biométhane de 274 mL de CH4/g VS obtenu avec la paille de blé non traitée a été augmenté de 11% par le prétraitement du NMMO et de 15% par le prétraitement organosolv et alcalin. Les coquilles de noisettes et de fèves de cacao, qui n'avaient jamais été étudiées auparavant comme substrats AD, présentaient un bon potentiel de production de biogaz, avec des rendements cumulatifs de biométhane respectivement de 223-261 et 199-231 mL CH4/g VS pour les charges non traitées. Cependant, les prétraitements à la fois de NMMO et d'organosolv n'ont pas conduit à une amélioration significative des rendements de production de biométhane de ces deux LM. La supplémentation des OE n'a eu qu'un effet mineur par rapport aux méthodes de prétraitement. L'ajout de Fe, Co, Ni et Se n'a pas entraîné d'amélioration significative de la DA de paille de riz, alors que l'utilisation du prétraitement de NaOH au cours de la même expérimentation a provoqué une augmentation considérable de la DA, augmentant la production de biogaz de 21%. L'effet négligeable observé après la supplémentation des OE sur la paille de riz pourrait être lié à sa structure lignocellulosique complexe qui nécessite une amélioration de l'hydrolyse qui est l'étape limitante

Biogas production via anaerobic digestion is a well-established technology for renewable energy production and a steadily growing bioprocess worldwide. It promotes a sustainable development of the energy supply, while offering the opportunity to deal with the reduction of the amount of organic wastes, decreasing the environmental impact (Jeihanipour et al., 2011). Lignocellulosic materials (LMs) present several features that make them particularly attractive among the organic substrates commonly employed in anaerobic bioreactors. In particular, LMs under the form of agricultural residues have been acknowledged as the most suitable biomass for biomethane production due to their high availability, low cost, sustainability and no direct competition with food and feed production (Kabir et al., 2015). However, their recalcitrance to biological conversion still hinders their application for commercial production of biogas and requires a pretreatment step to improve their microbial degradability. Thus, research is focusing to implement pretreatment strategies that are able to overcome the challenges due to the LMs structure, increasing their microbial degradability. Among the several methods applied to pretreat LMs, solvent pretreatments and organosolv are rising as the most promising (Karimi, 2013). This study investigates the effects of two different chemical pretreatments on the methane yields of three LMs, namely hazelnut skins and cocoa beans, generated during the industrial processing of the raw agricultural products, and rice straw, which is one of the most abundant agricultural wastes worldwide. Initially, the three LMs were separately pretreated with an organic solvent, N-Methylmorpholine-N-oxide (NMMO) at 120°C for both 1 and 3 h. Consequently, batch bio-methane production (BMP) tests were performed under mesophilic (i.e. 37 ± 2°C) conditions for approximately 45 d, as described by Esposito et al. (2011). Improvements on the cumulative methane yields were observed for all the substrates, compared to the untreated ones. In a similar experimental run, the effects of organosolv pretreatment on the three LMs were investigated. Ethanol was used as organic solvent and the pretreatment was carried out at 150 and 170°C for 30 min. The organosolv pretreatment was able to improve the bioconversion of the LMs, resulting in higher biomethane yields than the untreated feedstocks. Compositional analyses and Fourier transform infrared spectroscopy (FTIR) were performed in both experiments. Changes in chemical composition and crystallinity after the pretreatment were considered the most important factors affecting the biogas production enhancement from all of the investigated LMs.

In this note, we consider blow-up for solutions of the SU(3) Toda system on a compact surface σ. In particular, we give a complete proof of the compactness result stated by Jost, Lin and Wang in [11] and we extend it to the case of singularities. This is a necessary tool to find solutions through variational methods.

Biogas production via anaerobic digestion is a constantly growing technology all around the world. Lignocellulosic materials (LMs) present several features that make them particularly attractive among the organic substrates commonly employed in anaerobic bioreactors. However, their recalcitrance to biological conversion still hinders their application for commercial production of biogas and requires a pretreatment step to improve their microbial degradability. Among the several pretreatments proposed for LMs, cellulose solvents and organosolv pretreatments are arising as the most effective in disrupting the bonds among cellulose, hemicellulose, and lignin, thus increasing the accessible surface area of the biodegradable matter for microbes. Here, the solvents that have been employed as pretreatment to enhance the biogas production yields from the anaerobic digestion of LMs are reviewed, examining the dissolution mechanisms involved, as well as the main advantages and drawbacks for their full-scale application.

This research investigated the effects of three different chemical pretreatments on the methane yields of rice straw, which is one of the most abundant agricultural, lignocellulosic wastes worldwide. Initially, the raw agricultural residue was pretreated with the organic solvent N-methylmorpholine-N-oxide (NMMO) at 120°C for 3 h. Consequently, batch bio-methane production (BMP) tests were performed under mesophilic conditions for 40 days. In a similar experimental run, the effect of organosolv pretreatment on the rice straw was investigated. 50% (w/w) ethanol was used as organic solvent and the pretreatment was carried out at 150 and 180°C for 30 min. Finally, rice straw was pretreated with a 1.6% (w/w) NaOH solution at 30°C for 24 h in a third experimental setup. This study also focused in improving the rice straw biodegradability through the addition of trace elements. Cobalt, nickel and selenium were individually added to the rice straw at different concentrations. The NMMO, ethanol-organosolv and NaOH pretreatments were particularly effective in enhancing the biodegradability of the rice straw and increasing the biogas yields up to 82, 42 and 21%, respectively, compared to those of the untreated material. On the other hand, the addition of trace elements had only a minor effect (i.e. up to 8%) on the enhancement of the biogas yield from the AD of rice straw.

The effect of trace elements (TEs) addition and NaOH pretreatment on the anaerobic digestion of rice straw was investigated in batch tests. Co, Ni and Se were added to the raw rice straw at different dosages. The NaOH pretreatment was applied to the rice straw both alone and in combination with the addition of TEs, in order to evaluate potential synergistic effects of the pretreatment and the TEs supplementation on the biogas production yields. The results obtained showed that the alkaline pretreatment was more effective than the TEs addition in increasing the cumulative biogas production, causing a 21.4% enhancement of the final biomethane yield, whereas the increase due to TEs dosing was not statistically significant. The analysis of volatile fatty acids (VFAs) confirmed that the NaOH pretreatment resulted in a higher production of VFAs, indicating an increased hydrolysis, while TEs addition did not cause significant changes in the VFA concentrations.

This study investigated effects of chemical pretreatment with N-methylmorpholine-N-oxide (NMMO) on methane yields of rice straw, cocoa bean shell, and hazelnut skin. Three lignocellulosic materials were separately pretreated with NMMO at 120°C for 3 h. Subsequently, batch biomethane production tests were performed under mesophilic (37°C ± 2°C) conditions, also with the untreated feedstocks, to provide methane production baseline data. Pretreatment was particularly effective for rice straw, with an 82% increased biomethane production yield from 206 mL CH4/g volatile solids (VS) obtained with the untreated substrate. A lower enhancement of the biomethane yield from 199 to 226 mL CH4/g VS (i.e., 14% increase) was observed for cocoa shell. For hazelnut skin, NMMO pretreatment resulted in a faster digestion rate in the initial 7 days, increasing the biomethane yield from 17 to 27 mL CH4/g VS·day. However, the cumulative biomethane yield after 40 days was not affected by NMMO pretreatment.

We extend the Moser-Trudinger inequality to any Euclidean domain satisfying Poincar\'e's inequality. We find out that the same equivalence does not hold in general for conformal metrics on the unit ball, showing counterexamples. We also study the existence of extremals for the Moser-Trudinger inequalities for unbounded domains, proving it for the infinite planar strip., Comment: 32 pages, accepted on Advances in Nonlinear Analysis