Chemical structures of corn stover and its residue after dilute acid prehydrolysis and enzymatic hydrolysis: insight into factors limiting enzymatic hydrolysis

Humic acid enhanced pyrene degradation by Mycobacterium sp. NJS-1

The search for nature-based tools to enhance bioremediation is essential for the sustainable restoration of contaminated ecosystems. Humic acid (HA) is an important component of organic matter in soil and water, but its effect on the microbial degradation of organic pollutants remains unclear. In this study, the biodegradation of pyrene by Mycobacterium sp. NJS-1 with and without HA was investigated. Only around 10.5% of pyrene was biodegraded in the pyrene treatment alone, whereas the addition of HA significantly enhanced biodegradation to the point where over 90% of pyrene was biodegraded. The production of 4,5-dihydropyrene-4,5-diol and phenanthrene-3,4-diol indicated the metabolic pathway via attacking of 4,5-positions of pyrene. Interestingly, 1,2-dimethoxypyrene was detected with the addition of HA, suggesting that HA induced a new ring-opening pathway involving the attack on the 1,2-positions of pyrene. The addition of HA first induced protein self-cleavage behavior with a significant increase in phenylalanine, tyrosine, and tryptophan containing large numbers of COO^- groups. Furthermore, it altered the intracellular and extracellular ultrastructure of bacterial cells, promoting their growth in size and number as well as reducing the space between them. Overall, HA increased the ring-opening positions of pyrene and facilitated its interaction with bacterial cells, thus improving its biodegradability. Building upon the findings of this study to further research is conducive to the sustainable solution of environmental pollution.

Low-Temperature Synthesis of Magnetic Carbonaceous Materials Coated with Nanosilica for Rapid Adsorption of Methylene Blue

This work reports the synthesis of nanosilica-coated magnetic carbonaceous adsorbents (MCA@SiO₂) using low-temperature hydrothermal carbonization technique (HCT) and the feasibility to utilize it for methylene blue (MB) adsorption. Initially, a carbon precursor (CP) was synthesized from corn starch under saline conditions at 453 K via HCT followed by the magnetization of CP again via HCT at 453 K. Subsequently, MCA was coated with silica nanoparticles. MCA and MCA@SiO₂ were characterized using X-ray diffraction, Fourier transform infrared, scanning electron microscopy/energy-dispersive spectroscopy, transmission electron microscopy, and Brunauer-Emmett-Teller (BET) N₂ adsorption-desorption isotherms. The BET surface area of MCA and MCA@SiO₂ were found to be 118 and 276 m² g^-1, respectively. Adsorption of MB onto MCA@SiO₂ was performed using batch adsorption studies and in the optimum condition, MCA@SiO₂ showed 99% adsorption efficiency with 0.5 g L^-1 of MCA@SiO₂ at pH 7. Adsorption isotherm studies predicted that MB adsorption onto MCA@SiO₂ was homogeneous monolayer adsorption, which was best described using a Langmuir model with the maximum adsorption capacity of 516.9 mg g^-1 at 25 °C. During adsorption kinetics, a rapid dye removal was observed which followed pseudo-first- as well as pseudo-second-order models, which suggested that MB dye molecules were adsorbed onto MCA@SiO₂ via both ion exchange as well as the chemisorption process. The endothermic and spontaneous nature of the adsorption of MB onto MCA@SiO₂ was established by thermodynamics studies. Mechanism of dye diffusion was collectively governed by intraparticle diffusion and film diffusion processes. Furthermore, MB was also selectively adsorbed from its mixture with an anionic dye, that is, methyl orange. Column adsorption studies showed that approximately 500 mL of MB having 50 mg L^-1 concentration can be treated with 0.5 g L^-1 of MCA@SiO₂. Furthermore, MCA@SiO₂ was repeatedly used for 20 cycles of adsorption-desorption of MB. Therefore, MCA@SiO₂ can be effectively utilized in cationic dye-contaminated wastewater remediation applications.

Simultaneous and Efficient Production of Furfural and Subsequent Glucose in MTHF/H2O Biphasic System via Parameter Regulation

Efficient production of furfural from cornstalk in 2-Methyltetrahydrofuran/aqueous (MTHF/H₂O) biphasic system via parameter regulation (e.g., V_MTHF/V_H2O, temperature, time, and H₂SO₄ concentration) was proposed. The resulting solid residues achieved from the different MTHF/H₂O system conditions for furfural production were also to prepare glucose by adding cellulases to increase the high-value applications of cornstalk. A maximum furfural yield (68.1%) was obtained based on reaction condition (V_MTHF:V_H2O = 1:1, 170 °C, 60 min, 0.05 M H₂SO₄). Among these parameters, the concentration of H₂SO₄ had the most obvious effect on the furfural production. The glucose yields of the residues acquired from different MTHF/H₂O processes were enhanced and then a maximum value of 78.9% based on the maximum furfural production conditions was observed. Single factor may not be sufficient to detail the difference in glucose production, and several factors affected the hydrolysis efficiency of the residues. Overall, the MTHF/H₂O system effectively converted cornstalk into furfural and glucose via a simple and environment-friendly process, thus was an ideal manner for the food industries.

Lignin Transformation of One-Year-Old Plants During Anaerobic Digestion (AD)

The aim of the research is to identify the changes which occur in lignin from miscanthus and sorghum, one of the main biomass components, as a result of an anaerobic digestion (AD) process. The percentage content and structure of lignin before and after the fermentation process were analysed using biomass harvested in two growing periods—before and after vegetation. It was shown that plants at different developmental stages differ in lignin content. During plant growth, the lignin structure also changes—the syringyl-to-guaiacyl ratio (S/G) increases, whereas the aliphatic and aromatic structure ratio (Al/Ar) decreases. The AD process leads to an increase in percentage lignin content in cell walls, and the increase is higher for plants harvested during vegetation. It has been shown in studies that the methane fermentation of miscanthus and sorghum produces waste containing a large amount of lignin, the structure of which is altered relative to native lignin. The quantity and the new, simplified structure of lignin create new possibilities for using this aromatic polymer.

Recent advances in nanoscale-metal assisted biochar derived from waste biomass used for heavy metals removal

Pollution of heavy metals (HMs) is a detrimental treat to human health and need to be cleaned up in a proper way. Biochar (BC), a low-cost and "green" adsorbent, has attracted significant attention due to its considerable HMs removal capacity. In particular, nano-metals have recently been used to assist BC in improving its reactivity, surface texture and magnetism. Synthesis methods and metal precursors greatly influence the properties and structures of the nanocomposites, thereby affecting their HMs removal performance. This review presents advances in synthesis methods, formation mechanisms and surface characteristics of BC nanocomposites, along with the discussions on HMs removal mechanisms and the effects of environmental factors on HMs removal efficiency. Performance of using BC nanocomposites to remediate real HMs-containing wastewater and issues associated with its process scale-up are also discussed. This review aims to provide useful information to facilitate the development of HMs removal by nanoscale-metal assisted BC.

T, Das P, Meng X, Stoklosa RJ, Bhalla A, Hodge DB, Yuan JS, Ragauskas AJ. Conversion of corn stover alkaline pre-treatment waste streams into biodiesel via Rhodococci

The bioconversion of second-generation cellulosic ethanol waste streams into biodiesel via oleaginous bacteria, Rhodococcus, is a novel optimization strategy for biorefineries with substantial potential for rapid development.

Novel synthesis of a versatile magnetic adsorbent derived from corncob for dye removal

Corncob, an agricultural waste, was successfully converted into a novel magnetic adsorbent by a low-temperature hydrothermal method (453K), including carbonization under saline conditions and magnetization using iron (III) salt. The resultant magnetic carbonaceous adsorbent (MCA) exhibited a porous structure with a higher specific surface area and more oxygen-containing functional groups than its carbonaceous precursor (CP), which can be attributed to the catalytic effect of Fe (III). The adsorption behaviors of both MCA and CP could be described well by Langmuir isotherm and pseudo-second-order model. The adsorption capacity for Methylene blue (MB) revealed by adsorption isotherms were 163.93mg/g on MCA and 103.09mg/g on CP, respectively. Moreover, MCA was demonstrated as a versatile adsorbent for removal of both anionic and cationic dyes, and it showed good reusability in regeneration studies. This work provides an alternative approach for effective conversion of biomass waste and application of them in pollutant removal.

Lignin removal and benzene-alcohol extraction effects on lignin measurements of the hydrothermal pretreated bamboo substrate

Lignin content of hydrothermal pretreated bamboo chips was determined by the two methods: TAPPI standard method (222om-06) and TAPPI standard method without benzene-alcohol extraction (BAE). The results showed that including BAE resulted in lower Klason lignin (KL) and acid soluble lignin (ASL) measurements in the prehydrolyzed substrate, that is to say, BAE removed parts of KL and ASL. Therefore, the TAPPI standard method should be modified by omitting the BAE for lignin measurements of pretreated substrate. The following lignin removal analysis suggested that lignin was removed from the bamboo substrate during pretreatment by a combination of degradation reaction and deconstruction; thereafter the pseudo lignin generated in the hydrothermal pretreatment and condensation reaction between the lignin fragments accounted for the later KL increase.

Cellulose digestion and metabolism induced biocatalytic transitions in anaerobic microbial ecosystems

Anaerobic digestion of highly polymerized biomass by microbial communities present in diverse microbial ecosystems is an indispensable metabolic process for biogeochemical cycling in nature and for industrial activities required to maintain a sustainable society. Therefore, the evaluation of the complicated microbial metabolomics presents a significant challenge. We here describe a comprehensive strategy for characterizing the degradation of highly crystallized bacterial cellulose (BC) that is accompanied by metabolite production for identifying the responsible biocatalysts, including microorganisms and their metabolic functions. To this end, we employed two-dimensional solid- and one-dimensional solution-state nuclear magnetic resonance (NMR) profiling combined with a metagenomic approach using stable isotope labeling. The key components of biocatalytic reactions determined using a metagenomic approach were correlated with cellulose degradation and metabolic products. The results indicate that BC degradation was mediated by cellulases that contain carbohydrate-binding modules and that belong to structural type A. The degradation reactions induced the metabolic dynamics of the microbial community and produced organic compounds, such as acetic acid and propionic acid, mainly metabolized by clostridial species. This combinatorial, functional and structural metagenomic approach is useful for the comprehensive characterization of biomass degradation, metabolic dynamics and their key components in diverse ecosystems.

Solid-, solution-, and gas-state NMR monitoring of ¹³C-cellulose degradation in an anaerobic microbial ecosystem

Anaerobic digestion of biomacromolecules in various microbial ecosystems is influenced by the variations in types, qualities, and quantities of chemical components. Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for characterizing the degradation of solids to gases in anaerobic digestion processes. Here we describe a characterization strategy using NMR spectroscopy for targeting the input solid insoluble biomass, catabolized soluble metabolites, and produced gases. ¹³C-labeled cellulose produced by Gluconacetobacter xylinus was added as a substrate to stirred tank reactors and gradually degraded for 120 h. The time-course variations in structural heterogeneity of cellulose catabolism were determined using solid-state NMR, and soluble metabolites produced by cellulose degradation were monitored using solution-state NMR. In particular, cooperative changes between the solid NMR signal and ¹³C-¹³C/¹³C-¹²C isotopomers in the microbial degradation of ¹³C-cellulose were revealed by a correlation heat map. The triple phase NMR measurements demonstrated that cellulose was anaerobically degraded, fermented, and converted to methane gas from organic acids such as acetic acid and butyric acid.

Differences in Cellulosic Supramolecular Structure of Compositionally Similar Rice Straw Affect Biomass Metabolism by Paddy Soil Microbiota

Because they are strong and stable, lignocellulosic supramolecular structures in plant cell walls are resistant to decomposition. However, they can be degraded and recycled by soil microbiota. Little is known about the biomass degradation profiles of complex microbiota based on differences in cellulosic supramolecular structures without compositional variations. Here, we characterized and evaluated the cellulosic supramolecular structures and composition of rice straw biomass processed under different milling conditions. We used a range of techniques including solid- and solution-state nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy followed by thermodynamic and microbial degradability characterization using thermogravimetric analysis, solution-state NMR, and denaturing gradient gel electrophoresis. These measured data were further analyzed using an "ECOMICS" web-based toolkit. From the results, we found that physical pretreatment of rice straw alters the lignocellulosic supramolecular structure by cleaving significant molecular lignocellulose bonds. The transformation from crystalline to amorphous cellulose shifted the thermal degradation profiles to lower temperatures. In addition, pretreated rice straw samples developed different microbiota profiles with different metabolic dynamics during the biomass degradation process. This is the first report to comprehensively characterize the structure, composition, and thermal degradation and microbiota profiles using the ECOMICS toolkit. By revealing differences between lignocellulosic supramolecular structures of biomass processed under different milling conditions, our analysis revealed how the characteristic compositions of microbiota profiles develop in addition to their metabolic profiles and dynamics during biomass degradation.

Removal of copper and cadmium from aqueous solution using switchgrass biochar produced via hydrothermal carbonization process

Biochar produced from switchgrass via hydrothermal carbonization (HTC) was used as a sorbent for the removal of copper and cadmium from aqueous solution. The cold activation process using KOH at room temperature was developed to enhance the porous structure and sorption properties of the HTC biochar. The sorption efficiency of HTC biochar and alkali activated HTC biochar (HTCB) for removing copper and cadmium from aqueous solution were compared with commercially available powdered activated carbon (PAC). The present batch adsorption study describes the effects of solution pH, biochar dose, and contact time on copper and cadmium removal efficiency from single metal ion aqueous solutions. The activated HTCB exhibited a higher adsorption potential for copper and cadmium than HTC biochar and PAC. Experiments conducted with an initial metal concentration of 40 mg/L at pH 5.0 and contact time of 24 h resulted in close to 100% copper and cadmium removal by activated HTCB at 2 g/L, far greater than what was observed for HTC biochar (16% and 5.6%) and PAC (4% and 7.7%). The adsorption capacities of activated HTCB for cadmium removal were 34 mg/g (0.313 mmol/g) and copper removal was 31 mg/g (0.503 mmol/g).

Pseudo-lignin formation and its impact on enzymatic hydrolysis

Pseudo-lignin, which can be broadly defined as aromatic material that yields a positive Klason lignin value and is not derived from native lignin, has been recently reported to form during the dilute acid pretreatment of poplar holocellulose. To investigate the chemistry of pseudo-lignin formation, GPC, FT-IR and 13C NMR were utilized to characterize pseudo-lignin extracted from dilute-acid pretreated α-cellulose and holocellulose. The results showed that pseudo-lignin consisting of carbonyl, carboxylic, aromatic and aliphatic structures was produced from dilute acid pretreated cellulose and hemicellulose. Pseudo-lignin extracted from holocellulose pretreated at different conditions had similar molecular weights (Mn∼1000 g/mol; Mw∼5000 g/mol) and structural features (carbonyl, carboxylic, aromatic and methoxy structures). These characterizations have provided the pseudo-lignin formation mechanisms during pretreatment. The presence and structure of pseudo-lignin is important since pseudo-lignin decreases the enzymatic conversion.

Mild acetosolv process to fractionate bamboo for the biorefinery: structural and antioxidant properties of the dissolved lignin

Fractionation of lignocellulosic material into its constitutive components is of vital importance for the production of biofuels as well as other value-added chemicals. The conventional acetosolv processes are mainly focused on the production of pulp from woody lignocelluloses. In this study, a mild acetosolv process was developed to fractionate bamboo under atmospheric pressure to obtain cellulosic pulp, water-soluble fraction, and acetic acid lignin. The structural features of the lignins obtained under various conditions were characterized with elemental analysis, sugar analysis, alkaline nitrobenzene oxidation, gel permeation chromatography (GPC), (1)H nuclear magnetic resonance ((1)H NMR), and heteronuclear single-quantum coherence (HSQC) spectroscopy. As compared to milled wood lignin (MWL) of bamboo, acetic acid lignins had low impurities (carbohydrates 2.48-4.56%) mainly due to the cleavage of linkages between lignin and carbohydrates. In addition, acetic acid lignins showed a low proportion of syringyl (S) units. Due to the cleavage of linkages between lignin units, acetic acid lignins had weight-average molecular weights ranging from 4870 to 5210 g/mol, less than half that of MWL (13000 g/mol). In addition, acetic acid lignins showed stronger antioxidant activity mainly due to the significant increase of free phenolic hydroxyls. The lignins obtained with such low impurities, high free phenolic hydroxyls, and medium molecular weights are promising feedstocks to replace petroleum chemicals.