Waste to Energy: Steam explosion-based torrefaction process to produce solid biofuel for power generation utilizing various waste biomasses.

Currently, humankind is facing a serious environmental and climate crisis, which has accelerated the research on producing bioenergy from waste biomass as a carbon-neutral feedstock. In this study, the aim was to develop an upcycling strategy for waste biomass to solid-type biofuel conversion for power generation. Various types of waste biomass (i.e., waste wood after lumbering, sawdust-type mushroom waste wood, kudzu vine, and empty fruit bunches from palm) were used as sustainable feedstocks for steam explosion-based torrefaction. The reaction conditions were optimized for each waste biomass by controlling the severity index (Ro); the higher heating value increased proportional to the Ro increase. Additionally, component analysis revealed that steam explosion torrefaction mainly degraded hemicellulose, and most of the torrefied waste biomass met the Bio-Solid Refuse Fuel quality standard. The results provide not only a viable waste-to-energy strategy but also insights to address global climate change.

Development of bioprocess for corncob-derived levulinic acid production.

Levulinic acid is a significant platform chemical obtained from biomass and can potentially be used to produce value-added biofuels, biopolymers, and biopharmaceuticals. This study aims at statistically optimizing levulinic acid production from agrowastes. Based on the total carbohydrate content (71.93 %), corncob was selected as the target feedstock. A Box-Behnken design with four factors, such as feedstock concentration, reaction time, reaction temperature, and catalyst concentration, was used to optimize the hydrothermal conversion of corncob to levulinic acid at 180 °C for 30 min using 1 M H2SO4 as the acid catalyst and 120 g/L corncob. The maximum yield of 19.9 % was obtained. Additionally, 8.1 g/L formic acid was co-produced. The results of this study can contribute toward valorization of levulinic acid. Moreover, our results can be useful in developing strategies to utilize agrowastes as a renewable feedstock for recent biorefineries to cope with the climate crisis.

Lytic polysaccharide monooxygenase (LPMO)-derived saccharification of lignocellulosic biomass.

Given that traditional biorefineries have been based on microbial fermentation to produce useful fuels, materials, and chemicals as metabolites, saccharification is an important step to obtain fermentable sugars from biomass. It is well-known that glycosidic hydrolases (GHs) are responsible for the saccharification of recalcitrant polysaccharides through hydrolysis, but the discovery of lytic polysaccharide monooxygenase (LPMO), which is a kind of oxidative enzyme involved in cleaving polysaccharides and boosting GH performance, has profoundly changed the understanding of enzyme-based saccharification. This review briefly introduces the classification, structural information, and catalytic mechanism of LPMOs. In addition to recombinant expression strategies, synergistic effects with GH are comprehensively discussed. Challenges and perspectives for LPMO-based saccharification on a large scale are also briefly mentioned. Ultimately, this review can provide insights for constructing an economically viable lignocellulose-based biorefinery system and a closed-carbon loop to cope with climate change.

Newly explored formate dehydrogenases from Clostridium species catalyze carbon dioxide to formate.

With concerns over global warming and climate change, many efforts have been devoted to mitigate atmospheric CO2 level. As a CO2 utilization strategy, formate dehydrogenase (FDH) from Clostridium species were explored to discover O2-tolerant and efficient FDHs that can catalyze CO2 to formate (i.e. CO2 reductase). With FDH from Clostridium ljungdahlii (ClFDH) that plays as a CO2 reductase previously reported as the reference, FDH from C.autoethanogenum (CaFDH), C. coskatii (CcFDH), and C. ragsdalei (CrFDH) were newly discovered via genome-mining. The FDHs were expressed in Escherichia coli and the recombinant FDHs successfully catalyzed CO2 reduction with a specific activity of 15 U g-1-CaFDH, 17 U g-1-CcFDH, and 8.7 U g-1-CrFDH. Interestingly, all FDHs newly discovered retain their catalytic activity under aerobic condition, although Clostridium species are strict anaerobe. The results discussed herein can contribute to biocatalytic CO2 utilization.

Paradigm shift in algal biomass refinery and its challenges.

Microalgae have been studied and tested for over 70 years. However, biodiesel, the prime target of the algal industry, has suffered from low competitiveness and current steps toward banning the internal combustion engine all over the world. Meanwhile, interest in reducing CO2 emissions has grown as the world has witnessed disasters caused by global warming. In this situation, in order to maximize the benefits of the microalgal industry and surmount current limitations, new breakthroughs are being sought. First, drop-in fuel, mandatory for the aviation and maritime industries, has been discussed as a new product. Second, methods to secure stable and feasible outdoor cultivation focusing on CO2 sequestration were investigated. Lastly, the need for an integrated refinery process to simultaneously produce multiple products has been discussed. While the merits of microalgae industry remain valid, further investigations into these new frontiers would put algal industry at the core of future bio-based economy.

Improving hydrogen production by pH adjustment in pressurized gas fermentation.

Gas fermentation utilizes syngas converted from biomass or waste as feedstock. A bubble column reactor for pressurizing was designed to increase the mass transfer rate between gas and liquid, and reduce energy consumption by medium agitation. Thermococcus onnurineus, a hydrogenic CO-oxidizer, was cultured initially under ambient pressure with the initial inlet gas composition; 60% CO and 40% N2. The maximum H2 productivity was 363 mmol/l/h, without pH adjustment. When additional pressure was applied, the pH rapidly declined; this may be attributed to the increased CO2 solubility under pressure. By controlling pH, H2 productivity increased up to 450 mmol/l/h; which is comparable to the previously reported H2 productivity in a continuous stirred tank reactor. The results may suggest energy saving potentials of bubble column reactors in gas fermentation. This finding may be applied to other gas fermentation processes, as syngas itself contains CO2 and many microbial processes also release CO2.

Chemoenzymatic valorization of agricultural wastes into 4-hydroxyvaleric acid via levulinic acid.

Given that (i) levulinic acid (LA) is one of the most significant platform chemicals derived from biomass and (ii) 4-hydroxyvaleric acid (4-HV) is a potential LA derivative, the aim of this study is to achieve chemoenzymatic valorization of LA, which was obtained from agricultural wastes, to 4-HV. The thermochemical process utilized agricultural wastes (i.e., rice straw and corncob) as feedstocks and successfully produced LA, ranging from 25.1 to 65.4 mM. Additionally, formate was co-produced and used as a hydrogen source for the enzymatic hydrogenation of LA. Finally, engineered 3-hydroxybutyrate dehydrogenase from Alcaligenes faecalis (eHBDH) was applicable for catalyzing the conversion of agricultural wastes-driven LA, resulting in a maximum concentration of 11.32 mM 4-HV with a conversion rate of 48.2%. To the best of our knowledge, this is the first report describing the production of 4-HV from actual biomass, and the results might provide insights into the valorization of agricultural wastes.

Recent developments and key barriers to microbial CO2 electrobiorefinery.

The electrochemical conversion of CO2 can include renewable surplus electricity storage and CO2 utilisation. This review focuses on the microbial CO2 electrobiorefinery based on microbial electrosynthesis (MES) which merges electrochemical and microbial conversion to produce biofuels and higher-value chemicals. In this review, recent developments are discussed about bioelectrochemical conversion of CO2 into biofuels and chemicals in MES via microbial CO2-fixation and electricity utilisation reactions. In addition, this review examines technical approaches to overcome the current limitations of MES including the following: engineering of the biocathode, application of electron mediators, and reactor optimisation, among others. An in-depth discussion of strategies for the CO2 electrobiorefinery is presented, including the integration of the biocathode with inorganic catalysts, screening of novel electroactive microorganisms, and metabolic engineering to improve target productivity from CO2.

Elevated conversion of CO2 to versatile formate by a newly discovered formate dehydrogenase from Rhodobacter aestuarii.

Due to climate change, recent research interests have increased towards CO2 utilization as a strategy to mitigate the atmospheric CO2 level. Herein, we aimed to explore formate dehydrogenases (FDHs) from chemoautotroph to discover an efficient and O2-tolerant biocatalyst for catalyzing the CO2 reduction to a versatile formate. Through genome-mining and phylogenetic analysis, the FDH from Rhodobacter aestuarii (RaFDH) was newly discovered as a promising O2-tolernat CO2 reductase and was successfully expressed in Escherichia coli. In this study, the optimum conditions and turnover rates of RaFDH were examined for CO2 reduction and formate oxidation. In particular, the RaFDH-driven CO2 reduction far surpassed the formate oxidation with a turnover rate of 48.3 and 15.6 min-1, respectively. The outstanding superiority of RaFDH towards CO2 reduction can be applicable for constructing a feasible electroenzymatic system that produce a versatile formate from CO2 as a cheap, abundant, and renewable resource.

Critical Point Drying: An Effective Drying Method for Direct Measurement of the Surface Area of a Pretreated Cellulosic Biomass.

The surface area and pore size distribution of Eucalyptus samples that were pretreated by different methods were determined by the Brunauer⁻Emmett⁻Teller (BET) technique. Three methods were applied to prepare cellulosic biomass samples for the BET measurements, air, freeze, and critical point drying (CPD). The air and freeze drying caused a severe collapse of the biomass pore structures, but the CPD effectively preserved the biomass morphology. The surface area of the CPD prepared Eucalyptus samples were determined to be 58⁻161 m²/g, whereas the air and freeze dried samples were 0.5⁻1.3 and 1.0⁻2.4 m²/g, respectively. The average pore diameter of the CPD prepared Eucalyptus samples were 61⁻70 Å. The CPD preserved the Eucalyptus sample morphology by replacing water with a non-polar solvent, CO2 fluid, which prevented hydrogen bond reformation in the cellulose.

Optimization of NaOH-catalyzed steam pretreatment of empty fruit bunch.

BACKGROUND: Empty fruit bunch (EFB) has many advantages, including its abundance, the fact that it does not require collection, and its year-round availability as a feedstock for bioethanol production. But before the significant costs incurred in ethanol production from lignocellulosic biomass can be reduced, an efficient sugar fractionation technology has to be developed. To that end, in the present study, an NaOH-catalyzed steam pretreatment process was applied in order to produce ethanol from EFB more efficiently. RESULTS: The EFB pretreatment conditions were optimized by application of certain pretreatment variables such as, the NaOH concentrations in the soaking step and, in the steam step, the temperature and time. The optimal conditions were determined by response surface methodology (RSM) to be 3% NaOH for soaking and 160°C, 11 min 20 sec for steam pretreatment. Under these conditions, the overall glucan recovery and enzymatic digestibility were both high: the glucan and xylan yields were 93% and 78%, respectively, and the enzymatic digestibility was 88.8% for 72 h using 40 FPU/g glucan. After simultaneous saccharification and fermentation (SSF), the maximum ethanol yield and concentration were 0.88 and 29.4 g/l respectively. CONCLUSIONS: Delignification (>85%) of EFB was an important factor in enzymatic hydrolysis using CTec2. NaOH-catalyzed steam pretreatment, which can remove lignin efficiently and requires only a short reaction time, was proven to be an effective pretreatment technology for EFB. The ethanol yield obtained by SSF, the key parameter determining the economics of ethanol, was 18% (w/w), equivalent to 88% of the theoretical maximum yield, which is a better result than have been reported in the relevant previous studies.

Enhancement of enzymatic digestibility of Eucalyptus grandis pretreated by NaOH catalyzed steam explosion.

NaOH catalyzed steam explosion was applied to improve the enzymatic digestibility of Eucalyptus grandis. The impregnation of wood chip with NaOH solutions before steam explosion was carried out to investigate the effects of alkaline catalysis on solid recovery, enzymatic digestibility, and glucose recovery. The lignin removal was significantly affected by NaOH as a catalyst and the glucose recovery increased with increased severity index. The use of NaOH showed higher enzymatic digestibility than the use of water at most severity indexes due to the delignification of biomass and the increase of accessibility to cellulose of enzyme. The maximum glucose recovery was 65.55% having 4.4361 of severity index with 7wt.% of NaOH catalyzed steam explosion at 210°C during 9min. NaOH catalyzed steam explosion was effective to enhance the enzymatic digestibility due to the removal of lignin.

Pretreatment characteristics of waste oak wood by ammonia percolation.

A log of waste oak wood collected from a Korean mushroom farm has been tested for ammonia percolation pretreatment. The waste log has different physical characteristics from that of virgin oak wood. The density of the waste wood was 30% lower than that of virgin oak wood. However, there is little difference in the chemical compositions between the woods. Due to the difference in physical characteristics, the optimal pretreatment conditions were also quite different. While for waste oak the optimum temperature was determined to be 130 degrees C, for virgin oak wood the optimum pretreatment was only achieved at 170 degrees C. Presoaking for 12 h with ammonia solution before pretreatment was helpful to increase the delignification efficiency.

Blending effects of biodiesels on oxidation stability and low temperature flow properties.

To improve the oxidation stability and the low temperature flow properties of a biodiesel mixture, the dependence of the oxidation stability and the cold filter plugging point (CFPP) on the fatty acid compositions was examined. Three different kinds of biodiesels, palm, rapeseed, and soybean biodiesels, were blended with the different weight ratios. The oxidation stability and the CFPP of the blended biodiesels had a close relationship with the compositions of the major fatty acid components. The oxidation stability of the blended biodiesels decreased as the total contents of the linoleic and linolenic acids increased. The correlation was obtained as Y=117.9295/X+2.5905 (0

Acoustic microscope lens modeling and its application in determining biological cell properties from single- and multi-layered cell models.

The acoustic microscopy technique provides some extraordinary advantages for determining mechanical properties of living cells. It is relatively fast, of excellent spatial resolution, and of minimal invasiveness. Sound velocity is a measure of the cell stiffness. Attenuation of cytoplasm is a measure of supramolecular interactions. These parameters are of crucial interest for studying cell motility and volume regulations and to establish the functional role of the various elements of the cytoskeleton. Using a scanning acoustic microscope, longitudinal wave speed, attenuation and thickness profile of a biological cell were measured earlier by Kundu et al. [Biophys. J. 78, 2270-2279 (2000)]. In that study it was assumed that the cell properties did not change through the cell thickness but could vary in the lateral direction. In that effort the acoustic-microscope-generated signal was modeled as a plane wave striking the cell at normal incidence. Such assumptions ignored the effect of cell inhomogenity and the surface skimming Rayleigh waves. In this paper a rigorous lens model, based on the DPSM (distributed point source method), is adopted. For the first time in the literature the cell is modeled here as a multi-layered material and the effect of some external drug stimuli on a living cell is studied.