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Chemical Reviews Aug 2009
Review
Topics: Electron Spin Resonance Spectroscopy; Electrons; Methane; Molecular Structure; Solvents; Thermodynamics
PubMed: 19449838
DOI: 10.1021/cr800518t -
Bioresource Technology Oct 2016We assessed the suitability of various biogenic materials for development of a gradient packed bed bio-filter to mitigate the methane (CH4) emission from landfills. Five...
We assessed the suitability of various biogenic materials for development of a gradient packed bed bio-filter to mitigate the methane (CH4) emission from landfills. Five different biogenic materials (windrow compost-WC; vermicompost-VC; landfill top cover-LTC; landfill bottom soil-LBS; and river soil sediment-SS) were screened. Among these materials, the VC showed a better CH4 oxidation potential (MOP) of 12.6μg CH4 gdw(-1)h(-1). Subsequently, the VC was used as a packing material along with wood chips in proto-type bio-filters. Wood chips were mixed at 5-15% to form three distinct gradients in a test bio-filter. Under the three different CH4 loading rates of 33, 44 and 55 gCH4 m(-3)h(-1), the achieved MOPs were 31, 41, and 47gCH4 m(-3)h(-1), respectively. The gradient packed bed bio-filter is effective for landfill CH4 mitigation than the conventional bio-filter as the latter shows gas channeling effects with poor MOPs.
Topics: Biodegradation, Environmental; Filtration; Methane; Soil; Waste Disposal Facilities; Wood
PubMed: 26883060
DOI: 10.1016/j.biortech.2016.01.059 -
Bioresource Technology Sep 2018Biogas upgrading technologies have received widespread attention recently and are researched extensively. Microbial biogas upgrading (biomethanation) relies on the... (Review)
Review
Biogas upgrading technologies have received widespread attention recently and are researched extensively. Microbial biogas upgrading (biomethanation) relies on the microbial performance in enriched H and CO environments. In this review, recent developments and applications of CH enrichment in microbial methanation processes are systematically reviewed. During biological methanation, either H can be injected directly inside the anaerobic digester to enrich CH by a consortium of mixed microbial species or H can be injected into a separate bioreactor, where CO contained in biogas is coupled with H and converted to CH, or a combination hereof. The available microbial technologies based on hydrogen-mediated CH enrichment, in particular ex-situ, in-situ and bioelectrochemical, are compared and discussed. Moreover, gas-liquid mass transfer limitations, and dynamics of bacteria-archaea interactions shift after H injection are thoroughly discussed. Finally, the summary of existing demonstration, pilot plants and commercial CH enrichment plants based on microbial biomethanation are critically reviewed.
Topics: Archaea; Biofuels; Bioreactors; Hydrogen; Methane
PubMed: 29908874
DOI: 10.1016/j.biortech.2018.06.013 -
Accounts of Chemical Research Jun 2021Carbohydrates (glycans, saccharides, and sugars) are essential molecules in all domains of life. Research on glycoscience spans from chemistry to biomedicine, including... (Review)
Review
Carbohydrates (glycans, saccharides, and sugars) are essential molecules in all domains of life. Research on glycoscience spans from chemistry to biomedicine, including material science and biotechnology. Access to pure and well-defined complex glycans using synthetic methods depends on the success of the employed glycosylation reaction. In most cases, the mechanism of the glycosylation reaction is believed to involve the oxocarbenium ion. Understanding the structure, conformation, reactivity, and interactions of this glycosyl cation is essential to predict the outcome of the reaction. In this Account, building on our contributions on this topic, we discuss the theoretical and experimental approaches that have been employed to decipher the key features of glycosyl cations, from their structures to their interactions and reactivity.We also highlight that, from a chemical perspective, the glycosylation reaction can be described as a continuum, from unimolecular S1 with naked oxocarbenium cations as intermediates to bimolecular S2-type mechanisms, which involve the key role of counterions and donors. All these factors should be considered and are discussed herein. The importance of dissociative mechanisms (involving contact ion pairs, solvent-separated ion pairs, solvent-equilibrated ion pairs) with bimolecular features in most reactions is also highlighted.The role of theoretical calculations to predict the conformation, dynamics, and reactivity of the oxocarbenium ion is also discussed, highlighting the advances in this field that now allow access to the conformational preferences of a variety of oxocarbenium ions and their reactivities under S1-like conditions.Specifically, the ground-breaking use of superacids to generate these cations is emphasized, since it has permitted characterization of the structure and conformation of a variety of glycosyl oxocarbenium ions in superacid solution by NMR spectroscopy.We also pay special attention to the reactivity of these glycosyl ions, which depends on the conditions, including the counterions, the possible intra- or intermolecular participation of functional groups that may stabilize the cation and the chemical nature of the acceptor, either weak or strong nucleophile. We discuss recent investigations from different experimental perspectives, which identified the involved ionic intermediates, estimating their lifetimes and reactivities and studying their interactions with other molecules. In this context, we also emphasize the relationship between the chemical methods that can be employed to modulate the sensitivity of glycosyl cations and the way in which glycosyl modifying enzymes (glycosyl hydrolases and transferases) build and cleave glycosidic linkages in nature. This comparison provides inspiration on the use of molecules that regulate the stability and reactivity of glycosyl cations.
Topics: Glycosylation; Ions; Methane; Models, Molecular; Molecular Conformation
PubMed: 33930267
DOI: 10.1021/acs.accounts.1c00021 -
Angewandte Chemie (International Ed. in... Feb 2006
Review
Topics: Heterocyclic Compounds; Hydrocarbons; Methane; Molecular Structure; Stereoisomerism
PubMed: 16447297
DOI: 10.1002/anie.200503858 -
Environmental Health Perspectives Jun 1995Chlorinated methanes are important industrial chemicals and significant environmental pollutants. While the highly chlorinated methanes, trichloromethane and... (Review)
Review
Chlorinated methanes are important industrial chemicals and significant environmental pollutants. While the highly chlorinated methanes, trichloromethane and tetrachloromethane, are not productively metabolized by bacteria, chloromethane and dichloromethane are used by both aerobic and anaerobic methylotrophic bacteria as carbon and energy sources. Some of the dehalogenation reactions involved in the utilization of the latter two compounds have been elucidated. In a strictly anaerobic acetogenic bacterium growing with chloromethane, an inducible enzyme forming methyltetrahydrofolate and chloride from chloromethane and tetrahydrofolate catalyzes dehalogenation of the growth substrate. A different mechanism for the nucleophilic displacement of chloride is observed in aerobic methylotrophic bacteria utilizing dichloromethane as the sole carbon and energy source. These organisms possess the enzyme dichloromethane dehalogenase which, in a glutathione-dependent reaction, converts dichloromethane to inorganic chloride and formaldehyde, a central metabolite of methylotrophic growth. Sequence comparisons have shown that bacterial dichloromethane dehalogenases belong to the glutathione S-transferase enzyme family, and within this family to class Theta. The dehalogenation reactions underlying aerobic utilization of chloromethane by a pure culture and anaerobic growth with dichloromethane by an acetogenic mixed culture are not known. It appears that they are based on mechanisms other than nucleophilic attack by tetrahydrofolate or glutathione.
Topics: Bacteria; Bacteria, Anaerobic; Hydrocarbons, Chlorinated; Methane; Methylene Chloride
PubMed: 8565906
DOI: 10.1289/ehp.95103s433 -
Biotechnology and Bioengineering Dec 2006Knowledge of the aqueous phase methane concentration is critical to understanding and controlling process kinetics in methanotrophic bioreactors. Unfortunately since no...
Knowledge of the aqueous phase methane concentration is critical to understanding and controlling process kinetics in methanotrophic bioreactors. Unfortunately since no dissolved methane probe is commercially available, this data must be obtained off-line by the time-consuming gas-liquid partition method. In this study we demonstrate how knowledge of the reactor's k(L)a for oxygen combined with gas phase methane analysis can be used to continuously estimate the aqueous phase concentration of dissolved methane. The on-line estimation was verified in two reactor systems with greatly different values of k (L)a. In both systems the measured and calculated dissolved methane concentrations were in good agreement although dissolved methane was underestimated in both cases. The utility of this methodology was demonstrated by revealing a possible metabolic bottleneck in the model system.
Topics: Automation; Bioreactors; Fermentation; Methane; Molecular Probe Techniques; Oxygen; Software; Soil Microbiology; Solubility; Wetlands
PubMed: 16850500
DOI: 10.1002/bit.21050 -
Bioresource Technology Dec 2017Surplus energy out of fluctuating energy sources like wind and solar energy is strongly increasing. Biological hydrogen (H) methanation (BHM) is a highly promising... (Review)
Review
Surplus energy out of fluctuating energy sources like wind and solar energy is strongly increasing. Biological hydrogen (H) methanation (BHM) is a highly promising approach to move the type of energy from electricity to natural gas via electrolysis and the subsequent step of the Sabatier-reaction. This review provides an overview of the numerous studies concerning the topic of BHM. The technical and biological parameters regarding the research results of these studies are compared and analyzed hereafter. A holistic view on how to overcome physical limitations of the fermentation process, such as gas-liquid mass transfer or a rise of the pH value, and on the enhancement of environmental circumstances for the bacterial biomass are delivered within. With regards to ex-situ methanation, the evaluated studies show a distinct connection between methane production and the methane percentage in the off-gas.
Topics: Biomass; Energy-Generating Resources; Hydrogen; Methane; Natural Gas
PubMed: 28893503
DOI: 10.1016/j.biortech.2017.08.176 -
Environmental Science and Pollution... Mar 2018China is the largest cotton producer with the cotton output accounting for 25% of the total world's cotton production. A large quantity of cotton stalk (CS) waste is...
China is the largest cotton producer with the cotton output accounting for 25% of the total world's cotton production. A large quantity of cotton stalk (CS) waste is generated which is burned and causes environmental and ecological problems. This study investigated the anaerobic digestibility of CS by focusing on improving the methane yield by applying central composite design of response surface methodology (RSM). The purpose of this study was to determine the best level of factors to optimize the desired output of methane production from CS. Thus, it was necessary to describe the relationship of many individual variables with one or more response values for the effective utilization of CS. The influences of feed to inoculum (F/I) ratio and organic loading (OL) on methane production were investigated. Results showed that the experimental methane yield (EMY) and volatile solid (VS) removal were calculated to be 70.22 mL/gVS and 14.33% at F/I ratio of 0.79 and organic loading of 25.61 gVS/L, respectively. Characteristics of final effluent showed that the anaerobic system was stable. This research laid a foundation for future application of CS to alleviate the problems of waste pollution and energy output.
Topics: Anaerobiosis; Bioreactors; China; Cotton Fiber; Methane
PubMed: 29285694
DOI: 10.1007/s11356-017-0682-y -
Trends in Biotechnology Nov 2016Bioelectrochemical power-to-gas (BEP2G) is considered a potentially convenient way of storing renewable surplus electricity in the form of methane. In methane-producing... (Review)
Review
Bioelectrochemical power-to-gas (BEP2G) is considered a potentially convenient way of storing renewable surplus electricity in the form of methane. In methane-producing bioelectrochemical systems (BESs), carbon dioxide and electrical energy are converted into methane, using electrodes that supply either electrons or hydrogen to methanogenic archaea. This review summarizes the performance of methane-producing BESs in relation to cathode potential, electrode materials, operational strategies, and inoculum. Analysis and estimation of energy input and production rates show that BEP2G may become an attractive alternative for thermochemical methanation, and biochemical methanogenesis. To determine if BEP2G can become a future power-to-gas technology, challenges relating to cathodic energy losses, choice of a suitable electron donor, efficient reactor design/operation, and experience with large reactors need to be overcome.
Topics: Archaea; Bioelectric Energy Sources; Bioreactors; Carbon Dioxide; Electrodes; Methane
PubMed: 27666730
DOI: 10.1016/j.tibtech.2016.08.010