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Biological Conversion of Natural Gas
Published in Jianli Hu, Dushyant Shekhawat, Direct Natural Gas Conversion to Value-Added Chemicals, 2020
Qiang Fei, Haritha Meruvu, Hui Wu, Rongzhan Fu
Methanotrophs are methanophilic prokaryotes which can metabolize methane for their growth and energy requirements. Methanotrophs’ capacity of using CH4 as the sole carbon and energy sources to produce platform chemicals, nutrients and biofuels, is a more favorable and ecofriendly alternative for the valorization of natural gas, compared to traditional thermo-chemical conversion methods (Henard, Smith et al. 2016, Clomburg, Crumbley, and Gonzalez 2017). Since the discovery of Bacillus methanicus in last century (Söhngen 1906), methanotrophs have been studied extensively due to their unique ability to oxidize CH4 aerobically or anaerobically into various bioproducts. Hence, by harnessing the potential of methanotrophs, it is possible to mitigate the potential threats posed by greenhouse gases and contribute to the global biogeochemical carbon cycle. This chapter will only focus on aerobic methanotrophs in terms of methanotrophic biodiversity, biocatalytic properties, and cultivation modes. The potential of genetic engineering and metabolic engineering to alter methanotrophic metabolism for improved technical performance and allied cost-cutting strategies will also be discussed. Readers who are interested in anaerobic methanotrophs may find more details in relevant literature (Cui et al. 2015, Winkel et al. 2018, Yang et al. 2018).
Literature review
Published in Tejaswini Eregowda, Anaerobic treatment and resource recovery from methanol rich waste gases and wastewaters, 2019
The bioconversion of methane to methanol is associated with low energy consumption, high conversion, high selectivity, and low capital costs compared with chemical methods since it is carried out by the methane monooxygenase (MMO) enzyme under mild conditions (Conrado and Gonzalez, 2014). Methanotrophs use MMO to convert methane to methanol, which is further converted to formaldehyde by the enzyme methanol dehydrogenase (MDH) and further to cell biomass through the ribulose monophosphate (RuMP) cycle or oxidised to formate and CO2 for biosynthesis. Thus, for successful production and accumulation of methanol, suitable inhibitors for MDH are required. Specific and non-specific inhibitors like cyclopropanol, EDTA and high concentrations of sodium chloride and phosphates can be applied for the inhibition of MDH and other enzymes or co-factors in the electron transport chain (Hur et al., 2017; Kim et al., 2010).
Alcohol Fuels
Published in M.R. Riazi, David Chiaramonti, Biofuels Production and Processing Technology, 2017
Elia Tomás-Pejó, Antonio D. Moreno, M.R. Riazi, David Chiaramonti
Final methanol concentrations, volumetric productivities, and conversion efficiencies are highly dependent on cultivation conditions. The most important physical variables affecting the cultures of methanotrophs are pH, temperature, dissolved O2 concentration, methane: O2 ratio, and cultivation time. Furthermore, the mass transfer rate of methane from the gas phase to the liquid phase and then into the cells is one of the major challenges to improve production yields. The use of 5% paraffin was reported to increase the mass transfer of methane between gas and aqueous phases (Duan et al. 2011). This strategy combined with a high cell density and a mixture of phosphate buffer and MgCl2 as the MDH inhibitor (17.3 g/L cell dry weight, 400 mM phosphate, 10 mM MgCl2, 20 mM sodium formate, 30°C, and pH 6.3) increased methanol production by Methylosinus trichosporium up to 1.12 g/L, which is the highest methanol concentration reported so far (Duan et al. 2011). This methanol concentration corresponds to 64% conversion efficiency within 40 h reaction time. Lower methanol concentrations (about 0.25 g/L) but higher conversion efficiencies (up to 80%) have been achieved by using a microorganism consortium including Methylosinus sporium, M. trichosporium, and Methylococcus capsulatus and 100 mM NaCl or 40 mM NH4Cl as inhibitors (Han et al. 2013).
A mathematical model of aerobic methane oxidation coupled to denitrification
Published in Environmental Technology, 2018
The focus of this study, however, is on methane oxidation coupled to denitrification under aerobic conditions. Aerobic methanotrophs are ubiquitous and fast-growing bacteria that use methane as their sole source of carbon and energy. They oxidize methane to carbon dioxide via methanol, formaldehyde, and formate. The initial oxidation of methane to methanol is catalyzed by methane monooxygenase, which requires molecular oxygen and two reducing equivalents. The following oxidation of methanol to carbon dioxide generates the reducing equivalents needed for maintenance and growth of the bacteria [4,5]. Phylogenetically, aerobic methanotrophs are located in the Gamma-proteobacteria, Alpha-proteobacteria, and Verrucomicrobia phyla [6,7]. Several nitrogen conversions can be catalyzed by aerobic methanotrophs, including N2-fixation [8], assimilatory nitrate reduction to ammonia [9], and cometabolic ammonium oxidation by the methane monooxygenase enzyme [10]. Some aerobic methanotrophs also possess denitrifying pathways [11]. Recently, Dam et al. [12] showed that Methylcystis sp. strain SC2 could denitrify using methanol or possibly intracellularly stored polyhydroxybutyrate as electron donor. Kits et al. [13] showed that Methylomonas denitrificans sp. nov strain FJG1 could reduce nitrate to nitrous oxide using methane as the electron donor, although molecular oxygen appeared to be needed for the initial oxidation of methane.
Design and shelf stability assessment of bacterial agents for simultaneous removal of methane and odors
Published in Journal of Environmental Science and Health, Part A, 2019
Yun-Yeong Lee, Sodaneath Hong, Kyung-Suk Cho
Methanotrophs utilize methane as carbon and energy sources.[1] Methanotrophs (Methylobacter, Methylocaldum, Methylocystis and Methylococcus) were detected in De-MO-1 and De-MO-2 even though their relative abundances were low (0.07–0.26%) during the operation period (Fig. 3, Supplemental Tables S1 and S2).