Boosting biomethane yield and production rate with graphene: The potential of direct interspecies electron transfer in anaerobic digestion.
TL;DR: Graphene-based DIET can sustained a much higher electron transfer flux than conventional hydrogen transfer and the ethanol degradation constant was accordingly improved by 29.1% in the presence of graphene.
About: This article is published in Bioresource Technology.The article was published on 2017-09-01. It has received 241 citations till now. The article focuses on the topics: Geobacter & Acidogenesis.
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TL;DR: This critical review presents the current understanding of DIET via conductive materials for methane production, summarizes the relevant studies published to date, and analyzes these studies with regard to conductive Materials, substrates, inocula, performance, and microorganisms.
300 citations
TL;DR: An overview of the effect of several iron-based and carbon-based CM in bioengineered systems, focusing on the improvement in methane production and in microbial communities' changes is presented.
Abstract: Conductive materials (CM) have been extensively reported to enhance methane production in anaerobic digestion processes. The occurrence of direct interspecies electron transfer (DIET) in microbial communities, as an alternative or complementary to indirect electron transfer (via hydrogen or formate), is the main explanation given to justify the improvement of methane production. Not disregarding that DIET can be promoted in the presence of certain CM, it surely does not explain all the reported observations. In fact, in methanogenic environments DIET was only unequivocally demonstrated in cocultures of Geobacter metallireducens with Methanosaeta harundinacea or Methanosarcina barkeri and frequently Geobacter sp. are not detected in improved methane production driven systems. Furthermore, conductive carbon nanotubes were shown to accelerate the activity of methanogens growing in pure cultures, where DIET is not expected to occur, and hydrogenotrophic activity is ubiquitous in full-scale anaerobic digesters...
260 citations
TL;DR: A state-of-art review focusing on the fundamental mechanisms, key microbial players, the role of electrical conductivity, the effectiveness of various conductive additives, the significance of substrate characteristics and organic loading rates in promoting DIET in anaerobic digestion is presented.
258 citations
Cites background from "Boosting biomethane yield and produ..."
...Mixed-culture 435 studies conducted with ethanol identified Geobacter species as a key microbial player involved 436 in DIET with methanogens (Lin et al., 2017; Zhao et al., 2016a)....
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...In comparison, Lin et al. (2017) found that DIET between 344 exoelectrogens and hydrogenotrophic methanogens can be engineered at a relatively high 345 concentration of graphene (1 g/L)....
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...…in Table 1, various DIET-active electron donating bacteria have been 106 isolated from methanogenic digesters (Chen et al., 2014a; 2014b; Rotaru et al., 2014a; 2014b; 107 Lin et al., 2017; Lee et al., 2016; Zhuang et al., 2015; Jing et al., 2017; Dang et al., 2016; 2017; 108 Lei et al., 2016)....
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TL;DR: In this paper, the authors summarize the recent advances in biogas dry reforming toward hydrogen production, including the preparation of catalysts, the optimization of operation conditions, and the influence of impurities in Biogas.
239 citations
TL;DR: It was revealed that syntrophic degradation of butyrate to acetate occurred under high H2 partial pressure, and biochar addition brought about the enrichment of Anaerolineaceae and Methanosaeta, typical microorganisms for direct interspecies electron transfer.
226 citations
References
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TL;DR: A 16S rRNA gene database (http://greengenes.lbl.gov) was used to provide chimera screening, standard alignment, and taxonomic classification using multiple published taxonomies as mentioned in this paper.
Abstract: A 16S rRNA gene database (http://greengenes.lbl.gov) addresses limitations of public repositories by providing chimera screening, standard alignment, and taxonomic classification using multiple published taxonomies. It was found that there is incongruent taxonomic nomenclature among curators even at the phylum level. Putative chimeras were identified in 3% of environmental sequences and in 0.2% of records derived from isolates. Environmental sequences were classified into 100 phylum-level lineages in the Archaea and Bacteria.
9,593 citations
TL;DR: In this paper, the antibacterial activity of four types of graphene-based materials (graphite (Gt), graphite oxide (GtoO), reduced graphene oxide (rGO), and reduced GtO) toward a bacterial model (Escherichia coli) was investigated.
Abstract: Health and environmental impacts of graphene-based materials need to be thoroughly evaluated before their potential applications. Graphene has strong cytotoxicity toward bacteria. To better understand its antimicrobial mechanism, we compared the antibacterial activity of four types of graphene-based materials (graphite (Gt), graphite oxide (GtO), graphene oxide (GO), and reduced graphene oxide (rGO)) toward a bacterial model—Escherichia coli. Under similar concentration and incubation conditions, GO dispersion shows the highest antibacterial activity, sequentially followed by rGO, Gt, and GtO. Scanning electron microscope (SEM) and dynamic light scattering analyses show that GO aggregates have the smallest average size among the four types of materials. SEM images display that the direct contacts with graphene nanosheets disrupt cell membrane. No superoxide anion (O2•–) induced reactive oxygen species (ROS) production is detected. However, the four types of materials can oxidize glutathione, which serves ...
2,279 citations
"Boosting biomethane yield and produ..." refers background in this paper
...Cytotoxicity of carbon 14 nanomaterials (such as graphene and carbon nanotube) to microbes has been demonstrated using 15 different microbial strains such as Escherichia coli and Bacillus subtilis (Liu et al., 2011; Pasquini 16 et al., 2012; Zhu et al., 2014)....
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TL;DR: Results indicate that the pili of G. sulfurreducens might serve as biological nanowires, transferring electrons from the cell surface to the surface of Fe(iii) oxides, indicating possibilities for other unique cell-surface and cell–cell interactions, and for bioengineering of novel conductive materials.
Abstract: Microbes that can transfer electrons to extracellular electron acceptors, such as Fe(iii) oxides, are important in organic matter degradation and nutrient cycling in soils and sediments. Previous investigations on electron transfer to Fe(iii) have focused on the role of outer-membrane c-type cytochromes. However, some Fe(iii) reducers lack c-cytochromes. Geobacter species, which are the predominant Fe(iii) reducers in many environments, must directly contact Fe(iii) oxides to reduce them, and produce monolateral pili that were proposed, on the basis of the role of pili in other organisms, to aid in establishing contact with the Fe(iii) oxides. Here we report that a pilus-deficient mutant of Geobacter sulfurreducens could not reduce Fe(iii) oxides but could attach to them. Conducting-probe atomic force microscopy revealed that the pili were highly conductive. These results indicate that the pili of G. sulfurreducens might serve as biological nanowires, transferring electrons from the cell surface to the surface of Fe(iii) oxides. Electron transfer through pili indicates possibilities for other unique cell-surface and cell-cell interactions, and for bioengineering of novel conductive materials.
2,225 citations
"Boosting biomethane yield and produ..." refers background in this paper
...It was 13 demonstrated that Pseudomonas aeruginosa yielded poorly conductive pili (Reguera et al., 2005), 14 which cannot be used as conduit for extracellular electron transfer....
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TL;DR: An up-to-date review of the literature available on the subject of liquid bio-fuels can be found in this article, which includes information based on the research conducted globally by scientists according to their local socio-cultural and economic situations.
1,948 citations
"Boosting biomethane yield and produ..." refers background in this paper
...Due to 9 the high growth rate and carbohydrate content, algae including micro- and macro-algae are 10 considered to be a viable alternative energy feedstock that is devoid of the major drawbacks 11 associated with first and second-generation feedstock (Chen et al., 2015; Nigam & Singh, 2011)....
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TL;DR: S syntrophically fermenting bacteria synthesize ATP by substrate-level phosphorylation and reinvest part of the ATP-bound energy into reversed electron transport processes, to release the electrons at a redox level accessible by the partner bacteria and to balance their energy budget.
Abstract: Fatty acids and alcohols are key intermediates in the methanogenic degradation of organic matter, e.g., in anaerobic sewage sludge digestors or freshwater lake sediments. They are produced by classical fermenting bacteria for disposal of electrons derived in simultaneous substrate oxidations. Methanogenic bacteria can degrade primarily only one-carbon compounds. Therefore, acetate, propionate, ethanol, and their higher homologs have to be fermented further to one-carbon compounds. These fermentations are called secondary or syntrophic fermentations. They are endergonic processes under standard conditions and depend on intimate coupling with methanogenesis. The energetic situation of the prokaryotes cooperating in these processes is problematic: the free energy available in the reactions for total conversion of substrate to methane attributes to each partner amounts of energy in the range of the minimum biochemically convertible energy, i.e., 20 to 25 kJ per mol per reaction. This amount corresponds to one-third of an ATP unit and is equivalent to the energy required for a monovalent ion to cross the charged cytoplasmic membrane. Recent studies have revealed that syntrophically fermenting bacteria synthesize ATP by substrate-level phosphorylation and reinvest part of the ATP-bound energy into reversed electron transport processes, to release the electrons at a redox level accessible by the partner bacteria and to balance their energy budget. These findings allow us to understand the energy economy of these bacteria on the basis of concepts derived from the bioenergetics of other microorganisms.
1,749 citations
"Boosting biomethane yield and produ..." refers background in this paper
...20 However, a free energy of about -20 to -15 kJ/mol is normally required to support syntrophic 21 microbial growth (Schink, 1997)....
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