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1.
Modelling the long-term effect of wastewater compositions on maximum sulfide and methane production rates of sewer biofilm.
Sun, J, Ni, BJ, Sharma, KR, Wang, Q, Hu, S, Yuan, Z
Water research. 2018;:58-65
Abstract
Reliable modelling of sulfide and methane production in sewer systems is required for efficient sewer emission management. Wastewater compositions affect sulfide and methane production kinetics through both its short-term variation influencing the substrate availability to sewer biofilms, and its long-term variation affecting the sewer biofilm structure. While the short-term effect is well considered in existing sewer models with the use of Monod or half-order equations, the long-term effect has not been explicitly considered in current sewer models suitable for network modelling. In this study, the long-term effect of wastewater compositions on sulfide and methane production activities in rising main sewers was investigated. A detailed biofilm model was firstly developed, and then calibrated and validated using experimental data measured during the entire biofilm development period of a laboratory sewer reactor. Based on scenario simulations using the detailed biofilm model, empirical equations describing the long-term effect of sulfate and sCOD (soluble chemical oxygen demand) concentrations on kH2S (the maximum sulfide production rate of sewer biofilm) and kCH4 (the maximum methane production rate of sewer biofilm) were proposed. These equations require further verification in future studies before their potential integration into network-wide sewer models.
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2.
Strains of the toxic and bloom-forming Nodularia spumigena (cyanobacteria) can degrade methylphosphonate and release methane.
Teikari, JE, Fewer, DP, Shrestha, R, Hou, S, Leikoski, N, Mäkelä, M, Simojoki, A, Hess, WR, Sivonen, K
The ISME journal. 2018;(6):1619-1630
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Abstract
Nodularia spumigena is a nitrogen-fixing cyanobacterium that forms toxic blooms in the Baltic Sea each summer and the availability of phosphorous is an important factor limiting the formation of these blooms. Bioinformatic analysis identified a phosphonate degrading (phn) gene cluster in the genome of N. spumigena suggesting that this bacterium may use phosphonates as a phosphorus source. Our results show that strains of N. spumigena could grow in medium containing methylphosphonic acid (MPn) as the sole source of phosphorous and released methane when growing in medium containing MPn. We analyzed the total transcriptomes of N. spumigena UHCC 0039 grown using MPn and compared them with cultures growing in Pi-replete medium. The phnJ, phosphonate lyase gene, was upregulated when MPn was the sole source of phosphorus, suggesting that the expression of this gene could be used to indicate the presence of bioavailable phosphonates. Otherwise, growth on MPn resulted in only a minor reconstruction of the transcriptome and enabled good growth. However, N. spumigena strains were not able to utilize any of the anthropogenic phosphonates tested. The phosphonate utilizing pathway may offer N. spumigena a competitive advantage in the Pi-limited cyanobacterial blooms of the Baltic Sea.
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3.
Methanogenic and Sulfate-Reducing Activities in a Hypersaline Microbial Mat and Associated Microbial Diversity.
Cadena, S, García-Maldonado, JQ, López-Lozano, NE, Cervantes, FJ
Microbial ecology. 2018;(4):930-940
Abstract
Methanogenesis and sulfate reduction are important microbial processes in hypersaline environments. However, key aspects determining substrate competition between these microbial processes have not been well documented. We evaluated competitive and non-competitive substrates for stimulation of both processes through microcosm experiments of hypersaline microbial mat samples from Guerrero Negro, Baja California Sur, Mexico, and we assessed the effect of these substrates on the microbial community composition. Methylotrophic methanogenesis evidenced by sequences belonging to methanogens of the family Methanosarcinaceae was found as the dominant methanogenic pathway in the studied hypersaline microbial mat. Nevertheless, our results showed that incubations supplemented with acetate and lactate, performed in absence of sulfate, also produced methane after 40 days of incubation, apparently driven by hydrogenotrophic methanogens affiliated to the family Methanomicrobiaceae. Sulfate reduction was mainly stimulated by addition of acetate and lactate; however, after 40 days of incubation, an increase of the H2S concentrations in microcosms amended with trimethylamine and methanol was also observed, suggesting that these substrates are putatively used for sulfate reduction. Moreover, 16S rRNA gene sequencing analysis showed remarkable differences in the microbial community composition among experimental treatments. In the analyzed sample amended with acetate, sulfate-reducing bacteria (SRB) belonging to the family Desulfobacteraceae were dominant, while members of Desulfohalobiaceae, Desulfomicrobiaceae, and Desulfovibrionaceae were found in the incubation with lactate. Additionally, we detected an unexpected high abundance of unclassified Hydrogenedentes (near 25%) in almost all the experimental treatments. This study contributes to better understand methanogenic and sulfate-reducing activities, which play an important role in the functioning of hypersaline environments.
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4.
Metals and Methanotrophy.
Semrau, JD, DiSpirito, AA, Gu, W, Yoon, S
Applied and environmental microbiology. 2018;(6)
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Abstract
Aerobic methanotrophs have long been known to play a critical role in the global carbon cycle, being capable of converting methane to biomass and carbon dioxide. Interestingly, these microbes exhibit great sensitivity to copper and rare-earth elements, with the expression of key genes involved in the central pathway of methane oxidation controlled by the availability of these metals. That is, these microbes have a "copper switch" that controls the expression of alternative methane monooxygenases and a "rare-earth element switch" that controls the expression of alternative methanol dehydrogenases. Further, it has been recently shown that some methanotrophs can detoxify inorganic mercury and demethylate methylmercury; this finding is remarkable, as the canonical organomercurial lyase does not exist in these methanotrophs, indicating that a novel mechanism is involved in methylmercury demethylation. Here, we review recent findings on methanotrophic interactions with metals, with a particular focus on these metal switches and the mechanisms used by methanotrophs to bind and sequester metals.
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5.
Technologies for the bioconversion of methane into more valuable products.
Cantera, S, Muñoz, R, Lebrero, R, López, JC, Rodríguez, Y, García-Encina, PA
Current opinion in biotechnology. 2018;:128-135
Abstract
Methane, with a global warming potential twenty five times higher than that of CO2 is the second most important greenhouse gas emitted nowadays. Its bioconversion into microbial molecules with a high retail value in the industry offers a potential cost-efficient and environmentally friendly solution for mitigating anthropogenic diluted CH4-laden streams. Methane bio-refinery for the production of different compounds such as ectoine, feed proteins, biofuels, bioplastics and polysaccharides, apart from new bioproducts characteristic of methanotrophic bacteria, has been recently tested in discontinuous and continuous bioreactors with promising results. This review constitutes a critical discussion about the state-of-the-art of the potential and research niches of biotechnologies applied in a CH4 biorefinery approach.
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A model based on feature objects aided strategy to evaluate the methane generation from food waste by anaerobic digestion.
Yu, M, Zhao, M, Huang, Z, Xi, K, Shi, W, Ruan, W
Waste management (New York, N.Y.). 2018;:218-226
Abstract
A model based on feature objects (FOs) aided strategy was used to evaluate the methane generation from food waste by anaerobic digestion. The kinetics of feature objects was tested by the modified Gompertz model and the first-order kinetic model, and the first-order kinetic hydrolysis constants were used to estimate the reaction rate of homemade and actual food waste. The results showed that the methane yields of four feature objects were significantly different. The anaerobic digestion of homemade food waste and actual food waste had various methane yields and kinetic constants due to the different contents of FOs in food waste. Combining the kinetic equations with the multiple linear regression equation could well express the methane yield of food waste, as the R2 of food waste was more than 0.9. The predictive methane yields of the two actual food waste were 528.22 mL g-1 TS and 545.29 mL g-1 TS with the model, while the experimental values were 527.47 mL g-1 TS and 522.1 mL g-1 TS, respectively. The relative error between the experimental cumulative methane yields and the predicted cumulative methane yields were both less than 5%.
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7.
Syntrophy Goes Electric: Direct Interspecies Electron Transfer.
Lovley, DR
Annual review of microbiology. 2017;:643-664
Abstract
Direct interspecies electron transfer (DIET) has biogeochemical significance, and practical applications that rely on DIET or DIET-based aspects of microbial physiology are growing. Mechanisms for DIET have primarily been studied in defined cocultures in which Geobacter species are one of the DIET partners. Electrically conductive pili (e-pili) can be an important electrical conduit for DIET. However, there may be instances in which electrical contacts are made between electron transport proteins associated with the outer membranes of the partners. Alternatively, DIET partners can plug into conductive carbon materials, such as granular activated carbon, carbon cloth, and biochar, for long-range electron exchange without the need for e-pili. Magnetite promotes DIET, possibly by acting as a substitute for outer-surface c-type cytochromes. DIET is the primary mode of interspecies electron exchange in some anaerobic digesters converting wastes to methane. Promoting DIET with conductive materials shows promise for stabilizing and accelerating methane production in digesters, permitting higher organic loading rates. Various lines of evidence suggest that DIET is important in terrestrial wetlands, which are an important source of atmospheric methane. DIET may also have a role in anaerobic methane oxidation coupled to sulfate reduction, an important control on methane releases. The finding that DIET can serve as the source of electrons for anaerobic photosynthesis further broadens its potential environmental significance. Microorganisms capable of DIET are good catalysts for several bioelectrochemical technologies and e-pili are a promising renewable source of electronic materials. The study of DIET is in its early stages, and additional investigation is required to better understand the diversity of microorganisms that are capable of DIET, the importance of DIET to carbon and electron flow in anaerobic environments, and the biochemistry and physiology of DIET.
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Simultaneous chemical oxygen demand removal, methane production and heavy metal precipitation in the biological treatment of landfill leachate using acid mine drainage as sulfate resource.
Li, YL, Wang, J, Yue, ZB, Tao, W, Yang, HB, Zhou, YF, Chen, TH
Journal of bioscience and bioengineering. 2017;(1):71-75
Abstract
Biological treatment played an important role in the treatment of landfill leachate. In the current study, acid mine drainage (AMD) was used as a source of sulfate to strengthen the anaerobic treatment of landfill leachate. Effects of chemical oxygen demand (COD) and SO42- mass concentration ratio on the decomposition of organic matter, methane production and sulfate reduction were investigated and the microbial community was analyzed using the high throughout methods. Results showed that high removal efficiency of COD, methane production and heavy metal removal was achieved when the initial COD/SO42- ratio (based on mass) was set at 3.0. The relative abundance of anaerobic hydrogen-producing bacteria (Candidatus Cloacamonas) in the experimental group with the addition of AMD was significantly increased compared to the control. Abundance of hydrogenotrophic methanogens of Methanosarcina and Methanomassiliicoccus was increased. Results confirmed that AMD could be used as sulfate resource to strengthen the biological treatment of landfill leachate.
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Effect of Ethylenediamine-N,N'-disuccinic acid (EDDS) on the speciation and bioavailability of Fe2+ in the presence of sulfide in anaerobic digestion.
Thanh, PM, Ketheesan, B, Yan, Z, Stuckey, D
Bioresource technology. 2017;:169-179
Abstract
The effects of a biodegradable chelating agent, Ethylenediamine-N,N'-disuccinic acid (EDDS), on the speciation and bioavailability of iron (Fe2+) in anaerobic digestion were examined. Fe2+ supplementation at 10mg/L increased methane yield, but the presence of 8mg/L sulfide led to the precipitation of Fe2+ as FeS which limited its bioavailability. The results confirmed that the EDDS could replace common chelating agents with low biodegradability (EDTA and NTA), and improve the bioavailability of Fe2+ by forming an Fe-EDDS complex, thereby protecting Fe2+ from sulfide precipitation. Experimental findings from sequential extraction using the Community Bureau of Reference (BCR) method, and quantification of free EDDS and Fe-EDDS complex using UHPLC, confirmed that 29.82% of Fe2+ was present in bioavailable forms, i.e. soluble and exchangeable, when EDDS was added at 1:1 molar ratio to Fe2+. As a result, the methane production rate increased by 11.17%, and the methane yield increased by 13.25%.
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High-pressure anaerobic digestion up to 100 bar: influence of initial pressure on production kinetics and specific methane yields.
Merkle, W, Baer, K, Haag, NL, Zielonka, S, Ortloff, F, Graf, F, Lemmer, A
Environmental technology. 2017;(3):337-344
Abstract
To ensure an efficient use of biogas produced by anaerobic digestion, in some cases it would be advisable to upgrade the biogenic gases and inject them into the transnational gas grids. To investigate biogas production under high-pressure conditions up to 100 bar, new pressure batch methane reactors were developed for preliminary lab-scale experiments with a mixture of grass and maize silage hydrolysate. During this investigation, the effects of different initial pressures (1, 50 and 100 bar) on pressure increase, gas production and the specific methane yield using nitrogen as inert gas were determined. Based on the experimental findings increasing initial pressures alter neither significantly, further pressure increases nor pressure increase rates. All supplied organic acids were degraded and no measurable inhibition of the microorganisms was observed. The results show that methane reactors can be operated at operating pressures up to 100 bar without any negative effects on methane production.