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1.
Environ Sci Technol ; 55(5): 2722-2742, 2021 03 02.
Artigo em Inglês | MEDLINE | ID: mdl-33559467

RESUMO

Despite ongoing management efforts, phosphorus (P) loading from agricultural landscapes continues to impair water quality. Wastewater treatment research has enhanced our knowledge of microbial mechanisms influencing P cycling, especially regarding microbes known as polyphosphate accumulating organisms (PAOs) that store P as polyphosphate (polyP) under oxic conditions and release P under anoxic conditions. However, there is limited application of PAO research to reduce agricultural P loading and improve water quality. Herein, we conducted a meta-analysis to identify articles in Web of Science on polyP and its use by PAOs across five disciplines (i.e., wastewater treatment, terrestrial, freshwater, marine, and agriculture). We also summarized research that provides preliminary support for PAO-mediated P cycling in natural habitats. Terrestrial, freshwater, marine, and agriculture disciplines had fewer polyP and PAO articles compared to wastewater treatment, with agriculture consistently having the least. Most meta-analysis articles did not overlap disciplines. We found preliminary support for PAOs in natural habitats and identified several knowledge gaps and research opportunities. There is an urgent need for interdisciplinary research linking PAOs, polyP, and oxygen availability with existing knowledge of P forms and cycling mechanisms in natural and agricultural environments to improve agricultural P management strategies and achieve water quality goals.


Assuntos
Reatores Biológicos , Polifosfatos , Agricultura , Fósforo , Águas Residuárias , Qualidade da Água
2.
Environ Sci Technol ; 49(5): 3195-202, 2015 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-25622928

RESUMO

Alternative metabolic options of exoelectrogenic biofilms in bioelectrochemical systems (BESs) are important not only to explain the fundamental ecology and performance of these systems but also to develop reliable integrated nutrient removal strategies in BESs, which potentially involve substrates or intermediates that support/induce those alternative metabolisms. This research focused on dissimilatory nitrate reduction as an alternative metabolism to dissimilatory anode reduction. Using the exoelectrogenic nitrate reducer Geobacter metallireducens, the critical conditions controlling those alternative metabolisms were investigated in two-chamber, potentiostatically controlled BESs at various anode potentials and biofilm thicknesses and challenged over a range of nitrate concentrations. Results showed that anode-reducing biofilms facultatively reduced nitrate at all tested anode potentials (-150 to +900 mV vs Standard Hydrogen Electrode) with a rapid metabolic shift. The critical nitrate concentration that triggered a significant decrease in BES performance was a function of anode biofilm thickness but not anode potential. This indicates that these alternative metabolisms were controlled by the availability of nitrate, which is a function of nitrate concentration in bulk solution and its diffusion into an anode-reducing biofilm. Coulombic recovery decreased as a function of nitrate dose due to electron-acceptor substrate competition, and nitrate-induced suspended biomass growth decreased the effluent quality.


Assuntos
Biofilmes , Técnicas Eletroquímicas/métodos , Geobacter/metabolismo , Nitratos/metabolismo , Poluentes Químicos da Água/metabolismo , Purificação da Água/métodos , Eletrodos , Oxirredução
3.
Appl Microbiol Biotechnol ; 99(21): 9319-29, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26286510

RESUMO

In bioelectrochemical systems, exoelectrogenic bacteria respire with anode electrodes as their extracellular electron acceptor; therefore, lower anode potentials can reduce the energy gain to each microbe and select against ones that are not able to respire at a lower potential range. Often fully developed anode communities are compared across bioelectrochemical systems with set anode potentials or fixed external resistances as different operational conditions. However, the comparative effect of the resulting constantly low versus dynamically low anode potentials on the development of anode microbial communities as well as the final cathode microbial communities has not been directly demonstrated. In this study, we used a low fixed anode potential of -250 mV and a higher-current control potential of -119 mV vs. Standard Hydrogen Electrode to approximately correspond with the negative peak anode potential values obtained from microbial fuel cells operated with fixed external resistances of 1 kΩ and 47 Ω, respectively. Pyrosequencing data from a 2-month time series show that a lower set anode potential resulted in a more diverse community than the higher- and variable-potential systems, likely due to the hindered enrichment of a Geobacter-dominated community with limited energy gain at this set potential. In this case, it appears that the selective pressure caused by the low set potential was counteracted by the low energy gain over a 2-month time scale. The air cathode microbial community with constant low anode potentials showed delayed enrichment of denitrifiers or perchlorate-reducing bacteria compared to the fixed external resistance condition.


Assuntos
Fontes de Energia Bioelétrica , Biota , Eletricidade , Eletrodos/microbiologia , Bactérias/classificação , Bactérias/crescimento & desenvolvimento
4.
Biotechnol Biofuels Bioprod ; 17(1): 76, 2024 Jun 03.
Artigo em Inglês | MEDLINE | ID: mdl-38831375

RESUMO

BACKGROUND: The aim of this study was to increase the accessibility and accelerate the breakdown of lignocellulosic biomass to methane in an anaerobic fermentation system by mechanical cotreatment: milling during fermentation, as an alternative to conventional pretreatment prior to biological deconstruction. Effluent from a mesophilic anaerobic digester running with unpretreated senescent switchgrass as the predominant carbon source was collected and subjected to ball milling for 0.5, 2, 5 and 10 min. Following this, a batch fermentation test was conducted with this material in triplicate for an additional 18 days with unmilled effluent as the 'status quo' control. RESULTS: The results indicate 0.5 - 10 min of cotreatment increased sugar solubilization by 5- 13% when compared to the unmilled control, with greater solubilization correlated with increased milling duration. Biogas concentrations ranged from 44% to 55.5% methane with the balance carbon dioxide. The total biogas production was statistically higher than the unmilled control for all treatments with 2 or more minutes of milling (α = 0.1). Cotreatment also decreased mean particle size. Energy consumption measurements of a lab-scale mill indicate that longer durations of milling offer diminishing benefits with respect to additional methane production. CONCLUSIONS: Cotreatment in anaerobic digestion systems, as demonstrated in this study, provides an alternative approach to conventional pretreatments to increase biogas production from lignocellulosic grassy material.

5.
J Environ Qual ; 2024 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-39014985

RESUMO

Excessive amounts of nitrogen (N) and phosphorus (P) can lead to eutrophication in water sources. Woodchip bioreactors have shown success in removing N from agricultural runoff, but less is known regarding P removal. Woodchip bioreactors are subsurface basins filled with woodchips installed downgradient of agricultural land to collect and treat drainage runoff. Microorganisms use the woodchips as a carbon (C) source to transform N in the runoff, with unresolved biological impacts on P. This study aims to explore microbial communities present in the bioreactor and determine whether milling woodchips to probe the microbial communities within them reveals hidden microbial diversities or potential activities. Metagenomic sequencing and bioinformatic analyses were performed on six woodchip samples (i.e., three unmilled and three milled) collected from a 10-year-old woodchip bioreactor treating agricultural tile drainage. All samples had similar DNA purity, yield, quality, and microbial diversity regardless of milling. However, when sequences were aligned against various protein libraries, our results indicated greater relative abundance of denitrification and P transformation proteins on the outside of the woodchips (unmilled), while the interior of woodchips (milled) exhibited more functional gene abundance for carbohydrate breakdown. Thus, it may be important to characterize microbial communities both within woodchips, and on woodchip surfaces, to gain a more holistic understanding of coupled biogeochemical cycles on N, P, and C in woodchip bioreactors. Based on these findings, we advise that future microbial research on woodchips (and potentially other permeable organic materials) examine both the surface biofilm and the interior organic material during initial studies. Once researchers determine where specific proteins or enzymes of interest are most prevalent, subsequent studies may then focus on either one or both aspects, as needed.

6.
Biotechnol Bioeng ; 110(3): 785-91, 2013 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-23097182

RESUMO

Single-chamber microbial fuel cells (MFCs) with nitrifiers pre-enriched at the air cathodes have previously been demonstrated as a passive strategy for integrating nitrogen removal into current-generating bioelectrochemical systems. To further define system design parameters for this strategy, we investigated in this study the effects of oxygen diffusion area and COD/N ratio in continuous-flow reactors. Doubling the gas diffusion area by adding an additional air cathode or a diffusion cloth significantly increased the ammonia and COD removal rates (by up to 115% and 39%), ammonia removal efficiency (by up to 134%), the cell voltage and cathode potentials, and the power densities (by a factor of approximately 2). When the COD/N ratio was lowered from 13 to 3, we found up to 244% higher ammonia removal rate but at least 19% lower ammonia removal efficiency. An increase of COD removal rate by up to 27% was also found when the COD/N ratio was lowered from 11 to 3. The Coulombic efficiency was not affected by the additional air cathode, but decreased by an average of 11% with the addition of a diffusion cloth. Ammonia removal by assimilation was also estimated to understand the ammonia removal mechanism in these systems. These results showed that the doubling of gas diffusion area enhanced N and COD removal rates without compromising electrochemical performance.


Assuntos
Fontes de Energia Bioelétrica , Gases/metabolismo , Nitrogênio/metabolismo , Análise da Demanda Biológica de Oxigênio , Difusão , Eletricidade , Eletrodos/microbiologia , Oxigênio/metabolismo
7.
Biotechnol Bioeng ; 110(11): 3059-62, 2013 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-23616357

RESUMO

Pyrosequencing was used to characterize bacterial communities in air-cathode microbial fuel cells across a volumetric (graphite fiber brush) and a planar (carbon cloth) anode, where different physical and chemical gradients would be expected associated with the distance between anode location and the air cathode. As expected, the stable operational voltage and the coulombic efficiency (CE) were higher for the volumetric anode than the planar anode (0.57 V and CE = 22% vs. 0.51 V and CE = 12%). The genus Geobacter was the only known exoelectrogen among the observed dominant groups, comprising 57 ± 4% of recovered sequences for the brush and 27 ± 5% for the carbon-cloth anode. While the bacterial communities differed between the two anode materials, results showed that Geobacter spp. and other dominant bacterial groups were homogenously distributed across both planar and volumetric anodes. This lends support to previous community analysis interpretations based on a single biofilm sampling location in these systems.


Assuntos
Bactérias/classificação , Bactérias/genética , Fontes de Energia Bioelétrica , Biota , Eletrodos/microbiologia , Ar , Carbono , Análise de Sequência de DNA
8.
Biogeochemistry ; 162(1): 25-42, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-36687142

RESUMO

Although metal redox reactions in soils can strongly affect carbon mineralization and other important soil processes, little is known about temporal variations in this redox cycling. Recently, potentiostatically poised electrodes (fixed-potential electrodes) have shown promise for measuring the rate of oxidation and reduction at a specific reduction potential in situ in riparian soils. Here for the first time, we used these electrodes in unsaturated soils to explore the fine-scale temporal redox fluctuations of both iron and manganese in response to environmental conditions. We used three-electrode systems with working electrodes fixed at 100 mV (vs. SHE) and 400 mV at 50 cm and 70 cm in the valley floor soil of a headwater watershed. Electrodes fixed at 100 mV to mimic iron oxides and at 400 mV to mimic manganese oxides allowed real-time reduction and oxidation rates to be calculated from temporal variations in the electric current. Electrode measurements were compared to soil porewater chemistry, pCO2, pO2, groundwater level, resistivity measurements, and precipitation. The fixed-potential electrodes recorded fluctuations over timescales from minutes to weeks. A consistently negative current was observed at 100 mV (interpreted as oxidation of Fe), while the 400-mV electrode fluctuated between negative and positive currents (Mn oxidation and reduction). When the water table rose above the electrodes, reduction was promoted, but above the water table, rainfall only stimulated oxidation. Precipitation frequency thus drove the multi-day reduction or oxidation events (return interval of 5-10 days). These measurements represent the first direct detections of frequency, period, and amplitude of oxidation and reduction events in unsaturated soils. Fixed-potential electrodes hold promise for accurately exploring the fast-changing biogeochemical impacts of metal redox cycling in soils and represent a significant advance for reactions that have been difficult to quantify.

9.
J Environ Monit ; 14(6): 1515-22, 2012 May.
Artigo em Inglês | MEDLINE | ID: mdl-22596061

RESUMO

Disinfection by-product formation potentials (DBPFPs) in wastewater effluents from eight wastewater treatment plants (WWTPs) were investigated. In addition, a WWTP with one primary effluent and two different biological treatment processes was selected for a comparative study. Formation potential tests were carried out to determine the levels of DBP precursors in wastewater. WWTPs that achieved better organic matter removal and nitrification tended to result in lower DBPFPs in effluents. For the WWTP with two processes, haloacetic acid, trihalomethane, and chloral hydrate precursors were predominant DBP precursors in the primary and secondary effluents. The percent reductions of haloacetonitrile and haloketone formation potentials averaged at 96% which was high in comparison to the reductions of other classes of DBPFPs. In addition, biological treatment changed the DBPFP speciation profile by lowering the HAAFP/THMFP ratio. The eight plant survey and the comparative analysis of the WWTP with two processes implied that besides nitrification, there may be other confounding factors impacting DBPFPs. Oxic and anoxic conditions, formation and degradation of soluble microbial products had impacts on the DBPFP reductions. This information can be used by water and wastewater professionals to better control wastewater-derived DBPs in downstream potable water supplies.


Assuntos
Desinfetantes/análise , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água/análise , Desinfecção , Pennsylvania , Trialometanos/análise , Microbiologia da Água , Poluição Química da Água/estatística & dados numéricos
10.
Materials (Basel) ; 15(1)2022 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-35009526

RESUMO

During the last decade, bioprospecting for electrochemically active bacteria has included the search for new sources of inoculum for microbial fuel cells (MFCs). However, concerning power and current production, a Geobacter-dominated mixed microbial community derived from a wastewater inoculum remains the standard. On the other hand, cathode performance is still one of the main limitations for MFCs, and the enrichment of a beneficial cathodic biofilm emerges as an alternative to increase its performance. Glucose-fed air-cathode reactors inoculated with a rumen-fluid enrichment and wastewater showed higher power densities and soluble chemical oxygen demand (sCOD) removal (Pmax = 824.5 mWm-2; ΔsCOD = 96.1%) than reactors inoculated only with wastewater (Pmax = 634.1 mWm-2; ΔsCOD = 91.7%). Identical anode but different cathode potentials suggest that differences in performance were due to the cathode. Pyrosequencing analysis showed no significant differences between the anodic community structures derived from both inocula but increased relative abundances of Azoarcus and Victivallis species in the cathodic rumen enrichment. Results suggest that this rarely used inoculum for single-chamber MFCs contributed to cathodic biofilm improvements with no anodic biofilm effects.

11.
Appl Environ Microbiol ; 77(2): 564-71, 2011 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-21075886

RESUMO

The external resistance (R(ext)) of microbial fuel cells (MFCs) regulates both the anode availability as an electron acceptor and the electron flux through the circuit. We evaluated the effects of R(ext) on MFCs using acetate or glucose. The average current densities (I) ranged from 40.5 mA/m(2) (9,800 Ω) to 284.5 mA/m(2) (150 Ω) for acetate-fed MFCs (acetate-fed reactors [ARs]), with a corresponding anode potential (E(an)) range of -188 to -4 mV (versus a standard hydrogen electrode [SHE]). For glucose-fed MFCs (glucose-fed reactors [GRs]), I ranged from 40.0 mA/m(2) (9,800 Ω) to 273.0 mA/m(2) (150 Ω), with a corresponding E(an) range of -189 to -7 mV. ARs produced higher Coulombic efficiencies and energy efficiencies than GRs over all tested R(ext) levels because of electron and potential losses from glucose fermentation. Biogas production accounted for 14 to 18% of electron flux in GRs but only 0 to 6% of that in ARs. GRs produced similar levels of methane, regardless of the R(ext). However, total methane production in ARs increased as R(ext) increased, suggesting that E(an) might influence the competition for substrates between exoelectrogens and methanogens in ARs. An increase of R(ext) to 9,800 Ω significantly changed the anode bacterial communities for both ARs and GRs, while operating at 970 Ω and 150 Ω had little effect. Deltaproteobacteria and Bacteroidetes were the major groups found in anode communities in ARs and GRs. Betaproteobacteria and Gammaproteobacteria were found only in ARs. Bacilli were abundant only in GRs. The anode-methanogenic communities were dominated by Methanosaetaceae, with significantly lower numbers of Methanomicrobiales. These results show that R(ext) affects not only the E(an) and current generation but also the anode biofilm community and methanogenesis.


Assuntos
Archaea/metabolismo , Bactérias/metabolismo , Biodiversidade , Fontes de Energia Bioelétrica/microbiologia , Eletricidade , Eletrodos/microbiologia , Metano/metabolismo , Acetatos/metabolismo , Archaea/classificação , Archaea/genética , Bactérias/classificação , Bactérias/genética , DNA Arqueal/química , DNA Arqueal/genética , DNA Bacteriano/química , DNA Bacteriano/genética , Glucose/metabolismo , Dados de Sequência Molecular , Análise de Sequência de DNA
12.
Environ Sci Technol ; 45(20): 9069-74, 2011 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-21902172

RESUMO

pH oppositely influences anode and cathode performance in microbial fuel cells. The differential electrochemical effects at each electrode and the resultant full-cell performance were analyzed in medium pH from 6.0 to 8.0. Potentials changed -60 mV/pH for the anode and -68 mV/pH for the cathode, coincident with thermodynamic estimations. Open circuit voltage reached a maximum (741 mV) at pH 7, and maximum power density was highest (712 mW/m²) at pH 6.5 as the cathode performance improved at lower pH. Maximum current density increased and apparent half-saturation potential (E(KA)) decreased with increasing medium pH due to improved anode performance. An equivalent circuit model composed of two time constant processes accurately fit bioanode impedance data. One of these processes was consistently the rate-limiting step for acetate-oxidizing exoelectrogenesis, with its pH-varying charge transfer resistance R2 ranging from 2- to 321-fold higher than the pH-independent charge transfer resistance R1. The associated capacitance C2 was 2-3 orders of magnitude larger than C1. R2 was lowest near E(KA) and increased by several orders of magnitude at anode potentials above E(KA), while R1 was nearly stable. However, fits deviated slightly at potentials above E(KA) due to emerging impedance possibly associated with diffusion and excessive potential.


Assuntos
Fontes de Energia Bioelétrica , Impedância Elétrica , Eletroquímica , Concentração de Íons de Hidrogênio
13.
Environ Sci Technol ; 45(6): 2435-41, 2011 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-21329346

RESUMO

The variable biocatalyst density in a microbial fuel cell (MFC) anode biofilm is a unique feature of MFCs relative to other electrochemical systems, yet performance characterizations of MFCs typically involve analyses at electrochemically relevant time scales that are insufficient to account for these variable biocatalyst effects. This study investigated the electrochemical performance and the development of anode biofilm architecture under different external loadings, with duplicate acetate-fed single-chamber MFCs stabilized at each resistance for microbially relevant time scales. Power density curves from these steady-state reactors generally showed comparable profiles despite the fact that anode biofilm architectures and communities varied considerably, showing that steady-state biofilm differences had little influence on electrochemical performance until the steady-state external loading was much larger than the reactor internal resistance. Filamentous bacteria were dominant on the anodes under high external resistances (1000 and 5000 Ω), while more diverse rod-shaped cells formed dense biofilms under lower resistances (10, 50, and 265 Ω). Anode charge transfer resistance decreased with decreasing fixed external resistances, but was consistently 2 orders of magnitude higher than the resistance at the cathode. Cell counting showed an inverse exponential correlation between cell numbers and external resistances. This direct link of MFC anode biofilm evolution with external resistance and electricity production offers several operational strategies for system optimization.


Assuntos
Fontes de Energia Bioelétrica/microbiologia , Bactérias/classificação , Bactérias/genética , Bactérias/crescimento & desenvolvimento , Sequência de Bases , Fontes de Energia Bioelétrica/classificação , Fontes de Energia Bioelétrica/estatística & dados numéricos , Biofilmes/crescimento & desenvolvimento , Espectroscopia Dielétrica , Técnicas Eletroquímicas , Dados de Sequência Molecular , Eliminação de Resíduos , Pesos e Medidas
14.
Appl Microbiol Biotechnol ; 85(5): 1575-87, 2010 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-19779712

RESUMO

The anode biofilm in a microbial fuel cell (MFC) is composed of diverse populations of bacteria, many of whose capacities for electricity generation are unknown. To identify functional populations in these exoelectrogenic communities, a culture-dependent approach based on dilution to extinction was combined with culture-independent community analysis. We analyzed the diversity and dynamics of microbial communities in single-chamber air-cathode MFCs with different anode surfaces using denaturing gradient gel electrophoresis based on the 16S rRNA gene. Phylogenetic analyses showed that the bacteria enriched in all reactors belonged primarily to five phylogenetic groups: Firmicutes, Actinobacteria, alpha-Proteobacteria, beta-Proteobacteria, and gamma-Proteobacteria. Dilution-to-extinction experiments further demonstrated that Comamonas denitrificans and Clostridium aminobutyricum were dominant members of the community. A pure culture isolated from an anode biofilm after dilution to extinction was identified as C. denitrificans DX-4 based on 16S rRNA sequence and physiological and biochemical characterizations. Strain DX-4 was unable to respire using hydrous Fe(III) oxide but produced 35 mW/m(2) using acetate as the electron donor in an MFC. Power generation by the facultative C. denitrificans depends on oxygen and MFC configuration, suggesting that a switch of metabolic pathway occurs for extracellular electron transfer by this denitrifying bacterium.


Assuntos
Fontes de Energia Bioelétrica/microbiologia , Comamonas/isolamento & purificação , Comamonas/metabolismo , Acetatos/metabolismo , Bactérias/classificação , Bactérias/genética , Bactérias/isolamento & purificação , Bactérias/metabolismo , Técnicas de Tipagem Bacteriana , Biodiversidade , Biofilmes , Clostridium/classificação , Clostridium/genética , Clostridium/isolamento & purificação , Clostridium/metabolismo , Comamonas/genética , DNA Bacteriano/genética , Eletricidade , Eletrodos/microbiologia , Eletroforese em Gel de Poliacrilamida , Genes de RNAr , Dados de Sequência Molecular , Oxigênio/metabolismo , Filogenia , Reação em Cadeia da Polimerase , RNA Bacteriano/genética , RNA Bacteriano/metabolismo , RNA Ribossômico 16S/genética
15.
Appl Microbiol Biotechnol ; 88(1): 371-80, 2010 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-20632002

RESUMO

Microbial fuel cell (MFC) anode communities often reveal just a few genera, but it is not known to what extent less abundant bacteria could be important for improving performance. We examined the microbial community in an MFC fed with formic acid for more than 1 year and determined using 16S rRNA gene cloning and fluorescent in situ hybridization that members of the Paracoccus genus comprised most (approximately 30%) of the anode community. A Paracoccus isolate obtained from this biofilm (Paracoccus denitrificans strain PS-1) produced only 5.6 mW/m(2), whereas the original mixed culture produced up to 10 mW/m(2). Despite the absence of any Shewanella species in the clone library, we isolated a strain of Shewanella putrefaciens (strain PS-2) from the same biofilm capable of producing a higher-power density (17.4 mW/m(2)) than the mixed culture, although voltage generation was variable. Our results suggest that the numerical abundance of microorganisms in biofilms cannot be assumed a priori to correlate to capacities of these predominant species for high-power production. Detailed screening of bacterial biofilms may therefore be needed to identify important strains capable of high-power generation for specific substrates.


Assuntos
Bactérias/classificação , Bactérias/metabolismo , Biodiversidade , Fontes de Energia Bioelétrica/microbiologia , Biofilmes/crescimento & desenvolvimento , Eletrodos/microbiologia , Bactérias/genética , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Formiatos/metabolismo , Hibridização in Situ Fluorescente , Dados de Sequência Molecular , RNA Ribossômico 16S/genética , Análise de Sequência de DNA
16.
Bioresour Technol ; 316: 123919, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32771939

RESUMO

Ferricyanide is often used in microbial fuel cells (MFCs) to avoid oxygen intrusion that occurs with air cathodes. However, MFC internal resistances using ferricyanide can be larger than those with air cathodes even though ferricyanide results in higher power densities. Using a graphite fiber brush cathode and a ferricyanide catholyte (FC-B) the internal resistance was 62 ± 4 mΩ m2, with 84 ± 8 mΩ m2 obtained using ferricyanide and a flat carbon paper cathode (FC-F) and only 51 ± 1 mΩ m2 using a 70% porosity air cathode (A-70). The FC-B MFCs produced the highest maximum power density of all configurations examined: 2.46 ± 0.26 W/m2, compared to 1.33 ± 0.14 W/m2 for the A-70 MFCs. The electrode potential slope (EPS) analysis method showed that electrode resistances were similar for ferricyanide and air-cathode MFCs, and that higher power was due to the larger experimental working potential (500 ± 12 mV) of ferricyanide compared to the air cathode (233 ± 5 mV).


Assuntos
Fontes de Energia Bioelétrica , Eletricidade , Eletrodos , Elétrons , Oxidantes , Oxigênio
17.
Appl Environ Microbiol ; 75(13): 4435-42, 2009 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-19447957

RESUMO

Methanogens are of great importance in carbon cycling and alternative energy production, but quantitation with culture-based methods is time-consuming and biased against methanogen groups that are difficult to cultivate in a laboratory. For these reasons, methanogens are typically studied through culture-independent molecular techniques. We developed a SYBR green I quantitative PCR (qPCR) assay to quantify total numbers of methyl coenzyme M reductase alpha-subunit (mcrA) genes. TaqMan probes were also designed to target nine different phylogenetic groups of methanogens in qPCR assays. Total mcrA and mcrA levels of different methanogen phylogenetic groups were determined from six samples: four samples from anaerobic digesters used to treat either primarily cow or pig manure and two aliquots from an acidic peat sample stored at 4 degrees C or 20 degrees C. Only members of the Methanosaetaceae, Methanosarcina, Methanobacteriaceae, and Methanocorpusculaceae and Fen cluster were detected in the environmental samples. The three samples obtained from cow manure digesters were dominated by members of the genus Methanosarcina, whereas the sample from the pig manure digester contained detectable levels of only members of the Methanobacteriaceae. The acidic peat samples were dominated by both Methanosarcina spp. and members of the Fen cluster. In two of the manure digester samples only one methanogen group was detected, but in both of the acidic peat samples and two of the manure digester samples, multiple methanogen groups were detected. The TaqMan qPCR assays were successfully able to determine the environmental abundance of different phylogenetic groups of methanogens, including several groups with few or no cultivated members.


Assuntos
Archaea/classificação , Biodiversidade , Microbiologia Ambiental , Metano/metabolismo , Oxirredutases/genética , Reação em Cadeia da Polimerase/métodos , Animais , Archaea/genética , Benzotiazóis , Bovinos , Primers do DNA/genética , DNA Arqueal/química , DNA Arqueal/genética , Diaminas , Esterco/microbiologia , Dados de Sequência Molecular , Compostos Orgânicos/metabolismo , Quinolinas , Análise de Sequência de DNA , Coloração e Rotulagem/métodos
18.
Appl Environ Microbiol ; 75(11): 3673-8, 2009 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-19346362

RESUMO

Electricity can be directly generated by bacteria in microbial fuel cells (MFCs) from many different biodegradable substrates. When cellulose is used as the substrate, electricity generation requires a microbial community with both cellulolytic and exoelectrogenic activities. Cellulose degradation with electricity production by a pure culture has not been previously demonstrated without addition of an exogenous mediator. Using a specially designed U-tube MFC, we enriched a consortium of exoelectrogenic bacteria capable of using cellulose as the sole electron donor. After 19 dilution-to-extinction serial transfers of the consortium, 16S rRNA gene-based community analysis using denaturing gradient gel electrophoresis and band sequencing revealed that the dominant bacterium was Enterobacter cloacae. An isolate designated E. cloacae FR from the enrichment was found to be 100% identical to E. cloacae ATCC 13047(T) based on a partial 16S rRNA sequence. In polarization tests using the U-tube MFC and cellulose as a substrate, strain FR produced 4.9 +/- 0.01 mW/m(2), compared to 5.4 +/- 0.3 mW/m(2) for strain ATCC 13047(T). These results demonstrate for the first time that it is possible to generate electricity from cellulose using a single bacterial strain without exogenous mediators.


Assuntos
Fontes de Energia Bioelétrica/microbiologia , Celulose/metabolismo , Eletricidade , Enterobacter cloacae/classificação , Enterobacter cloacae/isolamento & purificação , Análise por Conglomerados , Impressões Digitais de DNA , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Eletroforese em Gel de Poliacrilamida , Enterobacter cloacae/metabolismo , Dados de Sequência Molecular , Desnaturação de Ácido Nucleico , Filogenia , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Homologia de Sequência do Ácido Nucleico
19.
Water Res ; 43(5): 1480-8, 2009 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-19138783

RESUMO

The production of a useful and valuable product during swine wastewater treatment, such as hydrogen gas, could help to lower treatment costs. Hydrogen can theoretically be produced from wastewater by electrohydrogenesis in a microbial electrolysis cell (MEC) or by fermentation. Using a single-chamber MEC with a graphite-fiber brush anode, hydrogen gas was generated at 0.9-1.0 m(3) m(-3) day(-1) H2 using a full-strength or diluted swine wastewater. COD removals ranged from 8 to 29% in 20-h tests, and from 69 to 75% in longer tests (184 h) using full-strength wastewater. The gas produced was up to 77+/-11% hydrogen, with overall recoveries of up to 28+/-6% of the COD in the wastewater as hydrogen gas. Methane was also produced at a maximum of 13+/-4% of total gas volume. The efficiency of hydrogen production, based on the electrical energy needed (but excluding the energy in the wastewater) compared to the energy of the hydrogen gas produced, was as high as 190+/-39% in 42-h batch tests with undiluted wastewater, but was lower in longer batch tests of 184 h (91+/-6%). Hydrogen gas could not be recovered in fermentation tests using wastewater with a heat-treated inoculum. Hydrogen production was shown to be possible by fermentation when the wastewater was sterilized, but this process would not be practical or energy efficient. We therefore conclude from these tests that MECs are an effective method for hydrogen recovery from swine wastewater treatment, although the process needs to be further evaluated for reducing methane production, increasing the efficiency of converting the organic matter into current, and increasing recovery of hydrogen gas produced at the cathode.


Assuntos
Bactérias/metabolismo , Eletrólise/métodos , Hidrogênio/metabolismo , Metano/biossíntese , Sus scrofa , Eliminação de Resíduos Líquidos , Purificação da Água , Animais , Fermentação , Esgotos/microbiologia
20.
Sci Total Environ ; 678: 639-646, 2019 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-31078855

RESUMO

Exoelectrogenic communities for bioelectrochemical systems such as microbial fuel cells (MFCs) are usually enriched from microbial consortia of municipal wastewater treatment plants and other circumneutral and mesophilic environments. Thus, the study of extreme environments offers an enormous potential to find new exoelectrogens and expand the functionality and applications of MFC technology. In this study, a microbial community previously enriched from acid mine drainage (AMD) sediments was used as inoculum in single-chamber MFCs operated at pH 3.7. The power obtained from the AMD-derived inoculum reached 1 mW m-2 (27.1 ±â€¯7.8 mV with 1 kΩ external resistance), which compares to previous MFC studies operated under low-pH conditions. Additionally, polarization curves showed power-generation levels of 2.4 ±â€¯0.2 mW m-2 and 0.4 ±â€¯0.3 mW m-2, which were associated with the different inoculum sources: MFCs operated with sulfate concentrations of ~2000 and < 25 mg L-1, respectively. Microbial characterization performed at the end of the operation showed that both anodic and cathodic biofilm communities were highly dominated by the Proteobacteria phylum (>72% of 16S rRNA gene sequences), followed by Firmicutes (4-11%). Furthermore, the anodic microbial communities of the best-performing reactors were dominated by the Delftia genus (phylum Proteobacteria), which was recently identified as a taxon including exoelectrogenic candidates. These findings expand the literature of low-pH operated MFCs and acid-tolerant exoelectrogens, and also represent a starting point to apply this technology to treat acidic organic loads.


Assuntos
Fenômenos Fisiológicos Bacterianos , Fontes de Energia Bioelétrica/microbiologia , Biofilmes , Reatores Biológicos/microbiologia , Águas Residuárias/química , Poluentes da Água/química , Bactérias/classificação , Bactérias/metabolismo , Fenômenos Fisiológicos Bacterianos/efeitos dos fármacos , Chile , Ambientes Extremos , Mineração
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