Granular Graphite Research Articles

Biodegradation of surrogate naphthenic acids and electricity generation in microbial fuel cells: bioelectrochemical and microbial characterizations.

Waters contaminated with naphthenic acids (NAs) and associated tailings are one of the major environmental challenges associated with the processing of oil sands and production of heavy oil. In the current work biodegradation of linear and cyclic naphthenic acids, namely octanoic acid and 4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), individually and in mixture were evaluated in microbial fuel cells (MFCs). In batch MFCs with single rod electrodes and freely suspended bacteria, biodegradation rate increased as NA initial concentration increased from 100 to 250mg L-1 with no further improvement when a concentration of 500mg L-1 was evaluated. During the co-biodegradation, diauxic microbial growth and preferential use of octanoic acid were observed. Moreover, the presence of octanoic acid enhanced the biodegradation of trans-4MCHCA. In the continuous flow MFCs with granular graphite electrodes and biofilm, increases in NA concentration and loading rate led to higher biodegradation rates and improvement of electrochemical output. Furthermore, MFC operated with octanoic acid outperformed its counterpart that was fed with trans-4MCHCA, with the maximum biodegradation rate, current and power densities for octanoic acid and trans-4MCHCA being 49.9 and 36.5mg L-1 h-1, 6000.0 and 4296.3mA m-3, and 963.0 and 481.5mW m-3, respectively. Co-biodegradation of NAs in continuous flow MFCs with biofilm acclimated to octanoic acid or trans-4MCHCA revealed development of distinctly different microbial communities, simultaneous biodegradation of NAs albeit at faster rates for octanoic acid, and superior performance of MFC with the biofilm developed with trans-4MCHCA.

A novel conductivity mechanism of highly disordered carbon systems based on an investigation of graph zeta function

In the previous report (Matsutani and Suzuki, 2000 [21]), by proposing the mechanism under which electric conductivity is caused by the activational hopping conduction with the Wigner surmise of the level statistics, the temperature-dependent of electronic conductivity of a highly disordered carbon system was evaluated including apparent metal–insulator transition. Since the system consists of small pieces of graphite, it was assumed that the reason why the level statistics appears is due to the behavior of the quantum chaos in each granular graphite. In this article, we revise the assumption and show another origin of the Wigner surmise, which is more natural for the carbon system based on a recent investigation of graph zeta function in graph theory. Our method can be applied to the statistical treatment of the electronic properties of the randomized molecular system in general.

Biodegradation of phenol in batch and continuous flow microbial fuel cells with rod and granular graphite electrodes

ABSTRACTPhenol biodegradation was evaluated in batch and continuous flow microbial fuel cells (MFCs). In batch-operated MFCs, biodegradation of 100–1000 mg L−1 phenol was four to six times faster when graphite granules were used instead of rods (3.5–4.8 mg L−1 h−1 vs 0.5–0.9 mg L−1 h−1). Similarly maximum phenol biodegradation rates in continuous MFCs with granular and single-rod electrodes were 11.5 and 0.8 mg L−1 h−1, respectively. This superior performance was also evident in terms of electrochemical outputs, whereby continuous flow MFCs with granular graphite electrodes achieved maximum current and power densities (3444.4 mA m−3 and 777.8 mW m−3) that were markedly higher than those with single-rod electrodes (37.3 mA m−3 and 0.8 mW m−3). Addition of neutral red enhanced the electrochemical outputs to 5714.3 mA m−3 and 1428.6 mW m−3. Using the data generated in the continuous flow MFC, biokinetic parameters including μm, KS, Y and Ke were determined as 0.03 h−1, 24.2 mg L−1, 0.25 mg cell (mg phenol)−1 and 3.7 × 10−4 h−1, respectively. Access to detailed kinetic information generated in MFC environmental conditions is critical in the design, operation and control of large-scale treatment systems utilizing MFC technology.

The effects of microbial fuel cell integration into constructed wetland on the performance of constructed wetland

The present work is the first detailed study, which is about the performance of CW after MFC integration with it. The experiments were run in open and closed circuit mode for assessment purpose. The findings of this study indicate towards a more practical application of MFC in wastewater treatment along with electricity production. The closed circuit operations of CW–MFCs have performed 12–20% better than open circuit operation and 27–49% better than Normal-CW for chemical oxygen demand (COD) removal. The maximum power density of 320.8mW/m3 and current density of 422.2mA/m3 have been achieved in granular graphite anode and Pt coated carbon cloth cathode based CW–MFC.

Anode hydrodynamics in bioelectrochemical systems

This study assesses the hydrodynamics in the anode compartment of a bioelectrochemical system (BES) when using different electrode materials (graphite rod, granular graphite, stainless steel mesh or graphite plate).

Bioelectricity production from municipal leachate in a microbial fuel cell: Effect of two cathodic catalysts

The objective of this work was to evaluate the effect of the cathodic catalyst (either chalcogenide or Pt) on bioelectricity production from actual municipal leachate in a microbial fuel cell equipped with an anode made of granular graphite (MFC-G) and seeded with an inoculum enriched in Mn(IV)-reducing bacteria.Each face (I and II) of the MFC-G was characterized by separate (I and II), in series, and parallel connection. Parallel connection of faces increased the maximum volumetric power up to 1239 and 1799 mW m−3 for RuxMoySez and Pt, respectively. In general parallel connection of electrode faces significantly decreased the Rint (44 and 77 Ω for RuxMoySez and Pt, respectively). In the batch operation where the cells were connected to external resistances (Rext) the average volumetric powers PV-ave in the second cycle of batch operation were 1005 ± 5 and 1317 ± 687 mW m−3 whereas organic matter removal efficiencies of 70 and 85% were registered for the RuxMoySez and Pt, respectively. During the repetitive batch operation of the cells loaded with an actual leachate there was preliminary evidence of an in-cell enrichment process. In principle, the MFC with catalyst RuxMoySez exhibited a performance 24% and 20% lower than that with Pt (on PV-ave and organic matter removal basis, respectively). This would point to a trade-off or compromise solution, since the cost of RuxMoySez catalyst is 70% lower than that of Pt.

Electrochemical Enhancement on Utilizing Zero-Valent Iron to Degrade Trichloroethylene

The objective of this research is to enhance the degrading ability of zero-valent iron (ZVI) on trichloroethylene (TCE) by using electrochemical technique. ZVI has been shown to effectively degrade TCE by reductive dechlorination, a process in which the ZVI, acting as a reducing agent, causes the chlorine to separate from TCE sequentially. The efficiency of this technique could be enhanced by lowering the redox potential of ZVI using electrochemical methods. In this research the lowering of redox potential was achieved by filling granular ZVI into a cathode compartment in a reactor. The ZVI was mixed with granular graphite to increase the overall electrical conductivity before being filled into the cathode. The anode and cathode compartments were separated with a Nafion membrane. The loss of TCE due to adsorption by the granular graphite during the experiments was evaluated by conducting batch adsorption tests. The electrochemical experiments were conducted by applying a direct current using a potentiostat. The TCE concentration as well as possible degradation products was analyzed with gas chromatography equipped with a mass detector. Chloride concentration was measured with ion chromatography. The results of adsorption tests of TCE by granular graphite fits a linear isotherm with a Kd value of 2.3 L/kg, which is comparable to values reported in the literature. Results from the TCE degradation experiments leads to two major conclusions: (1) degradation of TCE was facilitated by the applied current even when the cathode was filled with only granular graphite and (2) degradation rate of TCE by ZVI was increased by the applied current. The degradation rate of TCE could be fitted with a pseudo-first-order kinetics; the reaction rate constant, kh, increases from 0.017 at no current to 0.064 h-1 at a current of 100 mA. No degradation product was observed in the liquid phase. In the gaseous phase, however, cis-1,2-dichloroethylene was observed. The applied current also caused the increasing rate of pH to decrease. The pH of the solution after 8h of processing time increased from 5.7 to 8.6 at no current, whereas it increased from 5.7 to 5.9 with the same processing time. This suggests the applied current caused the decrease of the corrosion rate of ZVI. The results of this study show the electrochemical technique not only increased the TCE degradation rate by ZVI but also decreased the consumption of ZVI by corrosion. Thus, the technique can be applied to prolong the life of ZVI installed in the field for TCE degradation.

An innovative micrometric granular graphite–glass system composite electrode “ready to use” in voltammetry techniques

A low cost composite electrodes employing tellurite oxide, vanadium oxide and micrometric granular graphite (NWE), were designed as an alternative to be used as working electrode in voltammetry techniques. The synthesis of these composite electrodes is carried out easily; in a short time and their surface not require previous preparation. X-ray diffraction, X-ray fluorescence spectrometry and optical microscopy studies were used to determine the morphology and chemical composition of these electrodes. The conductivity characterization was conducted with impedance and electrochemical measurements. The electrochemical properties of NWE were studied using potassium hexacyanoferrate (II) and ascorbic acid system.

Oxidation behavior of ammonium in a 3-dimensional biofilm-electrode reactor

Excess nitrogenous compounds are detrimental to natural water systems and to human health. To completely realize autohydrogenotrophic nitrogen removal, a novel 3-dimensional biofilm-electrode reactor was designed. Titanium was electroplated with ruthenium and used as the anode. Activated carbon fiber felt was used as the cathode. The reactor was separated into two chambers by a permeable membrane. The cathode chamber was filled with granular graphite and glass beads. The cathode and cathode chamber were inhabited with domesticated biofilm. In the absence of organic substances, a nitrogen removal efficiency of up to 91% was achieved at DO levels of 3.42 ± 0.37 mg/L when the applied current density was only 0.02 mA/cm2. The oxidation of ammonium in biofilm-electrode reactors was also investigated. It was found that ammonium could be oxidized not only on the anode but also on particle electrodes in the cathode chamber of the biofilm-electrode reactor. Oxidation rates of ammonium and nitrogen removal efficiency were found to be affected by the electric current loading on the biofilm-electrode reactor. The kinetic model of ammonium at different electric currents was analyzed by a first-order reaction kinetics equation. The regression analysis implied that when the current density was less than 0.02 mA/cm2, ammonium removal was positively correlated to the current density. However, when the current density was more than 0.02 mA/cm2, the electric current became a limiting factor for the oxidation rate of ammonium and nitrogen removal efficiency.

Thermal Conductivity of Bentonite Grout Containing Graphite or Chopped Carbon Fibers

The effectiveness of chopped carbon fibers to enhance the thermal conductivity of bentonite-based grout was examined. Fibers of 3 mm and 150 μm in length were added to sodium bentonite and silica sand mixtures at different volumetric concentrations. The thermal conductivity of the resulting composite material was then measured using a non-steady-state needle probe technique. The conductivities of the fibrous materials were compared to bentonite and sand mixtures containing natural flake graphite and milled, compressed exfoliated graphite at corresponding volumetric concentrations. The resulting conductivities for all tested materials increased with the volumetric fraction of additive. However, the 3-mm carbon fibers were more effective as compared to either granular graphite; at a volume fraction of 0.68% the 3-mm fibers were approximately twice as effective as either form of graphite.

도시철도 고속화에 대비한 금속계 소결마찰재에서의 흑연 형상 및 비율에 따른 마찰특성 연구

This study aims to establish the fundamental basis for the design of materials used in high-speed trains, by using a lab-scale dynamometer to evaluate the characteristic behavior of metallic sintered friction materials in relation to the shape of graphite. The test results clearly demonstrate that when flake graphite and granular graphite are added equivalently, the average coefficient of friction is much lower, and it is less influenced by speed variation; moreover, friction wear is observed to be insignificantly low. Adding flake graphite increases the coefficient of friction, which leads to higher friction wear. In addition, the roughness of the disc surface was equivalent regardless of the shape of the graphite.

Electrosynthesis of Commodity Chemicals by an Autotrophic Microbial Community

A microbial community originating from brewery waste produced methane, acetate, and hydrogen when selected on a granular graphite cathode poised at -590 mV versus the standard hydrogen electrode (SHE) with CO(2) as the only carbon source. This is the first report on the simultaneous electrosynthesis of these commodity chemicals and the first description of electroacetogenesis by a microbial community. Deep sequencing of the active community 16S rRNA revealed a dynamic microbial community composed of an invariant Archaea population of Methanobacterium spp. and a shifting Bacteria population. Acetobacterium spp. were the most abundant Bacteria on the cathode when acetogenesis dominated. Methane was generally the dominant product with rates increasing from <1 to 7 mM day(-1) (per cathode liquid volume) and was concomitantly produced with acetate and hydrogen. Acetogenesis increased to >4 mM day(-1) (accumulated to 28.5 mM over 12 days), and methanogenesis ceased following the addition of 2-bromoethanesulfonic acid. Traces of hydrogen accumulated during initial selection and subsequently accelerated to >11 mM day(-1) (versus 0.045 mM day(-1) abiotic production). The hypothesis of electrosynthetic biocatalysis occurring at the microbe-electrode interface was supported by a catalytic wave (midpoint potential of -460 mV versus SHE) in cyclic voltammetry scans of the biocathode, the lack of redox active components in the medium, and the generation of comparatively high amounts of products (even after medium exchange). In addition, the volumetric production rates of these three commodity chemicals are marked improvements for electrosynthesis, advancing the process toward economic feasibility.

Scanning Probe Microscope Observation to Morphology of Typical Carbon Materials

The morphology of typical carbon materials including granular graphite, carbon nanotubes and graphenes was observe by scanning probe microscope (SPM). When water is used as the dispersants for preparing observing samples of the above carbon materials, the typical morphology characteristics of spherical graphite, curved carbon nanotubes and graphene sheets are distinctly exhibited by SPM. However, for graphene materials, when alcohol or dimethylformamide (DMF) is used as dispersants, the quality of SPM images becomes poor. The interaction between the dispersants and materials should be responsible for these observation results.

Microbial community analysis in biocathode microbial fuel cells packed with different materials

Biocathode MFCs using microorganisms as catalysts have important advantages in lowering cost and improving sustainability. Electrode materials and microbial synergy determines biocathode MFCs performance. In this study, four materials, granular activated carbon (GAC), granular semicoke (GS), granular graphite (GG) and carbon felt cube (CFC) were used as packed cathodic materials. The microbial composition on each material and its correlation with the electricity generation performance of MFCs were investigated. Results showed that different biocathode materials had an important effect on the type of microbial species in biocathode MFCs. The microbes belonging to Bacteroidetes and Proteobacteria were the dominant phyla in the four materials packed biocathode MFCs. Comamonas of Betaproteobacteria might play significant roles in electron transfer process of GAC, GS and CFC packed biocathode MFCs, while in GG packed MFC Acidovorax may be correlated with power generation. The biocathode materials also had influence on the microbial diversity and evenness, but the differences in them were not positively related to the power production.

A membrane-free, continuously feeding, single chamber up-flow biocatalyzed electrolysis reactor for nitrobenzene reduction

A new bioelectrochemical system (BES), a membrane-free, continuous feeding up-flow biocatalyzed electrolysis reactor (UBER) was developed to reduce oxidative toxic chemicals to less- or non-toxic reduced form in cathode zone with oxidation of electron donor in anode zone. Influent was fed from the bottom of UBER and passed through cathode zone and then anode zone. External power source (0.5 V) was provided between anode and cathode to enhance electrochemical reactions. Granular graphite and carbon brush were used as cathode and anode, respectively. This system was tested for the reduction of nitrobenzene (NB) using acetate as electron donor and carbon source. The influent contained NB (50–200 mg L −1) and acetate (1000 mg L −1). NB was removed by up to 98% mainly in cathode zone. The anode potential maintained under −480 mV. The maximum NB removal rate was up to 3.5 mol m −3 TV d −1 (TV = total empty volume) and the maximum aniline (AN) formation rate was 3.06 mol m −3 TV d −1. Additional energy required was less than 0.075 kWh mol −1 NB. The molar ratio of NB removed vs acetate consumed varied from 4.3 ± 0.4 to 2.3 ± 0.1 mol mol −1. Higher influent phosphate or acetate concentration helped NB removal rate. NB could be efficiently reduced to AN as the power supplied of 0.3 V.

Electricity generation and microbial community changes in microbial fuel cells packed with different anodic materials

Four materials, carbon felt cube (CFC), granular graphite (GG), granular activated carbon (GAC) and granular semicoke (GS) were tested as packed anodic materials to seek a potentially practical material for microbial fuel cells (MFCs). The microbial community and its correlation with the electricity generation performance of MFCs were explored. The maximum power density was found in GAC, followed by CFC, GG and GS. In GAC and CFC packed MFCs, Geobacter was the dominating genus, while Azospira was the most populous group in GG. Results further indicated that GAC was the most favorable for Geobacter adherence and growth, and the maximum power densities had positive correlation with the total biomass and the relative abundance of Geobacter, but without apparent correlation with the microbial diversity. Due to the low content of Geobacter in GS, power generated in this system may be attributed to other microorganisms such as Synergistes, Bacteroidetes and Castellaniella.

Effect of ammonia as a complexing agent on electrokinetic remediation of copper-contaminated soil

Ammonium acetate was used as anolytes in the electrokinetic removal of copper from soil. The electrokinetic experiments were conducted using a rectangular reactor 7.5 cm in width, 10 cm in height, and 11 cm in length. Granular graphite was used as the electrode material. All experiments were conducted under constant current conditions (10 mA). The results show that a high concentration of ammonium acetate (>0.1 M) was needed to sustain electroosmotic flow. The apparent electrical conductivity of the system was dominated by a thin layer of soil (1 cm) close to the cathode. When the ammonium acetate concentration was less than 0.1 M, the apparent electrical conductivity of this soil layer decreased to less than 0.001 S/m and caused large voltage loss. The electroosmotic conductivity of the soil was increased and sustained at 1 × 10 −4 cm 2/V-s by a high concentration of ammonium acetate, whereas it decreased to less than 1 × 10 −6 cm 2/V-s when the concentration of ammonium acetate was low. The efficiency of copper removal increased with the concentration of ammonium acetate, reaching 36% after 1 wk of treatment. Most of the un-removed copper was concentrated in the soil close to the cathode. For the 0.5 M ammonium acetate experiment, the volume of copper containing soil was less than 10% of the original soil after treatment. Therefore, a remediation strategy can be developed to first treat the contaminated soil by electrokinetics and then, focus on removing copper from the soil close to the cathode.

Mathematical simulation of the electrochemical intercalation of graphite in concentrated sulfuric and dilute nitric acids

A mathematical model of the process of electrochemical intercalation of a granular graphite bed in nitric and sulfuric acids that takes into account the varying physicochemical properties of the graphite matrix is proposed. The numerical solution of the problem by the finite element method shows that, in agreement with the literature data, the current distribution is nonuniform even for a granular bed of a small height (∼2 × 10−2 m), which results in the synthesis of a nonuniform product. The methods of assessing the nonuniformity of intercalation and its elimination by passing to a multistage process are proposed. The results of numerical methods can be used in predicting the technological characteristics of the final product.

The New Methods of Graphite Nodules Detection in Ductile Cast Iron

The properties of nodular ductile cast iron are strongly influenced by morphology, size and distribution of graphite particles. Nodular ductile irons have spheroidal graphites in the as-cast state. In this work, these nodules are characterized by means of light optical microscopy (LOM) and electron microscopy (EM). Experimental data are represented by LOM. Metallography is processed to obtain an image where the graphite nodules are clearly distinguished from the similar inclusions which make doubts in microstructure characterization; this is formed by completely unconventional procedures. EM was used to show more clear aspects of granular graphite in cast irons. These data can provide a valid support towards a more confident quality control in the ductile iron production.

Dehalogenation of Iodinated X-ray Contrast Media in a Bioelectrochemical System

Iodinated X-ray contrast media (ICM) are only to a limited extent removed from conventional wastewater treatment plants, due to their high recalcitrance. This work reports on the cathodic dehalogenation of the ICM iopromide in a bioelectrochemical system (BES), fed with acetate at the anode and iopromide at the cathode. When the granular graphite cathode potential was decreased from -500 to -850 mV vs standard hydrogen electrode (SHE), the iopromide removal and the iodide release rates increased from 0 to 4.62 ± 0.01 mmol m(-3) TCC d(-1) and 0 to 13.4 ± 0.16 mmol m(-3) TCC d(-1) (Total Cathodic Compartment, TCC) respectively. Correspondingly, the power consumption increased from 0.4 ± 1 to 20.5 ± 3.3 W m(-3) TCC. The Coulombic efficiency of the iopromide dehalogenation at the cathode was less than 1%, while the Coulombic efficiency of the acetate oxidation at the anode was lower than 50% at various granular graphite cathode potentials. The results suggest that iopromide could be completely dehalogenated in BESs when the granular graphite cathode potential was controlled at -800 mV vs SHE or lower. This finding was further confirmed using mass spectrometry to identify the dehalogenated intermediates and products of iopromide in BESs. Kinetic analysis indicates that iopromide dehalogenation in batch experiments can be described by a first-order model at various cathode potentials. This work demonstrates that the BESs have a potential for efficient dehalogenation of ICM from wastewater or environmental streams.