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Bioelectrochemical hydrogen production with hydrogenophilic dechlorinating

Bioelectrochemical hydrogen production with hydrogenophilic dechlorinating bacteria as electrocatalytic agents

Marianna Villano a ,Luca De Bonis a ,Simona Rossetti b ,Federico Aulenta a ,Mauro Majone a ,?

a Department of Chemistry,Sapienza University of Rome,P.le Aldo Moro 5,00185Rome,Italy

Water Research Institute (IRSA-CNR),National Research Council,Area della Ricerca Roma 1Montelibretti,Via Salaria km.29.300,00015Monterotondo (RM),Italy

a r t i c l e i n f o Article history:

Received 11June 2010

Received in revised form 6October 2010Accepted 7October 2010

Available online 4November 2010Keywords:

Bioelectrochemical systems Biocathode

Dechlorinating bacteria Hydrogen production Redox mediator

a b s t r a c t

Hydrogenophilic dechlorinating bacteria were shown to catalyze H 2production by proton reduction,with electrodes serving as electron donors,either in the presence or in the absence of a redox mediator.In the presence of methyl viologen,Desul?tobacterium -and Dehalococcoides -enriched cultures produced H 2at rates as high as 12.4l eq/mgVSS (volatile suspended solids)/d,with the cathode set at à450mV vs.the standard hydrogen electrode (SHE),hence very close to the reversible H +/H 2potential value of à414mV at pH 7.Notably,the Desul?tobacterium -enriched culture was capable of catalyzing H 2produc-tion without mediators at cathode potentials lower than à700mV.At à750mV,the H 2production rate with Desul?tobacterium spp.was 13.5l eq/mgVSS/d (or 16l eq/cm 2/d),nearly four times higher than that of the abiotic controls.Overall,this study suggests the possibility of employing dechlorinating bacteria as hydrogen catalysts in new energy technologies such as microbial electrolysis cells.

1.Introduction

The production of hydrogen as energy source should ideally be based on renewable resources and sustainable processes (Turner,2004).Microbial electrolysis cells (MEC)have the potential to re-place conventional electrolytic systems operating with platinum or other precious metals.In a MEC ‘‘exoelectrogenic’’microorgan-isms (Logan,2009;Rabaey and Verstraete,2005)oxidize (waste)organic matter by releasing electrons to a solid-state electrode (an-ode)and carbon dioxide and protons into solution.By applying a small external voltage to the system,electrons can be forced to tra-vel from the anode to the cathode and combine with protons to produce molecular H 2(Logan et al.,2008).Typically,the equilib-rium anode potential generated from the bacterial oxidation of or-ganic substrates (e.g.,acetate)is around à300mV (vs.the standard hydrogen electrode,SHE).Under standard conditions and pH 7,the reversible potential of H +/H 2is à414mV,and therefore,the mini-mum theoretical voltage that has to be applied in order to produce H 2at the cathode is 114mV.This voltage is very low compared to the voltage necessary for conventional water electrolysis (i.e.,1.6–2.0V)(Zeng and Zhang,2010).

Currently,a major limitation of the process is that noble metal (e.g.,Pt-based)catalysts are typically used on the cathode to en-hance the rate and ef?ciency of hydrogen production.These noble metal catalysts are expensive and susceptible to poisoning.Various non-noble materials have been also studied (Call et al.,2009),but they typically exhibit insuf?cient chemical stability and/or reactiv-ity at neutral pH for ef?cient MEC operation (Daftsis et al.,2003;High?eld et al.,1999;Rabaey and Keller,2008;Selembo et al.,2009).

Microbial biocathodes,in which microorganisms are the elec-trocatalytic agents of the desired cathodic reaction,are potential alternatives to chemical cathodes since they are inexpensive,self-regenerating and can operate under neutral pH.Lojou et al.(2002)showed that a pure culture of Desulfovibrio vulgaris immo-bilized onto a carbon electrode could catalyze H 2production with methyl viologen (MV)(E °0=à446mV)as a redox mediator and Rozendal et al.(2008)tested a MEC with a mixed culture biocath-ode of unknown microbial composition which catalyzed H 2pro-duction likely via direct extracellular electron transfer.The occurrence of methanogens in the mixed culture was the main lim-iting factor which required the removal of bicarbonate from the medium to maintain acceptable H 2yields.

Based on our earlier ?ndings that a dechlorinating culture re-leased some H 2in the presence of excess MV,in addition to dechlo-rinating trichloroethene (TCE),as a strategy to dispose of an excess of reducing equivalents (Aulenta et al.,2008),we established TCE dechlorinating (Desul?tobacterium -enriched)and cis -DCE dechlori-nating (Dehalococcoides -enriched)cultures to produce H 2in short-term potentiostatic tests (i.e.,8h)either at à450mV (vs.SHE)in the presence of MV concentrations ranging from 0to 2.5mM or without exogenous redox mediators,at cathode potentials ranging from à650to à900mV (vs.SHE).

Corresponding author.Tel.:+390649913646;fax:+3906490631.

E-mail address:mauro.majone@uniroma1.it (M.Majone).

2.Methods

2.1.Microbial dechlorinating cultures

The TCE dechlorinating and cis-DCE dechlorinating cultures were established by enrichment from contaminated sediments of the Venice Lagoon(Aulenta et al.,2002)and maintained in anaer-obic bioreactors with a liquid volume of1.4and0.6L for the TCE dechlorinating and the cis-DCE dechlorinating culture,respec-tively.The reactors consisted of continuously stirred borosilicate glass bottles,sealed with a Te?on-faced butyl rubber stoppers and aluminum crimp seals.The bioreactors were operated at 25±1°C in?ll and draw mode.Every7days,they received a spike of neat trichloroethene(TCE)or cis-dichloroethene(cis-DCE)to a nominal concentration(i.e.,neglecting the partitioning of com-pounds into the gas phase)of0.5mM.Thereafter,hydrogen gas (99.5+%)was added to the headspace of the reactors to a nominal concentration of2.1and1.4mM,for the TCE dechlorinating and the cis-DCE dechlorinating culture,respectively.Before each feed-ing,the headspace of each bioreactor was?ushed with a N2/CO2 (70:30)gas mixture to remove all the volatile compounds.Weekly, a?xed volume of suspended culture was removed from each cul-ture and replaced by anaerobic basal medium,which contained (g/L):NH4Cl,0.5;MgCl

á6H2O,0.1;K2HPO4,0.4;CaCl2á2H2O, 0.05;10mL/L of a trace metal solution(Balch et al.,1979), 10mL/L of vitamin solution(Zeikus,1977),and15mL/L of NaHCO3 (10%w/v).The pH of the medium was7.5.For both cultures the average cell retention time was maintained at around60days. The pseudo steady-state biomass concentration was about 63mgVSS/L for the TCE dechlorinating culture and about 53mgVSS/L for the cis-DCE dechlorinating culture.During?ll and draw cycles,TCE was predominantly dechlorinated to cis-DCE and,in lower amounts,also to vinyl chloride(VC)and ethene;in the other bioreactor,cis-DCE was predominantly dechlorinated to VC and lower amounts of ethene.The two bioreactors were oper-ated for a period of over3years.Prior to the bioelectrochemical experiments,the microbial composition of the two cultures was analyzed by?uorescence in situ hybridization(FISH)and catalyzed reporter deposition(CARD)-FISH in order to quantify the relative abundance of the different dechlorinating bacteria as described previously(Fazi et al.,2008;Rossetti et al.,2008).Hybridizations with the speci?c probes DSF440and DSF475for Desul?tobacterium spp.;DHE1259t and DHE1259c for Dehalococcoides spp.were car-ried out simultaneously with DAPI and/or probes EUB338, EUB338-II,and EUB338-III combined in a mixture(EUB),speci?c for most Bacteria.Details on oligonucleotide probes are available at probeBase(Loy et al.,2007).The probes were synthesized with 50-FITC and-Cy3labels and purchased from MWG AG Biotech(Ger-many).The ratios of the cells binding the group-speci?c probes and of cells staining with DAPI or binding the EUB probes were estab-lished for at least20different,randomly selected?elds.Images were captured with Olympus F-view CCD camera and handled with AnalySIS software(SIS,Munster,Germany).

2.2.Bioelectrochemical cell setup

The bioelectrochemical cell setup used in this study consisted of two gastight borosilicate glass bottles(with a total volume of about 270mL per bottle)separated by a3cm2cross-sectional area, Na?onò117proton exchange membrane(PEM).The PEM was boiled successively in H2O2(3%v/v),DI water,then in0.5M H2SO4,and DI water each for2h,and stored in DI water.The cath-odes used were either a piece(50?10mm)of carbon paper(E-TEK;nominal surface area$8cm2)or a glassy carbon rod(HTW GambH,Germany;5mm diameter,50mm length,nominal surface area$8cm2);the anode was a glassy carbon rod(HTW GambH, Germany;5mm diameter,50mm length,nominal surface area $8cm2).The distance between the anode and cathode was around 10cm.The reference electrode(placed in the cathode chamber) was a KCl saturated Ag/AgCl electrode(+199mV vs.standard hydrogen electrode,SHE)(Amel S.r.l.,Milan,Italy).Voltages are re-ported with respect to SHE.Electrochemical potentiostatic mea-surements and monitoring were performed using a Galvanostat/ Potentiostat Amel551(Milan,Italy).

2.3.Bioelectrochemical experiments

The cathode and anode compartments of the bioelectrochemi-cal cell were anaerobically?lled with150mL of the dechlorinating culture and150mL of mineral medium,respectively,and?ushed with a N2/CO2(70:30v/v)gas mixture.

The bioelectrochemical cell was connected to the potentiostat and the cathode potential was set at the desired value.A set of batch experiments was carried out either in the absence or in the presence of methyl viologen(MV).In the latter case,appropriate volumes of a100mM stock solution of MV were added to achieve concentrations of0–2.5mM.Each batch experiment lasted8h and at regular intervals(e.g.,every2h),gaseous samples were taken from the headspace of the compartments using gastight,sample-lock Hamilton(Reno,NV)syringes,and500and40l L samples were analyzed by gas-chromatography for hydrogen and methane, respectively.In parallel,control tests were performed under the same operating conditions in the absence of the microbial culture or the redox mediator.The bioelectrochemical reactor was main-tained at25°C in a water bath,under vigorous magnetic stirring to ensure that current generation was not substantially affected by mass transfer phenomena.

The cumulative electric charge(l eq i)that was transferred at the electrodes was calculated by integrating the current(A)over the period of electrode polarization.Cumulative reducing equivalents (l eq H

)that were used for the formation of H2were calculated from the measured amounts of H2,considering the corresponding molar conversion factor of2l eq/l mol.Coulombic ef?ciency(CE)for H2 was accordingly calculated as CEe%T?el eq H

=l eq iT?100.The energy recovery was calculated as g Ee%T?W H2=W IN,where W H

?n H

?D G H

is the energy content(kJ)of the produced H2,cal-culated from the total amount of H2produced(n H

;mol)and the molar Gibbs free energy of H2oxidation by oxygen to water (D G H

?à237:1kJ=mol);W IN is the electricity input determined as C P?E APP,where C P is the total Coulombs calculated by integrat-ing the current over time and E APP is the hypothetical applied volt-age.This latter value was calculated by assuming a hypothetical anode potential ofà0.150V,as typical of acetate-fed bioanodes.

2.4.Analytical methods

The concentration of microorganisms in the source culture reac-tor was determined as volatile suspended solids(VSS),according to standard methods(APHA,1995).H2was analyzed in a500l L gas-eous sample by a Trace Analytical TA3000R reduction gas detector (RGD)(H2detection limit is0.02ppmv)(Menlo Park,CA).The H2 level above the range of the RGD(i.e.,$100ppmv)was quanti?ed using a Varian3400(Lake Forest,CA,USA)gas-chromatograph (stainless-steel column packed with molecular sieve,Supelco,He carrier gas18mL/min;oven temperature180°C;thermal-conduc-tivity detector(TCD)temperature200°C)(Aulenta et al.,2005). Methane was analyzed by injecting40l L of sample headspace (with a gas-tight Hamilton syringe)into a Varian(Lake Forest, CA,USA)3400gas chromatograph(GC;2m?2mm glass column packed with60/80mesh Carbopack B/1%SP-1000,Supelco;He car-rier gas at18mL/min;oven temperature at50°C;?ame ionization

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detector (FID)temperature 260°C).Headspace concentrations were converted to aqueous-phase concentrations using tabulated Henry’s law constants (Gossett,1987).2.5.Chemicals

Hydrogen (99.5+%)and all the other chemicals were purchased from Sigma–Aldrich (Milan,IT)(except where differently indi-cated).The chemicals used to prepare the mineral medium were of analytical grade and were used as received.3.Results and discussion

3.1.Molecular characterization of the dechlorinating cultures used in the bioelectrochemical tests

Over 91.5%and 99.5%of the microorganisms stained by DAPI in the TCE dechlorinating and cis -DCE dechlorinating cultures,respectively,were also stained with the eubacterial probe EUB (Fig.1).In the TCE dechlorinating culture,83.0%and 5.6%of EUB-positive cells were stained with the FISH probes targeting Desul?-tobacterium and Dehalococcoides species,respectively.In contrast,in the cis -DCE dechlorinating culture,Dehalococcoides spp.ac-counted for over 96%of bacterial cells (Fig.1).FISH images of Des-ul?tobacterium spp.and Dehalococcoides spp.cells after hybridization with speci?c probes can be found in Supplementary material .These results clearly demonstrate that the long-term operation of the bioreactors with TCE and cis -DCE as the sole elec-tron acceptors,and H 2as the sole electron donor,was highly effec-tive in selecting for Desul?tobacterium spp.and Dehalococcoides spp.,respectively.These ?ndings are also consistent with Desul?to-bacterium spp.being capable to dechlorinating TCE to cis -DCE,using H 2or other substrates as electron donors (Nonaka et al.,2006)and with Dehalococcoides spp.being the only isolated micro-organism capable to dechlorinating cis -DCE and VC with H 2as the sole electron donor (Maymo-Gatell et al.,1997).

3.2.Bioelectrochemical H 2production at à450mV (vs.SHE)in the presence of methyl viologen (MV)

Both dechlorinating cultures showed the ability to catalyze H 2production,with speci?c production rates showing a saturation dependency on the liquid phase MV concentration (Fig.2).Under all the experimental conditions,methane was not detected in the headspace of the cell.Importantly,over the entire range of MV con-centrations investigated,H 2production was negligible in abiotic (control)tests (data not shown).

Experimental data were ?tted to a Michaelis–Menten-type model,modi?ed to account for a MV threshold concentration (i.e.,the lowest MV concentration which sustained a measurable H 2production)(Fennell and Gossett,1998).Estimated maximum speci?c H 2production rates (k MAX )were similar for the two cul-tures (12.4±0.6l eq/mgVSS/d and 11.9±0.6l eq/mgVSS/d,for the TCE and the cis -DCE dechlorinating culture,respectively).Con-versely the half-velocity coef?cients (K m )and the MV threshold concentrations were substantially different,with the cis -DCE dechlorinating culture exhibiting a greater af?nity for the media-tor,namely a lower K m (0.177±0.038mM)and MV threshold con-centration (0.096±0.009mM)than the TCE dechlorinating culture (estimated K m and MV threshold concentration were 0.429±0.076and 0.222±0.016mM,respectively).

The values of current densities,recorded during each test,al-most linearly increased with the MV concentration,up to around 0.1mA/cm 2(at a mediator concentration of 2.5mM),regardless the culture used.

For both cultures,the coulombic ef?ciency (CE),calculated at the end of the 8-h tests,reached a maximum value when MV

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was in the range0.25–0.75mM,then it gradually decreased as the MV concentration increased.Notably,the highest CE values for the cis-DCE dechlorinating culture(i.e.,over40%at0.25mM)were typically higher than those observed with the TCE dechlorinating culture(i.e.,around25%at0.75mM).A possible explanation for the relatively low CE values is the irreversible reduction of the rad-ical MV+?(i.e.,the species thought to be involved in the electron transfer with the microorganisms)to MV0,as well as the formation of dimerization products from coupling reactions between MV+?radicals.

Regarding the mechanisms of H2production in the presence of dissolved MV,it is worth noting that many dechlorinating bacteria, including Desul?tobacterium spp.and Dehalococcoides spp.possess multiple periplasmic hydrogenases which probably directly re-acted with electrically reduced MV.A similar mechanism has been previously suggested for the sulfate-reducing bacterium Desulf-ovibrio vulgaris(Lojou et al.,2002).

3.3.Bioelectrochemical H2production in the absence of exogenous redox mediators

Short-term(i.e.,8h)H2production tests were also carried out in the absence of exogenous redox mediators,in a range of cathode potentials fromà650toà900mV.The aim of these tests was to explore the ability of the dechlorinating cultures to directly cata-lyze H2production(via direct electron transfer)upon adsorption onto the surface of the polarized electrode.For these tests,carbon paper cathodes having a greater surface area than the glassy car-bon cathodes(used in the tests with MV)were employed,in order to maximize bacterial adsorption onto the electrode surface.

Fig.3compares the time course of H2production,with the cath-ode potential set atà750mV,for the two dechlorinating cultures and the abiotic control(from separate batch tests under identical experimental conditions).Differently from the tests carried out in the presence of soluble MV,the Desul?tobacterium-enriched cul-ture showed a greater af?nity for the cathode than the Dehalococcoides-enriched culture.The H2production rate in the presence of the TCE dechlorinating(Desul?tobacterium-enriched) culture was nearly3.7times higher than in the abiotic control with a current density of0.025mA/cm2;conversely the rate of H2pro-duction in the presence of the cis-DCE dechlorinating(Dehalococco-ides-enriched)culture was not signi?cantly(95%con?dence) higher(<40%),than that of the abiotic control despite the fact that the two cultures had a very similar cell concentration.

As expected,the speci?c rate(i.e.,normalized with respect to the nominal surface area of the electrode)of H2production increased with decreasing cathode potential(i.e.,by setting the cathode at more reducing potentials)in the biotic and abiotic tests (Fig.4A).Notably,in the range of cathode potentials fromà700to à900mV,the speci?c rate of H2production in the presence of the TCE dechlorinating culture was always higher than that measured in abiotic tests and hence purely due to electrochemical H+reduc-tion.Atà900mV it reached a value of329±36l eq/cm2/d(or 278±31l eq/mgVSS/d)with a current density of0.44mA/cm2.In contrast,H2production in the presence of the cis-DCE dechlorinat-ing culture was almost indistinguishable from that measured in the abiotic control tests over the entire range of cathode potentials. These?ndings demonstrate the superior ability of Desul?tobacteri-um spp.,compared to Dehalococcoides spp.,to catalyze H2produc-tion with solid electrodes serving as electron donors.Also in these tests,no methane was ever detected in the headspace of the cells.

The TCE dechlorinating culture did not only result in consis-tently higher H2production rates than those of the abiotic controls, but also in higher CE and therefore reaction selectivity(Fig.4B). Remarkably,the bene?cial effect of the biocatalyst was greater at cathode potentials fromà700toà800mV where the abiotic reac-tion was sluggish.As shown in Fig.4,the CE approached100%for cathode potentials lower thanà800mV in the presence of the TCE dechlorinating culture as well as in abiotic controls.

For any given cathode potential,the contribution of bacterial catalysis to the rate of H2production was calculated by subtracting the abiotic H2production rate from the total biotic H2production rate measured in the presence of the microbial culture.For the TCE dechlorinating culture,the H2production due to bacterial catalysis accounted for at least70%of the total H2production at à750mV(Fig.5),and then gradually decreased at more negative cathode potentials where most of the H2was derived from abiotic processes.Atà900mV,less than15%of the H2was produced via bacterial catalysis(Fig.5).It is also worth mentioning that,for

3196M.Villano et al./Bioresource Technology102(2011)3193–3199

the TCE dechlorinating culture,the net biocatalytic H2formation rate almost linearly increased with decreasing cathode potential and accordingly by increasing the driving force for the electron transfer(Fig.5).The latter observation suggests that the rate of electron transfer from the electrode to the microorganisms,rather than the intrinsic biocatalyst activity,was limiting the rate of hydrogen production.

The mechanisms of H2production by the TCE dechlorinating culture in the absence of exogenous redox mediators could not be determined.A possible mechanism could have involved the di-rect interaction of adsorbed bacterial cells with the surface of the polarized electrode and routing of electrons to hydrogenases via redox active components(e.g.,cytochromes)located on the outer membrane of the microorganism(Rosenbaum et al.,2011).This hypothesis is in agreement with the fact that the genome of Desul-?tobacterium sp.encodes several c-type cytochromes(Nonaka et al.,2006)whereas the genome of Dehalococcoides strains does not(Seshadri et al.,2005).It cannot be excluded that self-produced soluble mediators and/or products of bacterial lysis(including hydrogenases)may have also contributed to the shuttling of elec-trons from the electrode to the microorganisms or may have cata-lyzed the H2production themselves(Freguia et al.,2010;Marsili et al.,2008).Importantly,it should be noted that the enhancement of H2production rate(with respect to the abiotic controls)was ob-served only with the TCE dechlorinating culture,but not with cis-DCE dechlorinating culture,though the two cultures had a very similar cell concentration.This?nding indicates that the mecha-nism of H2production was speci?c to the TCE dechlorinating cul-ture and likely ascribable to the presence of Desul?tobacterium species;however,further investigations are needed to shed light on this fundamental issue.

3.4.Energetic analysis of mediated and mediatorless bioelectrochemical H2production

The use of MV allowed production of H2atà450mV,a value that is very close to the reversible H+/H2potential,whereas a po-tential more negative thanà700mV was needed if the redox mediator was lacking.In other words,the mediator reduced the overpotentials for H2evolution by at least300mV,thereby poten-tially reducing the energy input to the H2-producing electrolyzer.A higher CE was typically obtained in the tests carried out in the ab-sence of MV,thereby indicating a more ef?cient usage of the elec-tric current.To account for these factors,we calculated the energy yield(i.e.,the energy recovery as H2relative to the electrical en-ergy input)for the mediatorless and mediated H2production.For this calculation we considered a hypothetical applied voltage for an electrolyzer or MEC having an anode potential ofà150mV[a value that is typical for acetate-fed MECs or MFCs(Aelterman et al.,2008)]and the different cathode con?gurations tested in this work(Fig.6).For the tests carried out in the presence of different MV concentrations,only those yielding the highest energy yields are shown in Fig.6(i.e.,0.25mM for the cis-DCE dechlorinating culture and0.75mM for the TCE dechlorinating culture).As shown in Fig.6,in the presence of MV,the cis-DCE dechlorinating culture (MV=0.25mM)resulted in a higher energy yield(about170%) than the TCE dechlorinating culture(about100%with MV concen-tration of0.75mM).This fact re?ects the relatively higher CE(over 40%)obtained with the cis-DCE dechlorinating culture than the TCE dechlorinating culture at a relatively low hypothetical applied volt-age(300mV)(i.e.,with the cathode atà450mV).Similar energy yields were obtained in the absence of MV,with the highest value (over180%)observed in the presence of the TCE dechlorinating cul-ture at a hypothetical applied voltage of650mV(i.e.,at a cathode potential ofà800mV).These values of energy yield are compara-ble with those reported in the literature with metal catalysts(Call et al.,2009;Selembo et al.,2009;Tartakovsky et al.,2009).

Clearly,identi?cation of the optimal biocathode conditions re-quires that other factors,besides energetic ones,are taken into consideration;these include the cost of the mediator(which is also function of its chemical and electrochemical stability under se-lected operating conditions)as well as the rate of H2production needed.Along this line,it needs to be considered that the maxi-mum volumetric H2production rate in the presence of excess MV(e.g.,0.011m3/m3/d for the TCE dechlorinating culture)was nearly the same than that obtained atà750mV in the absence of MV(i.e.,0.010m3/m3/d,for the TCE dechlorinating culture),but much higher production rates were obtained in the absence of MV at more negative potentials.

It is expected that both for the mediated and the mediatorless biocathodes,H2production rates could be greatly enhanced by increasing biomass density.The most appropriate strategies to achieve this will have to be identi?ed in future investigations. 3.5.Perspectives for application of hydrogenase-containing microorganisms in electrochemical systems

In this study we have shown that living hydrogenophilic dechlo-rinating bacteria(i.e.,Desul?tobacterium spp.and Dehalococcoides spp.),till now known for their ability to utilize hydrogen as an electron donor to respire chlorinated solvents(Holliger and Schum-acher,1994)can also carry out the reverse reaction of hydrogen generation(from water reduction),by using carbon-based

M.Villano et al./Bioresource Technology102(2011)3193–31993197

electrodes as electron donors.These dechlorinating bacteria are highly evolved to utilize H2by means of multiple hydrogenase sys-tems(Nonaka et al.,2006;Seshadri et al.,2005),which,most likely, are also involved in the observed bioelectrocatalytic activity toward H2generation.Hydrogenases,the enzymes catalyzing the rapid interconversion of hydrogen and water in the microbial hydrogen cycle(Baker et al.,2009;Cracknell et al.,2008;Vincent et al., 2007)are receiving considerable attentions as effective electrocat-alysts for fuel cells and electrolyzers.On the other hand,their high costs of isolation,dif?culties in attaching these delicate molecules onto electrodic surfaces while protecting their fragile active sites from inactivation,have greatly hampered their practical applica-tion(Armstrong et al.,2009;Fourmond et al.,2009).Here we dem-onstrate that whole cells of dechlorinating bacteria,thus far only considered for bioremediation applications(Lovley,2001),hold a potential as‘‘novel’’hydrogen catalysts for possible applications in new energy technologies such as microbial electrolysis cells. Based on the results of this study,in the future other hydroge-nase-possessing microorganisms should also be assayed for similar applications.In this context,autotrophic microorganisms which do not rely on organic carbon for growth hold a signi?cant potential. Nonetheless,further studies will also have to evaluate whether the bioelectrocatalytic H2production is linked to energy conserva-tion and microbial growth.This issue will have direct and practical implications on the long-term process durability and sustainability.

4.Conclusions

In a bioelectrochemical system,a Desul?tobacterium-enriched culture and a Dehalococcoides-enriched culture catalyzed H2pro-duction with a carbon-based cathode set atà450mV(a value that is very close to the reversible H+/H2potential ofà414mV),pro-vided a soluble mediator(i.e.,MV)was present in the solution.

Notably,the Desul?tobacterium-enriched culture was also capa-ble to produce H2in the absence of exogenous redox mediators, when the cathode was set at potentials more negative than à700mV.This suggests that the different dechlorinating microor-ganisms employ different mechanisms for routing electrons to hydrogenases,which will necessarily have to be identi?ed in order to fully exploit their potential.

Acknowledgements

This study was carried out in the frame of the FITOLISI research project,funded by the Italian Ministry of Agriculture,Food,and Forestry(MIPAAF).The authors thank Prof.Stefania Panero,Dr. Priscilla Reale,and Dr.Judith Serra Moreno(Sapienza University of Rome)for their suggestions and comments with the experimen-tal setup.

Appendix A.Supplementary data

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家具行业英语(整理完整版)

Adjustable bed 可调床 Air bed 气床 Anti-slip strip for stairs （儿童床）防滑楼梯打击扶手Antique furniture 古式家具 Antique reproduction furniture 仿古家具 Armchair 扶手椅 B Baby crib 婴儿床 Backless wall-unit 不设背板的壁橱 Bamboo furniture 竹家具 Banqueting chair 宴会椅 Barstool 吧椅 Bathroom accessories 浴室配套装置 Bathroom combination 浴室组合柜 Bathroom consoles 浴室多用架 Bathroom furniture 浴室家具 Bathroom vanity 浴室盥洗台 Batten door 板条门 Bed base床架，床套 Bed base set 成套床架 Bedroom suite 卧室系列家具 Bedstead 床架 Bentwood furniture 曲木家具 Beside table 床头柜 Birch door 桦木门 Board-room and conference table 会议桌Bookcase 书柜 Bookshelf 书架 Built-in kitchen 配套厨房家具 Bunk 双层床 Bunk bed 双层床 C Cabin bed 儿童多功能床 Cabin furniture for ships 船用家具 Canopy bed 带天篷的床，四柱床 CD-video storage cabinet边音响组合柜 Chair with castors 脚轮椅 Changing table 可调桌 Chest of drawers 多屉橱柜 Child cot 童床 Children’s bed 儿童床 Children’s bedroom suite 儿童卧房系列家具Children’s chair 儿童椅 CKD(complete knock down) 整体拆装式家具Clothes rail 挂衣杆 Cocktail cabinet 吧柜，酒柜 Cocktail table 鸡尾酒桌 Coffee table 茶几，咖啡桌 Combine-unit 组合柜 Composite furniture 复合家具 Console 小桌 Console table （装在墙上的）蜗形腿台桌 Contract furniture 订做家具，承建家具 Contract programmes 订做家具 Corner sofa suite 拐角扶杆 Cot 童床（婴儿床） Couch 长沙发椅 Cupboard 橱柜Cupboard wall unit for flat 套房衣柜 Curtain 窗帘，挂帘 Customized furniture 订做家具 D Decorative lighting 装饰灯具 Dining room furniture 餐厅家具 Dining room set 起居室配套家具 Dining table 餐桌 Divan 长沙发，沙发床 Dividing wall and fitted wall unit 隔墙板及系列DIY furniture 自装式家具 Double-bed 双人床 Double function sofa-bed 双人沙发床Double sided mirror 双面镜 Draughtsman chair 吧椅 Drawer 抽屉 Dressing table 梳妆台 E Easy chair 轻便椅 End table 茶几 Entrance hall furniture 门厅家具 Exterior door户外门 F Filing cabinet 文件柜 Fireplace壁炉 Fitment 固定家具 Fitting 家居用品 Flap 翻门 Flower stand 花架 Flush door 平面门，全板门 Folding chair 折叠椅 Folding furniture 折叠家具 Folk furniture 民间家具 Foot-stool 踏脚凳 Framed mirror 带框镜子 French-type furniture 模式家具 French cabinet 法式桌椅弯脚 French door 玻璃门 Function sofa多功能沙发椅 Furniture for bedrooms 卧室家具 Furniture for public premises 公共场所家具 G Game table 玩具桌 Gate-leg table折叠桌 Glass cabinet 玻璃陈设柜 Glass case玻璃陈设柜 Glass unit and container 玻璃容器制品Glazed door 玻璃门 H Hall furniture 厅房家具 Hat and coat stand 衣帽架 Headboard 床头 Heirloom quality furniture 祖传家具 High bed 儿童高脚床（不带屉柜） High chair 高脚椅 Highback executive chair 高背办公椅 Home furniture 家庭家具，民用家具 Home office furniture 家庭办公家具 Hotel furniture 酒店家具 Household furniture 家庭家具

世纪商务英语---外贸英语实务翻译答案

1. 检验证书用来表明商品是否符合合同条款。 2. 有时，在合同中有必要订立一个罚金条款，以防万一出现未交货、迟交货、或迟开信用证等一方违约的情况。 3. 当发生不可抗力时，援引不可抗力条款的一方必须在规定期限内及时通知另一方。 4. 裁决指仲裁庭做出的决定。 5. 仲裁协定或合同中的仲裁条款应写明仲裁费用由谁承担。 6. In this case, who is to bear the losses? 7. A force majeure clause should also be specified in the sales contract. 8. Any claim by the buyer regarding the goods shall be filed within thirty days after the arrival of the goods at the port of destination. 9. If you want to file a claim, you should give us a survey report issued by an inspection agency approved by us. 10. I’ll ty pe a clean contract and we can sign it this afternoon. 1. 在信用证支付方式下指望银行付款，而非进口方付款的能力或意愿，但出口方只有遵从信用证的所有条款，才能得到货款。 2. 银行开出信用证就意味着该银行要承担在合适的汇票和单据被出示后付款的责任。 3. 受益人即信用证中所指定的有权接受货款的人，即出口商。 4. 在这一步骤中，买方应填写申请表，包括品名、质量、数量、单价、总值、贸易术语、付款时间、包装、装运期限等。通常买方还应该明确信用证的有效期。 5. 通常，信用证应在装运日期前至少15天内到达卖方，以留出充足的时间进行审核，必要时进行修改，并安排装运。 6. 如果修改通知书涉及两个以上条款，相关各方只能按照惯例全部接受或全部拒绝，而不能只接受其中的一部分，而拒绝其他部分。 7. Wang Ling found that all its clauses were all right except the shipment validity when checking the L/C. 8. As stipulated in the contract, the buyer should open a letter of credit in favor of the seller 30 days before the month of shipment. 9. The letter of credit has been opened in your favor. 10. Generally, the letter of credit specifies the beneficiary’s name, description of goods, quantity, unit price, total amou nt, ports of loading and destination, trade terms, payment terms, shipping documents, shipment validity, negotiation validity, etc. 1. 在中国，由国家质量监督检验检疫总局来主管全国进出口商品的检验工作。 2. 未经检验合格，《种类表》中的进口商品不准销售、使用，出口商品不准出口。 3. 应注意不同检验证书的有效期不同，如果检验证书到期，商品就需要重新报验。 4. 商检机构应当在对外贸易合同约定的索赔期限内完成检验，并签发检验证书。 5. 对这批货物进行30%的抽样检查所得的检验报告是最终的，对双方都有约束力。 6. What’s the time limit for the reinspection? 7. The reinspection fee should be borne by the seller. 8. These goods are not allowed to pass the customs without legal inspection. 9. The buyer is entitled to reinspect the goods upon their arrival even though inspection has been made before shipment. 10. Whose survey report will be taken as final if we find any shortage? Unit 12 1. 运输代理行是运输领域的专家，了解各种最新的运输方式及其相关运费。 2. 运费按以公吨为单位的重量（重量吨）来计算，这种方式用“W ”表示。运费也可以按尺码吨来计算，用“M ”表示。 3. 对于贵重物品，按商品估价的一定百分比收取从价运费，这种方式用“Ad V al.”表示。 4. 航空运费的性质是运费只适用于从一机场到另一机场（单程），且只是运费，不包括其他额外费用，如报关和仓储费用等。 5. 规定滞期费和速遣费的目的是为了促进装卸任务的及时完成。 6. 提单代表货物的所有权。 7. The freight is roughly based on weight and destination. 8. As we are in urgent need of the goods, please ship the goods immediately upon receipt of the L/C. 9. Under FOB, instead of the seller, it is the buyer who will arrange for the shipping space. 10. We await your shipping instructions. Unit 9 Unit 10 Unit 11

新世纪商务英语综合教程第二册复习资料

Unit1 1. Truly, the tongue spoken back in the 1300s only by the "low people" of England has come a long way. Paraphrase: Indeed, the language spoken as early as 1300s by the native people in England has developed for a long time 2. But however accommodating English might be the real reason for the latter day triumph of English is the triumph of the English-speaking United States as a world power. Paraphrase:Adaptable, as English might be, the English owes its success to the victory of the English-speaking United States as a world power. 3. As the 20th century drew on, however, and English continued to encroach, French was driven on to the defensive. Paraphrase:As the 20th century was approaching, and English kept on expanding beyond limits, French was put in a cornered position, having to fight for protection. 4. In India some people see English as an oppressive legacy of colonialism that should be exterminated. Paraphrase:India was once regarded as the Jewel in the Crown of the British Empire. People in India would think the English language reminds them of the period of colonialism, which should be wiped out. 5. But for many peoples the triumph of English is the defeat, if not outright destruction, of their own language. Paraphrase:But for many peoples, the success or the wide spread of English means the defeat, perhaps even a complete extinction, of their own language. 6. Thus the triumph of English not only destroys the tongues of others; it also isolates native English-speakers from the literature, history and ideas of other peoples. Paraphrase:Therefore, the success of English not only defeats other languages, but separates native English speakers from the literature, history and ideas of other ethnic groups.

国际商务英语函电答案.doc

国际商务英语函电答案【篇一：世纪商务英语外贸函电(第二版)课后习题答案】 letter 1.at, of, with, in, for letter 2.from, into, with, of, to p40 https://www.wendangku.net/doc/3f18469636.html,rming, interesting, dealing, sample, details, quality, prices, applied, items, inquiry unit 3 p55 letter 1.from, for, by, with, on letter 2.with, in, of, in, from p56 2.referring, established, cost, quality, opinion, responsibility, part, satisfied, information, decision unit 4 p71 letter 1. to, of, at, in, by letter 2.with, in, with, for, with p73 2.advertisement, leading, interested, details, dealers, line, market, replying, over, item unit 5 p88 letter 1.for, with, at, by, to letter 2.for, for, by, at, by/under p89 2.inquiring, quotation, receipt, subject, confirmation, discount, catalogue, brochure, separate, appreciate unit 6 p105 letter 1.of, on, in, with, to letter 2.of, in, by, for, at p106 2.offer, regret, price, sold, level, difference, transaction, counter-offer, samples, acceptance unit 7 p122 letter 1.to, of, of, in, for,

家具的英文单词

家具的英文单词 M Managerial mediumback chair 中背经理椅 Margined flush door 镶边平板门 Mattress 床垫，席梦思 Mediumback executive chair 中背办公椅Metal furniture金属家具 Mirror door 玻璃门 Mirror for chest of drawers 多屉柜梳妆镜Multi-purpose sofa 多用沙发 Multi-purpose table 多用桌 N Nest 茶几 O Occasional furniture 配套家具，休闲家具Occasional table 休闲桌 Office furniture 办公家具 Office seating 办公座椅 Office table 办公桌 P Partition wall 隔断 Pembroke table 折面桌 Planters chair 园艺工用椅 Plastic furniture 塑料家具 Play furniture 娱乐家具 Presidential highback chair 高背办公椅Pull-out table 伸缩餐具 R Rattan furniture 藤家具 Recliner 躺椅 Refectory table长餐桌 Rocking chair 摇摆椅 Rotary chair 转椅 Rustic style furniture 乡村风格家具 S School table 课桌 Screen 屏风 Seat痤椅 Seating element 痤垫 Secretarial chair 秘书椅 3-section mirror 三面梳妆镜 semi-CKD 半拆装家具 serving table送餐桌 shelving combination A Adjustable bed 可调床 Air bed 气床 Anti-slip strip for stairs （儿童床）防滑楼梯打击扶手 Antique furniture 古式家具 Antique reproduction furniture 仿古家具 Armchair 扶手椅 B Baby crib 婴儿床 Backless wall-unit 不设背板的壁橱 Bamboo furniture 竹家具 Banqueting chair 宴会椅 Barstool 吧椅 Bathroom accessories 浴室配套装置 Bathroom combination 浴室组合柜 Bathroom consoles 浴室多用架 Bathroom furniture 浴室家具 Bathroom vanity 浴室盥洗台 Batten door 板条门 Bed base床架，床套 Bed base set 成套床架 Bedroom suite 卧室系列家具 Bedstead 床架 Bentwood furniture 曲木家具 Beside table 床头柜 Birch door 桦木门 Board-room and conference table 会议桌 Bookcase 书柜 Bookshelf 书架 Built-in kitchen 配套厨房家具 Bunk 双层床 Bunk bed 双层床 C Cabin bed 儿童多功能床 Cabin furniture for ships 船用家具 Canopy bed 带天篷的床，四柱床 CD-video storage cabinet边音响组合柜

世纪商务英语Unit 9

Unit 9 职场 Background Knowledge I. Career Career is a term defined by the Oxford English Dictionary as an individual’s ―course or progress through life (or a distinct portion of life)‖. As of 2006, the word usually only pertains to one’s remunerative work (and sometimes also formal education). A career is traditionally seen as a course of successive situations that make up a person's worklife. One can have a sporting career or a musical career without being a professional athlete or musician, but most frequently "career" in the 20th century referenced the series of jobs or positions by which one earned one's money. It tended to look only at the past. As the idea of personal choice and self direction picks up in the 21st century, aided by the power of the Internet and the increased acceptance of people having multiple kinds of work, the idea of a career is shifting from a closed set of achievements, like a chronological résumé of past jobs, to a defined set of pursuits looking forward. In its broadest sense, career refers to an individual’s work and life roles over their lifespan. In the relatively static societies before modernism, many workers would often inherit or take up a single lifelong position (a place or role) in the workforce, and the concept of an unfolding career had little or no meaning. With the spread during the Enlightenment of the idea of progress and of the habits of individualist self-betterment, careers became possible, if not expected. II. Career Assessment Career Assessments are tests that come in a variety of forms and rely on both quantitative and qualitative methodologies. Career Assessments can help individuals identify and better articulate their unique interests, values, and skills. Career counselors, executive coaches, career development centers, and outplacement companies often administer career assessments to help individuals focus their search on careers that closely match their unique personal profile. Career counseling advisors assess people's interests, personality, values and skills, and also help them explore career options and research graduate and professional schools. Career counseling provides one-on-one or group professional assistance in exploration and decision making tasks related to choosing a major/occupation, transitioning into the world of work or further professional training. The field is vast and includes career placement, career planning, learning strategies and student development. By the late 20th century a plethora of choices (especially in the range of potential professions) and more widespread education had allowed it to become fashionable to plan (or design) a career: in this respect the careers of the career counsellor and of the career advisor have grown up. It is also not uncommon for adults in the late 20th/early 21st centuries to have dual or multiple careers, either sequentially or concurrently. Thus, professional identities have