Insoluble carbonaceous materials as electron shuttles enhance the anaerobic/anoxic bioremediation of redox pollutants:Recent advances

Carbonaceous materials can accelerate extracellular electron transfer for the biotransformation of many recalcitrant,redox-sensitive contaminants and have received considerable attention in fields related to anaerobic bioremediation.As important electron shuttles(ESs),carbonaceous materials effectively participate in redox biotransformation processes,especially microbially-driven Fe reduction or oxidation coupled with pollutions transformation and anaerobic fermentation for energy and by-product recovery.The related bioprocesses are reviewed here to show that carbonaceous ESs can facilitate electron transfer between microbes and extracellular substrates.The classification and characteristics of carbon-containing ESs are summarized,with an emphasis on activated carbon,graphene,carbon nanotubes and carbonbased immobilized mediators.The influencing factors,including carbon material properties(redox potential,electron transfer capability and solubility)and environmental factors(temperature,p H,substrate concentration and microbial species),on pollution catalytic efficiency are discussed.Furthermore,we briefly describe the prospects of carbonaceous ESs in the field of microbial-driven environmental remediation.

Transition from the Kondo effect to a Coulomb blockade in an electron shuttle

We investigate the effect of the mechanical motion of a quantum dot on the transport properties of a quantum dot shuttle, Employing the equation of motion method for the nonequilibrium Green＇s function, we show that the oscillation of the dot, i.e., the time-dependent coupling between the dot＇s electron and the reservoirs, can destroy the Kondo effect. With the increase in the oscillation frequency of the dot, the density of states of the quantum dot shuttle changes from the Kondo-like to a Coulomb-blockade pattern. Increasing the coupling between the dot and the electrodes may partly recover the Kondo peak in the spectrum of the density of states. Understanding of the effect of mechanical motion on the transport properties of an electron shuttle is important for the future application of nanoelectromechanical devices.

Activation of peroxymonosulfate by FeVO_(3-x)for the degradation of carbamazepine:Vanadium mediated electron shuttle and oxygen vacancy modulated interface chemistry

Fast Fe(III)/Fe(II)circulation in heterogeneous peroxymonosulfate(PMS)activation remains as a bottleneck issue that restricts the development of PMS based advanced oxidation processes.Herein,we proposed a facile ammonia reduction strategy and synthesized a novel FeVO3-x catalysts to activate PMS for the degradation of a typical pharmaceutical,carbamazepine(CBZ).Rapid CBZ removal could be achieved within 10 min,which outperforms most of the other iron or vanadium-based catalysts.Electron paramagnetic resonance analysis and chemical probe experiments revealed SO_(4)^(·-),·OH,O_(2)^(·-)and high valent iron(Fe(IV))were all generated in this system,but SO4·-and Fe(IV)primarily contributed to the degradation of CBZ.Besides,X-ray photoelectron spectroscopy and X-ray adsorption spectroscopy indicated that both the generated low-valent V provides and oxygen vacancy acted as superior electron donors and accelerated internal electron transfer via the unsaturated V-O-Fe bond.Finally,the proposed system also exhibited satisfactory performance in practical applications.This work provides a promising platform in heterogeneous PMS activation.

Simultaneous Feammox and anammox process facilitated by activated carbon as an electron shuttle for autotrophic biological nitrogen removal

Ferric iron reduction coupled with anaerobic ammonium oxidation(Feammox)is a novel ferric-dependent autotrophic process for biological nitrogen removal(BNR)that has attracted increasing attention due to its low organic carbon requirement.However,extracellular electron transfer limits the nitrogen transformation rate.In this study,activated carbon(AC)was used as an electron shuttle and added into an integrated autotrophic BNR system consisting of Feammox and anammox processes.The nitrogen removal performance,nitrogen transformation pathways and microbial communities were investigated during 194 days of operation.During the stable operational period(days 126–194),the total nitrogen(TN)removal efficiency reached 82.9%±6.8%with a nitrogen removal rate of 0.46±0.04 kg-TN/m^(3)/d.The contributions of the Feammox,anammox and heterotrophic denitrification pathways to TN loss accounted for 7.5%,89.5%and 3.0%,respectively.Batch experiments showed that AC was more effective in accelerating the Feammox rate than the anammox rate.X-ray photoelectron spectroscopy(XPS)analyses showed the presence of ferric iron(Fe(III))and ferrous iron(Fe(II))in secondary minerals.X-ray diffraction(XRD)patterns indicated that secondary iron species were formed on the surface of iron-AC carrier(Fe/AC),and Fe(III)was primarily reduced by ammonium in the Feammox process.The phyla Anaerolineaceae(0.542%)and Candidatus Magasanikbacteria(0.147%)might contribute to the Feammox process,and Candidatus Jettenia(2.10%)and Candidatus Brocadia(1.18%)were the dominative anammox phyla in the bioreactor.Overall,the addition of AC provided an effective way to enhance the autotrophic BNR process by integrating Feammox and anammox.

Cysteine-enhanced reductive degradation of nitrobenzene using nano-sized zero-valent iron by accelerated electron transfer

As an aliphatic amino acid,cysteine(CYS)is diffuse in the living cells of plants and animals.However,little is known of its role in the reactivity of nano-sized zero-valent iron(NZVI)in the degradation of pollutants.This study shows that the introduction of CYS to the NZVI system can help improve the efficiency of reduction,with 30%more efficient degradation and a reaction rate constant nine times higher when nitrobenzene(NB)is used as probe compound.The rates of degradation of NB were positively correlated with the range of concentrations of CYS from 0 to 10 mmol/L.The introduction of CYS increased the maximum concentration of Fe(Ⅲ)by 12 times and that of Fe(II)by four times in this system.A comparison of systems featuring only CYS or Fe(Ⅱ)showed that the direct reduction of NB was not the main factor influencing its CYS-stimulated removal.The reduction in the concentration of CYS was accompanied by the generation of cystine(CY,the oxidized form of cysteine),and both eventually became stable.The introduction of CY also enhanced NB degradation due to NZVI,accompanied by the regeneration of CYS.This supports the claim that CYS can accelerate electron transfer from NZVI to NB,thus enhancing the efficiency of degradation of NB.

Desulfovibrio vulgaris as a model microbe for the study of corrosion under sulfate-reducing conditions

Corrosion of iron-containing metals under sulfate-reducing conditions is an economically important problem.Microbial strains now known as Desulfovibrio vulgaris served as the model microbes in many of the foundational studies that developed existing models for the corrosion of iron-containing metals under sulfate-reducing conditions.Proposed mechanisms for corrosion by D.vulgaris include:(1)H2 consumption to accelerate the oxidation of Fe0 coupled to the reduction of protons to H2;(2)production of sulfide that combines with ferrous iron to form iron sulfide coatings that promote H2 production;(3)moribund cells release hydrogenases that catalyze Fe0 oxidation with the production of H2;(4)direct electron transfer from Fe0 to cells;and(5)flavins serving as an electron shuttle for electron transfer between Fe0 and cells.The demonstrated possibility of conducting transcriptomic and proteomic analysis of cells growing on metal surfaces suggests that similar studies on D.vulgaris corrosion biofilms can aid in identifying proteins that play an important role in corrosion.Tools for making targeted gene deletions in D.vulgaris are available for functional genetic studies.These approaches,coupled with instrumentation for the detection of low concentrations of H2,and proven techniques for evaluating putative electron shuttle function,are expected to make it possible to determine which of the proposed mechanisms for D.vulgaris corrosion are most important.