Electrochemically Active Biofilms Research Articles

Propionate outperforms conventional acetate as electron donors for highly-sensitive electrochemical active biofilm sensors in water biotoxicity early-warning

With the ability to generate in situ real-time electric signals, electrochemically active biofilm (EAB) sensors have attracted wide attention as a promising water biotoxicity early-warning device. Organic matters serving as the electron donors potentially affect the electric signal's output and the sensitivity of the EAB sensor. To explore the influence of organic matters on EAB sensor's performance, this study tested six different organic matters during the sensor's inoculation. Besides the acetate, a conventional and widely used organic matter, propionate and lactate were also found capable of starting up the sensor. Moreover, the propionate-fed (PF) sensor delivered the highest sensitivity, which are respectively 1.4 times and 2.8 times of acetate-fed (AF) sensor and lactate-fed (LF) sensor. Further analysis revealed that EAB of PF sensor had more vulnerable intracellular metabolism than the others, which manifested as the most severe energy metabolic suppression and reactive oxygen species attack. Regarding the microbial function, a two-component system that was deemed as an environment awareness system was found in the EAB of PF, which also contributed to its high sensitivity. Finally, PF sensor was tested in real water environment to deliver early-warning signals.

An innovative fast-start aerobic anode microbial fuel cell biosensor for copper ion detection

The potential of microbial fuel cells (MFCs) based biosensors for water monitoring and early warning is widely recognized. However, the electrochemically active biofilms (EABs) are typically obtained under anaerobic conditions and the formation requires a lengthy time span, which critically limits the application and advancement of the MFCs based monitoring technology. To accelerate the formation rate of EABs and thus shorten the establishment time of MFCs to better meet the needs for early warning and detection of pollutants in the actual aerobic water environment, the aerobic sludge was employed as an inoculation source to construct the MFCs sensing system in this study. It was revealed that biofilms with stable electrochemical properties could be promptly formed within 35 h, reaching a level far ahead of previous studies. Moreover, toxicity tests for copper (Cu2+) ions at concentrations of 1 mg/L, 10 mg/L, and 50 mg/L demonstrated outstanding performance with the maximum inhibition rates of 19.99%, 46.65%, and 53.02% respectively. Remarkably, the response time was found to decrease significantly with the increase of copper ion concentrations. Our results thus open up a new avenue for achieving rapid start-up of MFCs in aerobic conditions, which facilitates the applicability of MFCs based biosensing technology.

Engineering hybrid conductive electrochemically active biofilms enable efficient interfacial electron transfer and syntrophic carbon metabolism

Supply of carbon-based nanomaterials (e.g., carbon nanotubes, CNTs) to develop highly conductive electrochemically active biofilms (EABs) is a potential strategy for facilitating extracellular electron transfer (EET) in bioelectrochemical systems (BESs). Understanding of the underlying CNTs-mediated EET behaviors is helpful to further advance the practical application of BESs. Here, the cognitive influence of CNTs on bioelectrocatalytic activity and electron transfer efficiency of EABs were elucidated. CNTs can be embedded into EABs to form hybrid conductive biofilms (CNTs/EABs), achieving a high current density (7.4 ± 1.40 A m−2) and excellent coulombic recovery (46.0 ± 2.70 %) over 100 days of steady operation. The supply of CNTs can mitigate the dependence of exoelectrogens (such as Geobacter) on outer membrane cytochromes (OMCs) and conductive pili due to their down-regulated genes expression in CNTs/EABs, but it can significantly improve microbial carbon metabolism because physically high-conductive CNTs can establish rapid EET pathways, which may reduce the necessity for cells to invest metabolic energy in producing conductive pili and cytochromes that are required in the absence of CNTs. Such enhancement in electron transfer rate may be caused by the interfacial interaction between OMCs and CNTs, resulting in an order of magnitude higher than in the control (5.5 ± 1.60 s−1vs. 0.28 ± 0.04 s−1) and without compromising of mass diffusion. This study provides comprehensive insight into the role of carbon-based nanomaterials in provoking interfacial electron transfer and renewable energy recovery.

Biofilm-engineered fabrication of Ag nanoparticles with modified ZIF-8-derived ZnO for a high-performance supercapacitor

The particle size, pore structure, and surface area of nanomaterials are critical characteristics that govern their effectiveness in energy storage applications. In addition, as the accessibility of the surface to ions or reactants has a significant impact on the performance of the supercapacitor, thus the properties of designed nanostructures are essential and need to be considered. In this study, a ZnO-based nanomaterial with a high surface area and electronic conductivity was synthesized by combining the thermal treatment of a zeolitic imidazolate framework-8 (ZIF-8) with a biofilm-assisted surface modification method. A nanocomposite of ZnO and carbon (ZnO/C) was prepared by the systematic N2/O2 thermal treatment of ZIF-8. The ZnO/C composite underwent additional modification through the direct synthesis of Ag nanoparticles (Ag@ZnO/C) on the ZnO/C surface.An electrochemically active biofilm (EAB) was used as the reducing tool to synthesize the Ag nanoparticles. The final product, Ag@ZnO/C, was used as the electrode in a supercapacitor. Ag@ZnO/C exhibited a specific capacitance of 368.4C g−1 (921 F g−1) at a current density of 1 A g−1, which was remarkably higher than that of ZnO/C (383.5 F g−1). The cyclability of Ag@ZnO/C was also evaluated, demonstrating a 95 % capacity retention over 9000 cycles. The significantly enhanced surface area and electronic conductivity of Ag@ZnO/C resulted in an excellent supercapacitor performance.

Self-assembled electrochemically active biofilms doped with carbon nanotubes: Electron exchange efficiency and cytotoxicity evaluation

Thick electrochemically active biofilms (EABs) will lead to insufficient extracellular electron transfer (EET) rate because of the limitation of both substrate diffusion and electron exchange. Herein, carbon nanotubes (CNTs)-doped EABs are developed through self-assembly. The highly conductive biofilms (internal resistance of ∼211 Ω) are efficiently enriched at CNTs dosage of 1 g L−1, with the stable power output of 0.568 W m−2 over three months. The embedded CNTs can act as electron tunnel to accelerate the EET rate in thick biofilm. Self-charging/discharging experiments and Nernst-Monod model stimulation demonstrate a higher net charge storage capacity (0.15 C m−2) and more negative half-saturation potential (−0.401 V) for the hybrid biofilms than that of the control (0.09 C m−2, and −0.378 V). Enzyme activity tests and the observation of confocal laser scanning microscopy by live/dead staining show a nearly negligible cytotoxicity of CNTs, and non-targeted metabonomics analysis reveals fourteen differential metabolites that do not play key roles in microbial central metabolic pathways according to KEGG compound database. The abundance of typical exoelectrogens Geobacter sp. is 2-fold of the control, resulting in a better bioelectrocatalytic activity. These finding provide a possible approach to prolong electron exchange and power output by developing a hybrid EABs doped with conductive material.

Titanium mesh as the anode of electrochemically active biofilm sensor for improved sensitivity in water toxicity real-time early-warning

As serious water ecological pollution caused by toxicant leakage occurs frequently, early-warning for toxicity presented in water environment attracts increasing attentions as it saves time to retain water safety and human health. Electrochemically active biofilm (EAB) sensor is a promising device for in situ real-time water toxicity early-warning. To improve the sensitivity of EAB sensor particularly for low-concentration toxicity warning, this study employed titanium mesh (TiM) as the anode to construct an EAB sensor. Compared to traditional EAB sensor with carbon felt (CF) anode, the sensitivity of the TiM sensor was increased up to 37.4 times. The effects of mesh size (TiM50, TiM100, TiM150) and operation mode (flow-by and flow-through) on the sensitivity of TiM sensors were further investigated. Results showed the sensor with TiM100 anode had the highest inhibition rate (IR) in flow-by mode, attributed to low charge transfer resistance (Rct) and fast mass transfer. Flow-through operation could further enhance TiM100 sensor's sensitivity from flow-by operation and succeeded to signal as low as 0.0025% formaldehyde, the lowest so far tested in EAB sensor with sensing anode. Multiple toxicity shocks on flow-through TiM100 sensor revealed its good recoverability towards all tested formaldehyde concentration from 0.01% to 0.0025%, during which electrochemical activity degradation and biomass accumulation partially impaired the repeatability. This work highlights the great improvement of EAB sensors by utilizing titanium mesh as EAB carrier and provides a reference for the practical application of metallic materials for EAB sensors.

Electrochemically active biofilm-enabled biosensors: Current status and opportunities for biofilm engineering

Electrochemically active biofilms (EABs) are formed by electroactive bacteria capable of exchanging electrons with electrodes. EABs have been employed as bio-elements in bioelectrochemical sensors which sense analytes of interest by converting metabolic changes to easily detectable electrical signals. Although EAB-enabled biosensors have shown promise in environmental applications, such as water quality monitoring, their most perceived practical applications are limited by low sensitivity, low specificity and short-term stability. Engineering EABs could be an effective strategy to improve the performance of EAB-enabled biosensors. In this review, we briefly introduce EAB with the focus on its extracellular electron transfer, development and matrix, as well as EAB-enabled biosensors including their general principle and potential applications. We then discuss key limitations of EAB-enabled biosensors and the opportunities that biofilm engineering may provide to address these limitations.

Electrochemically active microorganisms sense charge transfer resistance for regulating biofilm electroactivity, spatio-temporal distribution, and catabolic pathway

Charge transfer resistance (CTR) is a key operating parameter for regulating energy harvesting efficiency, electrochemically active biofilms (ECABs) development, and microbial diversity and metabolism in microbial fuel cell (MFC). However, the response behaviors in terms of electroactivity, spatio-temporal distribution, and catabolic pathway of mixed-culture ECABs when being exposed to different CTR have not been well understood. Herein, we comprehensively investigated the effects of CTR on the characteristics of ECABs by varying external resistance in MFC. Specifically, R3-500 exhibited short ECABs maturation (∼8 d), high energy output (∼0.37 W m−2, ∼0.4 mA cm−2), low internal resistance (∼355 Ω) when ECABs was mature, and highly efficient and stable operation. Exopolysaccharides and extracellular DNA play critical roles in cells attachment on electrode surface and development a steady biofilms skeleton. The electron transfer rate was controlled by biofilm resistance (Rfilm, > 90% of total internal resistance), and a typical two-layer ECABs structure (inner dead layer and outer live layer) colonized on carbon fiber, with the dead-cells bearing inner layer as the major resistance causing increased Rfilm. Metagenomics analysis revealed that R3-500 facilitated the proliferation and co-existence of electricigens (e.g., Geobacter), and putative electric-syntrophy bacteria (e.g., Trichococcus), building a syntrophic relationship for potential interspecies electron/message exchange. Furthermore, the key functional genes families associated with cell activity (such as ftsZ, and rps/rpl series), electron transfer (such as torC, rib series, and pilA), and energy metabolism (hdr, mcr, fwd/fmd, and ntp) were upregulated (1.33–6.67-fold) in R3-500. Together these insights into ECABs’ behaviors by regulating CTR are of potential significance to help to sustain the long-term, highly active operation in bioelectrochemical systems.

Additional polypyrrole as conductive medium in artificial electrochemically active biofilm (EAB) to increase the sensitivity of EAB based biosensor in water quality early-warning

Researchers believe that adding conductive mediums in electrochemically active biofilms (EABs) would improve the sensitivity of EAB-based biosensor for real-time water quality early-warning through facilitating the extracellular electron transfer (EET), which has been hardly evidenced mostly because naturally formed EABs employed in previous biosensor studies were recognized distinct and incapable of delivering comparable electrical signals. By preparing artificial EABs where Shewanella oneidensis MR-1 was encapsulated in sodium alginate (SA), this study solved how polypyrrole (PPy) as conductive medium would affect the sensitivity of EAB-based biosensor, as well as mass transfer of toxicant during this process. Different mass ratios (0.125:1, 0.25:1 and 1:1) of PPy over SA were tested, and the sensitivity promoted by 20%, 15% and 6%, respectively. Results indicated that a small amount of PPy addition (PPy: SA = 0.125: 1 in mass ratio) was more effective to increase the biosensor's sensitivity compared to larger amount of PPy employed in EAB. This was when improved conductivity introduced by PPy would dominate in affecting the sensitivity over contrarily weakened mass transfer in the meantime.

Artificial electrochemically active biofilm for improved sensing performance and quickly devising of water quality early warning biosensors

A major challenge for devising an electrochemically active biofilm (EAB)-based biosensor for real-time water quality early-warning is the formation of EAB that requires several days to weeks. Besides the onerous and time-consuming preparation process, the naturally formed EABs are intensively concerned as they can hardly deliver repeatable electrical signals even at identical experimental conditions. To address these concerns, this study employed sodium alginate as immobilization agent to encapsulate Shewanella oneidensis MR-1 and prepared EAB for devising a biosensor in a short period of less than 1 h. The artificial EAB were found capable of delivering highly consistent electrical signals with each other when fed with the same samples. Morphology and bioelectrochemical properties of the artificial EAB were investigated to provide interpretations for these findings. Different concentrations of bacteria and alginate in forming the EAB were investigated for their effects on the biosensor's sensitivity. Results suggested that lower concentration of bacteria would be beneficial until it increased to 0.06 (OD660). Concentration of sodium alginate affected the sensitivity as well and 1% was found an optimum amount to serve in the formation of EAB. A long-term operation of the biosensor with artificial EAB for 110 h was performed. Clear warning signals for incoming toxicants were observed over random signal fluctuations. All results suggested that the artificial EAB electrode would support a rapid devised and highly sensitivity biosensor.

Spatial variation of electrical conductance in electrochemically active biofilm growing on interdigitated microelectrode array

Revealing the pathways of electron transport within electrochemically active biofilms (EABs) is of great importance. Here, mixed-culture EABs are grown on three interdigitated microelectrode arrays (IDAs) with different gap widths of 10 μm, 20 μm and 50 μm and their conductances are determined. The maximum conductive current increases with the decrease of the gap width and charge transfer resistance obtained for the biofilm attaching on the electrode is 3–11 fold less than that for biofilm bridging gaps, suggesting high conductance of biofilm closer to the electrode surface. Results from Raman analysis show high abundance of multi-heme cytochromes in biofilm bridging 10 μm gap, leading to small resistance of biofilm growing on the IDA with 10 μm gap. In addition, the maximum conductive current of biofilm bridging gaps at the potential of −0.40 V vs. Ag/AgCl suggests that electron transfer in biofilm growing on IDAs is redox driven. All these results indicate the spatial heterogeneity of electron transport processes acting within biofilm.

The Limits of Three-Dimensionality: Systematic Assessment of Effective Anode Macrostructure Dimensions for Mixed-Culture Electroactive Biofilms.

This study analyzes the biofilm growth and long‐term current production of mixed‐culture, electrochemically active biofilms (EABs) on macrostructured electrodes under low‐shear‐force conditions. The channel dimensions were altered systematically in the range 400 μm to 2 mm, and the channel heights were varied between 1 and 4 mm to simulate macrostructures of different scales. Electrodes with finer‐structured surfaces produced higher current densities in the short term owing to their large surface area but were outperformed in the long term because the accumulation of biomass led to limitations of mass transfer into the structures. The best long‐term performance was observed for electrodes with channel dimensions of 1×4 mm, which showed no significant decrease in performance in the long term. Channels with a diameter of 400 μm were overgrown by the biofilm, which led to a transition from 3 D to 2 D behavior, indicating that structures of this scale might not be suitable for long‐term operation under low‐shear‐stress conditions.

Scratching the Surface—How Decisive Are Microscopic Surface Structures on Growth and Performance of Electrochemically Active Bacteria?

This study elucidates the role of micrometer-scale electrode surface structures on the growth and the electrochemical performance of mixed culture electrochemically active biofilms (EAB). For this purpose, copper electrodes were machined to generate micro-scale surface structures (roughness and waviness) ranging from a few μm to over 100μm, which were characterized using confocal laser scanning microscopy (CLSM). The structured electrodes were used to cultivate acetate based, mixed culture, anodic EAB in order to establish relationships between the surface properties and (i) the growth behavior and (ii) the stationary electrocatalytic properties of the resulting EAB. On short time scale, the initial growth phase is shown to be significantly influenced behavior by the surface topology. The long term electrocatalytic biofilm performance, however, does not show any dependence on the surface structures and does thus not profit from the increased specific surface area and micro-scale surface area due to the increasing 3-dimensionality. The results of this study are of great importance for a more systematic development of tailored electrodes for microbial electrochemical technologies.

Two-dimensional modelling of syntrophic glucose conversion in bioanodes for coulombic efficiency optimization

This work focuses on the segregation of microbial populations in Electrochemically Active Biofilms (EAB) fed by glucose under continuous flow, simulated with a 2D bioanode model. In the model several reactions take place in parallel (fermentation, electroactivity, methanogenesis), performed by four microbial metabolic groups. Bioconversion yields and rate parameters were estimated by a thermodynamic approach. The model results include biomass segregation according to metabolic activity, distribution of concentrations of solutes and current production along the anode. This numerical tool exhibits an acceptable numerical cost (7000 nodes and below 35,000 degrees of freedom) to evaluate innovative designs for enhancing the bioelectrochemical reactor efficiency using a multicriteria approach. Therefore, a multi-objective optimization (coulombic efficiencies and organic removal rates) was achieved and highlights a Pareto front, showing that relatively high coulombic efficiencies (60–70%) can be obtained with a high removal rate ranging from 0.3 to 0.5 g COD cm−3 d−1.

Inhibitory effect of cadmium(II) ion on anodic electrochemically active biofilms performance in bioelectrochemical systems

Cadmium(II) ion can affect the anode performance of bioelectrochemical systems (BES); however, how the presence of Cd2+ affect the extracellular electron transfer of anodic electrochemically active biofilms (EABs), the microbial viability and species composition of microorganism on the anode remain poorly understood. Here, we investigated the inhibitory effect of Cd2+ at different concentrations on the electrochemical performance and the biofilm community in mixed-culture enriched BES. The electrochemical performance of the BES was not inhibited at 2 mg L−1 Cd2+, while higher concentrations of 5–20 mg L−1 resulted in the decrease in the maximum power density, with 0.34 ± 0.01 W m−2 at 5 mg L−1, 0.28 ± 0.01 W m−2 at 10 mg L−1, and 0.17 ± 0 W m−2 at 20 mg L−1, respectively. When adding 30 mg/L Cd2+, there was almost no power output. The decline of the power output was possibly ascribed to the suppressed viability and the change of species richness as evident from confocal laser scanning microscopy and microbial community analysis. Cyclic voltammogram and electrochemical impedance spectroscopy revealed that high concentration of Cd2+ exceeding 5 mg L−1 can inhibit the secretion of outer membrane cytochromes, thus reducing the electron transfer between the EABs and the anode surface. Analysis of bacterial structures showed a decrease in Geobacter accompanied by an increase in Stenotrophomonas and Azospira in response to Cd2+ at 10 and 20 mg L−1. This study added to the in-depth analysis of the inhibition of Cd2+ on EABs, and provided new insights into the removing Cd2+ and organics simultaneously in BES.

Long-term effect of carbon nanotubes on electrochemical properties and microbial community of electrochemically active biofilms in microbial fuel cells

Carbon nanotubes (CNTs) have been widely exploited to improve anodic performance, but information is needed on their long-term stability for improvement. Herein, we prepared a novel CNTs-modified graphite felt (CNTs-GF) by a simple and scalable process and evaluated its long-term performance using anaerobic sludge as inoculum. the MFC with CNTs-GF yielded a sustained enhancement of power output, increasing from 1.93 ± 0.09 W m−2 after 1 month to 2.10 ± 0.05 W m−2 after 3 months and reaching 2.00 ± 0.10 W m−2 after 13 month, indicating the enhancement in electricity generation by the CNTs was not declined over one year. However, the bare GF showed a declining tendency of performance during 13 months. The long-term enhancement can be explained by the facts that the CNTs-GF was beneficial to electrochemically active biofilms (EABs) growth and interacted better with EABs and increased the extracellular electron transfer. Community analysis showed an increase in Geobacter in response to CNTs modification. These results demonstrated that CNTs modification could sustain a superior long-term enhancement in MFC performance.

Enhanced catalytic capability of electroactive biofilm modified with different kinds of carbon nanotubes

In this study two methods including coating carbon nanotubes (CNTs) layers on the electrode surface and adding CNTs-suspension during electrochemically active biofilms (EABs) growth were used, respectively, to develop CNTs hybrid EABs for enhancing electricity generation capability of EABs. EABs growth on the CNTs with functional groups of hydroxyl (CNTs-OH) or carboxyl (CNTs-COOH) and pristine CNTs without functionalization (P-CNTs) modified electrode was investigated. The maximum current densities of EABs growth on the P-CNTs, CNTs-OH and CNTs-COOH coated electrode were respective 1300 ± 117, 1082 ± 54 and 1124 ± 78 μA cm−2, which were much higher than unmodified electrode (663 μA cm−2). Meanwhile, EABs growth in doping CNTs-COOH or CNTs-OH suspensions system also produced twice higher current density than that on unmodified electrode. These results indicated that the current production of EABs can be significantly enhanced by coating P-CNTs, CNTs-OH, CNTs-COOH layers on the electrode surface or doping CNTs-OH and CNTs-COOH suspension into EABs. Furthermore, morphology analysis of as-obtained EABs had also been studied. It was found that there was no significant difference of the morphological characteristic for EABs growth on different types CNTs coated electrode surface. By comparison, a nano-hybrid porous structure of CNTs and EABs was observed when CNTs-COOH or CNTs-OH suspension was added into the medium during EABs growth, which will be responsible for high current generation.

Electrochemical and microbial community responses of electrochemically active biofilms to copper ions in bioelectrochemical systems

Heavy metals play an important role in the conductivity of solution, power generation and activity of microorganisms in bioelectrochemical systems (BESs). However, effect of heavy metal on the process of exoelectrogenesis metabolism and extracellular electron transfer of electrochemically active biofilms (EABs) was poorly understood. Herein, we investigated the impact of Cu2+ at gradually increasing concentration on the morphological and electrochemical performance and bacterial communities of anodic biofilms in mixed-culture BESs. The voltage output decreased continuously and dropped to zero at 10 mg L−1, which was attributed to the toxic inhibition that cased anodic biofilm damage and decreased secretion of outer membrane cytochromes. When stopping the introduction of Cu2+ to anodic chamber, the maximum voltage production recovered 75.1% of the voltage produced from BES and coulombic efficiency was higher but acetate removal rate was lower than that before Cu2+ addition, demonstrating the recovery capability of EABs was higher compared to nonelectroactive bacteria. Moreover, SEM-EDS and XPS suggested that most of Cu2+ was adsorbed by the anode electrode and reduced by EABs on anode. Compared to the open-circuit BES, the flow of electrons through a circuit could improve the reduction of copper. Community analysis showed a decrease in Geobacter accompanied by an increase in Stenotrophomonas in response to Cu2+ shock in anodic chamber.

Analysis of electricity generation and community of electroactive biofilms enriched from various wastewater treatment stages

Inoculum sources related to electrochemically active biofilm (EAB) development or electricity production from different wastewater tanks of a wastewater treatment plant (WWTP) were studied. EABs established on working electrodes and the related microbial communities in three different inoculum sources from the various stages of wastewater treatment in the same WWTP including primary clarifier wastewater (PCW), aeration tank wastewater (ATW), and anaerobic activated sludge (AAS), were explored for the first time. Enriched EABs, including PCW, AAS, and ATW-EABs, were further selected using Fe(III) oxide/acetate medium and their electricity generation capability were systematically compared. The results showed that the mean current densities of PCW-EAB after selection using Fe(III) oxide achieved a higher plateau of 1500μA·cm−2 than the 1250μA·cm−2 of AAS-EAB. Meanwhile, the corresponding microbial diversities of three EAB varieties were characterized with polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE). More bacterial diversity was found in PCW-EAB with the highest current density. This indicated that the microbial community structures of enriched EABs were highly dependent on initial inoculum sources. On the other hand, sequencing and relative abundance analysis of bacterial diversities showed that all three kinds of enriched EABs mainly contained γ-proteobacteria and Bacteroidia at the class level with main functions of fermentation and electricity generation. This study revealed that the inoculum sources from various stages of wastewater treatment in the same WWTP are all suitable to grow EABs, which is the first time to study the community composition of the enriched EAB at different treatment stages of a WWTP. This work will help investigators in understanding the characteristics of wastewater from different treatment tanks for a single WWTP in terms of microbial communities and their related influence on the electricity generation capability of enriched EABs.

Polarity inversion of bioanode for biocathodic reduction of aromatic pollutants

The enrichment of specific pollutant-reducing consortium is usually required prior to the startup of biocathode bioelectrochemical system (BES) and the whole process is time consuming. To rapidly establish a non-specific functional biocathode, direct polar inversion from bioanode to biocathode is proposed in this study. Based on the diverse reductases and electron transfer related proteins of anode-respiring bacteria (ARB), the acclimated electrochemically active biofilm (EAB) may catalyze reduction of different aromatic pollutants. Within approximately 12 d, the acclimated bioanodes were directly employed as biocathodes for nitroaromatic nitrobenzene (NB) and azo dye acid orange 7 (AO7) reduction. Our results indicated that the established biocathode significantly accelerated the reduction of NB to aniline (AN) and AO7 to discolored products compared with the abiotic cathode and open circuit controls. Several microbes possessing capabilities of nitroaromatic/azo dye reduction and bidirectional electron transfer were maintained or enriched in the biocathode communities. Cyclic voltammetry highlighted the decreased over-potentials and enhanced electron transfer of biocathode as well as demonstrated the ARB Geobacter containing cytochrome c involved in the backward electron transfer from electrode to NB. This study offers new insights into the rapid establishment and modularization of functional biocathodes for the potential treatment of complicated electron acceptors-coexisting wastewaters.