Anodic Biofilm Research Articles

Starvation combined with constant anode potential triggers intracellular electron storage in electro-active biofilms

The accumulation of electrons in the form of Extracellular Polymeric Substances (EPS) and poly-hydroxyalkanoates (PHA) has been studied in anaerobic processes by adjusting the access of microorganisms to the electron donor and final electron acceptor. In Bio-electrochemical systems (BESs), intermittent anode potential regimes have also recently been used to study electron storage in anodic electro-active biofilms (EABfs), but the effect of electron donor feeding mode on electron storage has not been explored. Therefore, in this study, the accumulation of electrons in the form of EPS and PHA was studied as a function of the operating conditions. EABfs were grown under both constant and intermittent anode potential regimes and fed with acetate (electron donor) continuously or in batch. Confocal Laser Scanning Microscopy (CLSM) and Fourier-Transform Infrared Spectroscopy (FTIR) were used to assess electron storage. The range of Coulombic efficiencies, from 25 to 82%, and the biomass yields, between 10 and 20%, indicate that storage could have been an alternative electron consuming process. From image processing, a 0.92 pixel ratio of poly-hydroxybutyrate (PHB) and amount of cells was found in the batch fed EABf grown under a constant anode potential. This storage was linked to the presence of living Geobacter and shows that energy gain and carbon source starvation were the triggers for intracellular electron storage. The highest EPS content (extracellular storage) was observed in the continuously fed EABf under an intermittent anode potential, showing that constant access to electron donor and intermittent access to the electron acceptor leads to the formation of EPS from the excess energy gained. Tailoring operating conditions can thus steer the microbial community and result in a trained EABf to perform a desired biological conversion, which can be beneficial for a more efficient and optimized BES.

Mechanisms of magnetic sensing and regulating extracellular electron transfer of electroactive bacteria under magnetic fields

Electroactive bacteria can display notable plasticity in their response to magnetic field (MF), which prompted bioelectrochemical system as promising candidates for magnetic sensor applications. In this study, we explored the sensing and stimulatory effect of MF on current generation by Geobacter sulfurreducens, and elucidated the related molecular mechanism at the transcriptomic level. MF treatment significantly enhanced electricity generation and overall energy efficiency of G. sulfurreducens by 50 % and 22 %, respectively. The response of current to MFs was instantaneous and reversible. Cyclic voltammetry analysis of the anode biofilm revealed that the redox couples changed from −0.31 to −0.39 V (vs. Ag/AgCl), suggesting that MFs could alter electron transfer related components. Differential gene expression analysis further verified this hypothesis, genes associated with electron transfer were upregulated in G. sulfurreducens under MF treatment relative to the control group, specifically, genes encoding periplasmic c-type cytochromes (ppcA and ppcD), outer membrane cytochrome (omcF, omcZ, omcB), pili (pilA-C, pilM, and pilV2), and ribosome. The enhanced bacterial extracellular electron transfer process was also linked to the overexpression of the NADH dehydrogenase I subunit, the ABC transporter, transcriptional regulation, and ATP synthase. Overall, our findings shed light on the molecular mechanism underlying the effects of magnetic field stimuli on EAB and provide a theoretical basis for its further application in magnetic sensors and other biological system.

Identification of predominant bacterial species involved in microbial fuel cell assisted electricity generation using fish market wastewater

Microbial Fuel Cells (MFCs) are a rapidly expanding area of sustainable technology that treats wastewater and generates energy from biodegradable wastes at the same time. However, the power generation from MFC is strongly restricted by the biofilm (microorganism) electron transfer rate which improves electrical power density. The current study provides insight into the effectiveness in electricity production, and wastewater treatment using MFC technique by identifying microbial electricigens on various electrodes using raw fish market wastewater effluent as a substrate. Galvanised iron, aluminium, brass, stainless steel (metal-based electrodes), and graphite rod (carbon-based electrode) were used for the study. MALDI-TOF MS tests were performed to identify the predominant bacterial species from each electrode containing reactors. Raoultella ornithinolytica, Comamonas testosteroni, and Klebsiella pneumonia were among the microbes that were identified and isolated from the anodic biofilm of different MFC reactors. In the current study, four out of the five reactors contained R. ornithinolytica, which was found to be effective at generating electricity. The fuel cell produced maximum current density of 325.13 mA/m2, and power density of 87.78 mW/m2. The COD removal efficiency was found to be 86 %. This study demonstrates the significance of bacterial community characterization and identification in MFC-assisted current generation in fish market wastewater.

Effects of the applied voltage on electroactive microbial biofilm viability and hydrogen production in a recalcitrant organic waste-fed single-chamber membrane-free microbial electrolysis cell performance

The microbial electrolysis cell (MEC) is a future clean technology with a wide range of applications in energy recycling fields, particularly for hydrogen production. Applied voltage governs the electrochemically active microbial activities in MEC and further affects hydrogen production. Therefore, this study investigated the impacts of the applied voltages on MEC performance and anodic biofilm viability during the biotransformation of straw waste biomass into green hydrogen energy in an anaerobic environment. The results revealed that the COD removal efficiency and bioH2 yield increased with the augmentation of the applied voltage and beyond 0.8 V started decreasing. Among the performed protocols MEC0.8 depicted the best performance with a maximum H2 production of 6.017 mmoles H2/g-COD which was ∼28.2 % and ∼9.8 % higher than that of MEC0.5 and MEC1.0 respectively. Moreover, it also achieved a maximum COD removal of 73.4% and a coulombic efficiency (CE) of 68.4%. Consistently, the anodic biofilm viability and bacterial cell shape in the MECs performed with 0.5 V and 0.8 V were less affected but largely damaged in a high potential operated protocol (MEC1.0), suggesting that the mixed electroactive consortia were so sensitive to high potentials. Furthermore, MEC1.0 displayed a high charge transfer resistance of 16.06 Ω which was ∼22.1 %, and ∼73.7 % higher than that of MEC0.8, and MEC0.5 respectively. Based on our novel study’s results, the optimal applied voltage for the best performance of MEC was 0.8 V; and this information will be a pillar for future MEC operations prior to maintaining its industrial practice.

Impact of sandwich-type composite anodic membrane on membrane fouling and methane recovery from sewage sludge and food waste via electrochemical anaerobic membrane bioreactor

Membrane fouling presents a big challenge for the real-world implementation of anaerobic membrane bioreactors (AnMBRs) in digesting high-solid biowastes. In this study, an electrochemical anaerobic membrane bioreactor (EC-AnMBR) with a novel sandwich-type composite anodic membrane was designed and constructed for controlling membrane fouling whilst improving the energy recovery. The results showed that EC-AnMBR produced a higher methane yield of 358.5 ± 74.8 mL/d, rising by 12.8% compared to the AnMBR without applied voltage. Integration of composite anodic membrane induced a stable membrane flux and low transmembrane pressure through forming an anodic biofilm while total coliforms removal reached 97.9%. The microbial community analysis further provided compelling evidence that EC-AnMBR enriched the relative abundance of hydrolyzing (Chryseobacterium 2.6%) bacteria and methane-producing (Methanobacterium 32.8%) archaea. These findings offered new insights into anti-biofouling performance and provided significant implications for municipal organic waste treatment and energy recovery in the new EC-AnMBR.

Evolution and interaction of microbial communities in mangrove microbial fuel cells and first description of Shewanella fodinae as electroactive bacterium

Understanding exoelectrogenic bacteria mechanisms and their interactions in complex biofilm is critical for the development of microbial fuel cells (MFCs). In this article, assumptions concerning the benefits of the complex sediment microbial community for electricity production were explored with both the complex microbial community and isolates identified as Shewanella. Analysis of the microbial community revealed a strong influence of the sediment community on anodes and electrolytes compared to that of only water. Moreover, while Pelobacteraceae-related genera were dominant in our MFCs instead of Desulfuromonas and Geobacter as usually reported, the electroactive Shewanella algae and Shewanella fodinae were isolated and cultivated from the anodic biofilm. S. fodinae, described for the first time as an electroactive bacterium to the best of our knowledge, led to a maximal current density of 3.6 A/m2 set as 0.3 V/SCE in a three-electrode set-up fed with lactate. S. algae, in a complex medium containing several available substrates, showed several preferential oxidative behaviors including a diauxic behavior. In pure culture and under our conditions, S. fodinae and S. algae were not able to use acetate as a sole electron donor. However, their presence in our acetate-fed MFCs and the adaptive behavior of S. algae hint a syntrophic interaction between the bacteria to optimize the use of the substrate in a complex environment.

Evaluation of the respective contribution of anode and cathode for triclosan degradation in a bioelectrochemical system

In this work, the bioelectrochemical system (BES) is a feasible alternative for successfully degrading typical refractory emerging contaminant triclosan (TCS). A single-chamber BES reactor with an initial TCS concentration of 1 mg/L, an applied voltage of 0.8 V, and a solution buffered with 50 mM PBS degraded 81.4 ± 0.2% of TCS, exhibiting TCS degradation efficiency improvement to 90.6 ± 0.2% with a biocathode formed from a reversed bioanode. Both bioanode and biocathode were able to degrade TCS with comparable efficiencies of 80.8 ± 4.9% and 87.3 ± 0.4%, respectively. Dechlorination and hydrolysis were proposed as the TCS degradation pathway in the cathode chamber, and another hydroxylation pathway was exclusive in the anode chamber. Microbial community structure analysis indicated Propionibacteriaceae was the predominant member in all electrode biofilms, and the exoelectrogen Geobacter was enriched in anode biofilms. This study comprehensively revealed the feasibility of operating BES technology for TCS degradation.

Anode Biofilm Formation With Applied External Voltage

Background. The formation of an exoelectrogenic biofilm in a microbial fuel cell (MFC) is an important stage, because it affects later on current generation by the system. The fermented residue after methanogenesis as an inoculum contains not only exoelectrogenic microorganisms, but also methanogens, which reduce the productivity of MFC. The use of current allows the formation of a biofilm enriched with exoelectrogenic microorganisms. Objective. The purpose of our study was to establish the parameters of MFC under periodic application of external voltage. Methods. A two-chamber H-type MFC with a salt bridge between the chambers was used for the study. The anolyte was stirred with a magnetic stirrer for 4 h a day and a 3V voltage was simultaneously applied to create selective conditions for exoelectrogenic biofilm growth. Results. The application of external voltage stimulated the increase in the current and voltage of the MFC. With the periodic application of an external voltage, the MFC current increased to 788 ± 40 mA for the MFC with a resistor and without load. After disconnection and discharge, the MFC current dropped to 189 ± 10 mA for the MFC without load and to 154 ± 8 mA for the MFC with a resistor, respectively. Under the conditions of MFC operation without applying external voltage, the current was 960 ± 50 mA for MFC with an open circuit and 672 ± 35 mA for MFC with a closed circuit when a resistor is connected. For all MFC, the current gradually decreased over time. MFC demonstrated capacitive behaviour: after accumulating charge for 4 h, a discharge from 622 ± 30 mV to 462 ± 23 mV was observed. Microscopy showed fouling of the anode. Since the fermented residue after methanogenesis is mixed consortium, the anodic biofilm was also mixed consortium enriched with different species of exoelectrogens. Conclusions. Periodic application of external voltage allowed to increase the current by 17% and double the voltage compared to MFC without external voltage supply. However, after disconnecting the external voltage source, the MFC gradually discharged, that is, the current and voltage decreased. The maximum value of the current of the MFC with an open circuit was 22% more than the MFC with a closed circuit.

Highly efficient nitrobenzene removal by coupling electrochemical filtration with a microbial electrolysis cell

Conventional microbial electrolysis cell (MEC) for treating nitrobenzene (NB) suffers from insufficient mass transfer, leading to low removal efficiency. Electrochemical filtration (EF) was coupled with MEC to construct an EF-MEC system, which increased the removal rate of NB by 6.5 times in comparison with a conventional MEC. The EF process enhanced the convection mass transfer of NB and hence increased its removal. The EF process was also accompanied by a lower loading rate of NB so that 88.1% of NB in the feed could be reduced and the conversion ratio of NB to AN was high up to 98.2%. Therefore, the toxic effects on anode biofilms were relieved, leading to the enrichment of electroactive microorganisms, especially Geobacter, Desulfovibrio, and Rhodopseudomonas. The enriched anode electroactive microorganisms reciprocally promoted electrogenesis and hence the removal of NB. This EF-MEC system has functionally complemented the benefits between the EF and MEC processes, and it is very promising in treating NB-contained wastewater.

Influence of carbon-based cathodes on biofilm composition and electrochemical performance in soil microbial fuel cells

Increasing energy demands and environmental pollution concerns press for sustainable and environmentally friendly technologies. Soil microbial fuel cell (SMFC) technology has great potential for carbon-neutral bioenergy generation and self-powered electrochemical bioremediation. In this study, an in-depth assessment on the effect of several carbon-based cathode materials on the electrochemical performance of SMFCs is provided for the first time. An innovative carbon nanofibers electrode doped with Fe (CNFFe) is used as cathode material in membrane-less SMFCs, and the performance of the resulting device is compared with SMFCs implementing either Pt-doped carbon cloth (PtC), carbon cloth, or graphite felt (GF) as the cathode. Electrochemical analyses are integrated with microbial analyses to assess the impact on both electrogenesis and microbial composition of the anodic and cathodic biofilm. The results show that CNFFe and PtC generate very stable performances, with a peak power density (with respect to the cathode geometric area) of 25.5 and 30.4 mW m−2, respectively. The best electrochemical performance was obtained with GF, with a peak power density of 87.3 mW m−2. Taxonomic profiling of the microbial communities revealed differences between anodic and cathodic communities. The anodes were predominantly enriched with Geobacter and Pseudomonas species, while cathodic communities were dominated by hydrogen-producing and hydrogenotrophic bacteria, indicating H2 cycling as a possible electron transfer mechanism. The presence of nitrate-reducing bacteria, combined with the results of cyclic voltammograms, suggests microbial nitrate reduction occurred on GF cathodes. The results of this study can contribute to the development of effective SMFC design strategies for field implementation.

N-doped GO cathode catalyst boosting capacity of denitrification for air-cathode microbial fuel cell by shifting microbial community composition in treating marine wastewater

Air-cathode microbial fuel cell (AMFC) is a promising technology with considerable potential for treating contaminants, while obtaining energy has gained a substantial interest. The oxygen reduction reaction (ORR) performance of the cathode electrode is the pivotal factor for boosting AMFC ability. In this study, nitrogen-doped GO cathodic catalysts were prepared using direct heat treatment (NGO) and one-step hydrothermal method (H-NGO). The electrochemical experiments showed the AMFC equipped with NGO10 (wt% of urea: GO was 10:1) achieved the highest output voltage of 391.8 mV with a power density of 1800 mWm-3 in comparison with H-NGO and Pt/C electrodes, i.e. The diversity of bacterial communities for different biofilms was analyzed using high-throughput sequencing, the result showed the relative abundance of denitrifying bacteria including Marinobacter (34.9 %), Methylophaga (4.6 %), Pseudidiomarina (2.7 %) and Glaciecola (3.0 %) significantly increased at cathodic biofilms, moreover, Marinobacter, Methylophaga and Arcobacter were enriched at NGO10 cathode electrode. Reconstruction of Unobserved States (PICRUSt2) predicted differences in metabolic pathways between anode and cathode biofilm, indicating that L-threonine metabolism was significantly down-regulated, while spirilloxanthin, 2,2′-diketo-spirilloxanthin biosynthesis and syringate degradation were significantly up-regulated. A real-time PCR (RT-PCR) represented the genes related to denitrification involving napA, nirK, nirS, nosZ and norB possessed relative higher expression in NGO10 cathode biofilm.

Biocathode electrochemical activity and reduction characteristics of Cr(VI) system in microbial fuel cells

AbstractBACKGROUNDThe biocathode of microbial fuel cells (MFCs) offers a simple method for the reductive treatment of Cr(VI), and Cr(VI) is an electron acceptor in cathodes in MFCs. In this study, MFCs with different Cr(VI) contents (7.07–35.35 mg L−1) were considered to evaluate the overall performance of MFCs.RESULTSThe results of electrochemical analysis confirmed that the MFC‐2 biocathode exhibited a higher effective reaction surface, stronger conductivity, and smaller charge transfer resistance (53.63 Ω) than the others. In addition, Cr(VI) had a power output of 75.6 mW m−2 in MFC‐2 and a Cr(VI) cathodic coulombic efficiency of 103.8%. With 14.14 mg L−1 Cr(VI) content, the cathode microbe had the best activity. Cr(VI) reduction followed a pseudo‐first‐order kinetic model, with the rate constant being 0.0139 h−1. Meanwhile, this study analyzed the Cr(VI) reduction in MFCs and the release and acceptance of electrons and protons. Electrically active bacteria such as Proteobacteria were highly enriched on the anode and cathode biofilm, while the Cr(VI)‐reducing bacteria Gammaproteobacteria increased in the biofilm of the cathode.CONCLUSIONThis study helps in the selection of Cr(VI) concentration for the cathode, guaranteeing microbial activity and power generation performance. Microbes have the best electrochemical activity in MFC‐2 (14.14 mg L−1). Meanwhile, the change in anode microbial activity was affected by cathode performance. The microbial community was significantly influenced by Cr(VI). © 2023 Society of Chemical Industry (SCI).

Digested extracellular DNA shortens the anodic startup of microbial electrolysis cell

While the multiple functions of extracellular DNA (exDNA) in biofilm formation and electron transfer have been extensively studied in pure culture, its role in mixed anodic biofilm was still unknown. In this study, we employed DNase I enzyme to digest exDNA, thereby investigating its role in anodic biofilm formation based on the performance of four microbial electrolysis cells (MECs) groups with different DNase I enzyme concentration (0, 0.05, 0.1, 0.5 mg/mL). The responding time to reach 60 % maximum current of treatment group with DNase I enzyme has been significantly reduced to 83 %–86 % of the blank group (t-test, p < 0.01), indicating the exDNA digestion could promote the biofilm formation at the early stage. The anodic coulombic efficiency was enhanced by 10.74– 54.42 % in treatment group (t-test, p < 0.05), which could be ascribed to the higher absolute abundance of exoelectrogens. The lower relative abundance of exoelectrogens indicated the DNase I enzyme addition was beneficial for the enrichment of extensive species rather than exoelectrogens. As the DNase I enzyme augments the fluorescence signal of exDNA distribution in the small molecular weight region, implying the short chain exDNA could contribute to the biomass enhancement via boosting the most species enrichment. Furthermore, the exDNA alteration improved the complexity of microbial network. Our findings provide a new insight into the role of exDNA in the extracellular matrix of anodic biofilms.

Accelerating anaerobic oxidation of methane coupled with extracellular electron transfer to electrodes via magnetite stimulating membrane-bound proteins of anaerobic methanotrophic (ANME) archaea/methanogens

Methane-dependent bioelectrochemcial systems (BESs) have been recently considered as a promising approach for mitigating methane emission, energy harvesting as well as water environment remediation. However, the mechanisms of extracellular electron transfer (EET) from anaerobic methanotrophic (ANME) archaea/methanogens to electrodes are still poorly understood, which limits the further improvement of methane oxidation and current generation. The study presented here showed that, in the presence of magnetite, anodic biofilms primarily comprised of ANME archaea/methanogens were highly conductive, compared to that without magnetite. Further examination with scanning electrochemical microscopy and electrochemical Fourier transform infrared spectra found that, anodic biofilms with magnetite were redox-based conductive, with a higher concentration of redox-active proteins displayed on their surface than that without magnetite. Metagenomic analysis showed that, the difference in the abundance of genes encoding the cytochrome c (CYC)-like proteins in the anodic biofilms with or without magnetite was not significant. However, magnetite specially increased the abundance of genes encoding the membrane-bound proteins, Rnf, and periplasmic heterodisulfide reductase, HdrABC, contained in ANME archaea/methanogens, providing a possibility that magnetite sped up methane oxidation as well as electron transfer from inner membrane to outer membrane in AOM coupled with EET to electrodes. As a result, the current density in methane-dependent BES with magnetite was increased by approximately 6–9 folds.

Waste volatile fatty acids as a good electron donor in microbial fuel cell with the iron-modified anode

The commercialization of microbial fuel cell technology is limited by high operating costs and low electricity production due to poor electron transfer to the anode. Operational costs can be lowered by utilizing waste materials, and cell performance can be improved by anode modification. This study investigated how anode modification with iron compounds changed the efficiency of energy generation and the microbiome of microbial fuel cells fueled with waste volatile fatty acids from a full-scale anaerobic digestion. Anode modification with 2.5 g Fe2O3/m2 increased the power density, current density, and voltage by 3.6-fold, 1.8-fold, and 1.4-fold, respectively. In the microbial fuel cell influent, propionic, enanthic, and iso-caproic acids predominated (60, 15, and 13% of all volatile fatty acids, respectively); in the outflow, propionic (71%) and valeric acids (17%) predominated. In anodic biofilms, Acidovorax sp. were most abundant; they have a great capacity for volatile fatty acids decomposition, and their abundance doubled in the microbial fuel cell with an iron-modified anode. The presence of iron significantly increased the abundance of the genera Pseudomonas and Geothrix, which were mainly responsible for electricity production. These results indicate that anode modification with iron changes the anode microbiome, favoring efficient volatile fatty acids metabolism and a greater abundance of electrogens in the biofilm, which ensures better electricity generation.

Use of Microbial Fuel Cells for the Treatment of Residue Effluents Discharged from an Anaerobic Digester Treating Food Wastes.

One of practical challenges in anaerobic-digestion (AD) technology is the cost-effective treatment of residue effluents containing high concentrations of organics, nitrogen and phosphorus (CNP). In order to evaluate the utility of microbial fuel cells (MFCs) for treating anaerobic-digester effluents (ADEs) and generating power from them, laboratory-scale single-chamber MFCs were filled with ADE obtained from a commercial AD plant treating food wastes and thereafter operated by routinely supplying ADE at different hydraulic residence times (HRTs, 5 to 20 days). It is shown that MFCs were able to reduce not only organics in ADE but also nitrogen and phosphorus. For instance, data demonstrated that over 50% of CNP was removed in MFCs operated at an HRT of 10 days, at which the maximum power density reached over 200 mW m-2 (based on the projected area of anode). Metabarcoding of 16S rRNA genes showed that some bacteria were specifically enriched in anode biofilms, suggesting their involvement in power generation. Our study suggests that MFCs are applicable to reducing CNP in ADEs at reasonable rates, and provides subsequent work with fundamental data useful for setting targets for further developments.

Microbially mediated molecular transformations of dissolved organic matter in bioelectrochemical systems treating beer brewery wastewater

Microbial communities can grow as anodic and cathodic biofilms and in suspended form (planktonic) in a single-chamber bioelectrochemical system (BES). However, the roles of these microbial communities at different niches on dissolved organic matter (DOM) transformations remain largely unknown. Herein, microorganisms and DOM during beer brewery wastewater (BBW) treatment by the BESs were characterized using a combination of high-throughput sequencing and high-resolution mass spectrometry analyses. The BESs showed promising in degrading the DOM in BBW with over 80% and 90% of COD and TOC removal efficiencies, respectively. The BES treatments significantly increased the aromaticity and unsaturation of DOM by degrading preferentially those molecules with low O/C and high H/C ratios, and also enhanced chemodiversity of DOM due to the generation of thousands of N- and S-containing compounds. The co-occurrence networks displayed that the molecular composition of DOM was shaped by the combination of anodic, planktonic and cathodic microbial communities, but those microorganisms in the anodic biofilms and planktons played more significant roles. Furthermore, the network analyses identified those keystone taxa in each niche responsible for the DOM transformations, showing that some microorganisms situated in different microbial communities would cooperate to drive the transformation of the same DOM patterns. The unveiled interactions between bacterial diversity and chemical diversity of DOM will deepen our understanding of DOM transformations during bioelectrochemical wastewater treatment, which may guide to advance this technique for more efficient DOM control.

Performance and mechanism of sacrificed iron anode coupled with constructed wetlands (E-Fe) for simultaneous nitrogen and phosphorus removal.

Three anodic biofilm electrode coupled CWs (BECWs) with graphite (E-C), aluminum (E-Al), and iron (E-Fe), respectively, and a control system (CK) were constructed to evaluate the removal performance of N and P in the secondary effluent of wastewater treatment plants (WWTPs) under different hydraulic retention time (HRT), electrified time (ET), and current density (CD). Microbial communities, and different P speciation, were analyzed to reveal the potential removal pathways and mechanism of N and P in BECWs. Results showed that the optimal average TN and TP removal rates of CK (34.10% and 55.66%), E-C (66.77% and 71.33%), E-Al (63.46% and 84.93%), and E-Fe (74.93% and 91.22%) were obtained under the optimum conditions (HRT 10h, ET 4h, CD 0.13mA/cm2), which demonstrated that the biofilm electrode could significantly improve N and P removal. Microbial community analysis showed that E-Fe owned the highest abundance of chemotrophic Fe(II) (Dechloromonas) and hydrogen autotrophic denitrifying bacteria (Hydrogenophaga). N was mainly removed by hydrogen and iron autotrophic denitrification in E-Fe. Moreover, the highest TP removal rate of E-Fe was attributed to the iron ion formed on the anode, causing co-precipitation of Fe(II) or Fe(III) with PO43--P. The Fe released from the anode acted as carriers for electron transport and accelerated the efficiency of biological and chemical reactions to enhance the simultaneous removal of N and P. Thus, BECWs provide a new perspective for the treatment of the secondary effluent from WWTPs.

Biogas utilization without desulfurization pretreatment in a bioelectrochemical system

Utilizing biogas as a fuel for heating and power generation usually requires desulfurization pretreatment. In this study, the biogas utilization without desulfurization pretreatment in a bioelectrochemical system (BES) was explored. The results showed that the biogas-fueled BES was successfully started up within 36 d and the presence of hydrogen sulfide promoted both methane consumption and electricity generation. The optimal performance (i.e., a methane consumption of 0.523 ± 0.004 mmol/d, a peak voltage of 577 ± 1 mV, a coulomb production of 37.86 ± 0.43C/d, a coulombic efficiency of 9.37 ± 0.06 % and the maximum power density of 2.070 W/m3) was obtained under bicarbonate buffer solution and 40 °C conditions. The addition of 1 mg/L sulfide and 5 mg/L L-cysteine facilitated methane consumption and electricity generation. In the anode biofilm, the dominant bacteria were Sulfurivermis, unclassified_o__Ignavibacteriales and Lentimicrobium, while Methanobacterium, Methanosarcina and Methanothrix were the predominant archaea. Besides, the metagenomics profiles reveal that anaerobic methane oxidation and electricity generation were closely related to sulfur metabolism. These findings provide a novel approach for utilizing biogas without desulfurization pretreatment.

Thermophilic anaerobic digestion of kitchen waste driven by microbial electrolysis cell (MEC): Digestion performances, anodic microorganisms’ distribution and current utilization efficiency

The aims of present study were to investigate the performances of kitchen waste thermophilic anaerobic digestion driven by microbial electrolysis cell (MEC), and to clarify the methanogenic metabolism pathways on the electrodes (especially on the anodic biofilm). The results showed that both 0.6 V and 1.0 V voltages supplementation could enhance methane yields and production rates, while efficient methanogenesis failed to be sustained after power outages under high organic loading rate (OLR, 4.22 gVS/L/day) condition. Voltages supplementation could also enhance VS removal efficiencies from 83.24–83.35% to 87.01–87.46%, and strengthened the hydrolysis and acidogenesis of dissolved organic matters (DOMs) on the outer layer of anodic biofilm. Voltages supplementation accelerated the β-oxidation of volatile organic acids (VFAs) on the inner layer of anodic biofilm and facilitated acetoclastic methanogenesis on the outer layer of anodic biofilm. The generated electrons on the anode were transferred to the cathode for producing hydrogen as a substrate of hydrogenotrophic methanogenesis, rather than directly generating methane by reducing carbon dioxide through direct interspecies electron transfer (DIET) pathway. On the anodic biofilm, the syntrophic relationship between Syntrophomonas and Methanosarcina was confirmed as the main contributor of methanogenesis. Analysis of current utilization efficiency proved that a little amount of energy input could lead several folds of current utilization efficiencies in return, especially under high OLRs condition, which was anticipated to be applied into practical engineering of kitchen waste thermophilic digestion for higher economic benefits.