Anodic Biofilm Research Articles

Effect of model methanogens on the electrochemical activity, stability, and microbial community structure of Geobacter spp. dominated biofilm anodes

Combining anaerobic digestion (AD) and microbial electrochemical technologies (MET) in AD-MET holds great potential. Methanogens have been identified as one cause of decreased electrochemical activity and deterioration of Geobacter spp. biofilm anodes. A better understanding of the different interactions between methanogenic genera/species and Geobacter spp. biofilms is needed to shed light on the observed reduction in electrochemical activity and stability of Geobacter spp. dominated biofilms as well as observed changes in microbial communities of AD-MET. Here, we have analyzed electrochemical parameters and changes in the microbial community of Geobacter spp. biofilm anodes when exposed to three representative methanogens with different metabolic pathways, i.e., Methanosarcina barkeri, Methanobacterium formicicum, and Methanothrix soehngenii. M. barkeri negatively affected the performance and stability of Geobacter spp. biofilm anodes only in the initial batches. In contrast, M. formicicum did not affect the stability of Geobacter spp. biofilm anodes but caused a decrease in maximum current density of ~37%. M. soehngenii induced a coloration change of Geobacter spp. biofilm anodes and a decrease in the total transferred charge by ~40%. Characterization of biofilm samples after each experiment by 16S rRNA metabarcoding, whole metagenome nanopore sequencing, and shotgun sequencing showed a higher relative abundance of Geobacter spp. after exposure to M. barkeri as opposed to M. formicicum or M. soehngenii, despite the massive biofilm dispersal observed during initial exposure to M. barkeri.

Facilely Prepared Carbon Dots as Effective Anode Modifier for Enhanced Performance of Microbial Fuel Cells.

Microbial fuel cells (MFCs) are a promising technology for obtaining energy in wastewater. Effective extracellular electron transfer is one of the key factors for its practical application. In this work, carbon dots (CDs) enriched with oxygen-containing groups on the surface were synthesized as an efficient anode modifier using a simple hydrothermal method and common reactants. The experimental findings indicated that anodes modified with CDs exhibited increased electrical conductivity and greater hydrophilicity. These modifications facilitated increased microorganism loading and contributed to enhancing electrochemical processes within the anode biofilm. The CD-modified MFCs exhibited higher maximum power density (661.1 ± 42.6 mW·m-2) and open-circuit voltage (534.50 ± 6.4 mV), which were significantly better than those of the blank group MFCs (484.1 ± 14.1 mW·m-2 and 447.50 ± 12.1 mV). The use of simple carbon materials to improve the microbial loading on the MFCs anode and the electron transfer between the microbial-electrode may provide a new idea for the design of efficient MFCs.

Extracellular polymeric substances in electroactive biofilms play a crucial role in improving the efficiency of microbial fuel and electrolysis cells.

In microbial electrochemical cells (MECs), electroactive microbial biofilms can transmit electrons from organic molecules to anodes. To further understand the production of anodic biofilms, it is essential to investigate the composition and distribution of extracellular polymeric substance (EPS) in the MECs. In this study, the structure of EPS was examined in microbial electrolysis cells from mixed cultures forming biofilm using carbon fiber fabric anode. EPS was extracted from the anode biofilm of microbial electrolysis cells inoculated with mixed microbial culture. The anode biofilm yielded 0.4mg of EPS, of which 51.2% was humic substance, 16.2% was protein, 12.6% was carbohydrates, and 20% consisted of undetermined substances. Using epifluorescence microscopy, the composition of bacterial cells and their location inside EPS were studied, and the distribution of microbial communities was compared based on current density results in the presence of various carbohydrates. On the electrode surface, bacteria and EPS gathered or overlapped in various locations can affect microbial electrochemical performance. Our findings showed that EPS formation in electroactive biofilms would be important for enhanced efficiency of electricity- or hydrogen-producing microbial electrolysis cells.

A genetic engineering strategy to enhance outer membrane vesicle-mediated extracellular electron transfer of Geobacter sulfurreducens

Bioelectrochemical systems (BESs) are unique devices that harness the metabolic activity of electroactive microorganisms (EAMs) to convert chemical energy stored in organic substrates into electrical energy. Enhancing electron transfer efficiency between EAMs and electrodes is the key to practical implementation of BESs. Considering the role of outer membrane vesicles (OMVs) in mediating electron transfer of EAMs, a genetic engineering strategy to achieve OMVs overproduction was explored to enhance electron transfer efficiency and the underlying mechanisms were investigated. This study constructed a mutant strain of Geobacter sulfurreducens that lacked the ompA gene encoding an outer membrane protein. Experimental results showed that the mutant strain produced more OMVs and possessed higher electron transfer efficiency in Fe(III) reduction, dye degradation and current generation in BESs than the wild-type strain. More cargoes such as c-type cytochromes, functional proteins, eDNA, polysaccharides and signaling molecules that might be favorable for electron transfer and biofilm formation were found in OMVs produced by ompA-deficient anodic biofilm, which possibly contributed to the improved electron transfer efficiency of ompA-deficient biofilm. The results indicate that overproduction of OMVs in EAMs might be a potential strategy to enhance BESs performance.

Refining microbial potentiometric sensor performance with unique cathodic catalytic properties for targeted application scenarios

Traditional microbial electrochemical sensors encounter challenges due to their inherent complexity. In response to these challenges, the microbial potentiometric sensor (MPS) technology was introduced, featuring a straightforward high-impedance measurement circuit tailored for environmental monitoring. Nonetheless, the practical implementation of conventional MPS is constrained by issues such as the exposure of the reference electrode to the monitored water and the absence of methodologies to stimulate microbial metabolism. In this study, our objective was to enhance MPS performance by imbuing it with unique cathodic catalytic properties, specifically tailored for distinct application scenarios. Notably, the anodic region served as the sensing element, with both the cathodic region and reference electrode physically isolated from the analyzed water sample. In the realm of organic monitoring, the sensor without Pt/C coated in the cathodic region exhibited a faster response time (1 h) and lower detection limits (1 mg L−1 BOD, 1 mM acetic acid). Conversely, when monitoring toxic substances, the sensor with Pt/C showcased a lower detection limit (0.004% formaldehyde), while the Pt/C-free sensor demonstrated superior reusability. The sensor with Pt/C displayed a heightened anode biofilm thickness and coverage, predominantly composed of Rhodococcus. In conclusion, this study introduces simple, cost-effective, and tailorable biosensors holding substantial promise for water quality monitoring.

Exogenous electric field as a biochemical driving factor for extracellular electron transfer: Increasing power output of microbial fuel cell

Although microbial fuel cells (MFCs) offer a promising avenue for clean power production, they are hindered by inefficient extracellular electron transfer (EET), thereby resulting in a low power output. This study focused on augmenting MFC power by boosting the EET rate using an exogenous electric field (EEF). By leveraging the dual benefits of microbial electrolysis cells (MECs) in organic waste treatment and energy recovery, we developed an MFC–MEC system that utilizes the EEF from MEC as a connecting link. Two configurations, EEF in the same direction (SD-MFC–MEC) and EEF in the reverse direction (RD-MFC–MEC), were used to examine the EET kinetic rate at the MFC anode in the EEF environment using various electrochemical methods for quantitative evaluation. Our findings revealed that EEF significantly enhanced MFC anode biofilm formation and electrochemical activity, leading to a prominent improvement in electrode reaction rates. The EET rate constants in the SD-MFC–MEC and RD-MFC–MEC were more than double those in the control R-MFC, with power density increases of 117.8% and 108.4%, respectively. The formation of electrochemically active sites within the biofilm induced by EEF has emerged as a crucial factor in amplifying the EET rate, and consequently, the MFC power output. Additionally, the variation in EET rate constants between the SD-MFC–MEC and RD-MFC–MEC was minimal, thereby indicating the negligible impact of the EEF orientation on the EET efficiency. This study provides a novel method for quantitatively examining EET rates, opens up new avenues for further facilitating microbe-to-electrode electron transfer, and promotes the application of MFC–MEC systems in energy recovery, CO2 emission reduction, and waste treatment.

Enhanced electricity generation of a 1.2-L microbial fuel cell with acclimation of applied voltage

The aim of this study was to investigate the effect of acclimation at different applied voltages on the electricity generation and composition of anodic biofilm in microbial fuel cell (MFC). Single-chamber air-cathode 1.2-L MFCs were acclimated by different applied voltages (i.e., 0.5, 1.0, 1.5 and 2.0 V). The maximum power density of 1587 mW/m2 and maximum current density of 32.2 ± 0.3 A/m2 were obtained in the MFC after the acclimation by 1.0 V, respectively, which were 10.5 and 1610 times that of the unacclimated MFC. The MFC acclimated by 2.0 V could remain in stable operation with an average maximum current density of 7.8 ± 0.1 A/m2 and a maximum power density of 1439 ± 30 mW/m2 within 40 cycles (∼20 d). The average biomass of the anodic biofilms increased from 3.8 ± 0.9 mg/g before the acclimation to 11.3 ± 1.6 mg/g after the acclimation by 2.0 V. Correspondingly, the anode bacterial viability increased from 0.74 ± 0.02 to 0.91 ± 0.02. The relative abundance of Geoalkalibacter decreased from 18.7 % to 36.1 % before the acclimation to 1.3 %–18.0 % after the acclimation by 2.0 V in the bacterial communities of the anodic biofilms in the MFC. Results from this study should provide an easy way to enhance electrochemically active bacteria acclimation and improve electricity generation in the MFC.

All roads lead to Rome: Cyclic di-GMP differentially regulates extracellular electron transfer in <i>Geobacter</i> biofilms

<p>Microbial extracellular electron transfer (EET) in dissimilatory metal-reducing microorganisms (DMRMs) is a widespread biological process and is involved in biogeochemical cycling of a variety of elements on the planet of Earth. However, the regulatory networks controlling such important process have been under-investigated. Here, we reported that the intracellular messenger bis-(3��-5��) cyclic dimeric guanosine monophosphate (c-di-GMP) signaling network controls EET in <i>Geobacter sulfurreducens</i>. The low and high levels of c-di-GMP both improved EET in <i>G. sulfurreducens</i> electrode-respiring biofilms by differentially regulating the expression of EET-associated genes. In particular, we found that a low c-di-GMP level reduced the formation of the anode biofilm but enhanced EET by upregulating the transcription of all known nanowire genes (i.e., <i>pilA</i>, <i>omcS</i>, <i>omcZ</i> and <i>omcE</i>). Upregulated <i>omcZ</i> transcription was further determined to play a decisive role in improving EET. Given that c-di-GMP is present in diverse DMRMs, this study substantially expands our understanding of the regulatory role of c-di-GMP signaling and the varied strategies for efficient EET employed by DMRMs. In addition to be fundamentally significant to understand microbe-mineral and microbe-microbe interactions driven by EET, it is also instructive to develop effective engineered microbial systems for practical applications.</p>

Synchronous hydrogen and electricity production by dual-cathodes in a bioelectrochemical system

Achieving a self-driven microbial electrolysis cell (MEC) to produce hydrogen is important to its applications but remains challenging. Herein, a dual-cathode bioelectrochemical system (BES) was developed, where one cathode produced electricity energy (Power-cathode) and the other cathode produced hydrogen (H2-cathode). When the applied voltage of the H2-cathode was 0.6 V, the maximum voltage generated by the Power-cathode was 0.47 ± 0.03 V, and the hydrogen rate of the H2-cathode was 0.19 ± 0.003 m3/m3/d. The applied voltage of the H2-cathode was ≤0.4 V, which could be supplied entirely with the power generated by the Power-cathode. Geobacter could accumulate in the anodic biofilm through electric potential differences stimulation. The proportion of electroactive bacteria at the bottom of the anode biofilm was higher than that at the top, while denitrifying bacteria were the opposite. A peak-like distribution of electroactive bacteria in the anodic biofilm and denitrifying bacteria formed a valley-like distribution. Those results have demonstrated a new approach based on dual-cathode BES to produce hydrogen and electricity synchronously, and further proposed a bacterial distribution pattern in anode biofilms. This is of great significance for improving the performance of BES in sustainable wastewater treatment and resource recovery.

Bidirectional extracellular electron transfer pathways of Geobacter sulfurreducens biofilms: Molecular insights into extracellular polymeric substances

The basis for bioelectrochemical technology is the capability of electroactive bacteria (EAB) to perform bidirectional extracellular electron transfer (EET) with electrodes, i.e. outward- and inward-EET. Extracellular polymeric substances (EPS) surrounding EAB are the necessary media for EET, but the biochemical and molecular analysis of EPS of Geobacter biofilms on electrode surface is largely lacked. This study constructed Geobacter sulfurreducens-biofilms performing bidirectional EET to explore the bidirectional EET mechanisms through EPS characterization using electrochemical, spectroscopic fingerprinting and proteomic techniques. Results showed that the inward-EET required extracellular redox proteins with lower formal potentials relative to outward-EET. Comparing to the EPS extracted from anodic biofilm (A-EPS), the EPS extracted from cathodic biofilm (C-EPS) exhibited a lower redox activity, mainly due to a decrease of protein/polysaccharide ratio and α-helix content of proteins. Furthermore, less cytochromes and more tyrosine- and tryptophan-protein like substances were detected in C-EPS than in A-EPS, indicating a diminished role of cytochromes and a possible role of other redox proteins in inward-EET. Proteomic analysis identified a variety of redox proteins including cytochrome, iron-sulfur clusters-containing protein, flavoprotein and hydrogenase in EPS, which might serve as an extracellular redox network for bidirectional EET. Those redox proteins that were significantly stimulated in A-EPS and C-EPS might be essential for outward- and inward-EET and warranted further research. This work sheds light on the mechanism of bidirectional EET of G. sulfurreducens biofilms and has implications in improving the performance of bioelectrochemical technology.

Resorufin retainment by extracellular DNA ensures efficient extracellular electron transfer of Geobacter biofilm

Electrochemically active bacteria (EAB) have promising applications in renewable energy recovery, biofuel production, environmental remediation, and wastewater treatment. Resazurin (RZ) is an effective exogenous electron mediator to facilitate extracellular electron transfer (EET) in EAB, but it is not fully understood that how it catalyzes EET within thick electroactive biofilm. Using Geobacter sulfurreducens as a model EAB, this study investigated the effect and mechanisms of RZ-mediated electron transfer in anode biofilm in a bioelectrochemical system. It was found that the amendment of RZ substantially enhanced current generation of anode biofilm, and the facilitating effect of RZ remained even after fresh electrolyte replacement without RZ replenishment. As an intermediate product of RZ, resorufin (RR) was the actual electron shuttle retained within the entire anode biofilm, responsible for the observed stable electron shuttling efficiency. The retention of RR in anode biofilm might be the consequences of insoluble RR deposition and RR binding with extracellular DNA (eDNA) through intercalative interactions. This study provided in vivo and in vitro evidences for the first time that eDNA provided binding sites for RR in Geobacter biofilm, and proposed a novel electron shuttling mechanism of phenoxazine catalyzing efficient EET of electroactive biofilm.

Enhancing microbial extracellular electron transfer efficiency through increased configuration entropy of bioanodes

Microbial fuel cells (MFCs) have garnered significant attention in the field of bioelectrochemistry as a clean energy source, with a focus on increasing their power density. This study reports the successful application of a spinel-type high-entropy oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Fe2O4 as an anode material for microbial fuel cells. The samples were prepared through ball milling and sintering at 900 °C. Electrochemical tests demonstrated that the high-entropy oxide significantly enhanced the electrochemical performance and biocompatibility of the anode. The MFCs loaded with (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Fe2O4 exhibited a power density of up to 3.43 W/m2, which is significantly higher than that of a simple mixture of six metals (2.61 W/m2) and pure Fe2O3 (2.64 W/m2). This outstanding performance results from the disorder induced by the high-entropy composition. This disorder facilitates improved coordination among the primary constituent oxides, maximizing their advantages. Simultaneously, it minimizes the reduction in active sites caused by uneven distribution. High-throughput sequencing results revealed an enrichment of Geobacter in the anodic biofilm, reaching a content as high as 52.51% after domestication. This study elucidates the contribution of entropy to biocatalysis from an entropy perspective and provides a new strategy for developing high-performance materials for microbial fuel cells.

Enhancing energy efficiency and H2 production in lab-scale dual chamber microbial electrolysis cells: A focus on catholyte composition and voltage losses

Microbial electrolysis cells (MECs) have emerged as a promising technology for sustainable hydrogen production from wastewater treatment. An MEC consists of a microbial anode and a hydrogen evolution cathode, where microorganisms in the anode oxidize organic compounds, allowing the cathodic hydrogen production at lower potentials compared to abiotic electrolysis. The present study focuses on optimizing the catholyte composition and configuration in a MEC reactor to maximize hydrogen production rates while minimizing energy consumption. Indeed, buffer solutions of HCO3-, HPO42-, and H2PO4- at different concentrations and operation mode were tested as catholytes analysing hydrogen production rates and energy consumptions of the process. The results demonstrate the stability of the anodic electroactive biofilm over a 220-day period, achieving consistent COD removal and hydrogen production. The findings reveal that the catholyte composition and operating mode significantly affect the cathodic performances of the MEC. Indeed, catholytes with higher buffer concentrations allow for a limited catholyte alkalinisation improving hydrogen production rates while a low buffer solution promotes an increase in process energy consumption. Bicarbonate buffer solution utilized under batch operation mode showed the better performances for hydrogen production at the cathodic side of MECs showing a higher cathodic coulombic efficiency coupled with stable pH levels and cathodic potentials. Overall, this research demonstrates the potential of MECs for sustainable hydrogen production and highlights the importance of optimizing catholyte composition and operating mode to increase energy efficiency of process.

Influence of Hydrodynamic Forces on Electroactive Bacterial Adhesion in Microbial Fuel Cell Anodes.

This investigation examined the role of shear stress on the dynamic development of microbial communities within anodic biofilms in single-chamber microbial fuel cells (MFCs). Bacterial attachment to surfaces, often regarded as a crucial step in biofilm formation, may significantly contribute to the selection of electroactive bacteria (EAB). It is well established that hydrodynamic forces, particularly shear forces, have a profound influence on bacterial adhesion. This study postulates that shear stress could select EAB on the anode during the adhesion phase by detaching non-EAB. To examine this hypothesis, MFC reactors equipped with a shear stress chamber were constructed, creating specific shear stress on the anode. The progression of adhesion under various shear stress conditions (1, 10, and 50 mPa) was compared with a control MFC lacking shear stress. The structure of the microbial community was assessed using 16S rRNA gene (rrs) sequencing, and the percentage of biofilm coverage was analyzed using fluorescence microscopy. The results indicate a significant impact of shear stress on the relative abundance of specific EAB, such as Geobacter, which was higher (up to 30%) under high shear stress than under low shear stress (1%). Furthermore, it was noted that shear stress decreased the percentage of biofilm coverage on the anodic surface, suggesting that the increase in the relative abundance of specific EAB occurs through the detachment of other bacteria. These results offer insights into bacterial competition during biofilm formation and propose that shear stress could be utilized to select specific EAB to enhance the electroactivity of anodic biofilms. However, additional investigations are warranted to further explore the effects of shear stress on mature biofilms.

Polyethylene glycol hydrogel coatings for protection of electroactive bacteria against chemical shocks

Loss of bioelectrochemical activity in low resource environments or from chemical toxin exposure is a significant limitation in microbial electrochemical cells (MxCs), necessitating the development of materials that can stabilize and protect electroactive biofilms. Here, polyethylene glycol (PEG) hydrogels were designed as protective coatings over anodic biofilms, and the effect of the hydrogel coatings on biofilm viability under oligotrophic conditions and ammonia-N (NH4+-N) shocks was investigated. Hydrogel deposition occurred through polymerization of PEG divinyl sulfone and PEG tetrathiol precursor molecules, generating crosslinked PEG coatings with long-term hydrolytic stability between pH values of 3 and 10. Simultaneous monitoring of coated and uncoated electrodes co-located within the same MxC anode chamber confirmed that the hydrogel did not compromise biofilm viability, while the coated anode sustained nearly a 4 × higher current density (0.44 A/m2) compared to the uncoated anode (0.12 A/m2) under oligotrophic conditions. Chemical interactions between NH4+-N and PEG hydrogels revealed that the hydrogels provided a diffusive barrier to NH4+-N transport. This enabled PEG-coated biofilms to generate higher current densities during NH4+-N shocks and faster recovery afterwards. These results indicate that PEG-based coatings can expand the non-ideal chemical environments that electroactive biofilms can reliably operate in.

Influence of shear stress on electroactive biofilm characteristics and performance in microbial fuel cells

This study has provided comprehensive insights into the intricate relationship between shear stress and the development, structure, and functionality of electroactive biofilms in Microbial Fuel Cells (MFCs). A multichannel microfluidic MFC reactors that created specific shear stress on the anode, were designed for the simultaneous study of multiple flow conditions using the same medium. Then, the evolution of the biofilm growth under different shear stress conditions (1, 5 and 10 mPa) were compared. The taxonomic and functional structure was studied by 16S rRNA gene and metagenomic sequencing and the physical biofilm characteristics were measured via fluorescence microscopy. The results demonstrate the pivotal role of shear stress in influencing the growth kinetics, electrical performance, and physical structure of anodic biofilms. Notably, the selection of specific EAB was observed to be shear stress-dependent, with a marked increase in specific EAB abundance as shear stress increased. The power density, while not directly correlated with the relative abundance of specific or nonspecific EAB, exhibited a strong linear relationship with biofilm coverage. This suggests that factors beyond the microbial composition, potentially including mass transport or electrochemical conditions, might be instrumental in determining electricity production. The functional metagenomic analysis further highlighted the complexities of extracellular electron transfer (EET) mechanisms in electroactive biofilm. While certain genes associated with EET in known species such as Geobacter and Shewanella were identified, the study also examined the limitations of solely relying on genetic markers to infer EET capabilities, emphasizing the need for complementary metaproteomic analyses. This study demonstrates the multifaceted impact of shear stress on electroactive biofilm and paves the way for future investigations aimed at harnessing the potential of electroactive biofilms in microbial fuel cell applications.

Selective Sensing in Microbial Fuel Cell Biosensors: Insights from Toxicity-Adapted and Non-Adapted Biofilms for Pb(II) and Neomycin Sulfate Detection.

This study introduces the utilization of self-powered microbial fuel cell (MFC)-based biosensors for the detection of biotoxicity in wastewater. Current MFC-based biosensors lack specificity in distinguishing between different pollutants. To address this limitation, a novel approach is introduced, capitalizing on the adaptive capabilities of anodic biofilms. By acclimating these biofilms to specific pollutants, an enhancement in the selectivity of MFC biosensors is achieved. Notably, electrochemically active bacteria (EAB) were cultivated on 3D porous carbon felt with and without a model toxicant (target analyte), resulting in the development of toxicant-resistant anodic biofilms. The model toxicants, Pb2+ ions and the antibiotic neomycin sulfate (NS), were deployed at a concentration of 1 mg L-1 during MFC operation. The influence of toxicity on biofilm growth and power production was investigated through polarization and power density curves. Concurrently, the electrochemical activity of both non-adapted and toxicity-adapted biofilms was investigated using cyclic voltammetry. Upon maturation and attainment of peak powers, the MFC reactors were evaluated individually as self-powered biosensors for pollutant detection in fresh wastewater, employing the external resistor (ER) mode. The selected ER, corresponding to the maximum power output, was positioned between the cathode and anode of each MFC, enabling output signal tracking through a data logging system. Subsequent exposure of mature biofilm-based MFC biosensors to various concentrations of the targeted toxicants revealed that non-adapted mature biofilms generated similar current-time profiles for both toxicity models, whereas toxicity-adapted biofilms produced distinctive current-time profiles. Accordingly, these results suggested that merely by adapting the anodic biofilm to the targeted toxicity, distinct and identifiable current-time profiles can be created. Furthermore, these toxicity-adapted and non-adapted biofilms can be employed to selectively detect the pollutant via the differential measurement of electrical signals. This differentiation offers a promising avenue for selective pollutant detection. To the best of our current knowledge, this approach, which harnesses the natural adaptability of biofilms for enhanced sensor selectivity, represents a pioneering effort in the realm of MFC-based biosensing.

Microbial electrolysis drives ammonium removal from saline wastewater through marine anammox bacteria

Currently, ammonium removal from saline wastewater still poses a challenge to conventional biological nitrogen removal process. Herein, the conversion of NH4+-N to N2 was successfully driven by marine anammox bacteria (MAB) in a single chamber microbial electrolytic cell (MEC) using NH4+-N as the sole substrate. Compared with no ammonium removal in the abiotic reactor with applied voltage (0–1.5 V), the maximum ammonium and total nitrogen removal rate (ARR and TNRR) of 55 and 50 g/m3•d were obtained at the voltage of 1.1 V, which were 78 % and 76 % higher than that of 0.5 V, respectively. At the voltage ≥ 1.1 V, the accumulation of NO2–-N and NO3–-N was observed in the MEC, and the nitrifying bacteria Nitrosmonas and Nitrospira were detected on the anode surface with the relative abundances of 0.84 % and 0.21 %, respectively. It was proved that the production of NO2–-N and NO3–-N was an electrochemical biological process by electroactive nitrifying bacteria. Candidatus Scalindua was the main functional genus for ammonium removal at anode biofilm with the relative abundance of 19.27 %. Therefore, ammonium was successfully removed by integrating anodic anammox and anodic nitrification. Applied voltage increased the microbial diversities at anode surface and promoted the formation of electrode biofilm. These findings indicated a promising saline wastewater treatment by employing salt-tolerant MAB for ammonium removal.

Treatment of phenolic wastewater by anaerobic fluidized bed microbial fuel cell using carbon brush as anode: microbial community analysis and m-cresol degradation mechanism.

Anaerobic fluidized bed microbial fuel cell (AFB-MFC) is a technology that combines fluidized bed reactor and microbial fuel cell to treat organic wastewater and generate electricity. The performance and the mechanism of treating m-cresol wastewater in AFB-MFC using carbon brush as biofilm anode were studied. After 48h of operation, the m-cresol removal efficiency of AFB-MFC, MAR-AFB (fluidized bed bioreactor with acclimated anaerobic sludge), MAR-FB (ordinary fluidized bed reactor with only macroporous adsorptive resin) and AST (traditional anaerobic sludge treatment) were 95.29 ± 0.67%, 85.78 ± 1.81%, 71.24 ± 1.86% and 70.41 ± 0.32% respectively. The maximum output voltage and the maximum power density of AFB-MFC using carbon brush as biofilm anode were 679.7mV and 166.6 mW/m2 respectively. The results of high-throughput sequencing analysis indicated the relative abundance of dominant electroactive bacteria, such as Trichococcus, Geobacter, and Pseudomonas, on the anode carbon brushes was higher than that of AST, and also identified such superior m-cresol-degrading bacteria as Bdellovibrio, Thermomonas, Hydrogenophaga, etc. Based on the determination of m-cresol metabolites detected by Gas Chromatography-Mass Spectrometry (GC-MS), the possible biodegradation pathway of m-cresol under anaerobic and aerobic conditions in AFB-MFC was speculated. The results showed that m-cresol was decomposed into formic acid-acetic anhydride and 3-methylpropionic acid under the action of electrochemistry, which is a simple degradation pathway without peripheral metabolism in AFB-MFC.

Statistical optimization of waste molasses-based exopolysaccharides and self-sustainable bioelectricity production for dual chamber microbial fuel cell by Bacillus piscis

BackgroundThe application of exopolysaccharide-producing bacteria (EPS) in dual chamber microbial fuel cells (DCMFC) is critical which can minimize the chemical oxygen demand (COD) of molasses with bioelectricity production. Hence, our study aimed to evaluate the EPS production by the novel strain Bacillus piscis by using molasses waste. Therefore, statistical modeling was used to optimize the EPS production. Its structure was characterized by UV, FTIR, NMR, and monosaccharides compositions. Eventually, to highlight B. piscis' adaptability in energy applications, bioelectricity production by this organism was studied in the BCMFC fed by an optimized molasses medium.ResultsB. piscis OK324045 characterized by 16S rRNA is a potent EPS-forming organism and yielded a 6.42-fold increase upon supplementation of molasses (5%), MgSO4 (0.05%), and inoculum size (4%). The novel exopolysaccharide produced by Bacillus sp. (EPS-BP5M) was confirmed by the structural analysis. The findings indicated that the MFC's maximum close circuit voltage (CCV) was 265 mV. The strain enhanced the performance of DCMFC achieving maximum power density (PD) of 31.98 mW m−2, COD removal rate of 90.91%, and color removal of 27.68%. Furthermore, cyclic voltammetry (CV) revealed that anodic biofilms may directly transfer electrons to anodes without the use of external redox mediators. Additionally, CV measurements made at various sweep scan rates to evaluate the kinetic studies showed that the electron charge transfer was irreversible. The SEM images showed the biofilm growth distributed over the electrode’s surface.ConclusionsThis study offers a novel B. piscis strain for EPS-BP5M production, COD removal, decolorization, and electricity generation of the optimized molasses medium in MFCs. The biosynthesis of EPS-BP5M by a Bacillus piscis strain and its electrochemical activity has never been documented before. The approach adopted will provide significant benefits to sugar industries by generating bioelectricity using molasses as fuel and providing a viable way to improve molasses wastewater treatment.