Anodic Biofilm Formation Research Articles

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.

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.

Effects of anode materials in electricity generation of microalgal-biophotovoltaic system - part I: Natural biofilm from floating microalgal aggregation

A biophotovoltaic (BPV) system is an emerging photo-bio-electrochemical technology that promises bioelectricity generation through the photosynthesis of exoelectrogenic microorganisms. An algal pool or floating photobioreactor with algae cultivation medium is a potential electron source for sustainable operation of such BPV device. Therefore, bioelectricity generation from algae cultivation medium should be studied to demonstrate this value-added feature. In natural conditions, self-aggregated microalgae form biofilms on the medium surface. One technical concern is that previous studies emphasized the role of anode materials and biofilm formation for the enhancement of electron transmission in BPV device, whereas cell performance by free-floating microalgae medium and natural biofilm still has research value. Hence, cell performance under different anode materials is a crucial decision-making factor of the system with a natural biofilm. In this paper, the experiment was repeated three times to investigate the bioelectrical power generation of BPV device in natural conditions from using three different anode materials, namely graphite, indium tin oxide (ITO)-coated glass, and ITO-coated plastic. In the experiments, BPV devices with ITO anode experienced power overshoot problems by the use of natural floating Spirulina (Arthrospira) platensis aggregation. ITO-coated glass- and plastic-based BPV devices produced maximum power densities of 0.118 mW/m2 and 0.215 mW/m2, respectively. The findings are expected to contribute to further understanding on the correlation of these parameters with regards to power generation by BPV device.

N-acyl-homoserine lactones in extracellular polymeric substances from sludge for enhanced chloramphenicol-degrading anode biofilm formation in microbial fuel cells

Exploring an efficient acclimation strategy to obtain robust bioanodes is of practical significance for antibiotic wastewater treatment by bioelectrochemical systems (BESs). This study investigated the effects of two acclimation conditions on chloramphenicol (CAP)-degrading anode biofilm formation in microbial fuel cells (MFCs). The one was continuously added the extracellular polymeric substances (EPS) extracted from anaerobic sludge and increasing concentrations of CAP after the first start-up phase, while the other was added the EPS-1 (N-acyl-homoserine lactones, namely AHLs were extracted from the EPS) at the same conditions. The results demonstrated that AHLs in the sludge EPS played a crucial role for enhanced CAP-degrading anode biofilm formation in MFCs. The AHL-regulation could not only maintain stable voltage outputs but also significantly accelerate CAP removal in the EPS MFC. The maximum voltage of 653.83 mV and CAP removal rate of 1.21 ± 0.05 mg/L·h were attained from the EPS MFC at 30 mg/L of CAP, which were 0.84 and 1.57 times higher than those from the EPS-1 MFC, respectively. These improvements were largely caused by the thick and 3D structured biofilm, strong and homogeneous cell viability throughout the biofilm, and high protein/polysaccharide ratio along with more conductive contents in the biofilm EPS. Additionally, AHLs facilitated the formation of a biofilm with rich biodiversity and balanced bacterial proportions, leading to more beneficial mutualism among different functional bacteria. More bi-functional bacteria (for electricity generation and antibiotic resistance/degradation) were specifically enriched by AHLs as well. These findings provide quorum sensing theoretical knowledge and practical instruction for rapid antibiotic-degrading electrode biofilm acclimation in BESs.

Antimony reduction by a non-conventional sulfate reducer with simultaneous bioenergy production in microbial fuel cells

Environmental toxicity of antimony (Sb) is significantly increased through the widespread industrial application. The extended release of Sb above the regulatory level became a risk to humans habituated in the ecosystem. Conventional methods to remediate Sb demand high energy or resource input, which further leads to secondary pollution. The bio-electrochemical system offers a promising bioremediation strategy to remove or reduce toxic heavy metals. Thus, this research explores the possibilities of simultaneous metal sulfide (MeS) precipitation and electricity production using a full biological Microbial fuel cell (MFC). A non-conventional sulfate-reducing bacteria (SRB) Citrobacter freundii SR10 was used for this investigation, where the MFC was operated for lactate utilization in the bio-anode and Sb reduction at the bio-cathode. This study observed 81% of coulombic efficiency (bio-anode) and 97% of sulfate reduction with 99.3% Sb (V) reduction (bio-cathode), and it was concluded that the MeS precipitation entirely depends on sulfide concentration via SR10 sulfate reduction. The MFC-SR10 offers a maximum power density of 1652.9 ± 32.1 mW/m3, and their performance was depicted using cyclic voltammetry and electrochemical impedance spectroscopy. The Sb reduction was evaluated through fluorescence spectroscopy, and the Sb (V) MeS precipitation was confirmed as stibnite (Sb2S3) by Raman spectroscopy and X-ray photoelectron spectroscopy. Furthermore, the matured anodic and cathodic biofilm formation was confirmed by Scanning electron microscopy with Energy-dispersive X-ray spectroscopy. Thus the MFC with SRB bio-cathode can be used as an alternative to simultaneously remove sulfate and Sb from the wastewater with electricity production.

A Critical Review on Microbial Fuel Cells Technology: Perspectives on Wastewater Treatment

Increasing demand for renewable energy in the backdrop of global change calls for waste valorization and circular economy strategies. Public health concerns and demand for clean energy provide impetus to the development of wastewater based MFC. Wastewater treatment and simultaneous generation of bioelectricity offer a myriad of environmental benefits. Nevertheless, it is pertinent to know the challenges with the microbial fuel cell (MFC) technology to upscale the wastewater based MFC. This paper attempts to critically analyse the processes, application, challenges and opportunities of wastewater based MFCs. A literature survey was conducted to find out the advances in the field of wastewater based MFCs and the focus was to decipher the challenges to the implementation of wastewater based MFCs. Recent developments in MFC technology have improved the power output and studies show that a diverse group of organic-rich wastewater can be treated with MFCs. The developments include improvements in MFC configuration, development of biocatalysts and biocathode, anodic biofilm formation, microbial community interactions, and progress in the organic and pollutant removal. Nevertheless, the MFC technology is replete with challenges about the organic removal rate, power density, electrode performance limiting factors, economic viability, high initial and maintenance cost and difficulty to maintain the exoelectrogens activity in a complex wastewater environment. Opportunities exist in scaling up of MFCs, integration with other wastewater treatment methods and measures to minimise the operating costs. MFCs have the potential to increase the resilience capacity of the sustainable wastewater treatment plant.

Microbial community dynamic shifts associated with sulfamethoxazole degradation in microbial fuel cells

Though sulfamethoxazole (SMX) degradation at the low or medium concentration (SMX< 30 mg/L) has been reported in the microbial fuel cell (MFC), further exploration is still urgently required to investigate how the high concentration of SMX affect the anode biofilm formation. In this study, the degradation mechanism of SMX and the response of microbial community to SMX at different initial concentrations (0, 0.5, 5 and 50 mg/L) were investigated in MFCs. The highest SMX removal efficiency of 98.4% was obtained in MFC (5 mg/L). SMX at optimal concentration (5 mg/L) could serve as substrate accelerating the extracellular electron transfer. However, high concentration of SMX (50 mg/L) conferred significant inhibition on the electron transfer with SMX removal decline to 84.4%. The 16S rRNA high-throughput sequencing revealed the significant shift of the anode biofilms communities with different initial SMX concentrations were observed in MFCs. Thauera and Geobacter were the predominant genus, with relative abundance of 31.9% in MFC (50 mg/L SMX) and 52.7% in MFC (5 mg/L SMX). Methylophilus exhibited a huge increase with the highest percentage of 16.4% in MFC (50 mg/L). Hence, the functional bacteria of Thauera, Geobacter and Methylophilus endowed significant tolerance to the selection pressure from high concentration of SMX in MFCs. Meanwhile, some bacteria including Ornatilinea, Dechloromonas and Longilinea exhibited a decrease or even disappeared in MFCs. Therefore, initial concentrations of SMX played a fundamental role in modifying the relative abundance of predominant populations. This finding would promote theories support for understanding the evolution of anode biofilm formation related to the different initial concentrations of SMX in MFCs.

Shear Stress Affects Biofilm Structure and Consequently Current Generation of Bioanode in Microbial Electrochemical Systems (MESs).

Shear stress is an important factor that affects the formation and structure of anode biofilms, which are strongly related to the extracellular electron transfer phenomena and bioelectric performance of bioanodes. Here, we show that using nitrogen sparging to induce shear stress during anode biofilm formation increases the linear sweep voltammetry peak current density of the mature anode biofilm from 2.37 ± 0.15 to 4.05 ± 0.25 A/m2. Electrochemical impedance spectroscopy results revealed that the shear-stress-enriched anode biofilm had a low charge transfer resistance of 46.34 Ω compared to that of the unperturbed enriched anode biofilm (72.2 Ω). Confocal laser scanning microscopy observations showed that the shear-stress-enriched biofilms were entirely viable, whereas the unperturbed enriched anode biofilm consisted of a live outer layer covering a dead inner-core layer. Based on biomass and community analyses, the shear-stress-enriched biofilm had four times the biofilm density (136.0 vs. 27.50 μg DNA/cm3) and twice the relative abundance of Geobacteraceae (over 80 vs. 40%) in comparison with those of the unperturbed enriched anode biofilm. These results show that applying high shear stress during anode biofilm enrichment can result in an entirely viable and dense biofilm with a high relative abundance of exoelectrogens and, consequently, better performance.

Effects of applied voltage on the anode biofilm formation and extracellular polymers substances in a single chamber microbial electrolysis cell

Effects of applied voltage on the anode biofilm formation and extracellular polymers substances in a single chamber microbial electrolysis cell

Influence of Initial pH on Anodic Biofilm Formation in Single-Chambered Microbial Electrolysis Cells

Influence of Initial pH on Anodic Biofilm Formation in Single-Chambered Microbial Electrolysis Cells

In situ continuous current production from marine floating microbial fuel cells

In order to power remote sensors and/or data transmission devices in an aquatic environment, sedimentary microbial fuel cells and floating microbial fuel cells have been proposed in the literature, representing a continuous source of renewable and sustainable energy. However, both classes of devices are characterized by large dimensions and are immobilized in the environment within which they are working. Accordingly, when portability and small dimensions are strict requirements, these configurations cannot be exploited.The present work proposes a novel, compact and cost-effective floating set-up based on small-scale microbial fuel cells. A method for in situ anodic biofilm formation was validated through experiments conducted in laboratory and in a real marine environment. Carbon felt-based anodic electrodes were used to build different replicas of floating microbial fuel cells. Their overall performance was evaluated during two field measurement campaigns carried out in the Mediterranean Sea. The study demonstrated a high stability of the floating microbial fuel cells even in a real, uncontrolled environment. The devices were able to continuously produce electricity using seawater as fuel and electrolyte.This study suggests that these devices can be used as portable power supplies for sensors in a complex environment such as the open sea due to the easy preparation of anodic electrodes, together with the simple architecture of floating microbial fuel cells.

Using sewage sludge pyrolytic gas to modify titanium alloy to obtain high-performance anodes in bio-electrochemical systems

Titanium is under consideration as a potential stable bio-anode because of its high conductivity, suitable mechanical properties, and electrochemical inertness in the operating potential window of bio-electrochemical systems; however, its application is limited by its poor electron-transfer capacity with electroactive bacteria and weak ability to form biofilms on its hydrophobic surface. This study reports an effective and low-cost way to convert a hydrophobic titanium alloy surface into a hydrophilic surface that can be used as a bio-electrode with higher electron-transfer rates. Pyrolytic gas of sewage sludge is used to modify the titanium alloy. The current generation, anodic biofilm formation surface, and hydrophobicity are systematically investigated by comparing bare electrodes with three modified electrodes. Maximum current density (15.80 A/m2), achieved using a modified electrode, is 316-fold higher than that of the bare titanium alloy electrode (0.05 A/m2) and that achieved by titanium alloy electrodes modified by other methods (12.70 A/m2). The pyrolytic gas-modified titanium alloy electrode can be used as a high-performance and scalable bio-anode for bio-electrochemical systems because of its high electron-transfer rates, hydrophilic nature, and ability to achieve high current density.

Microbial community composition and electricity generation in cattle manure slurry treatment using microbial fuel cells: effects of inoculum addition.

Microbial fuel cell (MFC) is a sustainable technology to treat cattle manure slurry (CMS) for converting chemical energy to bioelectricity. In this work, two types of allochthonous inoculum including activated sludge (AS) and domestic sewage (DS) were added into the MFC systems to enhance anode biofilm formation and electricity generation. Results indicated that MFCs (AS + CMS) obtained the maximum electricity output with voltage approaching 577±7mV (~196h), followed by MFCs (DS + CMS) (520±21mV, ~236h) and then MFCs with autochthonous inoculum (429±62mV, ~263.5h). Though the raw cattle manure slurry (RCMS) could facilitate electricity production in MFCs, the addition of allochthonous inoculum (AS/DS) significantly reduced the startup time and enhanced the output voltage. Moreover, the maximum power (1.259±0.015W/m2) and the highest COD removal (84.72±0.48%) were obtained in MFCs (AS + CMS). With regard to microbial community, Illumina HiSeq of the 16S rRNA gene was employed in this work and the exoelectrogens (Geobacter and Shewanella) were identified as the dominant members on all anode biofilms in MFCs. For anode microbial diversity, the MFCs (AS + CMS) outperformed MFCs (DS + CMS) and MFCs (RCMS), allowing the occurrence of the fermentative (e.g., Bacteroides) and nitrogen fixation bacteria (e.g., Azoarcus and Sterolibacterium) which enabled the efficient degradation of the slurry. This study provided a feasible strategy to analyze the anode biofilm formation by adding allochthonous inoculum and some implications for quick startup of MFC reactors for CMS treatment.

Enhanced Shewanella oneidensis MR-1 anode performance by adding fumarate in microbial fuel cell

The anode biofilm plays an important role in the microbial fuel cell (MFC) performance, which relies on the catalytic function of the anodic biofilm to transform the chemical energy into electricity energy. In this study, fumarate, as a kind of electron acceptor, is added into the anode system of MFC to figure out its effect on the biofilm formation of S. oneidensis MR-1. With fumarate addition, more bacteria are observed on the anode surface, and the power density has been promoted by 2.41 times than that without fumarate. Mechanism analysis shows that the fumarate addition could impair the secretion of riboflavin and inhibit the indirect electron transfer process, by finishing the respiration process with fumarate as electron acceptor, which promoted the bacteria proliferation and the anode biofilm formation.

An integrated aerobic-anaerobic strategy for performance enhancement of Pseudomonas aeruginosa-inoculated microbial fuel cell

Microbial fuel cell (MFC) is a promising device for energy generation and organic waste treatment simultaneously by electrochemically active bacteria (EAB). In this study, an integrated aerobic-anaerobic strategy was developed to improve the performance of P. aeruginosa-inoculated MFC. With an aerobic start-up and following an anaerobic discharge process, the current density of MFC reached a maximum of 99.80µA/cm2, which was 91.6% higher than the MFC with conventional constant-anaerobic operation. Cyclic voltammetry and HPLC analysis showed that aerobic start-up significantly increased electron shuttle (pyocyanin) production (76% higher than the constant-anaerobic MFC). Additionally, enhanced anode biofilm formation was also observed in the integrated aerobic-anaerobic MFC. The increased pyocyanin production and biofilm formation promoted extracellular electron transfer from EAB to the anode and were the underlying mechanism for the MFC performance enhancement. This work demonstrated the integrated aerobic-anaerobic strategy would be a practical strategy to enhance the electricity generation of MFC.

Accelerating anodic biofilms formation and electron transfer in microbial fuel cells: Role of anionic biosurfactants and mechanism

Anodic electron transfer is the predominant electricity generation process of MFCs. To accelerate anodic biofilms formation and electron transfer, 40mg/L, 80mg/L, and 120mg/L of rhamnolipid biosurfactants were added to the anolyte, resulting in an increased abiotic capacitance from 15.12F/m2 (control) to 16.54F/m2, 18.00F/m2, and 19.39F/m2, respectively. Anodic biofilm formation was facilitated after dosing 40mg/L of rhamnolipids on the 7th day after inoculation, resulting in an increased anodic biofilm coverage from 0.43% to 42.51%, and an increased maximum power density from 6.92±1.18W/m3 to 9.93±0.88W/m3. Furthermore, the adsorption of rhamnolipids on the anode caused the Frumkin effect, leading to a decrease of equilibrium potential from −0.43V to −0.56V, and an increase of exchange current density from 5.09×10−3A/m2 to 8.72×10−3A/m2. However, electron transfer was blocked when the rhamnolipid concentration was further increased to 80mg/L, and 120mg/L. Analysis of the anodic bacterial communities revealed that rhamnolipids facilitated the enrichment of exoelectrogen, increasing the total proportion from 65% to 81%. Additionally, biosurfactants were found to have significant impacts on the composition of exoelectrogens.

Polydopamine as a new modification material to accelerate startup and promote anode performance in microbial fuel cells

Abstract The bacterial anode material is important to the performance of microbial fuel cells (MFCs) because its characteristics affect the biofilm formation and extracellular electron transfer. Here we find that a superhydrophilic semiconductor, polydopamine (PDA), is an effective modification material for the anode to accelerate startup and improve power density. When the activated carbon anode is added with 50% (wt.) PDA, the startup time is 14% shorter than the control (from 88 h to 76 h), with a 31% increase in maximum power density from 613 ± 9 to 803 ± 6 mW m−2, and the Columbic efficiency increases from 19% to 48%. These can be primarily attributed to the abundant functional groups (such as amino group, and catechol functions) introduced by PDA that improve hydrophilicity and extracellular electron transfer. PDA also increases proportions of Proteobacteria and Firmicutes families, indicating that PDA has a selective effect on anode microbial community. Our findings provide a new approach to accelerate anode biofilm formation and enhance MFC power output by modification of biocompatible PDA.

Enhancement of anodic biofilm formation and current output in microbial fuel cells by composite modification of stainless steel electrodes

In this paper, we first systematically investigate the current output performance of stainless steel electrodes (SS) modified by carbon coating (CC), polyaniline coating (PANI), neutral red grafting (NR), surface hydrophilization (SDBS), and heat treatment (HEAT). The maximum current density of 13.0 A m−2 is obtained on CC electrode (3.0 A m−2 of the untreated anode). Such high performance should be attributed to its large effective surface area, which is 2.3 times that of the unmodified electrode. Compared with SS electrode, about 3-fold increase in current output is achieved with PANI. Functionalization with hydrophilic group and electron medium result in the current output rising to 1.5–2 fold, through enhancing bioadhesive and electron transport rate, respectively. CC modification is the best choice of single modification for SS electrode in this study. However, this modification is not perfect because of its poor hydrophilicity. So CC electrode is modified by SDBS for further enhancing the current output to 16 A m−2. These results could provide guidance for the choice of suitable single modification on SS electrodes and a new method for the perfection of electrode performance through composite modification.

TiO2 Nanotube Arrays Modified Titanium: A Stable, Scalable, and Cost-Effective Bioanode for Microbial Fuel Cells

Titanium has been widely used as a dimensionally stable anode in the electrolysis industry because of its excellent corrosion resistance, conductivity, and scalability. However, because of its poor biocompatibility and poor performance as a bioanode, it has drawn little attention in the field of microbial fuel cells (MFCs). This study reports an efficient way to convert a titanium electrode into a high-performance anode for MFCs, in situ growth of titanium dioxide nanotubes (TNs) on its surface. After TN modification, the titanium surface became rougher, more hydrophilic, and more conducive for anodic biofilm formation. The maximal current density achieved on this TN-modified titanium electrode was 12.7 A m–2, which was 190-fold higher than that of the bare titanium electrode and even higher than that of the most commonly used carbon felt electrode. Therefore, the high conductivity, corrosion resistance, and current density make the TN-modified titanium electrode a promising and scalable anode for MFCs.

Quorum sensing autoinducers enhance biofilm formation and power production in a hypersaline microbial fuel cell

Intensive hydraulic fracturing of shale oil and gas reservoirs and other industrial activities can produce large volumes of high-organic-strength and high-salinity wastewaters that are difficult to treat by conventional technologies. Microbial fuel cells (MFC) can treat high-strength wastewater while generating electricity. We enhanced anodic biofilm formation by the extremophile Halanaerobium praevalens, a prevalent species in saline oil and gas reservoirs, in a hypersaline MFC (100g/L NaCl), by promoting quorum sensing (QS) through addition of exogenous QS signals (i.e., Pseudomonas aeruginosa QS signal (PQS) and 4-hydroxy-1-methyl-2-quinolone (quinolone)). A 95% increase in biofilm mass was observed with the addition of 100nM quinolone, yielding a sustained 30% increase in generated power density. Enhanced bacterial attachment to the anode’s surface was corroborated by confocal microscopy. Overall, QS stimulation through the addition of trace levels of such autoinducers might be a feasible approach to enhance MFC performance under high-salinity conditions.