Bacterial community structure of electrogenic biofilm developed on modified graphite anode in microbial fuel cell

Harnessing the power of microbial fuel cells as pioneering green technology: advancing sustainable energy and wastewater treatment through innovative nanotechnology

The purpose of this review is to gain attention about intro the advanced and green technology that has dual action for both clean wastewater and produce energy. Water scarcity and the continuous energy crisis have arisen as major worldwide concerns, requiring the creation of ecologically friendly and sustainable energy alternatives. The rapid exhaustion of fossil resources needs the development of alternative energy sources that reduce carbon emissions while maintaining ecological balance. Microbial fuel cells (MFCs) provide a viable option by producing power from the oxidation of organic and biodegradable chemicals using microorganisms as natural catalysts. This technology has sparked widespread attention due to its combined potential to cleanse wastewater and recover energy. The review presents a complete examination of current advances in MFCs technology, with a focus on the crucial role of anode materials in improving their performance. Moreover, different anode materials and their nanoscale modifications are being studied to boost MFC efficiency. This current review also focused on the effects of surface modifications and different anode compositions on power generation and system stability. It also investigates the electrochemical principles behind these enhancements, providing insights into the economic potential of MFCs. MFCs provide a long-term solution to energy and environmental issues by addressing both wastewater treatment and energy production.

Electrochemical optimization of bioelectrochemically improved anaerobic digestion for agricultural digestates' valorisation to biomethane

Bioelectrochemically improved anaerobic digestion (AD-BES) represents an upgrading strategy for existing biogas plants, consisting of the integration of bioelectrodes within the AD reactor. For this study, a series of laboratory-scale AD-BES reactors were operated, valorising agricultural digestates through the production of biogas. The reactors were inoculated and started-up with three different digestates, leading to significant differences in the microbial community developed on the bioelectrodes. After the start-up was completed, the AD-BES were all fed with a unique digestate, to evaluate the stability of the bioelectrodes' biofilm performances against variations of the organic feedstock. In terms of methane (CH4) production rate, the presence of bioelectrodes allowed between 25 and 82% improvement, compared with control AD reactors. The application of an optimal voltage of 0.3 V resulted in an additional 40% improvement in CH4 production rate, but only when the biofilm was previously acclimated to the fed digestate. Comprehensive microbial characterization revealed that fed digestate significantly influences the composition and homogenization of microbial communities within AD-BES reactors, with applied voltage showing only a secondary effect. Even when reactors were transitioned to a uniform digestate feeding, resulting in closely similar microbial profiles, variations in CH4 production persisted, underscoring the lasting impact of initial microbial conditioning. A critical observation was the differentiation in archaeal colonization on bioelectrodes at 0.3 V, the voltage yielding the highest CH4 conversion. These insights suggest that while the microbial community structure depends on fed digestate, operational efficiency and methanogenic potential are intricately linked to both initial microbial establishment and the specific electrochemical conditions applied to AD-BES reactors.

Laccase-loaded CaCO3 sustained-release microspheres modified SBES anode for enhance performance in the remediation of soil contaminated with phenanthrene and pyrene

This study aimed to enhance the efficiency of SBES in remediating polycyclic aromatic hydrocarbon (PAH)-contaminated soils by modifying the anode with laccase. The experiment involved four SBES anodes: a carbon nanotube-modified anode (CNT), a free laccase-modified anode (Lac), a gelatin-encapsulated laccase-modified anode (Lac-Gel), and a CaCO3 sustained-release microsphere-loaded laccase-modified (CaCO3-SMs@Laccase) anode (Lac-SMs). The CaCO3-SMs@Laccase notably extended the active period of laccase, with laccase activity in the Lac-SMs measured at 1.646 U/g after 16 days, which was significantly higher than the 0.813 U/g observed in the Lac-Gel group and the 0.206 U/g in the Lac group. The superior electricity generation and degradation efficiency observed in the Lac-SMs group were due to the sustained enzymatic activity provided by the CaCO3-SMs@Laccase. The prevention of anode acidification through CaCO3 decomposition, and promote the forward progress of electrochemical reactions. The phenanthrene (Phe) and pyrene (Pyr) removal efficiency in the soil of the Lac-SMs reached 90.78 % and 84.72 %, surpassing those of the Lac-Gel (80.36 % and 79.14 %), Lac (79.38 % and 69.31 %), and CNT (63.22 % and 56.98 %). The degradation pathway from Pyr to Phe was possible started with hydroxylation. In addition, the laccase also transformed the predominant microbial communities and metabolism pathways.

Effect of Gold Nanoparticles in Microbial Fuel Cells Based on Polypyrrole-Modified Saccharomyces cerevisiae

Microbial fuel cells (MFCs) are a candidate for green energy sources due to microbes' ability to generate charge in their metabolic processes. The main problem in MFCs is slow charge transfer between microorganisms and electrodes. Several methods to improve charge transfer have been used until now: modification of microorganisms by conductive polymers, use of lipophilic mediators, and conductive nanomaterials. We created an MFC with a graphite anode, covering it with 9,10-phenatrenequinone and polypyrrole-modified Saccharomyces cerevisiae with and without 10 nm sphere gold nanoparticles. The MFC was evaluated using cyclic voltammetry and power density measurements. The peak current from cyclic voltammetry measurements increased from 3.76 mA/cm2 to 5.01 mA/cm2 with bare and polypyrrole-modified yeast, respectively. The MFC with polypyrrole- and nanoparticle-modified yeast reached a maximum power density of 150 mW/m2 in PBS with 20 mM Fe(III) and 20 mM glucose, using a load of 10 kΩ. The same MFC with the same load in wastewater reached 179.2 mW/m2. These results suggest that this MFC configuration can be used to improve charge transfer.

Design and Optimization of PEDOT/Graphene Oxide and PEDOT/Reduced Graphene Oxide Electrodes to Improve the Performance of Microbial Fuel Cells, Accompanied by Comprehensive Electrochemical Analysis

A comprehensive investigation into the design and electrochemical optimization of composite electrodes consisting of poly(3,4-ethylenedioxythiophene) (PEDOT)/graphene oxide (GO)/Methanococcus deltae and reduced graphene oxide (rGO)/Methanococcus deltae hybrids, anchored onto stainless-steel (SS) substrates, has been conducted. The GO and rGO materials were synthesized using a modified Hummer method. The resulting SS/PEDOT/GO and SS/PEDOT/rGO composite electrodes were subjected to systematic electrochemical characterization, focusing on the PEDOT p-type and n-type doping/undoping processes within diverse solvent environments (CH3CN and H2O) and electrolyte compositions (LiClO4 and KCl). Raman spectroscopy analysis confirmed the successful integration of graphene derivatives into the electrode structures, while field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) revealed increased surface roughness upon GO and rGO incorporation. This increase in surface roughness is believed to enhance the adhesion of Methanococcus deltae microorganisms and facilitate efficient electron transport. Electrochemical measurements showed that the resulting SS/PEDOT/GO and SS/PEDOT/rGO anodes exhibit remarkable electrocatalytic activity. The SS/PEDOT/GO electrode achieved a maximum power density of 1014.420 mW/cm2, while the SS/PEDOT/rGO electrode reached 632.019 mW/cm2.

Microbial approach towards anode biofilm engineering enhances extracellular electron transfer for bioenergy production

Applying microbial electrolysis cells (MEC) is a biological approach to enhance the growth of high amounts of electroactive biofilm for extracellular electron transfer. The electroactive biofilm degrades the organics by oxidizing them at the anode and producing electrical energy. Addition of waste-activated sludge (WAS) with fat grease oil (FOG) produces an optimal reactor environment for microbial growth to enhance the exchange of electrons between cells via microbial electrolysis. The present work aimed to investigate the microbial approach to increase the extracellular electron transfer (EET) in microbial electrolysis cells. Results revealed that metabolites in electroactive microbes (EAM) grow viable cells that initiate high EET at anode sites. At optimum WAS with FOG addition, volatile fatty acid and current generation yield production was 2.94 ± 0.19 g/L and 17.91 ± 7.23 mA, accompanied by COD removal efficiency of 89.5 ± 14.4%, respectively. This study introduces a novel approach to anode biofilm engineering that significantly enhances extracellular electron transfer, offering a fresh perspective on bioenergy production. Our approach, which demonstrates that anodic biofilm enhances intercellular electron transfer, increases NADH-NAD ratio, and increases metabolite yield-fluxes, has the potential to revolutionize bio-electricity production. Results indicated that the electrolysis highlights MEC performance in power generation of 788 mV with 200 mL of anode volume of active viable cells by utilizing WAS with 11% FOG. The achievements of this study provide critical parameters for the anode biofilm engineering, demonstrating how growth cell volume, intercellular electron transfer, and increases in NADH-NAD ratio are evidence of an increase in the EET, compelling evidence for the resilience treatment and efficient current production. These findings are significant in advancing our understanding of bioenergy production.

Microbial fuel cell in long-term operation and providing electricity for intermittent aeration to remove contaminants from sewage

Microbial fuel cells (MFCs) show promise in sewage treatment because they can directly convert organic matter (OM) into electricity. This study aimed to demonstrate MFCs stability over 750 days of operation and efficient removal of OM and nitrogenous compounds from sewage. To enhance contaminant removal, oxygen was provided into the anode chamber via a mini air pump. This pump was powered by the MFCs' output voltage, which was boosted using a DC-DC converter. The experimental system consisted of 12 sets of cylindrical MFCs within a 246L-scale reactor. The boosted voltage reached 4.7 V. This voltage was first collected in capacitors every 5 min and then dispensed intermittently to the air pump for the MFCs reactor in 4 s. This corresponds to receiving average DO concentration reaching 0.34 ± 0.44 mg/L at 10 cm above the air-stone. Consequently, the degradation rate constants (k) for chemical oxygen demand (COD) and biological oxygen demand (BOD) in the presence of oxygen were 0.048 and 0.069, respectively, which surpassed those without oxygen by 0.039 and 0.044, respectively. Aeration also marginally improved the removal of ammonia because of its potential to create a favorable environment for the growth of anammox and ammonia-oxidizing bacteria such as Candidatus brocadia and Nitrospira. The findings of this study offer in-depth insight into the benefits of boosted voltage in MFCs, highlighting its potential to enhance contaminant degradation. This serves as a foundation for future research focused on improving MFCs performance, particularly for the removal of contaminants from wastewater.

Batch and semi-continuous treatment of cassava wastewater using microbial fuel cells and metataxonomic analysis

The treatment of agroindustrial wastewater using microbial fuel cells (MFCs) is a technological strategy to harness its chemical energy while simultaneously purifying the water. This manuscript investigates the organic load effect as chemical oxygen demand (COD) on the production of electricity during the treatment of cassava wastewater by means of a dual-chamber microbial fuel cell in batch mode. Additionally, specific conditions were selected to evaluate the semi-continuous operational mode. The dynamics of microbial communities on the graphite anode were also investigated. The maximum power density delivered by the batch MFC (656.4 μW m- 2 ) was achieved at the highest evaluated organic load (6.8 g COD L- 1 ). Similarly, the largest COD removal efficiency (61.9%) was reached at the lowest organic load (1.17 g COD L- 1 ). Cyanide degradation percentages (50-70%) were achieved across treatments. The semi-continuous operation of the MFC for 2 months revealed that the voltage across the cell is dependent on the supply or suspension of the organic load feed. The electrode polarization resistance was observed to decreases over time, possibly due to the enrichment of the anode with electrogenic microbial communities. A metataxonomic analysis revealed a significant increase in bacteria from the phylum Firmicutes, primarily of the genus Enterococcus.

Microbial Biofilms: Features of Formation and Potential for Use in Bioelectrochemical Devices

Microbial biofilms present one of the most widespread forms of life on Earth. The formation of microbial communities on various surfaces presents a major challenge in a variety of fields, including medicine, the food industry, shipping, etc. At the same time, this process can also be used for the benefit of humans-in bioremediation, wastewater treatment, and various biotechnological processes. The main direction of using electroactive microbial biofilms is their incorporation into the composition of biosensor and biofuel cells This review examines the fundamental knowledge acquired about the structure and formation of biofilms, the properties they have when used in bioelectrochemical devices, and the characteristics of the formation of these structures on different surfaces. Special attention is given to the potential of applying the latest advances in genetic engineering in order to improve the performance of microbial biofilm-based devices and to regulate the processes that take place within them. Finally, we highlight possible ways of dealing with the drawbacks of using biofilms in the creation of highly efficient biosensors and biofuel cells.

Colony-Based Electrochemistry Reveals Electron Conduction Mechanisms Mediated by Cytochromes and Flavins in Shewanella oneidensis

Bacteria utilize electron conduction in their communities to drive their metabolism, which has led to the development of various environmental technologies, such as electrochemical microbial systems and anaerobic digestion. It is challenging to measure the conductivity among bacterial cells when they hardly form stable biofilms on electrodes. This makes it difficult to identify the biomolecules involved in electron conduction. In the present study, we aimed to identify c-type cytochromes involved in electron conduction in Shewanella oneidensis MR-1 and examine the molecular mechanisms. We established a colony-based bioelectronic system that quantifies bacterial electrical conductivity, without the need for biofilm formation on electrodes. This system enabled the quantification of the conductivity of gene deletion mutants that scarcely form biofilms on electrodes, demonstrating that c-type cytochromes, MtrC and OmcA, are involved in electron conduction. Furthermore, the use of colonies of gene deletion mutants demonstrated that flavins participate in electron conduction by binding to OmcA, providing insight into the electron conduction pathways at the molecular level. Furthermore, phenazine-based electron transfer in Pseudomonas aeruginosa PAO1 and flavin-based electron transfer in Bacillus subtilis 3610 were confirmed, indicating that this colony-based system can be used for various bacteria, including weak electricigens.

Novel Conductive Polymer Composite PEDOT:PSS/Bovine Serum Albumin for Microbial Bioelectrochemical Devices

A novel conductive composite based on PEDOT:PSS, BSA, and Nafion for effective immobilization of acetic acid bacteria on graphite electrodes as part of biosensors and microbial fuel cells has been proposed. It is shown that individual components in the composite do not have a significant negative effect on the catalytic activity of microorganisms during prolonged contact. The values of heterogeneous electron transport constants in the presence of two types of water-soluble mediators were calculated. The use of the composite as part of a microbial biosensor resulted in an electrode operating for more than 140 days. Additional modification of carbon electrodes with nanomaterial allowed to increase the sensitivity to glucose from 1.48 to 2.81 μA × mM-1 × cm-2 without affecting the affinity of bacterial enzyme complexes to the substrate. Cells in the presented composite, as part of a microbial fuel cell based on electrodes from thermally expanded graphite, retained the ability to generate electricity for more than 120 days using glucose solution as well as vegetable extract solutions as carbon sources. The obtained data expand the understanding of the composition of possible matrices for the immobilization of Gluconobacter bacteria and may be useful in the development of biosensors and biofuel cells.

Bioelectricity production from the anodic inoculation of Geobacter sulfurreducens DL-1 bacteria in constructed wetlands-microbial fuel cells

Environmental pollution problems caused by the use of fossil fuels have led to the search for renewable energy sources to mitigate greenhouse gas emissions. In addition, constructed wetlands-microbial fuel cells (CW-MFC) could contribute to sustainable development, considering that this technology focuses on the production of bioelectricity. One of the main challenges of CW-MFCs is to potentiate their bioelectrochemical performance. Therefore, this research used the Geobacter sulfurreducens DL-1 bacterium (biofilm) as a bioelectrocatalyst to increase bioelectricity generation. For this, three bioreactors were built as CW-MFCs, using Juncus effusus root exudates and Philodendron cordatum macrophytes as endogenous substrates. The biofilm was developed in a nutrient broth acetate fumarate and directly inoculated onto the anodes of each CW-MFC. The results of bioelectrochemical analyses showed that the biofilm generated more bioelectricity when it consumed the exudates of the Juncus effusus macrophyte, resulting in a maximum performance of 107 mW/m2 power density, -361 mV anodic potential, 290 mV cathodic potential, and 124 Ω internal resistance, using a concentration of 27.5 mg/L of total organic carbon as an endogenous substrate. The results determined that the quantity of root exudates consumed by the anodic biofilm is directly related to the production of bioelectricity in CW-MFCs.

Investigation of microbial fuel cell performance based on the nickel thin film modified electrodes

Microbial fuel cells (MFCs) are a self-sustaining and environmentally friendly system for the simultaneous was tewater treatment and bioelectricity generation. The type and material of the electrode are critical factors that can influence the efficiency of this treatment process. In this study, graphite plates and carbon felt were modified through the electrodeposition of nickel followed by the formation of a biofilm, resulting in conductive bio-anode thin film electrodes with enhanced power generation capacity. The structural and morphological properties of the electrode surfaces were characterized using X-ray diffraction, energy-dispersive X-ray spectroscopy, elemental mapping, and field-emission scanning electron microscopy techniques. Maximum voltage, current density, and power generation were investigated using a dual-chamber MFC equipped with a Nafion 117 membrane and bio-nickel-doped carbon felt (bio-Ni@CF) and bio-nickel-doped graphite plate (bio-Ni@GP) electrodes under constant temperature conditions. The polarization and power curves obtained using different anode electrodes revealed that the maximum voltage, power and current density achieved with the bio-Ni@CF electrode were 468.0 mV, 130.72 mW/m2 and 760.0 mA/m2 respectively. Moreover, the modified electrodes demonstrated appropriate stability and resistance during successful runs. These results suggest that nickel-doped carbon-based electrodes can serve as suitable and stable supported catalysts and conductors for improving efficiency and increasing power generation in MFCs.

Mechanistic insights into the response of electroactive biofilms to Cd2+ shock: bacterial viability and electron transfer behavior at the cellular and community levels

Electroactive biofilms (EABs) play a crucial role in environmental bioremediation due to their excellent extracellular electron transfer (EET) capabilities. However, Cd2+ can have toxic effects on the electrochemical performance of EABs, and the comprehensive inhibition mechanism of EABs in response to Cd2+ shock remains elusive. This study indicated that Cd2+ shock significantly reduced biomass and increased oxidative stress in EABs at the cellular level. The bacterial viability of EABs in phase III under 0.5 mM Cd2+ shock (EABCd2+-III0.5) decreased by 16.31% compared to EABCK-III. Moreover, intracellular NADH, c-Cyts, and the abundance of electroactive species were essential indicators to evaluate EET behavior of EABs. In EABCd2+-III0.5, these indicators decreased by 26.32%, 33.40%, and 20.65%, respectively. Structural equation modeling analysis established quantitative correlations between core components and electrochemical activity at cellular and community levels. The correlation analysis revealed that the growth and electron transfer functions of EABs were predictive indicators for their electrochemical performance, with standardized path coefficients of 0.407 and 0.358, respectively. These findings enhance our understanding of EABs' response to Cd2+ shock and provide insights for improving their performance in heavy metal wastewater.

Conductive Polymers and Their Nanocomposites: Application Features in Biosensors and Biofuel Cells

Conductive polymers and their composites are excellent materials for coupling biological materials and electrodes in bioelectrochemical systems. It is assumed that their relevance and introduction to the field of bioelectrochemical devices will only grow due to their tunable conductivity, easy modification, and biocompatibility. This review analyzes the main trends and trends in the development of the methodology for the application of conductive polymers and their use in biosensors and biofuel elements, as well as describes their future prospects. Approaches to the synthesis of such materials and the peculiarities of obtaining their nanocomposites are presented. Special emphasis is placed on the features of the interfaces of such materials with biological objects.

Generation of green electricity from sludge using photo-stimulated bacterial consortium as a sustainable technology

Microbial fuel cell (MFC) is a bio-electrical energy generator that uses respiring microbes to transform organic matter present in sludge into electrical energy. The primary goal of this work was to introduce a new approach to the green electricity generation technology. In this context a total of 6 bacterial isolates were recovered from sludge samples collected from El-Sheikh Zayed water purification plant, Egypt, and screened for their electrogenic potential. The most promising isolates were identified according to 16S rRNA sequencing as Escherichia coli and Enterobacter cloacae, promising results were achieved on using them in consortium at optimized values of pH (7.5), temperature (30°C) and substrate (glucose/pyruvate 1%). Low level red laser (λ = 632.8nm, 8mW) was utilized to promote the electrogenic efficiency of the bacterial consortium, maximum growth was attained at 210 sec exposure interval. In an application of adding standard inoculum (107 cfu/mL) of the photo-stimulated bacterial consortium to sludge based MFC a significant increase in the output potential difference values were recorded, the electricity generation was maintained by regular supply of external substrate. These results demonstrate the future development of the dual role of MFCs in renewable energy production and sludge recycling.

Electroactive Bacteria in Natural Ecosystems and Their Applications in Microbial Fuel Cells for Bioremediation: A Review

Electroactive bacteria (EAB) are natural microorganisms (mainly Bacteria and Archaea) living in various habitats (e.g., water, soil, sediment), including extreme ones, which can interact electrically each other and/or with their extracellular environments. There has been an increased interest in recent years in EAB because they can generate an electrical current in microbial fuel cells (MFCs). MFCs rely on microorganisms able to oxidize organic matter and transfer electrons to an anode. The latter electrons flow, through an external circuit, to a cathode where they react with protons and oxygen. Any source of biodegradable organic matter can be used by EAB for power generation. The plasticity of electroactive bacteria in exploiting different carbon sources makes MFCs a green technology for renewable bioelectricity generation from wastewater rich in organic carbon. This paper reports the most recent applications of this promising technology for water, wastewater, soil, and sediment recovery. The performance of MFCs in terms of electrical measurements (e.g., electric power), the extracellular electron transfer mechanisms by EAB, and MFC studies aimed at heavy metal and organic contaminant bioremediationF are all described and discussed.