Effect of anodic pH microenvironment on microbial fuel cell (MFC) performance in concurrence with aerated and ferricyanide catholytes

Scale-up single chamber of microbial fuel cell using agitator and sponge biocarriers

Despite the high efficiency of microbial fuel cells (MFCs), MFCs cannot be a suitable alternative for treatment plants because of insufficient power generation and tiny reactors. Additionally, the increased reactor size and MFC stack result in a reduction in production power and reverse voltage. In this study, a larger MFC with a volume of 1.5 L has been designed called LMFC. A conventional MFC, called SMFC, with a volume of 0.157 L, was constructed and compared with LMFC. Moreover, the designed LMFC can be integrated with other treatment systems and generate significant electricity. In order to evaluate MFC's ability to integrate with other treatment systems, the LMFC reactor was converted into MFC-MBBR by adding sponge biocarriers. A 9.5 percent increase in reactor volume resulted in a 60 percent increase in power density from 290 (SMFC) to 530 (LMFC). An agitator effect was also investigated for better mixing and circulating substrate, which positively affected the power density by about 18%. Compared with LMFCs, the reactor with biocarriers generated a 28% higher power density. The COD removal efficiency of SMFC, LMFC, and MFC-MBBR reactors after 24 h was 85, 66, and 83%, respectively. After 80 h of operation, the Coulombic efficiency of the SMFC, LMFC, and MFC-MBBR reactors was 20.9, 45.43, and 47.28%, respectively. The doubling of coulombic efficiency from SMFC to LMFC reactor shows the design's success. The reduction of COD removal efficiency in LMFC is the reason for integrating this reactor with other systems, which was compensated by adding biocarriers.

Synergistic effect of TiO2 nanostructured cathode in microbial fuel cell for bioelectricity enhancement

Nano-bedecking of electrode with nanoparticles is an effective method to improve power generation of microbial fuel cells (MFCs). In this study, different concentrations (0.25 mg cm^-2, 0.50 mg cm^-2, 0.75 mg cm^-2 and 1.0 mg cm^-2) of TiO₂ nanoparticles of size 10-25 nm were overlaid on the carbon cloth (CC) using spray pyrolysis technique and used as catalytic cathode in a dual-chambered microbial fuel cell treating distillery wastewater. Results evidenced that TiO₂ nanoparticles modified cathode increased the power generation and recorded a highest power and current density of 162.5 ± 2 mW m^-2 and 1.4 ± 0.005 A m^-2, respectively. Carbon cloth coated with 0.50 mg cm^-2 TiO₂ nanoparticles showed 2.8 and 7.3 times higher current and power density as compared to uncoated cathode. MFC operated at a hydraulic retention time (HRT) and organic loading rate (OLR) of 72 h and 59.2 g COD L^-1 d^-1 showed a maximum chemical oxygen demand (COD) removal of 72.3% which was 15.3% higher than the control MFC. Likewise, the coulombic efficiency of control and modified MFC was 33% and 44%, respectively. The maximum NO₃^-- N, NO₂^-- N and NH₄⁺- N removal efficiency of 77.3%, 49.9% and 59.4% were observed for TiO₂ nanoparticles modified electrode which was 19.3%, 11.4% and 10.5% higher than control. TiO₂ modified cathode was effective in enhancing the bioelectricity generation in MFCs.

Microbial Fuel Cell Construction Features and Application for Sustainable Wastewater Treatment

A microbial fuel cell (MFC) is a system that can generate electricity by harnessing microorganisms' metabolic activity. MFCs can be used in wastewater treatment plants since they can convert the organic matter in wastewater into electricity while also removing pollutants. The microorganisms in the anode electrode oxidize the organic matter, breaking down pollutants and generating electrons that flow through an electrical circuit to the cathode compartment. This process also generates clean water as a byproduct, which can be reused or released back into the environment. MFCs offer a more energy-efficient alternative to traditional wastewater treatment plants, as they can generate electricity from the organic matter in wastewater, offsetting the energy needs of the treatment plants. The energy requirements of conventional wastewater treatment plants can add to the overall cost of the treatment process and contribute to greenhouse gas emissions. MFCs in wastewater treatment plants can increase sustainability in wastewater treatment processes by increasing energy efficiency and reducing operational cost and greenhouse gas emissions. However, the build-up to the commercial-scale still needs a lot of study, as MFC research is still in its early stages. This study thoroughly describes the principles underlying MFCs, including their fundamental structure and types, construction materials and membrane, working mechanism, and significant process elements influencing their effectiveness in the workplace. The application of this technology in sustainable wastewater treatment, as well as the challenges involved in its widespread adoption, are discussed in this study.

Investigation of electrochemical properties, leachate purification, organic matter characteristics, and microbial diversity in a sludge treatment wetland- microbial fuel cell

Sludge treatment wetland-microbial fuel cell (STW-MFC) is a unique sludge treatment process that produces bioelectricity, but its technology is still in its infancy. This study investigated the electrochemical properties, organic matter characteristics, leachate purification, and microbial community structure of STW-MFCs as affected by electrode location. When electrodes were placed in the filler layer, the STW-MFC system presented a higher power generation capacity (maximum output power density: 0.498 W/m³; peak cell voltage: 0.879 V) and organic matter degradation efficiency. The hydrophilic fraction was the main dissolved organic carbon fraction in sludge extracellular biological organic matter (EBOM) and leachate dissolved organic matter (DOM). Aromatics were mainly concentrated in the hydrophobic acid fraction. The UV-254 content of sludge EBOM decreased mainly in the hydrophilic and transphilic acid fractions. The excitation-emission matrix analysis showed that tryptophan-like protein was more easily eliminated than tyrosine-like protein. In addition, there was a strong correlation between voltage and NH₄⁺ removal efficiency; a negative correlation between total chemical oxygen demand (TCOD), total nitrogen (TN), and total phosphorus (TP) removal efficiency, and a negative correlation between pH and TN, TP, and NH₄⁺ removal efficiencies. High-throughput sequencing showed that the system was most abundant in Thermomonas, Geothrix and Geobacter when the electrodes were placed in the filled layer, while the levels of genes for membrane transport, carbohydrate metabolism and energy metabolism functions were higher than in other systems. This work will support STW- MFC widespread implementation by illuminating the underlying mechanics of different anode positions.

Rice husk-derived silicon nanostructured anode to enhance power generation in microbial fuel cell treating distillery wastewater

The present study aims to utilize rice husk as a source of silica to prepare rice husk derived silicon nanoparticles (RH-Si) and demonstrate its ability as an anode modifier in a two-chambered H-shaped microbial fuel cell (MFC). The silicon nanoparticles synthesized by magnesiothermal reduction process were spherical in shape and ranged in size from 15 to 60 nm. The anode modified with silicon nanoparticles of 0.50 mg cm^-2 recorded the maximum power and current density of 190.5 mW m^-2 and 1.5 A m^-2 corresponding to 7.6-fold and 3-fold increase as compared to the control . The modified anode also recorded a COD removal and coulombic efficiency of 74% and 49%, respectively in MFC operated with combined distillery and domestic wastewater at a HRT and OLR of 72 h and 59.2 gCOD L^-1 d^-1, respectively. The results evidence that RH derived silicon NPs are good anode modifiers and effective in enhancing bioelectricity generation and COD removal in MFCs.

An electricity-generating bacterium separated from oil sludge microbial fuel cells and its environmental adaptability

Electricity-generating bacteria as biocatalysts for microbial fuel cells (MFCs), their species, and power generation performance determine the pollution control and power generation performance of MFCs. And there are few studies on the types and performance of electricity-generating bacteria isolated from oily sludge microbial fuel cells. For improving the power generation performance of oily sludge MFCs, an electricity-generating bacterium was isolated from the oily sludge. More importantly, the adaptability of nitrogen to phosphorus ratio, temperature, and pH of the electricity-generating bacteria were adjusted by a controlled variable method. The results of this study showed that the electricity-generating bacterium was identified as Bacillus cereus, with a rod-shaped cell, about 0.5-1.0 μm in length. The optimal nitrogen-phosphorus ratio, temperature, and pH of MFCs were 4.67:1, 25 ℃, and pH = 7, respectively. Its maximum power density, COD, and oil removal rate was up to 65 mW·m^-3, 90.51%, and 87.76%, respectively. The study of this functional bacterium will provide beneficial assistance for the improvement of oil removal and power generation performance of oily sludge MFCs.

Increasing power generation to a single-chamber compost soil urea fuel cell for carbon-neutral bioelectricity generation: A novel approach

Microbial fuel cells (CS-UFC) utilize waste resources containing biodegradable materials that play an essential role in green energy. MFC technology generates "carbon-neutral" bioelectricity and involves a multidisciplinary approach to microbiology. MFCs will play an important role in the harvesting of "green electricity." In this study, a single-chamber urea fuel cell is fabricated that uses these different wastewaters as fuel to generate power. Soil has been used to generate electrical power in microbial fuel cells and exhibited several potential applications to optimize the device; the urea fuel concentration is varied from 0.1 to 0.5 g/mL in a single-chamber compost soil urea fuel cell (CS-UFC). The proposed CS-UFC has a high power density and is suitable for cleaning chemical waste, such as urea, as it generates power by consuming urea-rich waste as fuel. The CS-UFC generates 12 times higher power than conventional fuel cells and exhibits size-dependent behavior. The power generation increases with a shift from the coin cell toward the bulk size. The power density of the CS-UFC is 55.26 mW/m². This result confirmed that urea fuel significantly affects the power generation of single-chamber CS-UFC. This study aimed to reveal the effect of soil properties on the generated electric power from soil processes using waste, such as urea, urine, and industrial-rich wastewater as fuel. The proposed system is suitable for cleaning chemical waste; moreover, the proposed CS-UFC is a novel, sustainable, cheap, and eco-friendly design system for soil-based bulk-type design for large-scale urea fuel cell applications.

Nitrogen Removal from the High Nitrate Content Saline Denitration Solution of a Coal-Fired Power Plant by MFC

Oxidation denitration is one of the most efficient ways to remove NOx from flue gas in a coal-fired power plant. However, this oxidation denitration produces saline solution containing a high concentration of nitrate, which needs to be well treated. In this paper, MFC was firstly used to treat the high nitrate content saline denitration solution from ozone oxidation denitration of a coal-fired power plant. The influences of chemical oxygen demand (COD) and initial nitrate concentration on the nitrate removal and electricity generation of MFC were investigated by sequencing batch mode. The results showed that using MFCs could efficiently remove nitrate from coal-fired power plant saline denitration solution with nitrate nitrogen (NO3−-N) concentration up to 1510 mg/L. The average nitrate nitrogen removal rate was as high as 248.3 mg/(L·h) at initial nitrate nitrogen concentration of 745 mg/L and COD concentration of 6.5 g/L, which was eight times as high as that of the conventional biological method. Furthermore, the MFC required an average COD consumption of 3.42 g/g-NO3−-N which was lower than most of the conventional biological methods. In addition, MFC could produce a maximum power density of 241.1 mW/m2 while treating this saline denitration solution.

Electrical generation and methane emission from an anoxic riverine sediment slurry treated by a two-chamber microbial fuel cell

A two-chamber slurry microbial fuel cell (SMFC) was constructed using black-odorous river sediments as substrate for the anode. We tested addition of potassium ferricyanide (K₃[Fe(CN)₆]) or sodium chloride (NaCl) to the cathode chamber (0, 50, 100, 150, and 200 mM) and aeration of the cathode chamber (0, 2, 4, 6, and 8 h per day) to assess their response on electrical generation, internal resistance, and methane emission over a 600-h period. When the aeration time in the cathode chamber was 6 h and K₃[Fe(CN)₆] or NaCl concentrations were 200 mM, the highest power densities were 6.00, 6.45, and 6.64 mW·m^-2, respectively. With increasing K₃[Fe(CN)₆] or NaCl concentration in the cathode chamber, methane emission progressively decreased (mean ± SD: 181.6 ± 10.9 → 75.5 ± 9.8 mg/m³·h and 428.0 ± 28.5 → 157.0 ± 35.7 mg/m³·h), respectively, but was higher than the reference having no cathode/anode electrodes (~ 30 mg/m³·h). Cathode aeration (0 → 8 h/day) demonstrated a reduction in methane emission from the anode chamber for only the 6-h treatment (mean: 349.6 ± 37.4 versus 299.4 ± 34.7 mg/m³·h for 6 h/day treatment); methane emission from the reference was much lower (85.3 ± 26.1 mg/m³·h). Our results demonstrate that adding an electron acceptor (K₃[Fe(CN)₆]), electrolyte solution (NaCl), and aeration to the cathode chamber can appreciably improve electrical generation efficiency from the MFC. Notably, electrical generation stimulates methane emission, but methane emission decreases at higher power densities.

The reduction and fate of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in microbial fuel cell (MFC) during treatment of livestock wastewater

The fate and removal efficiency of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in livestock wastewater by microbial fuel cell (MFC) was evaluated by High-throughput quantitative PCR. The results showed that 137 ARGs and 9 MGEs were detected in untreated livestock wastewater. The ARG number of macrolide-lincosamide-streptogramin group B (MLSB), tetracycline and sulfonamide were relatively higher. Throughout the treatment process, the number and abundance of ARGs and MGEs significantly decreased. The relative abundance of tetracycline, sulfonamide and chloramphenicol resistance genes showed the most obvious decreasing trend, and the relative abundance of MGEs decreased by 75% (from 0.012 copies/16S rRNA copies to 0.003 copies/16S rRNA copies). However, the absolute abundance of beta-lactamase resistance genes slightly increased. The operation process of MFC produces selective pressure on microorganisms, and Actinobacteria were predominant and had the ability to decompose antibiotics. The COD removal rate and TN removal rate of livestock wastewater were 67.81% and 62.09%, and the maximum power density and coulomb efficiency (CE) reached 11.49% and 38.40% respectively. This study demonstrated that although the removal of COD and TN by MFC was limited, MFC was quite effective in reducing the risk of antibiotic toxicity and horizontal gene transfer.

Enhanced bioelectrochemical performance of microbial fuel cell with titanium dioxide-attached dual metal organic frameworks grown on zinc aluminum - layered double hydroxide as cathode catalyst

In this study, a three-step distributed feeding method was used to prepare TiO₂-attached dual CoZn-metal organic frameworks growing on ZnAl-layered double hydroxide (TiO₂@ZIF-67/ZIF-8@ZnAl-LDH) as cathode catalyst of microbial fuel cell (MFC). The composite material was a composite core-shell structure constructed by multi-layer coating with sheet-like ZnAl-LDH as the base, dual MOFs as the magnetic core and TiO₂ as the rough surface. The composite material had crystal planes (009), (110), (101) interface. The rough surface, core-shell core and polyhedral structure of TiO₂@ZIF-67/ZIF-8@ZnAl-LDH were observed. The complete distribution of Ti, Zn, Al, and Co in the material was observed and offered active sites. The contents of Ti (15.97 %), Al (5.53 %), Na (5.04 %), N (3.52%), Zn (1.47 %) were found out. TiO₂@ZIF-67/ZIF-8@ZnAl-LDH was excellent in electrochemical activity and the maximum power density was 409.6 mW/m², the stable continuous output voltage was 538.4 mV for 8 d.

Microbial peroxide producing cell mediated lignin valorization

Lignin is one of the most abundant naturally occurring polymers and can produce value-added products such as vanillin and p-coumaric acid. In the current work, in-situ depolymerization of lignin for its valorization in a microbial peroxide-producing cell (MPPC) system was performed. It is an electrochemical cell that requires no external energy to produce H₂O₂ for the advanced oxidation process. Lignin in the MPPC system undergoes oxidative depolymerization to generate value-added products. The maximum open-circuit voltage (OCV) was 1.143 V, the current density and power densities were 14 mA/cm² and 13 mW/cm², respectively, along with the production of 26 mM of H₂O₂. The degradation of signature linkages such as β-β bond and β-0-4 bond were analyzed and confirmed using FTIR spectroscopy. Vanillin, p-coumaric acid, ferulic acid, etc. were generated during depolymerization and were detected using LC-QTOF-MS.

Effect of starch-derived organic acids on the removal of polycyclic aromatic hydrocarbons in an aquaculture-sediment microbial fuel cell

This study constructed sediment microbial fuel cells (SMFCs) for polycyclic aromatic hydrocarbons (PAHs) removal in contaminated aquaculture sediment. Starch, a waste deposited in aquaculture sediment, was employed as the co-substrate for electricity generation and PAHs removal, and the effect of starch-derived organic acids on SMFC performance was assessed. The results indicated that sufficient starch promoted PAHs removal (69.9% for naphthalene, 55.6% for acenaphthene, and 46.8% for pyrene) in dual-chamber SMFC, whereas excessive starch attenuated SMFC performance because the organic acids accumulation reduced anode pH, decreased species diversity, and changed the microbial communities. The electricity generation and PAHs removal were positively correlated (R > 0.96), and both of them were related to Macellibacteroides belonging to Bacteroidetes. However, a larger single-chamber SMFC device did not obtain enhanced PAHs removal owing to the restricted "effective range" of the anode. Hence, more challenges need to be addressed to realize the practical application of SMFC.

Bio-electrochemical frameworks governing microbial fuel cell performance: technical bottlenecks and proposed solutions

Microbial fuel cells (MFCs) are recognized as a future technology with a unique ability to exploit metabolic activities of living microorganisms for simultaneous conversion of chemical energy into electrical energy. This technology holds the promise to offer sustained innovations and continuous development towards many different applications and value-added production that extends beyond electricity generation, such as water desalination, wastewater treatment, heavy metal removal, bio-hydrogen production, volatile fatty acid production and biosensors. Despite these advantages, MFCs still face technical challenges in terms of low power and current density, limiting their use to powering only small-scale devices. Description of some of these challenges and their proposed solutions is demanded if MFCs are applied on a large or commercial scale. On the other hand, the slow oxygen reduction process (ORR) in the cathodic compartment is a major roadblock in the commercialization of fuel cells for energy conversion. Thus, the scope of this review article addresses the main technical challenges of MFC operation and provides different practical approaches based on different attempts reported over the years.

Sustainable operation requires addressing key MFC-bottleneck issues. Enhancing extracellular electron transfer is the key to elevated MFC performance.

Socio-Economic and Environmental Impacts of Biomass Valorisation: A Strategic Drive for Sustainable Bioeconomy

In the late twentieth century, the only cost-effective opportunity for waste removal cost at least several thousand dollars, but nowadays, a lot of improvement has occurred. The biomass and waste generation problems attracted concerned authorities to identify and provide environmentally friendly sustainable solutions that possess environmental and economic benefits. The present study emphasises the valorisation of biomass and waste produced by domestic and industrial sectors. Therefore, substantial research is ongoing to replace the traditional treatment methods that potentially acquire less detrimental effects. Synthetic biology can be a unique platform that invites all the relevant characters for designing and assembling an efficient program that could be useful to handle the increasing threat for human beings. In the future, these engineered methods will not only revolutionise our lives but practically lead us to get cheaper biofuels, producing bioenergy, pharmaceutics, and various biochemicals. The bioaugmentation approach concomitant with microbial fuel cells (MFC) is an example that is used to produce electricity from municipal waste, which is directly associated with the loading of waste. Beyond the traditional opportunities, herein, we have spotlighted the new advances in pertinent technology closely related to production and reduction approaches. Various integrated modern techniques and aspects related to the industrial sector are also discussed with suitable examples, including green energy and other industrially relevant products. However, many problems persist in present-day technology that requires essential efforts to handle thoroughly because significant valorisation of biomass and waste involves integrated methods for timely detection, classification, and separation. We reviewed and proposed the anticipated dispensation methods to overcome the growing stream of biomass and waste at a distinct and organisational scale.

The influential role of external electrical load in microbial fuel cells and related improvement strategies: A review

The scope of the currentreviewis to discuss and evaluate the role of the external electrical load/resistor (EEL) on the overall behavior and functional properties of microbial fuel cells (MFCs). In this work, a comprehensive analysis is made by considering various levels of MFC architecture, such as electric and energy harvesting efficiency, anode electrode potential shifts, electro-active biofilm formation, cell metabolism and extracellular electron transfer mechanisms, as a function of the EEL and its control strategies. It is outlined that taking the regulation of EEL into account at MFC optimization is highly beneficial, and in order to support this step, in this review, a variety of guidelines are collected and analyzed.

Effect of heterotrophic anodic denitrification on anolyte pH control and bioelectricity generation enhancement of bufferless microbial fuel cells

Heterotrophic anodic denitrification (HAD) in the single-chamber microbial fuel cell (MFC) is a promising nitrogen removal technology. In this paper, the benefit (anolyte pH increase) and challenge (substrate consumption) brought by the heterotrophic anodic denitrification process for the electricity generation of bufferless MFCs were studied for the first time. Substrate anaerobic hydrolysis dramatically decreased the anolyte pH to 5.1, which seriously restricted the electric power output of the Control. The anolyte pH of the heterotrophic anodic denitrification MFCs (HADMFCs) with 60 mg/L (HADMFC-60), 90 mg/L (HADMFC-90), and 120 mg/L (HADMFC-120) nitrate nitrogen (NO₃^--N), retained above 6.0, 6.5, and 6.8 in every running cycles, due to the protons (H⁺) consumption by nitrate reduction. In the HADMFC-60 and HADMFC-90, 17.6% and 26.1% of the total organic carbons (TOC) were used for the nitrate reduction, but their electric power output significantly increased. The maximum power densities of the HADMFC-60 and HADMFC-90 were 3.3 and 5.4 times higher than that of the Control. However, when the proportion of TOC consumption for nitrate reduction increased to 35.8%, substrate insufficiency became a serious limitation for the electricity generation. The P_max of the HADMFC-120 dramatically decreased to 17.3 mW/m². Dysgonomonas was the dominant electro-active genus, and Petrimonas, Acidovorax and Devosia appeared as the denitrifying bacteria genera.

Investigating the specific role of external load on the performance versus stability trade-off in microbial fuel cells

The performance and behavior of microbial fuel cells (MFCs) are influenced by among others the external load (R_ext). In this study, the anode-surface biofilm formation in MFCs operated under different R_ext selection/tracking-strategies was assessed. MFCs were characterized by electrochemical (voltage/current generation, polarization tests, EIS), molecular biological (microbial consortium analysis) and bioinformatics (principal component analysis) tools. The results indicated that the MFC with dynamic R_ext adjustment (as a function of the actual MFC internal resistance) achieved notably higher performance but relatively lower operational stability, mainly due to the acidification of the biofilm. The opposite (lower performance, increased stability) could be observed with the static (low or high) R_ext application (or OCV) strategies, where adaptive microbial processes were assumed. These possible adaptation phenomena were outlined by a theoretical framework and the significant impact of R_ext on the anode colonization process and energy recovery with MFCs was concluded.

Electrogenic Biofilm Development Determines Charge Accumulation and Resistance to pH Perturbation

The electrogenic biofilm and the bio-electrode interface are the key biocatalytic components in bioelectrochemical systems (BES) and can have a large impact on cell performance. This study used four different anodic carbons to investigate electrogenic biofilm development to determine the influence of charge accumulation and biofilm growth on system performance and how biofilm structure may mitigate against pH perturbations. Power production was highest (1.40 W/m3) using carbon felt, but significant power was also produced when felt carbon was open-circuit acclimated in a control reactor (0.95 W/m3). The influence of carbon material on electrogenic biofilm development was determined by measuring the level of biofilm growth, using sequencing to identify the microbial populations and confocal microscopy to understand the spatial locations of key microbial groups. Geobacter spp. were found to be enriched in closed-circuit operation and these were in close association with the carbon anode, but these were not observed in the open-circuit controls. Electrochemical analysis also demonstrated that the highest mid-point anode potentials were close to values reported for cytochromes from Geobacter sulfurreductans. Biofilm development was greatest in felt anodes (closed-circuit acclimated 1209 ng/μL DNA), and this facilitated the highest pseudo-capacitive values due to the presence of redox-active species, and this was associated with higher levels of power production and also served to mitigate against the effects of low-pH operation. Supporting carbon anode structures are key to electrogenic biofilm development and associated system performance and are also capable of protecting electrochemically active bacteria from the effects of environmental perturbations.

Microbial fuel cell-based biosensor for online monitoring wastewater quality: A critical review

Recently, the application of the microbial fuel cell (MFC)-based biosensor for rapid and real-time monitoring wastewater quality is very innovative due to its simple compact design, disposability, and cost-effectiveness. This review represents recent advances in this emerging technology for the management of wastewater quality, where the emphasis is on biochemical oxygen demand, toxicity, and other environmental applications. In addition, the main challenges of this technology are discussed, followed by proposing possible solutions to those challenges based on the existing knowledge of detection principles and signal processing. Potential future research of MFC-based biosensor has been demonstrated in this review.

Performance evaluation of treating oil-containing restaurant wastewater in microbial fuel cell using in situ graphene/polyaniline modified titanium oxide anode

Most studies conducted nowadays to boost electrode performance in microbial fuel cell (MFC) have focused on carbonaceous materials. The titanium suboxides (Ti₄O₇, TS) are able to provide a new alternative for achieving better performance in MFC and have been tested and demonstrated in this study. The Ti₄O₇ electrode with high electrochemical activity was modified by graphene/polyaniline by the constant potential method. Electrogenic microorganisms were more conducive to adhere to the anode electrode due to the presence of graphene/polyaniline. The MFC reactor with polyaniline /graphene modified TS (TSGP) anode achieves the highest voltage with 980 mV, and produces a peak power density of 2073 mW/m², which is 2.9 and 12.7 times of those with the carbon cloth anode, respectively, at the 1000 Ω external resistance. In addition, this study evaluates the effects of anolyte conductivity, pH, and COD on the treatment of oil-containing restaurant wastewater (OCRW) in MFC using TSGP anode. The OCRW amended with 120 mS/cm obtains the lowest internal resistance (160.3 Ω). Increasing the anodic pH, gradually from acidic (pH 5.5) to alkaline conditions (pH 8.0), resulted in a gradual increase in maximum power density to 576.4 mW/m² and a decrease in internal cell resistance to 203.7 Ω. The MFC at the COD 1500 mg/L could obtain steady-state output voltage during 103 h while removing up to 65.2% of the COD of the OCRW.

Strategies for improving the electroactivity and specific metabolic functionality of microorganisms for various microbial electrochemical technologies

Electroactive microorganisms, which possess extracellular electron transfer (EET) capabilities, are the basis of microbial electrochemical technologies (METs) such as microbial fuel and electrolysis cells. These are considered for several applications ranging from the energy-efficient treatment of waste streams to the production of value-added chemicals and fuels, bioremediation, and biosensing. Various aspects related to the microorganisms, electrodes, separators, reactor design, and operational or process parameters influence the overall functioning of METs. The most fundamental and critical performance-determining factor is, however, the microorganism-electrode interactions. Modification of the electrode surfaces and microorganisms for optimizing their interactions has therefore been the major MET research focus area over the last decade. In the case of microorganisms, primarily their EET mechanisms and efficiencies along with the biofilm formation capabilities, collectively considered as microbial electroactivity, affect their interactions with the electrodes. In addition to electroactivity, the specific metabolic or biochemical functionality of microorganisms is equally crucial to the target MET application. In this article, we present the major strategies that are used to enhance the electroactivity and specific functionality of microorganisms pertaining to both anodic and cathodic processes of METs. These include simple physical methods based on the use of heat and magnetic field along with chemical, electrochemical, and growth media amendment approaches to the complex procedure-based microbial bioaugmentation, co-culture, and cell immobilization or entrapment, and advanced toolkit-based biofilm engineering, genetic modifications, and synthetic biology strategies. We further discuss the applicability and limitations of these strategies and possible future research directions for advancing the highly promising microbial electrochemistry-driven biotechnology.

Behavior of two-chamber microbial electrochemical systems started-up with different ion-exchange membrane separators

In this study, microbial fuel cells (MFCs) - operated with novel cation- and anion-exchange membranes, in particular AN-VPA 60 (CEM) and PSEBS DABCO (AEM) - were assessed comparatively with Nafion proton exchange membrane (PEM). The process characterization involved versatile electrochemical (polarization, electrochemical impedance spectroscopy - EIS, cyclic voltammetry - CV) and biological (microbial structure analysis) methods in order to reveal the influence of membrane-type during start-up. In fact, the use of AEM led to 2-5 times higher energy yields than CEM and PEM and the lowest MFC internal resistance (148 ± 17 Ω) by the end of start-up. Regardless of the membrane-type, Geobacter was dominantly enriched on all anodes. Besides, CV and EIS measurements implied higher anode surface coverage of redox compounds for MFCs and lower membrane resistance with AEM, respectively. As a result, AEM based on PSEBS DABCO could be found as a promising material to substitute Nafion.

Factors Affecting the Effectiveness of Bioelectrochemical System Applications: Data Synthesis and Meta-Analysis

Microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) are promising bioelectrochemical systems (BESs) for simultaneous wastewater treatment and energy/resource recovery. Unlike conventional fuel cells that are based on stable chemical reactions, these BESs are sensitive to environmental and operating conditions, such as temperature, pH, external resistance, etc. Substrate type, electrode material, and reactor configuration are also important factors affecting power generation in MFCs and hydrogen production in MECs. In order to discuss the influence of these above factors on the performance of MFCs and MECs, this study analyzes published data via data synthesis and meta-analysis. The results revealed that domestic wastewater would be more suitable for treatment using MFCs or MECs, due to their lower toxicity for anode biofilms compared to swine wastewater and landfill leachate. The optimal temperature was 25–35 °C, optimal pH was 6–7, and optimal external resistance was 100–1000 Ω. Although systems using carbon cloth as the electrodes demonstrated better performance (due to carbon cloth’s large surface area for microbial growth), the high prices of this material and other existing carbonaceous materials make it inappropriate for practical applications. To scale up and commercialize MFCs and MECs in the future, enhanced system performance and stability are needed, and could be possibly achieved with improved system designs.

Novel Applications of Microbial Fuel Cells in Sensors and Biosensors

A microbial fuel cell (MFC) is a type of bio-electrochemical system with novel features, such as electricity generation, wastewater treatment, and biosensor applications. In recent years, progressive trends in MFC research on its chemical, electrochemical, and microbiological aspects has resulted in its noticeable applications in the field of sensing. This review was consequently aimed to provide an overview of the most interesting new applications of MFCs in sensors, such as providing the required electrical current and power for remote sensors (energy supply device for sensors) and detection of pollutants, biochemical oxygen demand (BOD), and specific DNA strands by MFCs without an external analytical device (self-powered biosensors). Moreover, in this review, procedures of MFC operation as a power supply for pH, temperature, and organic loading rate (OLR) sensors, and also self-powered biosensors of toxicity, pollutants, and BOD have been discussed.

Microbial fuel cells as an alternative energy source: current status

Microbial fuel cell (MFC) technology is an emerging area for alternative renewable energy generation and it offers additional opportunities for environmental bioremediation. Recent scientific studies have focused on MFC reactor design as well as reactor operations to increase energy output. The advancement in alternative MFC models and their performance in recent years reflect the interests of scientific community to exploit this technology for wider practical applications and environmental benefit. This is reflected in the diversity of the substrates available for use in MFCs at an economically viable level. This review provides an overview of the commonly used MFC designs and materials along with the basic operating parameters that have been developed in recent years. Still, many limitations and challenges exist for MFC development that needs to be further addressed to make them economically feasible for general use. These include continued improvements in fuel cell design and efficiency as well scale-up with economically practical applications tailored to local needs.

Stacking of microbial fuel cells with continuous mode operation for higher bioelectrogenic activity

The effect of stacking multiple microbial fuel cells for stable power output was evaluated in continuous mode operation. Three single chambered air cathode CMFCs with Nafion (CMFC_N), Terry cotton (CMFC_T) as membranes and one without membrane (CMFC_ML) were operated in continuous mode. Maximum power density (PD) and COD removal efficiency was obtained for CMFC_N (0.1 W/m², 50%) followed by CMFC_ML (0.062 W/m², 47%) and CMFC_T (0.025 W/m², 39%) and were stable throughout the operation. To increase the power output further, stacking of CMFCs was carried in series/parallel circuitry, which yielded high power density in parallel (2.0 W/m²; 7.2 W/m³) and high voltage in series (1.1 V). Study also evidenced that stacking resulted in high and stable bioelectricity by minimizing the electron losses in comparison to individual CMFCs operation. Stable and high power output signifies the impact of continuous mode operation that constantlty replenishes the substrate.

Bioelectrochemical methane (CH4) production in anaerobic digestion at different supplemental voltages

Microbial electrolysis cells (MECs) at various cell voltages (0.5, 0.7 1.0 and 1.5V) were operated in anaerobic fermentation. During the start-up period, the cathode potential decreased from -0.63 to -1.01V, and CH₄ generation increased from 168 to 199ml. At an applied voltage of 1.0V, the highest methane yields of 408.3ml CH₄/g COD glucose was obtained, which was 30.3% higher than in the control tests (313.4ml CH₄/g COD glucose). The average current of 5.1mA was generated at 1.0V at which the maximum methane yield was obtained. The other average currents were 1.42, 3.02, 0.53mA at 0.5, 0.7, and 1.5V, respectively. Cyclic voltammetry and EIS analysis revealed that enhanced reduction currents were present at all cell voltages with biocatalyzed cathode electrodes (no reduction without biofilm), and the highest value was obtained with 1V external voltage.

Microbial fuel cell-photoelectrocatalytic cell combined system for the removal of azo dye wastewater

In this study, a novel parallel circuit microbial fuel cell-photoelectrocatalytic cell (MFC-PEC) combined system was established to enhance azo dye removal. Results showed that this system had synergistic effects compared with the MFC alone. In the MFC part, a 56% decrease in chemical oxygen demand (COD) and 85% decolorization were achieved, and further reduced by 25% and 12% in the PEC part where titania nanotube functioned as the photoelectrode. For one thing, the PEC raised the maximum current of the MFC by 14.2%, which facilitated COD removal and decolorization in the MFC and promoted adenosine triphosphate (ATP) level of anode microorganisms, for another, this system significantly increased the dye removal in the PEC. Besides, cyclic voltammograms illustrated intermediate products degradation in this system. Hence, the system achieved marked deep decolorization and rapid toxic intermediate products degradation of high concentration azo dyes.

A comprehensive overview on electro-active biofilms, role of exo-electrogens and their microbial niches in microbial fuel cells (MFCs)

Microbial fuel cells (MFCs) are biocatalyzed systems which can drive electrical energy by directly converting chemical energy using microbial biocatalyst and are considered as one of the important propitious technologies for sustainable energy production. Much research on MFCs experiments is under way with great potential to become an alternative to produce clean energy from renewable waste. MFCs have been one of the most promising technologies for generating clean energy industry in the future. This article summarizes the important findings in electro-active biofilm formation and the role of exo-electrogens in electron transfer in MFCs. This study provides and brings special attention on the effects of various operating and biological parameters on the biofilm formation in MFCs. In addition, it also highlights the significance of different molecular techniques used in the microbial community analysis of electro-active biofilm. It reviews the challenges as well as the emerging opportunities required to develop MFCs at commercial level, electro-active biofilms and to understand potential application of microbiological niches are also depicted. Thus, this review is believed to widen the efforts towards the development of electro-active biofilm and will provide the research directions to overcome energy and environmental challenges.

Single chamber microbial fuel cell (SCMFC) with a cathodic microalgal biofilm: A preliminary assessment of the generation of bioelectricity and biodegradation of real dye textile wastewater

An air exposed single-chamber microbial fuel cell (SCMFC) using microalgal biocathodes was designed. The reactors were tested for the simultaneous biodegradation of real dye textile wastewater (RTW) and the generation of bioelectricity. The results of digital image processing revealed a maximum coverage area on the biocathodes by microalgal cells of 42%. The atmospheric and diffused CO₂ could enable good algal growth and its immobilized operation on the cathode electrode. The biocathode-SCMFCs outperformed an open circuit voltage (OCV), which was 18%-43% higher than the control. Furthermore, the maximum volumetric power density achieved was 123.2 ± 27.5 mW m^-3. The system was suitable for the treatment of RTW and the removal/decrease of COD, colour and heavy metals. High removal efficiencies were observed in the SCMFCs for Zn (98%) and COD (92-98%), but the removal efficiencies were considerably lower for Cr (54-80%). We observed that this single chamber MFC simplifies a double chamber system. The bioelectrochemical performance was relatively low, but the treatment capacity of the system seems encouraging in contrast to previous studies. A proof-of-concept experiment demonstrated that the microalgal biocathode could operate in air exposed conditions, seems to be a promising alternative to a Pt cathode and is an efficient and cost-effective approach to improve the performance of single chamber MFCs.

Microbial fuel cell characterisation and evaluation of Lysinibacillus macroides MFC02 electrigenic capability

Microbial fuel cell (MFC) is the most prominent research field due to its capability to generate electricity by utilizing the renewable sources. In the present study, Two MFC designs namely, H type-Microbial fuel cell (HT-MFC) and U type-Microbial fuel cell (UT-MFC) were constructed based on standardized H shaped anode and cathode compartment as well as U shaped anode and cathode compartments, respectively. In order to lower the cost for MFC construction, Pencil graphite lead was used as electrode and salt agar as Proton exchange membrane. Results inferred that newly constructed UT-MFC showed high electron production when compared to the HT-MFC. UT-MFC displayed an output of about 377 ± 18.85 mV (millivolts); whereas HT-MFC rendered only 237 ± 11.85 mV (millivolts) of power generation, which might be due to the low internal resistance. By increasing the number of cathode in UT-MFC, power production was increased upto 313 ± 15.65 mV in Open circuit voltage (OCV). Electrogenic bacteria namely, Lysinibacillus macroides (Acc. No. KX011879) rendered enriched power generation. The attachment of bacteria as a biofilm on pencil graphite lead was analyzed using fluorescent microscope and Scanning Electron Microscope (SEM). Based on our findings, it was observed that UT-MFC has a tendency to produce high electron generation using pencil graphite lead as the electrode material.

Evaluation of the performance of zero-electrolyte-discharge microbial fuel cell based on the type of substrate

Acetic acid was found to be the most suitable candidate for zero-electrolyte-discharge MFC as it provides stable electrolyte environment and least cathodic biofilm growth.

Evaluation of the suitability and performance of cassava waste (peel) extracts in a microbial fuel cell for supplementary and sustainable energy production

In a number of energy-poor nations, peel from cassava processing represents one of the most abundant sources of lignocellulosic biomass. This peel is mostly discarded indiscriminately and eventually constitutes a problem to the environment. However, energy can be extracted from this peel in a microbial fuel cell. In this study, the viability of cassava peel extract as a substrate in a single-chamber air cathode microbial fuel cell is demonstrated, and optimum performance conditions are explored. The effects of different pretreatments on the extract are also discussed in the context of observed changes in the internal resistances, conductivity and Coulombic efficiencies. At the best conditions examined, the extract from cassava peel fermented for 168 h and adjusted to a pH of 7.63 attained a peak voltage of 687 mV ± 21 mV, a power density of 155 mW m^-3 of reactor volume and a Coulombic efficiency of 11 %. Although this energy is limited to direct use, systems exist that can effectively harvest and boost the energy to levels sufficient for supplementary energy usage in cassava producing regions.

Electro-biocatalytic treatment of petroleum refinery wastewater using microbial fuel cell (MFC) in continuous mode operation

Refinery wastewater (RW) treatment in microbial fuel cell (MFC) was studied in batch mode operation followed by continuous mode operation with 8h and 16h hydraulic retention time (HRT). The MFC performance was evaluated in terms of power density, organics removal, specific contaminants (oil & grease, phenol and sulfide) removal and energy conversion efficiency with respect to operation mode. Higher power density of 225±1.4mW/m² was observed during continuous mode operation with 16h HRT along with a substrate degradation of 84.4±0.8% including the 95±0.6 of oil content. The columbic efficiency during this operation was about 2±0.8% and the projected power yield was 340±20kWh/kg COD_R/day. Batch mode operation also showed good substrate degradation (81±1.8%) but took longer HRT which resulted in significantly low substrate degradation rate (0.036±0.002kgCOD_R/m³-day) over continuous mode operation (1.05±0.01kgCOD_R/m³-day). Overall, current study depicted the possibility of utilizing RW as substrate in MFC for power generation along with its treatment.

Effects of current generation and electrolyte pH on reverse salt flux across thin film composite membrane in osmotic microbial fuel cells

Osmotic microbial fuel cells (OsMFCs) take advantages of synergy between forward osmosis (FO) and microbial fuel cells (MFCs) to accomplish wastewater treatment, current generation, and high-quality water extraction. As an FO based technology, OsMFCs also encounter reverse salt flux (RSF) that is the backward transport of salt ions across the FO membrane into the treated wastewater. This RSF can reduce water flux, contaminate the treated wastewater, and increase the operational expense, and thus must be properly addressed before any possible applications. In this study, we aimed to understand the effects of current generation and electrolyte pH on RSF in an OsMFC. It was found that electricity generation could greatly inhibit RSF, which decreased from 16.3 ± 2.8 to 3.9 ± 0.7 gMH when the total Coulomb production increased from 0 to 311 C. The OsMFC exhibited 45.9 ± 28.4% lower RSF at the catholyte pH of 3 than that at pH 11 when 40 Ω external resistance was connected. The amount of sodium ions transported across the FO membrane was 18.3-40.7% more than that of chloride ions. Ion transport was accomplished via diffusion and electrically-driven migration, and the theoretical analysis showed that the inhibited electrically-driven migration should be responsible for the reduced RSF. These findings are potentially important to control and reduce RSF in OsMFCs or other osmotic-driven processes.

Recent advances in nutrient removal and recovery in biological and bioelectrochemical systems

Nitrogen and phosphorous are key pollutants in wastewater to be removed and recovered for sustainable development. Traditionally, nitrogen removal is practiced through energy intensive biological nitrification and denitrification entailing a major cost in wastewater treatment. Recent innovations in nitrogen removal aim at reducing energy requirements and recovering ammonium nitrogen. Bioelectrochemical systems (BES) are promising for recovering ammonium nitrogen from nitrogen rich waste streams (urine, digester liquor, swine liquor, and landfill leachate) profitably. Phosphorus is removed from the wastewater in the form of polyphosphate granules by polyphosphate accumulating organisms. Alternatively, phosphorous is removed/recovered as Fe-P or struvite through chemical precipitation (iron or magnesium dosing). In this article, recent advances in nutrients removal from wastewater coupled to recovery are presented by applying a waste biorefinery concept. Potential capabilities of BES in recovering nitrogen and phosphorous are reviewed to spur future investigations towards development of nutrient recovery biotechnologies.

Performance of sodium bromate as cathodic electron acceptor in microbial fuel cell

The potential of using sodium bromate as a cathodic electron acceptor in a microbial fuel cell (MFC) was determined in this study. The effects of sodium bromate concentration and initial catholyte pH on the electricity production of the MFC were investigated. The MFC performance improved with increasing sodium bromate concentration and decreasing catholyte pH. The maximum voltage output (0.538 V), power density (1.4908 W m(-3)), optimal open circuit potential (1.635 V), coulombic efficiency (11.1%), exchange current density (0.538 A m(-3)) and charge transfer resistance (4274.1 Ω) were obtained at pH 3.0 and 100 mM sodium bromate. This work is the first to confirm that sodium bromate could be used as an electron acceptor in MFCs.