Increased performance of a tubular microbial fuel cell with a rotating carbon-brush anode

Role played by the physical structure of carbon anode materials in MFC biosensor for BOD measurement

Microbial fuel cell (MFC) has been extensively studied as a biosensor for determining biochemical oxygen demand (BOD). The method for quantifying BOD by employing coulombic yield (Q) of a bio-electrochemical degradation process obtained from MFC biosensors is referred to as BOD_Q. The physical structures of anode materials greatly affect the sensitivity and accuracy of the biosensor. In this work, the effects of carbon cloth (CC) and carbon felt (CF) as anode substrate materials on the BOD_Q determination efficiencies were studied. The CF-MFC biosensor showed higher BOD_Q response than that of the CC-MFC within 25-400 mg L^-1 BOD concentration range, and the test value was very close to the theoretical BOD. The difference is resulting from higher coulombic efficiency (CE) of CF-MFC (64.89-65.38 %) than CC-MFC (55.58-63.51 %). It should be noted that for water samples with low BOD concentrations the physical structures of anode materials play a leading role in CE. For synthetic wastewaters with 25 mg L^-1 BOD, the CE of CF-MFC (65.38 %) was 17.63 % higher than that of CC-MFC (55.58 %). In contrast to the densely woven CC coated with thick biofilm, CF with loose carbon fiber and thin biofilm makes it good for organic diffusion and electron transportation, thus contributing to higher and more stable CE. These results indicate that the CF-MFC is more suitable for determining BOD_Q values over a wide concentration range. This work provides a useful strategy for selecting desirable MFC's anode material as the BOD biosensor. MFC biosensors with high-porosity biological anodes can obtain more accurate BOD test values.

General aspects and novel PEMss in microbial fuel cell technology: A review

The current scenario of energy production is mostly shifted towards sustainable renewable energy sources. Other than the energy production from natural resources such as sun, wind and water, microbial fuel cell system (MFC) has earned attraction in recent times. These microbial fuel cell systems are bioelectrochemical cell that possesses a unique ability to generate power as well as treats wastewater simultaneously. In this paper, an overview of the microbial fuel cell system and the effect of significant components on the performance of microbial fuel cell systems are reviewed. Firstly, the importance of the MFC system in power generation, its components, the working principle and various configurations of the MFC were briefly introduced. Biofilm plays a major role in the MFC system. Thus the importance of bio film, bio film formation and characterization techniques are summarised. Further, the review mainly addresses the mechanism of conventional and novel membrane materials on the performance of the MFC system. In addition, special emphasis on ceramic-based materials in the MFC system is presented. Finally, recent applications of the MFC systems are discussed.

Review on microbial fuel cells applications, developments and costs

The microbial fuel cell (MFC) technology has attracted significant attention in the last years due to its potential to recover energy in a wastewater treatment. The idea of using an MFC in industry is very attractive as the organic wastes can be converted into energy, reducing the waste disposal costs and the energy needs while increasing the company profit. However, taking aside these promising prospects, the attempts to apply MFCs in large-scale have not been succeeded so far since their lower performance and high costs remains challenging. This review intends to present the main applications of the MFC systems and its developments, particularly the advances on configuration and operating conditions. The diagnostic techniques used to evaluate the MFC performance as well as the different modeling approaches are described. Towards the introduction of the MFC in the market, a cost analysis is also included. The development of low-cost materials and more efficient systems, with high higher power outputs and durability, are crucial towards the application of MFCs in industrial/large scale. This work is a helpful tool for discovering new operation and design regimes.

Development of trickling bio-electrochemical reactor (TrickBER) for large scale energy efficient wastewater treatment

Bioelectrochemical systems such as microbial fuel cells are novel systems; those directly transform the chemical energy contained in organics of wastewater into electrical energy by the metabolic action of the microbial community. During the last two decades, bioelectrochemical systems astonishingly increased their wastewater treatment capabilities, sustainability, and power output. However, studies on scalable architectural designs of bioelectrochemical systems received less attention. Lower power yield and high cost are two major limitations for scaling up of bioelectrochemical systems. This study reports a low cost, scalable, air cathode bio-electrochemical reactor, constructed by adopting a trickling filtration approach (TrickBER) and operated in continuous mode. Various facets of construction, installation, and operation of TrickBER were investigated and optimized to achieve an efficient performance. TrickBER was found suitable in simultaneous electricity generation during continuous wastewater treatment and, in the future, could be used in small/cottage industries.

Single-Chamber Microbial Fuel Cell with Multiple Plates of Bamboo Charcoal Anode: Performance Evaluation

In this study, three single-chamber microbial fuel cells (MFCs), each having Pt-coated carbon cloth as a cathode and four bamboo charcoal (BC) plates as an anode, were run in a fed-batch mode, individually and in series. Simulated potato-processing wastewater was used as a substrate for supporting the growth of a mixed bacterial culture. The maximum power output increased from 0.386 mW with one MFC to 1.047 mW with three MFCs connected in series. The maximum power density, however, decreased from 576 mW/m2 (normalized to the cathode area) with one MFC to 520 mW/m2 with three MFCs in series. The experimental results showed that power can be increased by connecting the MFCs in series; however, choosing low resistance BC is crucial for increasing power density.

A novel UASB-MFC dual sensors system for wastewater treatment: On-line sensor recovery and electrode cleaning in the long-term operation

In this research, the UASB-MFC dual sensors system was established and treatment the brewery wastewater. The COD removal rate attain about 90% and the NH₄⁺-N concentration less than 15 mg/L, MFCs has a voltage range of 0.34-0.42 V. Meanwhile, as the biosensor for coupling system, MFCs can be used to make simultaneous monitor COD and TVFA. The potential distribution can in-situ accelerate the reattachment of micro-organisms, which shorten the recovery time to 55% of the original. The long-term performance of MFCs were tested by electrochemical methods and found that the degradation of biosensors was mainly caused by the precipitation of Ca²⁺ and Mg²⁺ on the cathode surface and affected by concentration. More importantly, cleaning the electrode by an self-enhanced method without external assistance ECS (Electrodes Connection Switching) can improve the MFCs performance to 83.2 %-84.6%. Dual sensors system in UASB gives a novel possibility for UASB-MFC sensor self-sustaining in a long-term.

Construction of innovative 3D-weaved carbon mesh anode network to boost electron transfer and microbial activity in bioelectrochemical system

Bioelectrochemical system (BES) is promising technology to simultaneously treat wastewater and recover energy, and electrode material is important for the system performance. Microbial fuel cell (MFC) is one of typical BES to be applied in wastewater treatment. How to improve the electrode material is significant to improve wastewater treatment, energy recovery and cost effectiveness. In this study, 3D-weaved carbon electrode entity, assembled by multiple pieces of carbon mesh (CM), was proposed to combine all electrode components as entity to facilitate electron conduction and ionic migration, compared with carbon brush (CB) and granular activated carbon (GAC). The result showed that current density and internal resistance of MFC using 3D-weaved CM as horizontally extended inside anode (CM(T)) were 30.9 A m-3 and 4.5 Ω, respectively, with higher output than traditional GAC (22.6 A m-3 and 6.2 Ω). Though GAC had greater electrode filling and surface area for biomass growth, the electron transfer efficiency per unit electrode biomass was only at 0.0019 ± 0.0002 mol g-1 d-1, much lower than CM(T) at 0.0077 ± 0.0009 mol g-1 day-1. Higher ionic migration rate of CM(T) suggested the assisting effect of composite electrode to enhance ionic transportation towards the cathode. Microbial analysis further indicated that 3D-CM electrode network could simultaneously enhance Geobacter abundance and methanogen activity, suggesting the importance of electrode network on electricigens. Furthermore, CM(T) could obtain 10 times higher energy output efficiency than traditional GAC when applied inside anode chamber. This study proved that network construction of anode electrode could promote the electrode performance and cost effectiveness, suggesting the future development of reactor design of bioelectrochemical system.

A 3D porous NCNT sponge anode modified with chitosan and Polyaniline for high-performance microbial fuel cell

A microbial fuel cell (MFC) is a potential bio-electrochemical technology that utilizes microorganisms to convert chemical energy into electrical energy. The low power output of MFCs remain the bottleneck for their practical applications. In this paper, a novel, biocompatible and bioelectrocatalytic composite chitosan-nitrogen doped carbon nanotubes-polyaniline (CS-NCNT-PANI) was prepared in situ on the 3D porous NCNT/sponge and applied to an MFC anode. The PANI was grafted on the CS-NCNT backbone to synthesize the ternary composite. This bioanode not only increased the active surface area and capacity but also facilitated bacterial adhesion and enrichment of microbes. Compared with the NCNT/sponge electrode, the charge transfer impedance of the ternary composite bioanode decreased from 14.07 Ω to 2.25 Ω, and the maximum power density increased from 1.4 W·m^-3 to 4.2 W·m^-3; meanwhile, during the chronoamperometric experiment with a charge-discharge time of 60-60 min, the cumulative charge of the composite bioanode was 18,865.8 C·m^-2, which is much higher than that of the NCNT/S anode (3625.3 C·m^-2). High-throughput sequencing technology revealed that the ternary composite bioanode had good biocompatibility and high diversity. Therefore, this synthesized ternary composite is a promising candidate as a capacitive and biocompatible anode material in MFC.

Alkaline treatment of used carbon-brush anodes for restoring power generation of microbial fuel cells

Long-term operation of microbial fuel cells (MFCs) results in an electrochemical activity decline by the degradation of the anodic biofilm. In this work, an alkaline soaking treatment is proposed as an efficient and simple method for anode regeneration. The alkaline treatment was employed in a used carbon-brush anode, and its performance was compared with those of two other traditional treatment methods, i.e. air drying and carbonization. Among all the treated MFC anodes, the one treated by alkaline soaking exhibited the highest recovery rate. A series of tests including a start-up process, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and MFC performance were performed. The results show that alkaline soaking can modify the carbon fiber by introducing carboxyl groups onto the carbon surface and completely remove the aged biofilm, demonstrating that the alkaline treatment of used anodes is a practically effective method for the performance recovery of MFCs.

An alkaline soaking treatment is proposed as an efficient and simple method for anode regeneration.

Microbial fuel cells: From fundamentals to applications. A review

In the past 10-15 years, the microbial fuel cell (MFC) technology has captured the attention of the scientific community for the possibility of transforming organic waste directly into electricity through microbially catalyzed anodic, and microbial/enzymatic/abiotic cathodic electrochemical reactions. In this review, several aspects of the technology are considered. Firstly, a brief history of abiotic to biological fuel cells and subsequently, microbial fuel cells is presented. Secondly, the development of the concept of microbial fuel cell into a wider range of derivative technologies, called bioelectrochemical systems, is described introducing briefly microbial electrolysis cells, microbial desalination cells and microbial electrosynthesis cells. The focus is then shifted to electroactive biofilms and electron transfer mechanisms involved with solid electrodes. Carbonaceous and metallic anode materials are then introduced, followed by an explanation of the electro catalysis of the oxygen reduction reaction and its behavior in neutral media, from recent studies. Cathode catalysts based on carbonaceous, platinum-group metal and platinum-group-metal-free materials are presented, along with membrane materials with a view to future directions. Finally, microbial fuel cell practical implementation, through the utilization of energy output for practical applications, is described.

Uneven biofilm and current distribution in three-dimensional macroporous anodes of bio-electrochemical systems composed of graphite electrode arrays

A 3-D macroporous anode was constructed using different numbers of graphite rod arrays in fixed-volume bio-electrochemical systems (BESs), and the current and biofilm distribution were investigated by dividing the 3-D anode into several subunits. In the fixed-volume chamber, current production was not significantly improved after the electrode number increased to 36. In the case of 100 electrodes, a significant uneven current distribution was found in the macroporous anode. This was attributed to a differential pH distribution, which resulted from proton accumulation inside the macroporous anode. The pH distribution influenced the biofilm development and led to an uneven biofilm distribution. With respect to current generation, the uneven distribution of both the pH and biofilm contributed to the uneven current distribution. The center had a low pH, which led to less biofilm and a lower contribution to the total current, limiting the performance of the BESs.

Three-Dimensional Electrodes for High-Performance Bioelectrochemical Systems

Bioelectrochemical systems (BES) are groups of bioelectrochemical technologies and platforms that could facilitate versatile environmental and biological applications. The performance of BES is mainly determined by the key process of electron transfer at the bacteria and electrode interface, which is known as extracellular electron transfer (EET). Thus, developing novel electrodes to encourage bacteria attachment and enhance EET efficiency is of great significance. Recently, three-dimensional (3D) electrodes, which provide large specific area for bacteria attachment and macroporous structures for substrate diffusion, have emerged as a promising electrode for high-performance BES. Herein, a comprehensive review of versatile methodology developed for 3D electrode fabrication is presented. This review article is organized based on the categorization of 3D electrode fabrication strategy and BES performance comparison. In particular, the advantages and shortcomings of these 3D electrodes are presented and their future development is discussed.

Carbon Material Optimized Biocathode for Improving Microbial Fuel Cell Performance

To improve the performance of microbial fuel cells (MFCs), the biocathode electrode material of double-chamber was optimized. Alongside the basic carbon fiber brush, three carbon materials namely graphite granules, activated carbon granules (ACG) and activated carbon powder, were added to the cathode-chambers to improve power generation. The result shows that the addition of carbon materials increased the amount of available electroactive microbes on the electrode surface and thus promote oxygen reduction rate, which improved the generation performance of the MFCs. The Output current (external resistance = 1000 Ω) greatly increased after addition of the three carbon materials and maximum power densities in current stable phase increased by 47.4, 166.1, and 33.5%, respectively. Additionally, coulombic efficiencies of the MFC increased by 16.3, 64.3, and 20.1%, respectively. These results show that MFC when optimized with ACG show better power generation, higher chemical oxygen demands removal rate and coulombic efficiency.

Optimized matching modes of bioelectrochemical module and anaerobic sludge in the integrated system for azo dye treatment

In this work, three matching modes (relative positions, catholyte flow sequences, and flow regimes) of bioelectrochemical module and anaerobic sludge were evaluated and optimized for azo dye treatment in the integrated system with embedding modular bioelectrochemical system into anaerobic sludge reactor. Results showed that it was favorable to operate this integrated system under the condition of 1/4 cathode soaking into sludge with spiral distributor in down-flow direction. Current, electrochemical impedance spectroscopy and pH clearly demonstrated the important role of 1/4 soaking in electron/proton transfer. The down-flow direction flowed through electrode zone and then sludge zone could benefit to the efficient use of cathode and improve AO7 treatment. Furthermore, the positive effect of spiral catholyte distributor might be due to its promoting role in mixing and creating a spiral flow channel around the cathode electrode-microbes-solution interface. These results exhibited great potential for matching modular bioelectrochemical system with anaerobic treatment process.