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

Applications of Nanomaterials in Microbial Fuel Cells: A Review

Microbial fuel cells (MFCs) are an environmentally friendly technology and a source of renewable energy. It is used to generate electrical energy from organic waste using bacteria, which is an effective technology in wastewater treatment. The anode and the cathode electrodes and proton exchange membranes (PEM) are important components affecting the performance and operation of MFC. Conventional materials used in the manufacture of electrodes and membranes are insufficient to improve the efficiency of MFC. The use of nanomaterials in the manufacture of the anode had a prominent effect in improving the performance in terms of increasing the surface area, increasing the transfer of electrons from the anode to the cathode, biocompatibility, and biofilm formation and improving the oxidation reactions of organic waste using bacteria. The use of nanomaterials in the manufacture of the cathode also showed the improvement of cathode reactions or oxygen reduction reactions (ORR). The PEM has a prominent role in separating the anode and the cathode in the MFC, transferring protons from the anode chamber to the cathode chamber while preventing the transfer of oxygen. Nanomaterials have been used in the manufacture of membrane components, which led to improving the chemical and physical properties of the membranes and increasing the transfer rates of protons, thus improving the performance and efficiency of MFC in generating electrical energy and improving wastewater treatment.

Accelerating anaerobic digestion process with novel single chamber microbial electrochemical systems with baffle

A newly designed microbial electrochemical system (MES) with the addition of a baffle between the electrodes was integrated with the anaerobic digestion (AD) process for biogas upgradation. Novel MES configuration attained an increased methane production rate of 292.6 mL/L∙d and methane yield of 0.36 ± 0.006 [Formula: see text] /g_COD, which were higher than the values (185.3 mL/L∙d and 0.33 ± 0.009 [Formula: see text] /g_COD) from the MES operation without baffle, respectively. Moreover, the MES with baffle operation resulted in increased substrate removal (88.4 ± 0.5%) and less volatile fatty acids accumulation with a high energy efficiency of 99.6 %. Microbial community analysis revealed that acids metabolizing bacteria, Firmicutes, and Methanothrix were highly enriched in the cathode biofilm of MES with baffle. This study suggests that the baffle addition into the single chamber MES is beneficial to further improve the methanogenesis process for practical applications in the scaled-up MES-AD process.

Mainstreaming microfluidic microbial fuel cells: a biocompatible membrane grown in situ improves performance and versatility

A recent trend in microfluidic microbial fuel cells (MFCs) is to exclude a separation membrane, instead, relying on the physics of laminar flow to maintain isolation between anode and cathode compartments. To avoid solution crossover, the electrodes may be separated by distances of several millimeters, but this negatively affects the internal resistance and undermines a prime advantage of microscale MFCs. Therefore, we propose a facile method for in situ synthesis of a micromembrane that supports sub-millimeter electrode spacing. Membrane synthesis in situ reduces device fabrication complexity, and the proposed design avoids electrode contamination during its synthesis. Comparing results to a state-of-the-art membraneless MFC with 6 mm inter-electrode distances, the sub-millimeter membrane MFC under comparable flow conditions had an internal resistance that was 60% lower, power and current densities that were respectively 45% and 290% higher, and acetate conversion efficiencies that were 8 times higher. The enhanced flow stability provided stable operation under imbalanced flow conditions and delivered continuous increases to power density of up to 30% for flow rate increases of 100 times over baseline levels. As a result, maximum outputs obtained were 660 mW m^-1 and 3.5 A m^-1. These are the highest reported for microfluidic MFCs using pure culture bacteria, which advances the goal of competing with mainstream MFC formats.

Bacterial signalling mechanism: An innovative microbial intervention with multifaceted applications in microbial electrochemical technologies: A review

Microbial electrochemical technologies (METs) are a set of inventive tools that generate value-added by-products with concomitant wastewater remediation. However, due to the bottlenecks, like higher fabrication cost and inferior yield of resources, these inventive METs are still devoid of successful field-scale implementation. In this regard, application of quorum sensing (QS) mechanism to improve the power generation of the METs has gained adequate attention. The QS is an intercellular signalling mechanism that controls the bacterial social network in its vicinity via the synthesis of diffusible signal molecules labelled as auto inducers, thus ameliorating yield of valuables produced through METs. This state-of-the-art review elucidates different types of QS molecules and their working mechanism with the special focus on the widespread application of QS in the field of METs for their performance enhancement. Thus, this review intends to guide the researchers in rendering scalability to METs by integrating innovative QS mechanisms into them.

Modified cobalt-manganese oxide-coated carbon felt anodes: an available method to improve the performance of microbial fuel cells

The novel MnCo₂O₄ (MCO/CF), CNTs-MnCo₂O₄ (CNTs-MCO/CF) and MnFe₂O₄-MnCo₂O₄ (MFO-MCO/CF) electrodes were prepared on carbon felt (CF) by simple hydrothermal and coating method as anodes for MFC. The modified anodes combine the electrocatalytic properties of transition metal oxides (TMOs), the high electrical conductivity of CNTs and the good biocompatibility of CF. These anodes play a synergistically role in the synthesis of structural, to realize high-efficiency electron transfer, low resistance and sufficient space for microbial colonization, while also ensuring high power density. The maximum power density of the composite electrodes CNTs-MCO/CF and MFO-MCO/CF were 4268 mW/m³ and 3660 mW/m³, respectively. The synergistic effect of multi-component effectively improves the performance of MFC. This work not only offers a good design and preparation concept for functional TMOs composite electrodes, but also provides an important guide for the fabrication of CNTs-doped MFC anodes.

The influence of external resistance on the performance of microbial fuel cell and the removal of sulfamethoxazole wastewater

Microbial fuel cells (MFCs) are promising equipment for simultaneous treatment of sewage and power generation. External resistance (R_ext) plays a crucial impact in the performance of MFCs in antibiotic wastewater treatment and antibiotic resistance genes (ARGs) reduction. In this study, R_ext and whether to add 20 mg/L sulfamethoxazole (SMX) as variables, it was observed that the performance of several chemical properties of MFCs was optimal when R_ext was 1000 Ω. The power density before and after addition of SMX was 1220.5 ± 24.5 mW/m² and 1186.2 ± 9.2 mW/m², respectively; Furthermore, the degradation rate of SMX was as high as 87.52 ± 1.97% within 48 h. High-throughput sequencing results showed that both R_ext and SMX affected the microbial community and relative abundance of the phylum and genera. Meanwhile, the MFCs with 1000 Ω R_ext generated less the targeted ARGs. Experimental results showed that 1000 Ω was the most suitable R_ext for MFCs in the treatment of antibiotic wastewater.

Efficiency, operational stability and biofouling of novel sulfomethylated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene cation exchange membrane in microbial fuel cells

In this work, a novel cation exchange membrane, PSEBS SU22 was deployed in microbial fuel cells (MFCs) to examine system efficacy in line with membrane characteristics and inoculum source. It turned out that compared to a reference membrane (Nafion), employing PSEBS SU22 resulted in higher current density and electricity generation kinetics, while the electron recoveries were similar (19-28%). These outcomes indicated more beneficial ion transfer features and lower mass transfer-related losses in the PSEBS SU22-MFCs, supported by membrane water uptake, ion exchange capacity, ionic conductivity and permselectivity. By re-activating the membranes after (bio)foulant removal, PSEBS SU22 regained nearly its initial conductivity, highlighting a salient functional stability. Although the particular inoculum showed a clear effect on the microbial composition of the membrane biofouling layers, the dominance of aerobic species was revealed in all cases. Considering all the findings, the PSEBS SU22 seems to be promising for application in MFCs.

Evaluation and ranking of polymeric ion exchange membranes used in microbial electrolysis cells for biohydrogen production

This work characterizes and comparatively assess two cation exchange membranes (PSEBS SU22 and CF22 R14) and one bipolar membrane (FBM) in microbial electrolysis cells (MEC), fed either by acetate or the mixture of volatile fatty acids as substrates. The PSEBS SU22 is a new, patent-pending material, while the CF22 R14 and FBM are developmental and commercialized products. Based on the various MEC performance measures, membranes were ranked by the EXPROM-2 method to reveal which of the polymeric membranes could be more beneficial from a complex, H₂ production efficiency viewpoint. It turned out that the substrate-type influenced the application potential of the membranes. Still, in total, the PSEBS SU22 was found competitive with the other alternative materials. The evaluation of MEC was also supported by analyzing anodic biofilms following electroactive bacteria's development over time.

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.

Characterization of electricity generation and microbial community structure over long-term operation of a microbial fuel cell

In this study, a continuous-flow microbial fuel cell (MFC) system was constructed to treat azo dye wastewater for 400 days. The electrical properties of the MFC after 400-day operation and the removal efficiencies of the MFC after long- and short-term operation were analyzed with respect to co-substrate concentrations. The power output of the MFC system decreased from 586 to 330 mV with increasing operating time, and the removal efficiencies of the MFC remained stable after long-term operation in comparison to those after short-term operation, even when the co-substrate concentration was reduced. Analysis of the degradation products showed that products generated from long-term operation of the MFC were present at low concentrations. The microbial community analysis revealed that the relative abundance of microorganisms related to the degradation of organics in the MFC increased after long-term operation, and microorganisms related to electricity generation decreased.

Biofouling of membranes in microbial electrochemical technologies: Causes, characterization methods and mitigation strategies

The scope of the review is to discuss the current state of knowledge and lessons learned on biofouling of membrane separators being used for microbial electrochemical technologies (MET). It is illustrated what crucial membrane features have to be considered and how these affect the MET performance, paying particular attention to membrane biofouling. The complexity of the phenomena was demonstrated and thereby, it is shown that membrane qualities related to its surface and inherent material features significantly influence (and can be influenced by) the biofouling process. Applicable methods for assessment of membrane biofouling are highlighted, followed by the detailed literature evaluation. Finally, an outlook on e.g. possible mitigation strategies for membrane biofouling in MET is provided.