Comparison of different chemical treatments of brush and flat carbon electrodes to improve performance of microbial fuel cells

Performance of pharmaceutical products removal in a bioelectrochemical system at low temperatures and changes in microbial communities and antibiotic resistance genes

Biological methods do not effectively remove pharmaceutical products (PPs) and antibiotic resistance genes (ARGs) from wastewater at low temperatures, leading to environmental pollution. Therefore, anaerobic-aerobic-coupled upflow bioelectrochemical reactors (AO-UBERs) were designed to improve the removal of PPs at low temperatures (10 ± 2 °C). The result shows that diclofenac (DIC) and ibuprofen (IBU) removals in the system with aerobic anodic and anaerobic cathodic chambers were 91.7% and 94.7%, higher than that in the control system (12.2 ± 1.5%, 36.5 ± 5.9%), and aerobic zone favors DIC and IBU removal; fluoroquinolone antibiotics (FQs) removals in the system with aerobic cathodic and anaerobic anodic chambers were 17.5-22.4% higher than that in the control system (9.1-22.4%), and anaerobic zone favors FQs removal. Analysis of microbial community structure and ARGs showed that different electrotrophic microbes (Flavobacterium, Acinetobacter, and Delftia) with cold-resistant ability to degrade PPs were enriched in different electrode combinations, and the aerobic cathodic chambers could remove certain ARGs. These results showed that AO-UBERs under intermittent electrical stimulation mode are an alternative method for the effective removal of PPs and ARGs at low temperatures.

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.

Untreated vs. Treated Carbon Felt Anodes: Impacts on Power Generation in Microbial Fuel Cells

This research sought to enhance the efficiency and biocompatibility of anodes in bioelectrochemical systems (BESs) such as microbial fuel cells (MFCs), with an aim toward large-scale, real-world applications. The study focused on the effects of acid-heat treatment and chemical modification of three-dimensional porous pristine carbon felt (CF) on power generation. Different treatments were applied to the pristine CF, including coating with carbon nanofibers (CNFs) dispersed using dodecylbenzene sulfonate (SDBS) surfactant and biopolymer chitosan (CS). These processes were expected to improve the hydrophilicity, reduce the internal resistance, and increase the electrochemically active surface area of CF anodes. A high-resolution scanning electron microscopy (HR-SEM) analysis confirmed successful CNF coating. An electrochemical analysis showed improved conductivity and charge transfer toward [Fe(CN)6]3-/4- redox probe with treated anodes. When used in an air cathode single-chamber MFC system, the untreated CF facilitated quicker electroactive biofilm growth and reached a maximum power output density of 3.4 W m-2, with an open-circuit potential of 550 mV. Despite a reduction in charge transfer resistance (Rct) with the treated CF anodes, the power densities remained unchanged. These results suggest that untreated CF anodes could be most promising for enhancing power output in BESs, offering a cost-effective solution for large-scale MFC applications.

A three-dimensional phenolic-based carbon anode for microbial electrochemical system with customized macroscopic pore structure to promote interior bacteria colonization

Microbial electrochemical system (MES) is an emerging wastewater treatment technology that compensates the energy demands of containments removal by in situ converting the chemical energy of organic pollutants. As the structure for exoelectrogens and the reaction site of extracellular electron transfer (EET), the anode is essential for MES. The future commercial application of MES requires efficiency and large-scale fabrication available anode. In this study, a 3D anode with millimeter-scale pores (3D-MPA) was successfully constructed by sacrificial template method, with low-cost phenolic resin as carbon precursor and polymethyl methacrylate (PMMA) pellets as template. With customized and ordered pore of 1 mm, the 3D-MPAs allowed the microorganisms to colonize inside, improving anodic space utilization efficiency. Different carbonization temperature in tested range from 700 °C to 1000 °C regulated the micrometer-scale convex structures and surface roughness of 3D-MPAs, causing electrochemical performance changes. The 3D-MPA-900 obtained the largest electroactive surface area (102 ± 4.1 cm²) and smallest ohmic resistance (1.8 ± 0.09 Ω). Equipped with MES, 3D-MPA-900 reached the highest power density and current density (2590 ± 25 mW m^-2 and 5.20 ± 0.07 A m^-2). Among tested 3D-MPA, the excellent performance of 3D-MPA-900 might be attributed by its convex structures with suitable size and surface coverage. The surface roughness of 3D-MPA-900 enhanced the microorganism adherence, which then promoted EET on anode surface. Generally, phenolic-based 3D-MPA made of sacrificial-template method had controllable porous structure, large-scale fabrication availability, high chemical stability and excellent mechanical property, which could be promising for the commercial application of MES.

Simultaneous boost of anodic electron transfer and exoelectrogens enrichment by decorating electrospinning carbon nanofibers in microbial fuel cell

Microbial fuel cell (MFC) is a promising technology in wastewater recovery driven by microbial metabolism. However, the low power output resulting from the sluggish extracellular electron transfer (EET) between the anode surface and exoelectrogens dramatically restricted the further application. This study fabricated a high-performance anode by decorating porous and conductive electrospinning carbon nanofibers (CNFs). The maximum power density in MFC modified with 14 wt% polyacrylonitrile CNFs (M-CNF14, 9.6 ± 0.2 W m^-3) was 1.9 and 2.7 times higher than carbon black modified MFC (M-CB, 5.1 ± 0.1 W m^-3) and the blank (M-BA, 3.6 ± 0.1 W m^-3), respectively. Denser biofilm and more microbial nanowires were observed in the M-CNF14 anode than in other conditions. Furthermore, the redox peak current of c-type cytochrome was 1.7-21 times higher in M-CNF14 than in the blank control, verifying the preferable EET activity. Several exoelectrogens like Petrimonas and Comamonas were enriched in M-CNF14 and showed a positive correlation to power generation. Besides, more simplified and modular interrelations among exoelectrogens and other bacteria were obtained in M-CNF14. This study revealed the microbial-related mechanism for simultaneously improving EET and exoelectrogens enrichment by CNFs modified anode, providing guidelines for high-performance wastewater recovery.

Microbial Fermentation of Polyethylene Terephthalate (PET) Plastic Waste for the Production of Chemicals or Electricity

Ideonella sakaiensis (I. sakaiensis) can grow on polyethylene terephthalate (PET) as the major carbon and energy source. Previous work has shown that PET conversion in the presence of oxygen released carbon dioxide and water while yielding adenosine triphosphate (ATP) through oxidative phosphorylation. This study demonstrates that I. sakaiensis is a facultative anaerobe that ferments PET to the feedstock chemicals acetate and ethanol in the absence of oxygen. In addition to PET, the pure monomer ethylene glycol (EG), the intermediate product ethanol, and the carbohydrate fermentation test substance maltose can also serve as fermenting substrates. Co-culturing of I. sakaiensis with the electrogenic and acetate-consuming Geobacter sulfurreducens produced electricity from PET or EG. This newly identified plastic fermentation process by I. sakaiensis provides thus a novel biosynthetic route to produce high-value chemicals or electricity from plastic waste streams.

3D Hierarchical Co8FeS8-FeCo2O4/N-CNTs@CF with an Enhanced Microorganisms-Anode Interface for Improving Microbial Fuel Cell Performance

Microbial fuel cells (MFCs) are promising ecofriendly techniques for harvesting bioenergy from organic and inorganic matter. Currently, it is challenging to design MFC anodes with favorable microorganism attachment and fast extracellular electron transfer (EET) rate for high MFC performance. Here we prepared N-doped carbon nanotubes (NCNTs) on carbon felt (CF) and used it as a support for growing hierarchical Co₈FeS₈-FeCo₂O₄/NCNTs core-shell nanostructures (FeCo/NCNTs@CF). We observed improved wettability, specific areal capacitance, and diffusion coefficient, as well as small charge transfer resistance compared with bare CF. MFCs equipped with FeCo/NCNTs@CF displayed a power density of 3.04 W/m² and COD removal amount of 221.0 mg/L/d, about 47.6 and 290.1% improvements compared with that of CF. Biofilm morphology and 16s rRNA gene sequence analysis proved that our anode facilitated the enrichment growth of exoelectrogens. Flavin secretion was also promoted on our hierarchical elelctrode, effectively driving the EET process. This work disclosed that hierarchical nanomaterials modified electrode with tailored physicochemical properties is a promising platform to simultaneously enhance exoelectrogen attachment and EET efficiency for MFCs.

Performance of bioelectrode based on different carbon materials in bioelectrochemical anaerobic digestion for methanation of maize straw

The performance of the bioelectrochemical anaerobic digestion (BEAD) reactor was investigated with different carbon material-modified electrodes for the methanation of maize straw. The carbon material-modified electrodes used titanium (Ti) mesh modified with carbon nanotube (CNT), carbon black (CB), and activated carbon (AC). The maximum cumulative methane production obtained in the Ti-CNT reactor was (616.4 ± 9.3) mL/g VS, while the maximum methane production rate in the Ti-AC reactor was (61.9 ± 1.0) mL/g VS.d.The electroactive bacteria were well enriched by the different electrodes, and the enriched electroactive bacteria further facilitate the direct interspecies electron transfer (DIET) for methane production. Additionally, we found the phylum Firmicutes showed a linear relationship to methanogenic performance, as well as the Genus Proteiniborus. The Ti-CNT electrode shows better performance by the electrochemical analysis. These findings provide critical knowledge for the large-scale use of the BEAD process and the treatment of maize straw.

Hydrogen Production in Microbial Electrolysis Cells Based on Bacterial Anodes Encapsulated in a Small Bioreactor Platform

Microbial electrolysis cells (MECs) are an emerging technology capable of harvesting part of the potential chemical energy in organic compounds while producing hydrogen. One of the main obstacles in MECs is the bacterial anode, which usually contains mixed cultures. Non-exoelectrogens can act as a physical barrier by settling on the anode surface and displacing the exoelectrogenic microorganisms. Those non-exoelectrogens can also compete with the exoelectrogenic microorganisms for nutrients and reduce hydrogen production. In addition, the bacterial anode needs to withstand the shear and friction forces existing in domestic wastewater plants. In this study, a bacterial anode was encapsulated by a microfiltration membrane. The novel encapsulation technology is based on a small bioreactor platform (SBP) recently developed for achieving successful bioaugmentation in wastewater treatment plants. The 3D capsule (2.5 cm in length, 0.8 cm in diameter) physically separates the exoelectrogenic biofilm on the carbon cloth anode material from the natural microorganisms in the wastewater, while enabling the diffusion of nutrients through the capsule membrane. MECs based on the SBP anode (MEC-SBPs) and the MECs based on a nonencapsulated anode (MEC control) were fed with Geobacter medium supplied with acetate for 32 days, and then with artificial wastewater for another 46 days. The electrochemical activity, chemical oxygen demand (COD), bacterial anode viability and relative distribution on the MEC-SBP anode were compared with the MEC control. When the MECs were fed with artificial wastewater, the MEC-SBP produced (at −0.6 V) 1.70 ± 0.22 A m⁻², twice that of the MEC control. The hydrogen evolution rates were 0.017 and 0.005 m³ m⁻³ day⁻¹, respectively. The COD consumption rate for both was about the same at 650 ± 70 mg L⁻¹. We assume that developing the encapsulated bacterial anode using the SBP technology will help overcome the problem of contamination by non-exoelectrogenic bacteria, as well as the shear and friction forces in wastewater plants.

Scalability of microbial electrochemical technologies: Applications and challenges

During wastewater treatment, microbial electrochemical technologies (METs) are a promising means for in situ energy harvesting and resource recovery. The primary constraint for such systems is scaling them up from the laboratory to practical applications. Currently, most research (∼90%) has been limited to benchtop models because of bioelectrochemical, economic, and engineering design limitations. Field trials, i.e., 1.5 m³ bioelectric toilet, 1000 L microbial electrolysis cell and industrial applications of METs have been conducted, and their results serve as positive indicators of their readiness for practical applications. Multiple startup companies have invested in the pilot-scale demonstrations of METs for industrial effluent treatment. Recently, advances in membrane/electrode modification, understanding of microbe-electrode interaction, and feasibility of electrochemical redox reactions have provided new directions for realizing the practical application. This study reviews the scaling-up challenges, success stories for onsite use, and readiness level of METs for commercialization that is inexpensive and sustainable.

Recent Developments in Carbon-Based Nanocomposites for Fuel Cell Applications: A Review

Carbon-based nanocomposites have developed as the most promising and emerging materials in nanoscience and technology during the last several years. They are microscopic materials that range in size from 1 to 100 nanometers. They may be distinguished from bulk materials by their size, shape, increased surface-to-volume ratio, and unique physical and chemical characteristics. Carbon nanocomposite matrixes are often created by combining more than two distinct solid phase types. The nanocomposites that were constructed exhibit unique properties, such as significantly enhanced toughness, mechanical strength, and thermal/electrochemical conductivity. As a result of these advantages, nanocomposites have been used in a variety of applications, including catalysts, electrochemical sensors, biosensors, and energy storage devices, among others. This study focuses on the usage of several forms of carbon nanomaterials, such as carbon aerogels, carbon nanofibers, graphene, carbon nanotubes, and fullerenes, in the development of hydrogen fuel cells. These fuel cells have been successfully employed in numerous commercial sectors in recent years, notably in the car industry, due to their cost-effectiveness, eco-friendliness, and long-cyclic durability. Further; we discuss the principles, reaction mechanisms, and cyclic stability of the fuel cells and also new strategies and future challenges related to the development of viable fuel cells.