Improving performance of microbial fuel cell by enhanced bacterial-anode interaction using sludge immobilized beads with activated carbon

Hydrogen Production in Microbial Electrolysis Cells Using an Alginate Hydrogel Bioanode Encapsulated with a Filter Bag

The bacterial anode of microbial electrolysis cells (MECs) is the limiting factor in a high hydrogen evolution reaction (HER). This study focused on improving biofilm attachment to a carbon-cloth anode using an alginate hydrogel. In addition, the modified bioanode was encapsulated by a filter bag that served as a physical barrier, to overcome its low mechanical strength and alginate degradation by certain bacterial species in wastewater. The MEC based on an encapsulated alginate bioanode (alginate bioanode encapsulated by a filter bag) was compared with three controls: an MEC based on a bare bioanode (non-immobilized bioanode), an alginate bioanode, and an encapsulated bioanode (bioanode encapsulated by a filter bag). At the beginning of the operation, the Rct value for the encapsulated alginate bioanode was 240.2 Ω, which decreased over time and dropped to 9.8 Ω after three weeks of operation when the Geobacter medium was used as the carbon source. When the MECs were fed with wastewater, the encapsulated alginate bioanode led to the highest current density of 9.21 ± 0.16 A·m-2 (at 0.4 V), which was 20%, 95%, and 180% higher, compared to the alginate bioanode, bare bioanode, and encapsulated bioanode, respectively. In addition, the encapsulated alginate bioanode led to the highest reduction currents of (4.14 A·m-2) and HER of 0.39 m3·m-3·d-1. The relative bacterial distribution of Geobacter was 79%. The COD removal by all the bioanodes was between 62% and 88%. The findings of this study demonstrate that the MEC based on the encapsulated alginate bioanode exhibited notably higher bio-electroactivity compared to both bare, alginate bioanode, and an encapsulated bioanode. We hypothesize that this improvement in electron transfer rate is attributed to the preservation and the biofilm on the anode material using alginate hydrogel which was inserted into a filter bag.

Anode amendment with kaolin and activated carbon increases electricity generation in a microbial fuel cell

The bacterial anode is a key factor for microbial fuel cell (MFC) performance. This study examined the potential of kaolin (fine clay) to enhance bacteria and conductive particle attachment to the anode. The bio-electroactivity of MFCs based on a carbon-cloth anode modified by immobilization with kaolin, activated carbon, and Geobacter sulfurreducens (kaolin-AC), with only kaolin (kaolin), and a bare carbon-cloth (control) anodes were examined. When the MFCs were fed with wastewater, the MFCs based on the kaolin-AC, kaolin, and bare anodes produced a maximum voltage of 0.6 V, 0.4 V, and 0.25 V, respectively. The maximum power density obtained by the MFC based on the kaolin-AC anode was 1112 mW‧m^-2 at a current density of 3.33 A‧m^-2, 12% and 56% higher than the kaolin and the bare anodes, respectively. The highest Coulombic efficiency was obtained by the kaolin-AC anode (16%). The relative microbial diversity showed that Geobacter displayed the highest relative distribution of 64% in the biofilm of the kaolin-AC anode. This result proved the advantage of preserving the bacterial anode exoelectrogens using kaolin. To our knowledge, this is the first study evaluating kaolin as a natural adhesive for immobilizing exoelectrogenic bacteria to anode material in MFCs.

Semi-wet methanogen cathode composed of oak white charcoal for developing sustainable microbial fuel cells

The present study aimed to evaluate a semi-wet biocathode composed of oak white charcoal and agarose gel as an alternative to the standard carbon felt biocathodes used in microbial fuel cells (MFCs). The MFC containing the oak white charcoal cathode (Oak-MFC) recorded a higher current value than that of the MFC containing a carbon felt cathode (CF-MFC). The Oak-MFC produced approximately 4.0-fold more electrons in the external circuit and 1.7-fold more methane (CH₄) than the CF-MFC. A real-time PCR targeting mcrA showed that the number of methanogens adhering to the oak white charcoal cathode was approximately 15-fold that adhering to the carbon felt cathode. These results suggest that the methanogens attached to the cathode of both MFCs received electrons and CH₄ was produced from carbon dioxide (CO₂). Furthermore, Oak-MFC performed better than CF-MFC, thereby suggesting that oak white charcoal bound by agarose gel can be used as an alternative methanogen cathode. The propionic acid degradation rate of Oak-MFC was faster than that of CF-MFC suggesting that the cathodic reaction may affect the anodic reaction. The use of oak-derived electrode as a methanogen cathode also could contribute to sustainable forest management and promote regular thinning of oak trees. Further, its use will enable carbon fixation and efficient energy conversion from CO₂ to CH₄, thus contributing to sustainable energy use.

Modification of Graphite Sheet Anode with Iron (II, III) Oxide-Carbon Dots for Enhancing the Performance of Microbial Fuel Cell

The present study explores the use of carbon dots coated with Iron (II, III) oxide (Fe3O4) for its application as an anode in microbial fuel cells (MFC). Fe3O4@PSA-C was synthesized using a hydrothermal-assisted probe sonication method. Nanoparticles were characterized with XRD, SEM, FTIR, and RAMAN Spectroscopy. Different concentrations of Fe3O4- carbon dots (0.25, 0.5, 0.75, and 1 mg/cm2) were coated onto the graphite sheets (Fe3O4@PSA-C), and their performance in MFC was evaluated. Cyclic voltammetry (CV) of Fe3O4@PSA-C (1 mg/cm2) modified anode indicated oxidation peaks at −0.26 mV and +0.16 mV, respectively, with peak currents of 7.7 mA and 8.1 mA. The fluxes of these anodes were much higher than those of other low-concentration Fe3O4@PSA-C modified anodes and the bare graphite sheet anode. The maximum power density (Pmax) was observed in MFC with a 1 mg/cm2 concentration of Fe3O4@PSA-C was 440.01 mW/m2, 1.54 times higher than MFCs using bare graphite sheet anode (285.01 mW/m2). The elevated interaction area of carbon dots permits pervasive Fe3O4 crystallization providing enhanced cell attachment capability of the anode, boosting the biocompatibility of Fe3O4@PSA-C. This significantly improved the performance of the MFC, making Fe3O4@PSA-C modified graphite sheets a good choice as an anode for its application in MFC.

Degradation of phenol in the bio-cathode of a microbial desalination cell with power generation and salt removal

In this study, the performance of a three-chamber microbial desalination cell (MDC) was assessed to simultaneously remove salt (35 g.L^-1) from water and degrade phenol as a hazardous compound. Two parallel MDCs with the same configurations were run using glucose as the chemical oxygen demand (COD) at an initial concentration of 1.5 g.L^-1 as the anolyte. MDC#1 operated with 10 mM phosphate buffer solution (PBS), while MDC#2 operated with bio-cathode as the catholyte for the degradation of 100 mg.L^-1 of phenol. The use of MDC#1 resulted in a power density, desalination efficiency, and COD removal of 366.2 mW.m^-2, 50.3 ± 4.0 %, and 79.3 ± 2.2 %, respectively. All performance parameters were improved in MDC#2 with bio-cathode so that power density, desalination efficiency, and COD removal reached 660.1 mW.m^-2, 72.1 ± 3.0 %, and 92.6 ± 2.4 %, respectively. Also, more than 96 % of phenol was degraded using bio-cathode within 7 h of operation. Bio-cathode could enhance the performance of the MDC reactor through catalyzing the final reactions of electron acceptors compared to MDC#1 with a chemical cathode. In general, the results indicated that heterotrophic microorganisms, able to grow alongside autotrophic bacteria, could effectively extend the applications of MDC reactors to degrade hazardous compounds in cathode chambers.

Sustainable strategy on microbial fuel cell to treat the wastewater for the production of green energy

Microbial fuel cell (MFC) is one of the promising alternative energy systems where the catalytic conversion of chemical energy into electrical energy takes places with the help of microorganisms. The basic configuration of MFC consists of three major components such as electrodes (anode and cathode), catalyst (microorganism) and proton transport/exchange membrane (PEM). MFC classified into four types based on the substrate utilized for the catalytic energy conversion process such as Liquid-phase MFC, Solid-phase MFC, Plant-MFC and Algae-MFC. The core performance of MFC is organic substrate oxidation and electron transfer. Microorganisms and electrodes are the key factors that decide the efficiency of MFC system for electricity generation. Microorganism catalysis degradation of organic matters and assist the electron transfer to anode surface, the conductivity of anode material decides the rate of electron transport to cathode through external circuit where electrons are reduced with hydrogen and form water with oxygen. Not limited to electricity generation, MFC also has diverse applications in different sectors including wastewater treatment, biofuel (biohydrogen) production and used as biosensor for detection of biological oxygen demand (BOD) of wastewater and different contaminants concentration in water. This review explains different types of MFC systems and their core performance towards energy conversion and waste management. Also provides an insight on different factors that significantly affect the MFC performance and different aspects of application of MFC systems in various sectors. The challenges of MFC system design, operations and implementation in pilot scale level and the direction for future research are also described in the present review.

Effects of Metal Nanoparticles and Other Preparative Materials in the Environment on Plants: From the Perspective of Improving Secondary Metabolites

The influence of preparation material residues in wastewater and soil on plants has been paid more and more attention by researchers. Secondary metabolites play an important role in the application of plants. It was found that nanomaterials can increase the content of plant secondary metabolites in addition to their role in pharmaceutical preparations. For example, 800 mg/kg copper oxide nanoparticles (NPs) increased the content of p-coumaric acid in cucumber by 225 times. Nanoparticles can cause oxidative stress in plants, increase signal molecule, and upregulate the synthase gene expression, increasing the content of secondary metabolites. The increase of components such as polyphenols and total flavonoids may be related to oxidative stress. This paper reviews the application and mechanism of metal nanomaterials (Ag-NP, ZnO-NP, CeO₂-NP, Cds-NP, Mn-NP, CuO-NP) in promoting the synthesis of secondary metabolites from plants. In addition, the effects of some other preparative materials (cyclodextrins and immobilized molds) on plant secondary metabolites are also involved. Finally, possible future research is discussed.

Flavin mononucleotide-stimulated microbial fuel cell for efficient gaseous toluene abatement

Chemical park is regarded as a major contributor of VOCs emissions in China. Currently, a green and safe technology, microbial fuel cells (MFCs), is being developed for the VOCs abatement. Noting that effective electron transfer is critical to the MFC performance. In this work, flavin mononucleotide (FMN) was dosed as an electron shuttle to improve the removal of the typical toxic VOCs, toluene. The experimental results revealed that the performance of toluene removal and power generation were accelerated with the dosage of 0.2-2 μM FMN. With the addition of 1 μM FMN, the removal efficiency, the maximum output voltage and the coulombic efficiency of MFC were increased by 18.4%, 64.4% and 56.3%, respectively. However, a further increase in FMN concentration to 2 μM caused a reduction in the removal efficiency and coulombic efficiency. The images of scanning electron microscopy and confocal laser scanning microscopy showed that the presence of FMN greatly promoted the microbial growth and its activity. Furthermore, microbial community analysis also implied that the moderate dosage of FMN (0.2-1 μM) was beneficial for the growth of the typical exoelectrogens, Geobacter sp., and thus the coulombic efficiency was increased. In addition, an electron transfer pathway involving in cytochrome b, OMCs, cytochrome c, and MtrA was proposed based on the cyclic voltammetry analysis. This work will provide a fundamental theoretical support for its application of toxic VOCs abatement from the chemical park.

Bioelectrochemical systems for environmental remediation of estrogens: A review and way forward

Globally estrogenic pollutants are a cause of concern in wastewaters and water bodies because of their high endocrine disrupting activity leading to extremely negative impacts on humans and other organisms even at very low environmental concentrations. Bioremediation of estrogens has been studied extensively and one technology that has emerged with its promising capabilities is Bioelectrochemical Systems (BESs). Several studies in the past have investigated BESs applications for treatment of wastewaters containing toxic recalcitrant pollutants with a primary focus on improvement of performance of these systems for their deployment in real field applications. But the information is scattered and further the improvements are difficult to achieve for standalone BESs. This review critically examines the various existing treatment technologies for the effective estrogen degradation. The major focus of this paper is on the technological advancements for scaling up of these BESs for the real field applications along with their integration with the existing and conventional wastewater treatment systems. A detailed discussion on few selected microbial species having the unusual properties of heterotrophic nitrification and extraordinary stress response ability to toxic compounds and their degradation has been highlighted. Based on the in-depth study and analysis of BESs, microbes and possible benefits of various treatment methods for estrogen removal, we have proposed a sustainable Hybrid BES-centered treatment system for this purpose as a choice for wastewater treatment. We have also identified three pipeline tasks that reflect the vital parts of the life cycle of drugs and integrated treatment unit, as a way forward to foster bioeconomy along with an approach for sustainable wastewater treatment.